Trenchless 101

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AASHTO -
American Association of State Highway and Transportation Officials
Abrasion - Removal of material due to a frictional contact.
Abrasion and Scratch Resistance - Ability of a material to resist the infliction of damage in the form of scratches, grooves, and other minor imperfections.
ABS - Acrylonitrile-Butadiene-Styrene; a form of thermoplastic.
AC - Asbestos Cement; a composite material used in pipe construction.
Acceptance - By the owner of the work as being fully complete in accordance with the contract documents.
Adapter Ring - In microtunneling, a fabricated ring, usually made from steel, that is mounted on the first pipe of the pipe string. This ring is intended to transfer the jacking force from the MTBM’s bearing area to the jacking pipe and to create a waterproof seal between the machine and the spigot of the first joint.
Addenda - Written or graphic instruments issued prior to the execution of the agreement, which modify or interpret the contract documents, drawings and specifications, by addition, deletions, clarifications, or corrections.
Additive - A substance added in a small amount, usually to a fluid, for a special purpose such as to reduce friction, corrosion, etc.
Admixture - Ingredients added during mixing; often in construction to aid workability of concrete, mortar or grout.
Advance - The motion of the machine in a direction toward the face wall of the entrance pit.
Advance Rate - Forward progress over a given period of time; includes penetration rate, make-up time, downtime, and idle time; typically measured in feet or meters per shift.
Aerial Sewer - An unburied sewer (generally sanitary type), supported on pedestals or bents to provide a suitable grade line.
Aerobic - Presence of unreacted or free oxygen (O2).
Aggressive - A property of water which favors the corrosion of its conveying structure.
Aggressive Index (AI) - Corrosion index established by the American Water Works Association (AWWA) Standard C-400; established as a criterion for determining the corrosive tendency of the water relative to asbestos-cement pipe; calculated from the pH, calcium hardness (H), and total alkalinity (A) by the formula AI = pH + log (A * H).
Agreement - The written agreement between the owner and the contractor covering the work to be performed; the contract documents are attached to and made a part of the agreements. Also designated as the contract.
Alkalinity - The capacity of a water to neutralize acids; a measure of the buffer capacity of a water. The major portion of alkalinity in natural waters is caused by (1) hydroxide, (2) carbonates, and (3) bicarbonates.
Alumina - An oxide of aluminum present in clay.
AMP - Asset Management Plan; a structured approach for utilities to achieve long term defined service standards – or – an external bearing used to isolate the final drive from the thrusting force of the machine.
Anaerobic - Able to live and grow where there is no oxygen.
Angle of Repose - The angle which the sloping face of a bank of loose earth, gravel, or other material, makes with the horizontal.
Annular Filler - Material for grouting the annular space between the existing pipeline and the lining system.
Annular Space - The theoretical volume between the gauge cut and the outside radius of the jacking pipe times the length of the installation, equal to annulus x length of tunnel.
Annular Thickness - The radial distance between the excavated radius created by the gauge cutter and the outside radius of the jacking pipe. The radial distance is equal to the overcut (gauge cut) plus the shield cut.
Annulus - The theoretical area between the gauge cut and the pipe OD equal to (? x (Gauge Cut OD2 - Pipe OD2)/4). It is the combined area created by the overcut and the shield cut.
Anode - The electrode at which oxidation or corrosion occurs; opposite of cathode.
ANSI - American National Standards Institute, Inc.
Apparent Tensile Strength - A value of tensile strength used for comparative purpose that is determined by tensile testing pipe rings in accordance with ASTM D 2290. This differs from true tensile strength of the material due to a bending moment induced by the change in contour of the ring as it is tested. Apparent tensile strength may be at yield, rupture or both.
Apparent Tensile Yield - The apparent tensile strength calculated for the yield condition.
Application for Payments - The form furnished by the engineer which is to be used by the contractor in requesting progress payments, and an affidavit of the contractor that progress payments theretofore received from the owner on account of the work been applied by the contractor to discharge in full all of the contractor's obligations stated in prior applications for payment.
Approval - Accept as satisfactory.
Aqueduct - Large pipe or conduit to convey water from distant source.
Aqueous - Pertaining to water; an aqueous solution is a water solution.
ArcInfo - GIS program for sewer data collection and display.
Areaway - A paved surface, serving as an entry area basement or subsurface portion of a building, which is provided with some form of drainage that may be connected to a sewer line.
Arterials - Designation of a main road system with many connecting minor roads.
As-Built - After a sewer has been constructed it is checked for conformance to plan specifications. The actual measurements (As-Built) are written on the plan near the original plan measurements. The As-Built measurements are often set-off in a box to differentiate the two measurements. Measurements are of the elevations for the manhole top cover, manhole invert(s) and ground level, for percent grade, etc.
ASCE - American Society of Civil Engineers
Asset - A valuable resource.
ASTM - American Society of Testing and Materials; technical organization formed for the development of standards on characteristics and performance of materials, products, systems and services, and the promotion of related knowledge.
Auger - A flighted drive tube having hex couplings at each end, to transmit torque to the cutting head and transfer spoil back to the machine.
Auger Boring - A technique for forming a bore from a jacking or drive shaft to a receiving shaft by means of a rotating auger with cutting tools. The casings are jacked forward sequentially in a cyclic process while the auger is turned. Spoils are removed back to the drive shaft by helically wound auger flights rotating in the steel casing. The equipment may have limited guidance and steering capability.
Auger Machine - A machine used to drill earth horizontally by means of a cutting head and auger or other functionally similar device. The machine may be either cradle or track type.
Auger MTBM - A type of microtunnel boring machine that uses auger flights to remove the spoils through a separate, smaller casing placed through the jacking pipe.
Auger TBM - Tunnel boring machine in which the excavated soil is removed to the drive shaft by auger flights passing through the product pipeline pushed in behind the TBM.
Automated Spoil - An automated spoil transportation system that conveys.
Available Water - Water necessary for the performance of work, which may be taken from the fire hydrant nearest the worksite, given conditions of traffic and terrain which are compatible with the use of the hydrant for performance of work.
AWWA - American Water Works Association

Back Reamer - A cutting head attached to the leading end of a drill string to enlarge the pilot bore during a pull-back operation to enable the carrier or sleeve or casing to be installed in.
Backfall - Refers to a length of pipe having an upward gradient opposite to the direction of flow.
Backfill Density - Percent compaction for pipe backfill (required or expected).
Backflow Device - Mechanism that prevents wastewater from flowing back upstream.
Backstop - Reinforced area of the entrance pit wall directly behind the track.
Band - A ring of steel welded at or near the front of the lead section of casing to cut relief and strengthen the casing.
Baroid - Proprietary equipment to measure the density of annulus grout.
Barrel - The vertical section in a manhole between the cone and the benchwall.
Base - The slab structure which supports a manhole.
Base (Course) - A layer of specified or selected material of planned thickness, constructed on the subgrade (natural foundation) or subbase for the purpose of distributing load, providing drainage or upon which a wearing surface or a drainage structure is placed.
Base Resin - Plastic materials prior to compounding with other additives or pigments.
Base Track - See Master Track.
Batter - The slope or inclination from a vertical plane, as the face or back of a wall.
Bedding - A prepared layer of material below a pipeline to ensure uniform support.
Belly Pans - Shims or other steel plates added to the bottom of the MTBM to adjust the machine’s location within the excavation. Also known as belly plates.
Benching or Bench - The floor of a manhole into which the channel is set; the bench is raised so that it can drain to the channel.
Benchwall - The horizontal bottom of the manhole normally out of the flow path.
Bent Sub - An offset section of drill stem close behind the drill head that allows steering corrections to be made by rotation of the drill string to orientate the cutting head. Frequently used in directional drilling.
Bentonite - A colloidal clay sold under various trade names that forms a slick slurry or gel when water is added. Also known as drillers mud. See Drilling Fluid.
Berlin Construction Method - A sewer collection system developed in Berlin, Germany, whereby sewer laterals are brought to a manhole and then dropped into the sewer interceptor. This method of connecting laterals to sewer is more compatible with trenchless installations.
Berm - The space between the toe of a slope and excavation made for intercepting ditches or borrow pits.
Bid - The offer or process of the bidder submitted on the prescribed form setting forth the prices for the work to be performed.
Bidder - Any person, firm, or corporation submitting a bid for the work.
Biological Corrosion - Corrosion that results from a reaction between the pipe material and organisms such as bacterial, algae, and fungi.
Bits - Replaceable cutting tools on the cutting head or drill string.
Bitumen - A hard or semi-hard asphaltic residue; often used in construction as a waterproof/barrier layer.
Bituminous (Coating) - Of or containing bitumen; as asphalt or tar.
Blind Shield - Non-mechanical shield which has a controlled and partly sealed face.
BOD - Biological Oxygen Demand; a measure of the need for oxygen by organic processes.
Bonds - Bid, performance and payment bonds and other instruments of security furnished by the contractor and his surety in accordance with the contract documents and in accordance with the law of the place of the project.
Boots - Electrical grade boots worn by all operators.
Bore - A generally horizontal hole produced underground primarily for the purpose of installing services.
Boring - (1) The dislodging or displacement of spoil by a rotating auger or drill string to produce a hole called a bore. (2) An earth-drilling process used for installing conduits or pipelines. (3) Obtaining soil samples for evaluation and testing.
Boring Machine - A mechanism to drill earth.
Boring Pit - An excavation in the earth of specified length and width for placing the machine on line and grade.
Boulder - Per ASTM D653, a rock fragment, usually rounded by weathering or abrasion, with a dimension of 12 in. (305 mm) or more.
Box - See Female Hex Connector.
Branch Sewer - A sewer into which at least two sanitary, combined or stormwater sewers connect.
Breakout - Controls the joint make and/or break mechanism.
Bridge Plank (deck or flooring) - A corrugated steel sub-floor on a bridge to support a wearing surface.
Brittleness Temperature - Temperature at which 50% of the tested specimens will fail when subjected to an impact blow.
Budgets - An amount of money needed or allocated for a specific use.
Building Combined Sewers - A small diameter pipe that conveys both wastewater and drainstormwater from a single property to a combined sewer.
Building Sanitary Drain - A small diameter pipe that conveys wastewater from a single property (e.g. domestic home) to a sanitary sewer.
Building Sewer - The conduit which connects building wastewater sources, to the public or street sewer, including lines serving homes, public buildings, commercial establishments, and industry structures. In this specification, the building sewer is referred to in two sections. (1) the section between the building line and the property line, frequently specified and supervised by plumbing or housing officials; and (2) the section between the property line and the street sewer, including the connection thereto frequently specified and supervised by sewer, public works, or engineering officials (Referred to also as "house sewer," "building connection,)' "service connection," or "lateral connection").
Building Stormwater - A small diameter pipe that conveys stormwater runoff drain from the roof and any paved areas of a single property to a stormwater sewer.
Buoyancy - The power of supporting a floating body, including the tendency to float an empty pipe (by exterior hydraulic pressure).
Buried Objects - Items in the ground that can affect MTBM advancement and line and grade control. Buried objects that prevent continued advancement along the design path, which includes tolerances, are called obstructions.
Burst Strength - The internal pressure required to cause a pipe or fitting to fail within a specified time period.
Bushing - See Female Hex Connector.
Butt Fusion - A method of joining polyethylene pipe where two pipe ends and rapidly brought together under pressure to form a homogeneous bond.
Bypass - An arrangement of pipes and valves whereby the flow may be passed around a hydraulic structure or appurtenance. Also, a temporary setup to route flow around a part of a sewer system.
Bypass Pumping - The transportation of sewage which flows around a specific sewer pipe/line section or sections via any conduit for the purpose of controlling sewage flows in the specified section or sections without flowing or discharging onto public or private property.

Caisson - A watertight chamber used in shaft construction under water. The ground within the chamber is excavated allowing the chamber to sink under its own weight into the ground.
Camber - Rise or crown of the center of a bridge, or Bowline through a culvert, above a straight line through its ends.
Can - A principal module that is part of a shield machine such as an MTBM or tunnel boring machine (TBMs); its use depends on the installation dimensions required and the presence of an articulated joint to facilitate steering. The can may also be referred to as a trailing tube.
Cantilever - The part of a structure that extends beyond its support.
Capital - A sum of money used to implement projects.
Carbon Black - A black pigment produced by the incomplete burning of natural gas or oil, that possesses excellent ultraviolet protective properties.
Carbon Footprint - The amount of carbon dioxide generated and caused by a construction project, including any traffic impacts.
Carriage - The mechanical part of a non-split boring machine that includes the engine or drive motor, the drive train, thrust block and hydraulic cylinders.
Carrier Pipe - Pipe for conveyance of water, gas, sewage, or other products and services. Some carrier pipe can be installed by direct jacking (i.e. one-pass microtunneling).
Cased Bore - A bore in which a pipe, usually a steel casing, is inserted simultaneously with the boring operation.
Casing - A direct-jacked pipe in a two pass system that supports a bore. The casing is not a carrier pipe.
Casing Adapter - A circular mechanism to provide axial and lateral support of a smaller diameter casing than that of the casing pusher.
Casing Pipe - A pipe installed as external protection to a Product Pipe.
Casing Pipe Method - Method in which a casing, generally steel, is pipe jacked into place, within which a product pipe is inserted later.
Casing Pusher - The front section of a boring machine that distributes the thrusting force of the hydraulic cylinders to the casing and forms the outside of the spoil ejector system.
Cast Iron (CI) - Sewer pipe material, sometimes provided as ductile cast iron.
Catastrophic Rainfall - Rainfall event of return frequency far in excess of any event collection system design performance criteria typically, say, a 1 in 200 year storm.
Catch Basin - A small buried structure to divert overland stormwater flow into sewer flows.
Catchment - A geographical area draining to a sewer or receiving water.
Categorization - A structured process of placing items into sets according to related characteristics for prioritization.
Cathode - The electrode of an electrolytic cell at which reduction is the principal reaction (Electrons flow toward the cathode in the external circuit ). Typical cathodic processes are cations taking up electron and being discharged, oxygen being reduced, and the reduction of an element or group of elements from a higher to a lower valence state.
Cathodic - A process by which the corrosion of a metal pipeline may be protected by the use of an electrical current.
Cathodic Corrosion - An unusual condition (especially with Al, Zn, Pb) in which corrosion is accelerated at the cathode because the cathodic reaction creates an alkaline condition which is corrosive to certain metals.
Cathodic Protection - Preventing corrosion of a pipeline by using special cathodes (and anodes) to circumvent corrosive damage by electric current. Also a function of zinc coatings on iron and steel drainage products - galvanic action.
Caulking - General term which, in trenchless technology, refers to methods by which joints may be closed within a pipeline.

Formulation and sudden collapse of vapor bubbles in a liquid; usually resulting from local low pressures - as on the trailing edge of a propeller; this develops momentary high local pressure which can mechanically destroy a portion of a surface on which the bubbles collapse.

CCTV - Closed circuit television used to carry out internal inspection and survey of pipelines.
Cell - Electrochemical system consisting of an anode and a cathode immersed in an electrolyte. The anode and cathode may be separate metals or dissimilar areas on the same metal. The call includes the external circuit which permits the flow of electrons from the anode toward the cathode (See Electrochemical Cell).
Cell Classification - Method of identifying plastic materials, such as polyethylene, as specified by ASTM D 3350, where the Cell Classification is based on these six properties: (1) Density of Base Resin (2) Melt Index (3) Flexural Modulus (4) Tensile Strength at Yield (5) ESCR (6) Hydrostatic Design Basis and Color.
Cellar Drain - A pipe or series of pipe which collect wastewater which leaks, seeps, or flow into subgrade parts of structures and discharge them into a building sewers or by other means dispose of such wastewaters into sanitary, combined or storm sewers (Referred to also as "basement drain").
Cemented Soils - Soils in which the particles are held together by a naturally occurring or man-made chemical agent that changes the soils’ physical and mechanical properties.
Centerline - The vertical distance between the center of the drive chuck and the ground plane.
CFM - Cubic Feet per Minute; a measure of flow volume. One CFM equals 0.472 liters per second.
Change Order - A written order to the contractor authorizing an addition, deletion or revision in the work, within the general scope of work of the agreement, authorizing an adjustment in the agreement price or agreement time.
Channel - A prepared flow route within the bench of a manhole that conveys the incoming flow to the downstream pipe.
Charge Line - See Feed Line.
Chemical Grouting - Method for the treatment of the ground around a shaft or pipeline, using non-cementitious compounds, in order to facilitate or make possible the installation of an underground structure.
Chemical Resistance - Ability to render service in the transport of a specific chemical for a useful period of time at a specific concentration and temperature.
Chemical Stabilization - Renovation method in which a length of pipeline between two access points is sealed by the introduction of one or more compounds in solution into the pipe and surrounding ground and, where appropriate, producing a chemical reaction. Such systems may perform a variety of functions such as the sealing of cracks and cavities, the provision of a new wall surface with improved hydraulic characteristics or ground stabilization.
Chimney - The small vertical section between a manhole frame and cone which is built from brick, masonry, or concrete adjusting rings.
Chippers - See Bits.
CIP - Cast Iron Pipe
CIPP - Cured In Place Pipe; a rehabilitation technique whereby a flexible resin-impregnated tube is installed into an existing pipe and then cured to a hard finish, usually assuming the shape of the existing pipe.
Circumferential - Around the inner surface of a circular pipe cross section.
Circumferential Coefficient of Expansion and Contraction - The fractional change in circumference of a material for a unit change in temperature.
Cleaning - An action of a boring machine to remove spoil that occurs when the auger is rotating while axially stationary.
Close-fit - Description of a lining system in which the new pipe makes close contact with the defective pipe at normal or minimum diameter. An annulus may occur in sections where the diameter of the defective pipe is in excess of this.
Closed Face - Term referring to one mode of operation of a traditional tunnel boring machine (TBM).
Closed-Circuit Television Inspection (CCTV) - Inspection method utilizing a closed circuit television camera system with appropriate transport and lighting mechanisms to view the interior surface of sewer pipes and structures.
Clutch - A mechanical device that engages or disengages rotary torque from a power source.
Cobble - Per ASTM D653, a rock fragment, usually rounded or semirounded, with dimensions between 3 and 12 in. (75 and 305 mm).
COD - Chemical Oxygen Demand; a measure of the need for oxygen by chemical processes.
Coefficient - A scientifically based factor that is taken into account during calculations.
Coefficient of Thermal Expansion and Contraction - The fractional change in length of a material for a unit change in temperature.
Cofferdam - A barrier built in the water so as to form an enclosure from which the water is pumped to permit free access to the area within.
Cohesionless - A material that does not readily bond with other particles.
Cohesionless Soils (Noncohesive Soils) - Earth materials containing less than 20 percent soil particles passing the #200 sieve. Any free-running soil, such as sand or gravel, whose strength depends on friction between particles.
Cohesive Soil - Earth materials containing 20 percent or more soil particles passing the #200 sieve.
Colcrete - Proprietary equipment to measure the workability of annulus grout.
Cold Bend - To force the pipe into a curvature without damage, using no special tools, equipment or elevated temperatures.
Colebrook White Prandtl - A formula for calculating the flow through pipes.
Collapse - Critical failure of a pipeline when its structural fabric disintegrates.
Collaring - The initial entry of casing or a cutting head into the earth.
Collection System - A network of sewers which serves one or more catchment areas.
Collector Sewer - A sewer located in the public way collects the wastewaters discharged through building sewers and conducts such flows into larger interceptor sewers and pumping and treatment works. (Referred to also as "street sewer.")
Colloidal - Very small insoluble non diffusible particles that remain in suspension.
Combined Sewer Sytem - A single network of sewers designed to convey stormwater as well as sanitary flows.
Compaction - The densification of a soil by means of mechanical manipulation.
Composite Ring Brick Sewer - A brick sewer which consists of a greater number of layers of brick above the springing line than below the springing line.
Compounding - The process where additives and carbon black are homogeneously mixed with the base polyethylene.
Compressed Air Method - General term which, in trenchless technology, refers to the use of compressed air within a tunnel or shaft in order to balance ground water and prevent ingress into an open excavation.
Compression Gasket - A device which can be made of several materials in a variety of cross sections and which serves to secure a tight seal between two pipe sections (e.g., "O" rings).
Compression Ring - A ring fitted between the end-bearing area of the leading pipe bell and the trailing pipe spigot to help distribute jacking forces more uniformly. A compression ring is attached to the trailing end of each pipe and is compressed between the pipe sections during jacking. The compression ring compensates for steering corrections, pipe misalignment, and pipe dimensional tolerances. Also referred to as a packer.
Conductivity - A measure of the ability of a solution to carry an electrical current. conductivity varies both with the number and type of ions the solution carries.
Conduit - A broad term that can include pipe, casing, tunnels, ducts or channels. The term is so broad that it should not be used as a technical term in boring or tunneling.
Cone - The section between the top of a manhole wall and chimney or the frame. The diameter of the manhole is reduced over the cone section to receive the frame. The cone section may be concentric or eccentric.
Consolidation - The gradual reduction in the volume of a soil mass resulting from an increase in compaction.
Contact Grouting - Grouting injected into the void space between the jacking pipe and the ground after the drive is completed.
Contaminated Plume - The underground trace of an environmental pollutant.
Continuous Sliplining - See Sliplining or Lining with Continuous Pipe.
Contract Documents - Documents prepared by the owner and project engineer for bidding and for awarding a project; can include bid forms, general conditions, special conditions, technical specifications, drawings, geotechnical data reports, and geotechnical baseline reports.
Contract Price - The total moneys payable to the contractor under the contract documents.
Contract Time - The number of calendar days stated in the agreement for the completion of the work.
Contracting Officer - The owner (guarantee) - The individual who is authorized to sign the contract documents on behalf of the owner's governing body.
Contractor - The person, firm or corporation with whom the owner has executed the agreement.
Control Console - An electronic unit typically inside a container located on the ground surface that controls the operation of the microtunneling machine. As the machine operator drives the tunnel from the control console, electronic information is transmitted to the control console from the MTBM. This information includes head position, steering angle, jacking force, penetration rates, machine-face torque, slurry charge and discharge flow rates and pressures, and laser position. Some control consoles are equipped with a computer that tracks and stores the data and allows real‑time analysis of the tunnel drive.
Control Lever - A handle that activates or deactivates a boring machine function.
Controls - Part of the microtunneling system that allows synchronized excavation, removal of spoils, and jacking of pipe to balance forward movement with excavation so that ground settlement and heave are managed.
Conventional Trenching - Method in which access is gained by excavation from ground level to the required level underground for the installation, maintenance or inspection of a pipe, conduit or cable. The excavation is then backfilled and the surface reinstated.
Conventional Tunnelling - Methods of tunnel construction ranging from manual excavation to the use of self propelled tunnel boring machines. Where a lining is required bolted segmental rings are frequently used.
Corbel - For brick manholes this term is sometimes used in place of cone, and indicates the gradual reduction in diameter by indenting brick.
Core Area - That part of a sewer network containing the critical sewers, and other sewers where hydraulic problems are severe and merit detailed investigation.
Corrosion - The destruction of a material or its properties because of a reaction with its (environment) surroundings.
Corrosion Fatigue - Fatigue type cracking of metal caused by repeated or fluctuating stresses in a corrosive environment characterized by shorter life than would be encountered as a result of either the repeated or fluctuating stress alone or the corrosive environment alone.
Corrosion Index - Measurement of the corrosivity of a water (e.g. Langelier Index, Ryznar Index, Aggressive Index, etc.)
Corrosion Rate - The speed (usually an average) with which corrosion progresses (it may be linear for a while); often expressed as though it were linear, in units of mdd (milligrams per square decimeter per day) for weight change, or mpy (milligrams per year) for thickness changes.
Corrosion Resistance - Ability of a material to withstand corrosion in a given corrosion system.
Corrugated pipe - Pipe with ridges (corrugations) going around it to make it stiffer and stronger. The corrugations are usually in the form of a sine wave a+B181nd are usually made of galvanized steel or aluminum.
Cover - The lid at the top of the manhole which can be removed when access to the interior of the manhole is required.
Cracks - Fracture lines visible around the circumference and/or along the length of a sewer.
Cradle - A structure constructed from concrete or masonry that provides structural support to a sewer. It typically surrounds the bottom and sides of a sewer up to the springing line.
Cradle Machine - A boring machine typically carried by another machine that uses winches to advance the casing.
Creep - The dimensional change, with time, of a material under continuously applied stress after the initial elastic deformation.
Crew - The number of persons required for the performance of work at a site as determined by the contractor in response to task difficulty and safety considerations at the time or location of the work.
Critical Sewers - Sewers with the most significant consequences in the event of structural failure.
Cross members - The lateral supports under the track of a boring machine.
Crossing - Pipeline installation in which the primary purpose is to provide one or more passages beneath a waterway, road, or other surface obstruction.
Crown - The highest point of the pipe or tunnel.
Crush Lining - See Pipe Eating.
CSO - Combined Sewer Overflow; a hydraulic relief point within combined sewer systems designed to discharge excess flows during wet weather to receiving waters.
Cured-in-Place Pipe (CIPP) - A lining system in which a thin flexible tube of polymer or glass fibre fabric is impregnated with thermoset resin and expanded by means of fluid pressure into position on the inner wall of a defective pipeline before curing the resin to harden the material. The uncured material may be installed by winch or inverted by water or air pressure, with or without the aid of a turning belt.
Customer - Sewer structure owner, specifically the one requesting the inspection work.
Cut and Cover - See Open Cut.
Cutability - The capacity of rock to be spalled, ripped, chipped, and broken into smaller pieces to allow the advance of the MTBM. Key properties impacting cutability include the frequency of discontinuities, unconfined compressive strength, tensile strength, hardness
Cutter Chamber Access - See Face Access.
Cutter Wheel - Any rotating tool or system of tools on a common support thatexcavates at the face of a bore.
Cutterhead - Any rotating tool or system of tools on a common support that excavates at the face of a bore. Usually applies to mechanical methods of excavation.
Cutting Bit (Cutterhead) - The actual teeth and supporting structure that is attached to the front of the lead auger, drill stem or front face of the tunnel boring machine. It is used to reduce the material that is being drilled or bored to sand or loose dirt so that it can be conveyed out of the hole. Usually applies to mechanical methods of excavation, but may also include fluid jet cutting.
Cuttings - See Spoils.

Data Logger - (Also field data logger.) Keyboard-type device used to electronically record inspection data.
Data Reviewers - Personnel from other departments who will review the recorded inspection information for use in future repair planing or during the auditing process.
Dead Man - A fixed anchor point used in advancing a saddle or cradle type boring machine.
Debris - Accumulation of material consisting of organic (human waste, food wastes, etc.), (sand, gravel, wood, etc.), grease or roots.
Deck Assembly - Drive train assembly for a split design boring machine.
Deformed and Reshaped - See Modified Sliplining.
Delay Time - Lost time associated with the owner’s issues.
Department Contact - Assigned person responsible to represent the owning department for decision making and necessary notifications.
Dereliction - The gradual decay of a sewer network accelerated by the negligence of effective maintenance.
Design Specification - Establishes specific requirements the contractor must use, including means and methods. A design specification creates an implied warranty that if the contractor uses the specified means and methods along with industry-accepted good practices, the constructed product will meet the specification requirements.
Desktop Study - A compilation and review of available site, geotechnical, and other information pertinent to a project. Typically performed at the outset of a project, prior to field explorations and detailed design.
Dewater - The act of removing groundwater or lowering the groundwater elevation, using a system of wells and pumps.
Diameter of Reamer (d2) - Largest diameter of reamer.
Diameter of Standard Bit (d1) - Maximum outside diameter of standard bit.
Differential Cut - The spiral, screw like pattern created on the excavated surface as the gauge cutter is advanced while being rotated around the bored periphery of the cutter wheel.
Dimple - A term used in tight fitting pipeline reconstruction, where the new plastic pipe forms an external departure or a point of expansion slightly beyond the underlying pipe wall where unsupported at side connections. The dimples are used for location and reinstatement of lateral sewer service.
DIP - Ductile Iron Pipe
Directional Drilling - A steerable system for the installation of pipes, conduits and cables in a shallow arc using a surface launched drilling rig. Traditionally the term applies to large scale crossings in which a fluid-filled pilot bore is drilled using a fluid-driven motor at the end of a bend-sub, and is then enlarged by a washover pipe and back reamer to the size required for the product pipe. The required deviation during pilot boring is provided by the positioning of a bent sub. Tracking of the drill string is achieved by the use of a downhole survey tool.
Discharge Point - The point where the flows in a sewer are discharged to.
Discount - A reduction in the calculated price.
Discrete Sliplining - See Sliplining or Lining with Discrete Pipes.
Diurnal - To vary during the day.
Diverting - Modifying the normal wastewater flow to allow access to some specific sewer structure; often includes bypass pumping.
Dog Plate - See Thrust Block.
Dogs - Moveable protrusions in the thrust block that engage holes or blocks in the track.
Double Ring Brick Sewer - A brick sewer which consists of two layers of bricks.
Downtime - Time lost when the MTBM is unable to operate; generally associated with equipment failure.
Drainage Fixture Unit - A drainage fixture unit, often referred to as a fixture unit or FU, is a unit of measure of the waste water flow generated by an appliance, such as a sink or toilet. For example, the typical full bath has a value of 9 FUs. See availability fee for cost.
Drill Bit - A tool which cuts the ground at the head of a Drill String, usually by mechanical means but may include Fluid Jet Cutting.
Drill String - 1) The total length of drill rods/pipe, bit, swivel joint etc. in a drill bore-hole. 2) System of rods used with cutting bit or compaction bit attached to the drive chuck.
Drilling Fluid/Mud - Water that may contain additives, including bentonite, polymers, soda ash, surfactants, or other materials, to enhance stability and excavatability. If the drilling fluid contains additives, it is considered to be engineered drilling fluid, whether specified by the engineer or selected by the contractor. Some additives may increase the effectiveness of the drilling fluid and reduce adhesion of the spoils (cuttings). The drilling fluid is used in a closed-loop system for transporting spoils and for counterbalancing earth and groundwater pressures during microtunneling.
Dripper - Applied to infiltration to quantify water dripping into a sewer in a non-continuous way through a defect or faulty joint.
Drive - Designation of the pipe installed from a jacking shaft to a reception shaft.
Drive Chuck - The female hex connector located within the casing pusher.
Drive Shaft - See Jacking Shaft.
Drive/Entry Shaft/Pit - Excavation from which trenchless technology equipment is launched for the installation of a pipeline, conduit or cable. It may incorporate a thrust wall to spread reaction loads to the soil.
Drop Connection Manhole - A manhole in which the influent pipe enters from above the effluent invert depth. If the drop occurs in the manhole itself, it is called an "internal" drop manhole. If the drop occurs a few feet upstream of the manhole, it is referred to as a "external" drop.
Drop Manhole - If the upstream pipe is at a greater elevation than the manhole invert then two inlet connections to the manhole are made. One is through the wall at the same grade as the upstream pipe, the other is at the invert so to direct flows through the channel. The invert connection is made by incorporating a pipe drop in the upstream pipe. The pipe drop may be outside or inside the manhole.
Dry Bore - Any drilling or rod pushing system not employing drilling fluid in the process. Usually associated with guided impact moling, but also some rotary methods.
Duct - (1) In many instances, a term interchangeable with pipe. (2) In the boring industry, it is usually used for small plastic or steel pipes that enclose wires or cables for electrical or communication usage. (3) Conduit inside which a utility service is installed.
DWF - Dry Weather Flow; is the base flow in a sewer prior to rain induced flows.
DWI - Dry Weather Inflow; is the result of flow entering the collection system from connected sources which are not caused by rainfall. Typically, this could include water from fire fighting, hydrant abuse, street washing, sump pumps etc.

Earth Piercing - The use of a tool that comprises a percussive hammer within a suitable, generally torpedo-shaped casing. The hammer may be pneumatic or hydraulic. The term is usually associated with nonsteered devices.
Earth Pressure Balance (EPB) Machine - Type of microtunneling or tunneling machine in which mechanical pressure is applied to the material at the face and controlled to provide the correct counter-balance to earth pressures in order to prevent heave or subsidence. The term is usually not applied to those machines where the pressure originates from the main Pipe Jacking rig in the Drive Shaft/Pit or to systems in which the primary counter-balance of earth pressures is supplied by pressurized drilling fluid.
Earth Pressure Balance Shield - Mechanical tunnelling shield which utilises a full face to support the ground in front of the shield and usually employs an auger flight to extract the material in a controlled manner.
Easement - A liberty, privilege, or advantage without profit which the owner of one parcel of land may have in the hand of another. In this agreement, all land, other than public streets, in which the owner has sewer system lines or installations and right of access to such lines or installations.
Easement Access - Areas within an easement to which access is required for performance of work.
Effective Stresses - In a saturated mass of soil or rock, the total stress P minus pore water pressure, Uw.
Effluent - A generic term used to indicate the relative strength of sewer flows; from stormwater to wastewater to industrial effluent, for example.
Efflux - Flowing out of.
EHMWHD - Extra High Molecular Weight High Density as originally noted in ASTM D1248, Grade P34 materials were specifically EHMW high-density polyethylene materials.
Ejector Pump - See Sewage Ejector Pump.
Elastic Modulus - A measure of the stress buildup associated with a given strain.
Electrofusion - The joining together of parts using electrical energy.
Elongation - The increase in length of a material stressed in tension.
Embankment (or Fill) - A bank of earth, rock or other material constructed above the natural ground surface.
Embrittlement - Loss of ductility of a material resulting from a chemical or physical change.
Emergency Controls - Those controls that stop power to machine or components.
Emergency Recovery Shaft - See Rescue Shaft.
Emergency Repair - A repair that must be made while the main is pressurized, or flowing.
Emergency Stop - A red manually operated push button that, when activated, stops all functions of the machine.
Encrustation - Used to describe deposits left by the partial evaporation of infiltrating groundwater containing dissolved salts. Can be classified into light, medium or heavy by percentage loss of cross-sectional area.
End Section - Flared attachment on inlet and outlet of a culvert to prevent erosion of the roadbed improve hydraulic efficiency, and improve appearance.
Endurance Limit - The maximum stress that a material can withstand for an infinitely large number of fatigue cycles (See Fatigue Strength).
Energy Gradient - Slope of a line joining the elevations of the energy head of a stream.
Energy Head - The elevation of the hydraulic gradient at any section, plus the velocity head.
Engineer - The person, firm or corporation named as such in the contract documents; the "Engineer of Record".
Entrance Pit - 1) An opening in the earth of specified length and width for placing the machine on line and grade. 2) See Boring Pit.
Entrance Seal - See Launch Seal.
Entry Ring - See Launch Seal.
Entry/Exit Angle - Angle to the ground surface at which the drill string enters or exits in forming the pilot bore in a directional drilling/guided boring system.
Environment - The surroundings or conditions (physical, chemical, mechanical) in which a material exists.
Environmental Stress Cracking - The susceptibility to crack or craze under the influence of specific chemicals stress and/or mechanical stress.
EPA - United States Environmental Protection Agency
EPB - Earth Pressure Balance
EPB Machine - Earth pressure balance tunneling machine, by which mechanical pressure is applied to the material at the face and controlled to provide the correct counterbalance to earth and groundwater pressures in order to prevent heave or subsidence. The term is not applicable to microtunneling systems for which the primary counterbalance of earth and groundwater pressures is supplied by pressurized slurry.
Epoxy - Resin formed by the reaction of bisphenol and Epichlorohydrin.
Equalizer - A culvert placed where there is no channel but where it is desirable to have standing water at equal elevations on both sides of a fill.
Erosion - Deterioration of a surface by the abrasive action of moving fluids. This is accelerated by the presence of solid particles or gas bubbles in suspension. When deterioration is further increased by corrosion, the term "Corrosion-Erosion" is often used.
ERW - Electrical Resistance Welding
Estimated Remaining Life (ERL) - A value determined by the inspectors based on experience, judgment, and guidelines within the manual that predicts the amount of time that a sewer structure will remain in a "fit-for-use" condition.
Estuaries - Descriptive of the transition where rivers meet the sea, and currents meet tides.
Execution Department - A department that provides the sewer inspection service.
Exfiltration - The leakage or discharge of flows being carried by sewers out into the ground through leaks in pipes, joints, manholes, or other sewer system structures; the reverse of "infiltrations."
Exit Pit - An opening located at the exit of the cutting head or casing.
Exit Seal - Same as a launch seal except for the retrieval of the machine at the reception shaft. Used in high groundwater and unstable soils to prevent loss of ground.
Exit Shaft - See Reception Shaft.
Expander - A tool which enlarges a bore during a pull-back operation by compression of the surrounding ground rather than by excavation. Sometimes used during a thrust boring process as well as during directional drilling/guided boring pull-back.
Extension Track - An additional section of track used in front of the master track.
Eye - The opening in the shaft wall through which the MTBM is launched.

Fabric - Used to describe the physical material from which a pipe is made: vitrified clay; brick; concrete, for example.
Face - The location where excavation is taking place.
Face Access - Access to the location where excavation is taking place, typically through the cutting chamber. MTBM configuration may only allow limited personnel access to the back of the cutter wheel from within the pipe string. An airlock may also be required in the rear of the MTBM to maintain air pressure for counterbalancing earth and groundwater pressures.
Face Pressure - Earth and groundwater pressures applied against the cross-sectional area of the microtunnel face.
Face Stability - Stability of the excavated face of a tunnel or pipe jack.
Factor of Safety - The ratio of the structural capacity of a system to expected or actual loads on the system.
Fairings - Molding features at the ends at the ends of pipes, usually of varying dimensions to the main pipe, to facilitate easy jointing.
Fatigue - The phenomenon leading to fracture under repeated or fluctuating stresses having a maximum value less than the tensile strength of the material.
Fatigue Strength - The stress to which a material can be subjected for a specified number of fatigue cycles.
Feed Line - Pipeline that transports drilling fluid from the slurry separation plant to the face of the MTBM. Also known as an inlet line or charge line.
Feet - US customary unit for measuring length. One foot equals 304.8 mm; or 0.3048 meters. (abbrev. ft).
Feet Per Second - US customary unit for velocity. One foot per second equals 304.8 millimeters per second; or 0.3048 meters per second. (abbrev. ft/s).
Female Hex Connector - A hexagonal shaped socket.
Ferro-cement - A rehabilitation technique that employs steel fabric mesh, usually in multiple layers but with the maximum mesh diameter not exceeding 2 mm (1/8 inch), which is fixed to the existing sewer and then covered in high strength grout, either placed in situ by man entry work to form a structural lining or pre-formed into segments for later installation.
Field Data Logger - See Data Logger.
Field Orders - A written order issued by the engineer clarifies or interprets the contract documents in accordance with the terms of the contract or orders minor changes in the work in accordance with the terms of the contract.
Filter - Granular material placed around a submarine pipe to facilitate drainage and at the same time strain or prevent the admission of silt or sediment.
Filter Cake - A thin layer of clay or polymer from the slurry at the face and perimeter of the formation being excavated. The filter cake is formed through filtrate loss.
Final Drive - The final reduction unit in the drive line.
Fines - Portion of a soil finer than a No. 200 (75 mm) US standard sieve.
Fit-For-Use Criteria - Criteria used to determine if sewer structures are in a condition that justifies continued operation for its designated service.
Fixture Unit - See Drainage Fixture Unit.
Flare or Flaring - The bending out of the front end of the lead joint to give clearance. Depending on ground conditions, the flares may have all cracks, or cuts fully welded, or a complete flare not welded, or a segmented flare where only portions of the joint are flared.
Flash Point - Temperature at which a material begins to vaporize.
Flexible - Readily bent or deformed without permanent damage.
Flexural Modulus - The slope of the curve defined by flexural load versus resultant strain. A high flexural modulus indicates a stiffer material.
Flexural Strength - The strength of a material in bending expressed as the tensile stress of the outermost fibers at the instant of failure.
Flight - The spiral plates surrounding the tube of an auger.
Flow - (1) Turns drilling fluid flow on. (2) Turns air on.
Flow Attenuation - The process of reducing the peak flow rate in a collection system or of redistributing a proportion of the flow already in a collection system.
Flow Control - A method whereby normal sewer flows or a portion of normal sewer flows are blocked, retarded, or diverted (bypassed) within certain areas of the sewer collection system.
Flow Reduction - The process of decreasing flows into a collection system or of removing a proportion of the flow already in a collection system.
Flow Simulation - The replicating of flows in surface water or combined collection systems using a dynamic digital model.
Flow Split - Location where wastewater exits a manhole through more than one pipe. Also refers to a high point in the sewer system that causes wastewater to flow away from the manhole in more than one direction.
Fluid Jet Cut - See Jet Cutting.
Fluid-Assisted Boring/Drilling - A type of guided boring technique using a combination of mechanical drilling and pressurized fluid jets to provide the soil cutting action.
Fluorescein Dye - A potent Kelly-green fluorescent water dye used to "color" waste streams and identify their flow paths (flow path verification).
Fold and Form Lining - Method of pipeline rehabilitation in which a liner is folded to reduce its size before insertion and reversion to its original shape by the application of pressure and/or heat. See also Lining with Close-Fit Pipes.
Fold and Form Pipe - A pipe rehabilitation method where a plastic pipe manufactured in a folded shape of reduced cross-sectional area is pulled into an existing conduit and subsequently expanded will. pressure and heat. The reformed plastic pipe fits snugly to and takes the shape of the ID of the host pipe.
Force Main - A pipeline that conveys sanitary, combined or stormwater flow under pressure from a pumping (or lift) station to a discharge point.
Forward Rotation - The clockwise rotation of the auger as viewed from the machine end.
Fouling - An accumulation of deposits. This term includes accumulation and growth of marine organisms on a submerged metal surface and also includes the accumulation of deposits (usually inorganic) on heat exchanger tubing.
Foundation Drain - A pipe or series of pipes which collect groundwater from the foundation or footing of structures and discharge it into sanitary, storm, or combined sewers, or to other points of disposal for the purpose of draining unwanted waters away from such structures.
Frac-Out - See Inadvertent Return and Hydrofracture.
Fracture Mechanics - A quantitative analysis for evaluating structural reliability in terms of applied stress, crack length, and specimen geometry.
Fractures - Cracks visibly open along the length and/or circumference of the conduit with the pieces still in place.
Frame - A cast iron unit at the ground surface that provides entry into the manhole.
Frame Ring - In a manhole, it is the metal frame which supports the cover.
Free Boring - To bore or drill without the use of casing installed at the same time as the hole is cut. Not recommended for use with augers.
Front Drive - See Drive Chuck.

Gallons Per Minute - US customary unit to measure liquid volume discharge rate. One gallon per minute equals 0.063 liters per second (abbrev. GPM).
Galvanic Cell - A cell consisting of two dissimilar metals in contact with each other and with a common electrolyte (sometimes refers to two similar metals in contact with each other but with dissimilar electrolytes; differences can be small and more specifically defined as a concentration cell).
Galvanizing (Spelter Coating) - A plating for iron and steel composing primarily of zinc. It may be applied electronically or by dipping the pipe or casing in molten zinc (the fumes are poisonous to breathe).
Gauge Cut - The outermost projection of the excavation, measured as a diameter. The gauge cut is subject to cutter wear and to the differential cut.
Gauge Cutter - The cutter that creates the gauge cut and is subject to wear.
Gel - Per ASTM D653, the condition of a liquid that has begun to exhibit measurable shear strength.
Gel Time - The measured time interval between the point when the slurry mix is in a fluid state and the point when it begins to form a gel.
General Corrosion - Corrosion in a uniform manner.
Geographical Information System (GIS) - A computer software system designed to store,manipulate, analyze, and print geographically referenced information.
Gloves - Gloves (cloth, rubber & leather) used by operators, crew members and tracking locator operators that provide maximum protection against electrical shock if properly used.
Gradation - Sieve analysis of aggregates.
Grade - The elevations shown on plans and/or survey grade stakes for the installation of the carrier pipe. It is occasionally to give elevations for casing. In most cases, it is given to the flow line but can also be given to the top of the pipe or casing.
Gradient - See Grade.
Grain - A portion of a solid metal (usually a fraction of an inch in size) in which the atoms are arranged in an orderly pattern. The irregular junction of two adjacent grains is known as a grain boundary; also a unit of weight, 1/7000th of a pound; also used in connection with soil particles i.e. = grain of sand.
Granular - Technical term referring to the uniform size on grains of crystals in rock.
Graphitization (Graphitic corrosion) - Corrosion of gray cast iron in which the metallic constituents are converted to corrosion products, leaving the graphite flakes intact. Graphitization is also used in a metallurgical sense to mean the decomposition of iron carbide to form iron and graphite.
Gravel - Per ASTM D653, rounded or semirounded particles of rock that will pass a 3-in. (76.2-mm) sieve and be retained on a #4 (4.75-mm) US standard sieve.
Gravity Sewer - A sewer that is designed to operate under open channel conditions (below pipe full capacity) up to a maximum design flow at which point it will become surcharged.
GRC - Glass fiber Reinforced Concrete; a rehabilitation lining.
Grease Trap - Mechanism in a lateral that collects grease before it can reach a main line.
Grinder Pump - See Sewage Grinder Pump.
Grip - Applies travel to rod or pipe.
Ground Cover - Distance between the ground surface and the crown of the pipe.
Ground Mat - Metal mats rolled out on either side of drill rack for operators and crew to stand on during operation to give grounding protection in case of electrical strike.
Ground Mat Cables - Cables connecting the drill rack to the ground mats.
Ground Plane - The surface upon which the machine is placed.
Ground Rod - This is a copper/brass rod which is hand driven into the ground and is connected to the drill rack and mats to provide adequate grounding of unit and personnel.
Ground Rod Cable - Cable connecting the mats and drill rig to the ground rod.
Ground Water Table (or Level) - Upper surface of the zone of saturation in permeable rock or soil (when the upper surface is confined by impermeable rock, the water table is absent).
Groundwater - All subsurface water, as distinct from surface water.
Groundwater Table - See Reference Groundwater Level.
Grout - (1) Material used to seal pipeline and manhole cracks; also used to seal connections within sewer structures. (2) A material, usually cement based, used to fill the annulus between the existing pipe and the lining; and also to fill voids outside the existing pipeline. (3) A material such as a cement slurry, sand or pea gravel that is pumped into voids.
Grouting - The process of filling voids or modifying/improving ground conditions. Grouting materials may be cementitious, chemical, or composed of other mixtures.
GRP - Glass Reinforced Plastic, a family of rehabilitation linings. Often generically known as Reinforced Plastic Mortar (RPM) and Reinforced Thermosetting Resin (RTR).
Guard - A protective device fitted to the machine to minimize the possibility of inadvertent contact with hazards.
Guidance System - System that locates the actual position of the MTBM relative to the laser or other device. The laser or other device should be referenced to the design line and grade.
Guide Rail - Device used to support or guide, first the shield and then the pipe within the drive shaft during a pipe jacking operation.
Guided Auger Boring - A term applied to auger boring systems which are similar to microtunneling, but with the guidance mechanism actuator sited in the drive Shaft (e.g. a hydraulic wrench which turns a steel casing with an asymmetric face at the cutting head). The term may also be applied to those auger boring systems with rudimentary articulation of the casing near the head activated by rods from the drive pit.
Guided Boring - Method for the installation of pipes, conduits and cables using a surface-launched drilling rig. A pilot bore is drilled using a rotating drill string and is then enlarged by a back reamer to the size required for the product pipe. The necessary deviation during the pilot boring is provided by a slanted face to the drill head, an asymmetric drill head, eccentric fluid jets or a combination of these, usually in conjunction with a locator.
Guided Boring Method - Another term for the pilot tube method, in which an auger boring power unit is used with a pilot tube’s guidance and steering system.
Guided Drilling - See Guided Boring.
Gunite - A rehabilitation technique that employs steel reinforcement fixed to the existing sewer which is covered in concrete, usually spray applied.
Gusher - Applied to infiltration to quantify water flowing under pressure into a sewer in a continuous way through a defect or faulty joint.
GWI - Groundwater Infiltration; results from the movement of groundwater in the saturated zone into the collection system through defects in the components of the system located below the water table.

Hand Excavation - The technique used to remove the material (rock, dirt, sand, etc.) by hand held tools (pick, shovel, etc.) from the tunnel face or open ditch.
HDPE - High Density Polyethylene; see Polyethylene.
Head (Static) - The height of water above any plane or point of references (The energy possessed by each unit of weight of a liquid, expressed as the vertical height through which a unit of weight would have to fall to release the average energy posed.) Standard unit of measure shall be the foot. Head in feet for water at 68?/font> F is 1 psi = 2.310 ft.
Headwall - A wall (of any material) at the end of a culvert or, drain to serve one or more of the following purposes: protect fill from scour or undermining, increase hydraulic efficiency, divert direction of flow, and serve as a retaining wall.
Heave - Measurable upward movement of the ground or structure as the result of the excavation process.
Heaving - Process in which the ground in front of a pipe jack may be displaced forward and upward causing a lifting of the ground surface.
Height of Cover (HC) - Distance from crown of a culvert or conduit to the finished road surface, or ground surface, or the base of the rail.
Helicoid - A section of auger flight.
Hex Drive - See Drive Chuck.
High Density Polyethylene - A plastic resin made by the copolymerization of ethylene and a small amount of another hydrocarbon. The resulting base resin density, before additives or pigments, is greater than 0.941 gins/cc.
Highway Drain - A pipe that conveys stormwater runoff from a catchment area street catchbasin to a discharge point.
Hold Down - A hinged or removable assembly that secures the boring machine to the track.
Holiday - Any discontinuity or bare spot in a coated surface.
Hook Rollers - See Hold Down.
Hoop Stress - The circumferential force per unit areas, psi, in the pipe wall due to internal pressure.
Horizontal Directional Drilling (HDD) - A surface-launched trenchless technology for the installation of pipes, conduits, and cables. HDD creates a pilot bore along the design pathway and reams the pilot bore in one or more passes to a diameter suitable for the product, which is pulled into the prepared bore in the final step of the process.
Horizontal Earth Boring - Auger boring, boring, and jacking; the use of auger boring machines to prepare holes by the installation of a casing whereby the spoil is removed by the use of augers.
Horizontal Earth Boring Machine - A machine used to bore horizontally through the earth by means of a rotating tool, or nonrotating pushing or piercing tool.
Horizontal Rotary Drilling - The mechanical installation of pipe or casing by rotating methods which do not use augers for the removal of spoil. Usually uses a fluid of water and bentonite to remove spoil.
Host Pipe - The tube which carries the product being transported and which may go through casings at highway and railroad crossings. It may be made of steel, concrete, clay, plastic, ductile iron, or other materials. On occasion it may be bored direct under the highways and railroads.
Hydraulic Cleaning - Techniques and methods used to clean sewer lines with water e.g.: water pumped in the form of a high velocity spray and water flowing by gravity or head pressure. Devices include high velocity jet cleaners, cleaning balls, and hinged disc cleaners.
Hydraulic Grade Line (HGL) - See Hydraulic Gradient.
Hydraulic Gradient - An imaginary line through the points to which water would rise in a series of vertical tubes connected to the pipe. In an open channel, the water surface itself is the hydraulic grade line.
Hydraulic Radius - The area of the water prism in the pipe or channel divided by the wetted perimeter. Thus, for a round conduit flowing full or half full, the hydraulic radius is d/4, Another term sometimes used for this quantity is hydraulic mean depth.
Hydraulic Reinforcement - The provision of an additional sewer which in conjunction with an existing sewer increases overall flow capacity.
Hydraulics - That branch of science or engineering which treats water or other fluid in motions.
Hydrocarbons, Gaseous - An organic compound made up of the elements of carbon and hydrogen that exists as a gas at ambient conditions (14.7 psi, 73.4?/font> F).
Hydrocarbons, Liquid - An organic compound made up of the elements of carbon and hydrogen that exists as a liquid at ambient conditions (14.7 psi, 73.4?/font> F).
Hydrocleaning - Use of high pressure, high velocity water for cleaning; specifically as applied to passing hydrocleaning nozzles through sewer pipelines to clean walls and flush debris.
Hydrofracture - A special form of inadvertent return in which drilling fluid reaches the surface or waterway. Also called a frac-out.
Hydrogen Blistering - Subsurface voids produced in a metal by hydrogen absorption in (usually) low strength alloys with resulting surface bulges.
Hydrogen Induced Cracking (HIC) - A form of hydrogen blistering in which stepwise internal cracks are created that can affect the integrity of the metal.
Hydrogen Ion (pH) - Refers to acidity or alkalinity of water or soil. An ion is a charged atom or group of atoms in solution or in a gas. Solutions contain equivalent numbers of positive and negative ions.
Hydrogen Stress Cracking - A cracking process that results from the presence of hydrogen in a metal in combination with tensile stress. It occurs most frequently with high strength alloys.
Hydrogen Sulfide - An odorous gas sometimes found in sewer systems. Recognizable by a rotten egg odor. Chemical formula is H2S.
Hydrostatic Design Basis - Hydrostatic design basis can be defined as the normalized long-term strength or calculated hoop strength of the material at 100,000 hours obtained by long-term hydrostatic testing of pipe samples from which the probable safe life of the pipe at various stress levels (working pressures) and at various temperatures can be predicted.

I/I - Infiltration/Inflow; this is the sum of all the extraneous contributions to the collection system.
ICG - Internal Condition Grade; numeric criteria applied to visual images of sewers to develop a priority rating based on defects observed.
Idle Time - Lost time when the MTBM is not in operation; not including make-up time or downtime.
IGN - Information Guidance Notes; an international reference source for some lining materials.
Ignition Temperature - Temperature at which the vapors emitted from a material will ignite either without exposure to a flame (self-ignition) or when a flame is introduced (flash ignition).
Impact - Stress in a structure caused by the force of a vibratory, dropping,, or moving loads. This is generally a percentage of the live load.
Impact Machines - A type of machine that pierces the earth (piercing tool) or rams an object to produce a bore (ramming machine).
Impact Moling - Method of creating a bore using a pneumatic or hydaulic hammer within a casing, generally of torpedo shape. The term is usually associated with non-steered or limited steering devices without rigid attachment to the launch pit, relying upon the resistance of the ground for forward movement. During the operation the soil is displaced, not removed. An unsupported bore may be formed in suitable ground, or a pipe drawn in, or pushed in, behind the impact moling tool. Cables may also be drawn in.
Impact Ramming - See Pipe Ramming.
Impact Strength - The ability of a material to withstand shock loading.
Impervious - Impenetrable. Completely resisting entrance of liquids.
In situ - Describes work on site; in the original place. For example, in situ concrete would differentiate cast in place concrete from precast concrete.
In-line Microtunneling - A method of replacing an existing pipe by filling the pipe with flowable fill to prevent fluid loss and then excavating the entire pipe and surrounding ground with an MTBM for a new installation.
In-Line/On-Line Replacement - The breaking out of an existing pipeline and the installation of a new service on the same line. See Replacement.
Inadvertent Contact - Contact between a person and a hazard resulting from the person’s unplanned actions during normal operation or servicing of the machine.
Inadvertent Return - The loss of drilling fluid, including slurry and lubrication, from the slurry or lubrication system. A special form of inadvertent return, where the fluid exceeds the strength and confining pressure of the ground and reaches the surface or waterway, is called a hydrofracture or frac-out.
Inclinometer - 1) A geotechnical instrument used to measure horizontal deflection transverse to an installed vertical pipe casing by passing a probe through a casing (via two sets of grooves in the casing). (2) An instrument used within the MTBM to measure pitch and roll.
Inert Material - A material which is not very reactive, such as a noble metal or plastic.
Infiltration - (1) Penetration of freshwater or groundwater into the sewer system through cracks, defective joints in the pipeline, and holes, or through lateral connections, manholes or inspection chambers. (2) All extraneous waters (storm water and ground water) which enter the wastewater collection system through various sources including, among others, pipe defects, defective service connections, manhole covers, roof leaders, and foundation drains.
Infiltration/Inflow (II) - The total quantity of water from both infiltration and inflow without distinguishing the source.
Inflow - Water discharged into a sewer system and service connections from sources on the surface.
Inhibitor - (1) A chemical substance or combination of substances which, when present in the environment, prevents or reduces corrosion without significant reaction with the components of the environment. (2) A substance which sharply reduces corrosion, when added to water, acid, or other liquid in small amounts; also, a chemical additive that delays the chemical reaction in epoxy resin systems.
Inlet Line - See Feed Line.
Input Parameter for Electrical Drive - Maximum continuous rated voltage and amperage.
Input Parameter for Hydraulic or Pneumatic Drive - Maximum continuous rated torque and shaft speed.
Input Parameter for Mechanical Drive - Maximum continuous rated torque and shaft speed.
Insertion - See Sliplining.
Inspection Event Number - The unique reference number used to identify a specific inspection of a sewer structure or a group of sewer structures, referred to as an inspection.
Inspector - The owner's on-site representative responsible for inspection and acceptance, approval, or rejection of work performed as set forth in these specifications.
Interaction - The division of load carrying between pipe and backfill and the relationship of one to the other.
Intercepting Drain - A ditch or trench filled with a pervious filter material around a subdrainage pipe.
Interceptor Sewer - A sewer that conveys flow from a trunk sanitary sewer or dry weather flow plus a small volume of stormwater from a trunk combined sewer to a wastewater treatment plant.
Intergranular Stress Corrosion Cracking (IGSCC) - Stress corrosion cracking in which the cracking occurs along grain boundaries.
Interjack Pipes - Pipes specially designed for use with an Intermediate Jacking Station.
Interjack Station - See Intermediate Jacking Station.
Intermediate Jacking Method - Pipe jacking method to redistribute the jacking force by the use of intermediate jacking stations.
Intermediate Jacking Station (IJS) - A fabricated steel cylinder fitted with hydraulic jacks, which is incorporated into a pipeline between two specially fabricated pipe segments. Its function is to provide additional thrust in order to overcome skin friction and distribute the jacking forces over the pipe string on long drives.
Internal Corrosion - Corrosion that occurs inside a pipe because of the physical, chemical, or biological interactions between the pipe and the water as opposed to forces acting outside the pipe, such as soil, weather, or stress conditions.
Internal Erosion - Abrasion and corrosion on the inside diameter of the pipe or tubing due to the fluid that is being transported.
Internal Inspection - Means of ascertaining the condition of pipelines, either by visual inspection for man-entry size or by the use of remote control instrumentation.
Internal Pipe Inspection - The television inspection of a sewer line section. A CC-TV camera is moved through the line at a slow rate and a continuous picture is transmitted to an above ground monitor; see also Physical Pipe Inspection.
Inversion - The process of turning a fabric tube inside out with water or air pressure as is done at installation of a cured in place pipe.
Invert - The lowest point of the pipe, tunnel, or shaft.
Invert Level (Elevation) - The level (elevation) of the lowest portion of a liquid-carrying conduit, such as a sewer, which determines the hydraulic gradient available for moving the contained liquid.
Ion - An electrically charged atom (Na+, Al+3, CL-, S-2) or group of atoms known as "radicals" (NH4+, SO4-2, PO4 3).
Ionization - Dissociation of ions in anaqueous solution (e.g., H2C03 - H+ + HCO3- or H2O - H+ OH).

Jacking - The actual pushing of pipe or casing in an excavated hole. This is usually done with hydraulic cylinders (jacks), but has been done with mechanical jacks, air jacks and just about anything else that man could imagine.
Jacking Force - The total force required to overcome the face pressure component and the frictional resistance component along the pipe so as to allow forward movement of the MTBM and the trailing pipe string.
Jacking Frame - A structural component that houses the hydraulic cylinders used to propel the microtunneling machine and pipeline. The jacking frame cradles the MTBM and jacking pipes, and serves to distribute the thrust load to the pipeline and the reaction load to the shaft wall or thrust block.
Jacking Loads - See Jacking Force.
Jacking Pipes - Pipes designed to be installed using pipe jacking techniques.
Jacking Pit - The excavation that the machinery is set into to install a casing or tunnel. In years past, it has also been known as a "Glory Hole."
Jacking Shaft - Excavation from which trenchless technology equipment is launched for the installation of a pipeline. The jacking shaft may incorporate a thrust wall to spread reaction loads to the ground and an entry ring to control inflows of groundwater and soil at the portal.
Jacking Shield - A fabricated steel cylinder from within which the excavation is carried out either by hand or machine. An articulated steering section and steering jacks are incorporated into the shield to allow it to be adjusted so as to control line and grade. The term is associated with traditional tunneling.
Jacking Station (IJS) - See Immediate Jacking Station.
Jersey Barrier - See K-Rail.
Jet Cutting (Jetting) - (1) A type of Directional Drilling or Guided Boring technique using pressurized fluid jets to provide the soil cutting action. (2) A process using high pressure water to wash out the face of a utility crossing without any mechanical or hand excavation of the soils in the face. This process has also been used to remove the material in open pit mining.
Joint Sealing - Method in which an inflatable packer is inserted into a pipeline to span a leaking joint, resin or grout being injected until the joint is sealed and the packer then removed.
Joints - The means of connecting sectional lengths of sewer pipe into a continuous sewer line using various types of jointing materials. The number of joints depends on the lengths of the pipe sections used in the specific sewer construction work.

K-Rail - A modular concrete or plastic barrier employed to separate lanes of traffic. Also known as Jersey Barrier.
Keepers - See Hold Down.
Kip - A stress unit equal to 1000 pounds.

Laser - A device commonly incorporated into the guidance system and used to track alignment and grade during the tunneling or jacking operation.
Lateral - A service line that transports wastewater from individual buildings to a main sewer line.
Lateral Connection - The point at which the downstream end of a building drain or sewer connects into a larger diameter sewer.
Lateral Spur - The lateral spur is that section of the sewer lateral which extends from the county sewer line to the end of the sewer lateral from the house/building which generally terminates one foot within the property line. Lateral spurs are installed at the time the sewer is constructed to prevent future dig-up of the street.
Launch Pit - Also known as Drive Pit, but more usually associated with "launching" an Impact Moling tool.
Launch Seal - A mechanical seal, usually consisting of a rubber flange that is mounted to the wall of the jacking shaft. The flange seal is distended by the MTBM as the machine passes through the shaft. The seal is intended to prevent the flow of groundwater, soils, slurry, and lubrication into the shaft during tunneling operations.
lb/ft - US customary units for weight per unit length. One lb/ft equals 1.488 kilograms per meter.
Lead Pipe - The leading pipe designed to fit the rear of a jacking shield and over which the trailing end of the shield is fitted.
Length of Drill Rod - Nominal length of drill rod.
Line - (1) The specified direction of the proposed bore in a horizontal plane. (2) (Path) The shortest distance between two points as laid out by a survey crew for the installation of pipelines and their bores and tunnels.
Liner Plate - A proprietary product, used to line tunnels instead of casing, and comes in formed steel segments. When these segments are bolted together they form a structural tube to protect the tunnel from collapsing. The segments are made so that they may be bolted together from inside the tunnel.
Lining - A rehabilitation process where a length of material is introduced to extend the life of the existing sewer. The lining may or may not utilize some structural strength from the existing sewer, and it may or may not function as a structural enhancement within the existing sewer, or an internal non-structural coating or lining material applied to a pipe.
Lining with Close-Fit Pipes - Method of lining with a continuous pipe for which the cross section is reduced to facilitate installation, and reverted after installation to provide a close fit to the existing pipe.
Lining with Continuous Pipe - Method of lining with a pipe made continuous for the length of the section to be renovated prior to insertion, and which has not been shaped to give a cross sectional diameter smaller than its final diameter after installation.
Lining with Cured-in-Place Pipes - Method of lining with a flexible tube impregnated with a thermosetting resin, which produces a pipe after resin cure.
Lining with Discrete Pipes - Method of lining with pipes shorter than the section to be renovated which are not jointed prior to insertion to form a continuous pipe, and which have not been shaped to give them a cross sectional diameter smaller than their final diameter after installation.
Lining with Inserted Hose - Method of lining with a loose fit reinforced hose to provide a pipe lining such that fluids may be conveyed under pressure.
Lining with Pipe Segments - Method of lining with pipe sections made of at least two pieces with both longitudinal and circumferential joints.
Lining with Spirally Wound Pipes - Method of lining with a profiled strip, spirally wound to form a continuous pipe after installation.
Lipping - A degree of overlap between adjacent units.
Live Insertion - Installation of a liner whilst the product pipe remains in service.
Localized (Spot) Repair - Repair work on a pipe, particularly sewerage, to an extent less than the run between two access points.
Locator - An electronic instrument used to determine the position and strength of electro-magnetic signals emitted from a transmitter sonde in the pilot head of a boring system, in an impact moling tool or from existing underground services which have been energized. Sometimes referred to as a Walkover System.
Long Term Strength - The hoop stress in the wall of the pipe is sufficiently low that creep (relaxation) of the materials is nil and assures service life in excess of 50 years.
Low Load Method - A pipe jacking method in which separate provision is made to carry the jacking load, the pipe being installed carrying little or none of the jacking force.
Lubrication - The act of injecting a fluid, normally bentonite and/or polymers, to reduce the skin friction and jacking forces on the jacking pipe during installation. The fluid fills the annular space.

Machine Roller - See Cam Follower.
Major Blockage - A blockage (structural defect, collapse, protruding service connection, debris) which prohibits manhole-to-manhole cleaning, TV inspections pipe flow, or rehabilitation procedures.
Make-Up Time - The time spent to add a pipe segment and make connections.
Male Hex Connector - See Shank.
Man-Accessible - Description of a pipe or excavation which can be physically entered by an operative.
Man-Entry - Describes any trenchless technology process which requires an operative to enter a pipe, duct or bore. OSHA has no minimum size limit for Man-Entry; however, they address a much broader concept of "confined space" in Title 29 Code of Federal Regulations Part 1910.146. The minimum size for which this is permissible in the UK is 900 mm (approximately 36 in.).
Manhole - A structure that allows access to the sewer system.
Manning's Formula - An equation for the value of coefficient c in the Chezy Formula, the factors of which are the hydraulic radius and a coefficient of roughness; an equation itself used to calculate flows in gravity channels and conduits.
Manual Inspection - Method of sewer inspection that usually involves physical entry and hands-on examination; also includes used of CCTV camera with manual puppetting (e.g., in manholes).
Manual Mechanical Shield - Open shield in which manpower is used to excavate the material but which has some steering capability.
Marsh Funnel Viscosity - A measure of the flow rate of a fluid through a calibrated funnel. A Marsh funnel is typically used to measure drilling fluid and slurry viscosity, in seconds per quart (sec/qt) of fluid. The Marsh funnel viscosity of water is 26 seconds per quart.
Master Casing Pusher - See Casing Pusher.
Master Track - The rear most track section.
Maximum Allowable Jacking Force - The largest jacking force that can be applied to the jacked pipe, allowing for an appropriate factor of safety.
Maximum Allowable Operating Pressure - The highest working pressure expected and designed for during the service-life of the main.
Maximum Anticipated Jacking Force - The largest anticipated jacking force required to advance jacking pipe and machine along a drive.
Measurement While Drilling (MWD) - Borehole survey instrumentation that provides continuous information simultaneously with drilling operations, usually transmitting to a display at or near the drilling rig.
Mechanical Cleaning - Methods used to clean sewer lines of debris mechanically with devices such as rodding machines, bucket machines winch-pulled brushes, etc.
Mechanical Props Repair - See Rerounding.
Median Barrier - A double-faced guardrail in the median or island dividing two adjacent roadways.
Melt Flow - A measure of the molten material's fluidity.
Melt Flow Rate - The quantity of thermoplastic material in grams that flows through an orifice during a 10-minute time span under conditions as specified by ASTM D 1238.
Melt Index - The melt flow of a thermoplastic material as determined under Condition E of ASTM D 1238. Condition C or high load melt index produces a higher melt flow for a given material as a result of the greater force applied to the sample during the test.
Melt Viscosity - The resistance of the molten material to flow.
Microtunnel Boring Machine (MTBM) - The microtunnel boring machine (MBTM) refers to the microtunnel shield jacked through the earth which excavates the ground in advance of the pipe being installed.
Microtunneling - A trenchless construction method for installing pipelines with the following attributes – remote control, guidance, pipe jacking, and continuous support.
Midi-Rig - Steerable surface-launched equipment for the installation of pipes, conduits and cables. Applied to intermediate sized drilling rigs used as either a small directional drilling machine or a large guided boring machine. Tracking of the drill string may be achieved be either a downhole survey tool or a locator.
Million Gallons per Day (MGD) - US customary unit for flow measurement. One MGD equals 43.81 liters per second.
Mini-Horizontal Directional Drilling (Mini-HDD) - A term sometimes applied to Guided Boring.
Mixed Face - An interface within the excavated tunnel zone between two geological units that have a significant contrast in engineering properties (e.g., rock overlain by soft ground, or very soft, low-strength soil overlain or underlain by a very stiff, high-strength soil).
Mixed Ground - The excavated tunnel zone, without a defined interface, that contains soil and coarse fractions of gravels, cobbles, and boulders (i.e., silt with boulders). This term is not currently defined by ASTM or USCS.
Mixed Reach - Refers to a significant change in ground type, characteristics, or behavior along the excavated tunnel between the jacking and receiving shafts. This term is not currently defined by ASTM or USCS.
Modifications - (1) A written amendment of the contract documents signed by both parties. (2) A change order. (c) A written clarification or interpretation issued by the engineer in accordance with the terms of the contract. (d) A written order for a minor change or alteration in the work issued by the engineer pursuant to the terms of the contract. A modification may only be issued after execution of the agreement.
Modified Sliplining - A range of techniques in which the liner is reduced in cross sectional diameter before insertion into the Carrier Pipe. It is subsequently restored to close to its original diameter, generally forming a close fit with the original pipe. Methods of cross sectional area reduction include squeezing, folding into a U-shape or stretching. See Lining with Close-fit Pipes.
Modulus of Elasticity (E) - The stress required to produce strain, which may be a change of length (Young's modulus); a twist or shear (modulus); a twist or sheat (modulus or rigidity); or a change of volume (bulk modulus), expressed in dynes per square centimeter.
Mole - See Impact Moling.
Mole Ploughing - Burying a pipeline by pulling a plough through the ground while a continuous length of pipe is fed into the top of the plough and laid out underground from the tail of the plough. An alternate ploughing technique may use a plough blade with a bullet at the end to create a tunnel beneath the surface into which a pipe may be pulled.
Molecular Weight Distribution - The ratio of the weight average molecular weight to the number average molecular weight. This gives a preliminary indication of the range of molecular weights.
Moling - A minimum excavation procedure for the construction of pipelines. In collection system re-engineering, moling is typically used as a form of on line replacement, breaking aside the existing sewer fabric and pulling through a new structural lining.
Moment of Inertia - Function of some property of a body or figure - such as weight, mass, volume, area, length, or position, equal to the summation of the products of the elementary portions by the squares of their distances from a given axis.
Moment, Bending - The moment which produces bending in a beam or other structure. It is measured by the algebraic sum of the products of all the forces multiplied by their respective lever arms.
Muck - Spoils or removal of same.
Multiple Ring Brick Sewer - A brick sewer that consists of three or more layers of bricks.
Multistaged New Installation - To plan and undertake projects with regard to a phased/milestone schedule.

N-Value - The number of blows per foot required to drive a standard penetration test (SPT) soil sampler into the ground during geotechnical exploration. The N-value is often used to estimate in situ consistency of clays and silts and relative density of sands.
Narrow Trenching - Method of excavation of a trench up to 100mm wider than the outside diameter of the service to be installed, usually employing either a rockwheel or chain type trencher.
Neutral Axis - An axis of no stress.
Nominal Size - Size of pipe or shaft used to define the internal working diameter.
Nominalize - To classify a value into an established range or category.
Non-Man Entry - Size of pipe, duct or bore less than that for man-entry.
Non-Uniform Corrosion - Corrosion that attacks small, localized areas of the pipe. Usually results less metal loss than uniform corrosion but causes more rapid failure of the pipe due to pits and holes.
Noncohesive Soils - See Cohesionless Soils.
Notch Sensitivity - The extent to which an inclination to fracture is increased by a notch, crack, scratch, or sudden change in section.
Notice of Award - The written notice by owner to the apparent successful bidder stating that upon compliance with the conditions precedent to be fulfilled by him within the time specified, the owner will execute and deliver the agreement to him.
Notice to Proceed - NTP, a written notice given by the owner to the contractor (with a copy to the engineer) fixing the date on which the contract time will commence to run and on which contractor shall start to perform his obligations under the contract documents.

Obstruction - Any buried object that lies completely or partially within the cross section of the microtunnel and that impedes continued forward progress along the design path and within allowable tolerances.
Ogee - A joint with an elongated "S" profile within the thickness of a sewer pipe wall.
Oiler - Changes amount of lubricating oil injected in supply air.
One-Pass - A procedure by which the carrier pipe is directly jacked into the ground.
OPC - Ordinary Portland Cement; customarily used for making concrete, mortar and grout in non-aggressive conditions.
Open Cut - The method by which access is gained to the required level underground for the installation, maintenance or inspection of a pipe, conduit or cable. The excavation is then backfilled and the surface restored. See Conventional Trenching.
Open Face Shield - Shield in which manual excavation is carried out from within a steel tube at the front of a pipe jack.
Open-Face - Term referring to one mode of operation of a traditional TBM.
Operator Presence Control - A control or mechanism designed so that operator presence is necessary to activate a specific function.
Orangeburg - Orangeburg is a bituminized fiber pipe. Manufactured as an alternative to metal pipe in response to a metal shortage due to World War II. The life expectancy from experience is about 25 years. This type of pipe has been known to collapse often necessitating replacement.
Organic Debris - Production waste and other material that accumulates in sewers or manholes.
OSHA - Occupational Safety and Health Administration
Other Sewer Structures - Other portions of the industrial sewer pipelines and manholes, including trap tanks, sumps, and any other structure not specifically identified.
Outfall - An outlet to a sewer system.
Ovality - There are two options: a) the difference between the maximum and mean diameter divided by the mean diameter, and b) the difference of the mean and minimum divided by the mean, at any one cross section of a pipe, generally expressed as a percentage.
Overcut - The theoretical difference between the radial measurement of the gauge cut and the MTBM shield; equal to (Gauge Cut OD - MTBM OD)/2. Actual overcut is reduced as the gauge cutter is worn and because of the differential cut.
Overflow - (1) The excess water that flows over the ordinary limits of a sewer, manhole, or containment structure. (2) An outlet, pipe, or receptacle for the excess water.
Owner - A public body of authority, corporation as partnership, or individual for whom the work in to be performed.
Oxidation - Loss of electrons, as when a metal goes from the metallic state to the corroded state.

Packer - See Compression Ring.
Parapet - Wall or rampart, breast high. Also, the wall on top of an abutment extending from the bridge seat to the underside of the bridge floor and designed to hold the backfill.
Pascal's Law - Pressure exerted at any point upon a confined liquid is transmitted undiminished in all directions.
Pavement, Invert - Lower segment of a corrugated metal pipe provided with a smooth bituminous material that completely fills the corrugations, intended to give resistance to scour, erosion, and to improve flow.
PE - Polyethylene; a form of thermoplastic pipe.
Penetration Rate - Instantaneous excavation distance per time while the MTBM is operating, typically measured in inches per minute or millimeters per minute.
Percent (%) - A dimensionless number with the ratio of one (1) to one hundred (100). In the construction industry, it is mostly used to give the rise of fall of a pipe line, or road, in feet per 100 feet (i.e., a one (1) foot rise in one hundred (100) feet would be a plus 1% (one percent) grade).
Perched Water Table - An accumulation of groundwater that is above the regional groundwater table in an unsaturated zone.
Performance Specification - Establishes the performance criteria the constructed product must meet. A performance specification leaves the selection of means and methods to the contractor.
Periphery - Circumference or perimeter of a circle, ellipse, pipe-arch, or other closed curvilinear figure.
Permeability - Penetrability.
PFA - Pulverized Fuel Ash; a fine powder residue after burning carbon based products. Especially from electricity generating stations.
pH - A measure of the acidity or alkalinity of a solution. A value of seven is neutral; low numbers.
Physical Pipe Inspection - The crawling or walking through manually accessible pipe lines. The logs for physical pipe inspection record information of the kind detailed under TELEVISION INSPECTION. Manual inspection is only undertaken when field conditions permit this to be done safely. Precautions are necessary.
Piercing Tool - See Earth Piercing.
Piezometer - A specialized monitoring well that provides discrete screens and underground seals to produce a measurement of the groundwater pressure at specific intervals below ground. The groundwater pressure may be measured using open standpipes or vibrating wire transducers.
Pile, Bearing - A member driven or jetted into the ground and deriving its support from the underlying strata and/or by the friction of the ground on its surface.
Piling - Rigid supports, driven vertically to provide wall support in the pit.
Pilot Bore - The action of creating the first (usually steerable) pass of any boring process which later requires back-reaming or similar enlarging. Most commonly applied to Guided Boring, Directional Drilling, and 2-pass microtunneling systems.
Pilot Tube Method - A multistage method of accurately installing a product pipe to line and grade by use of a guided pilot tube followed by upsizing to install the product pipe. The pilot tube method does not fit within the definition of microtunneling.
Pins - See Shank.
Pipe - A long tube of clay, concrete, steel, metal, wood, etc., for conveying water, gas, oil or other materials.
Pipe Break - A mechanical device designed to prevent the MTBM and pipe string from moving back into the shaft.
Pipe Bursting - A replacement method. A technique for breaking the existing pipe by brittle fracture, using force from within, applied mechanically, the remains being forced into the surrounding ground. At the same time a new pipe, of the same or larger diameter, is drawn in behind the bursting tool. The pipe bursting device may be based on an Impact Moling tool to exert diverted forward thrust to the radial bursting effect required, or by a hydraulic device inserted into the pipe and expanded to exert direct radial force. Generally a PVC or HDPE pipe is used. Also known as Pipe Cracking and Pipe Splitting.
Pipe Displacement - Term used in North America. See Pipe Bursting.
Pipe Drilling Cracking - See Pipe Bursting.
Pipe Eating - See In-Line Microtunneling.
Pipe Jacking - A system of using hydraulic jacking from a drive shaft to directly install pipes behind a shield machine so that they form a continuous string in the ground.
Pipe Joint Sealing - A method of sealing leaking or defective pipe joints which permit infiltration of groundwater into sewers by means of injecting chemical grout into and/or through the joints from within the pipe.
Pipe Lubricant - See Lubrication.
Pipe Pulling - Method of replacing small diameter pipes where a new product pipe is attached to the existing pipe which is then pulled out of the ground.
Pipe Pusher - A machine that pushes or pulls a rod or pipe to produce a bore by means of compaction without rotation or impact.
Pipe Ramming - A trenchless installation method whereby a percussive hammer is attached, via an adapter, to an open-end casing, which is then driven through the ground. To create an open casing, the spoils within the casing are removed after the drive is completed, or periodically during the drive.
Pipe Segment - A specific portion of the sewer system piping; usually runs between two structure (e.g., manhole, trap tanks, sumps); identified with unique sewer structure ID number.
Pipe Splitting - Replacement method for breaking an existing pipe by longitudinal slitting. At the same time a new pipe of the same or larger diameter may be drawn in behind the splitting tool. See also Pipe Bursting.
Pipe String - The succession of joined individual pipes being used to advance and support the excavation.
Pipeline (also pipe) - Portions of the sewer system that are constructed of piping as opposed to manholes and other structures (e.g., trap tank, sumps, etc.).
Pipeline Reconstruction - The in situ repair of an existing pipeline that has suffered loss of pressure integrity or has been structurally damaged. The liner becomes the principal pressure containment or structural element of the in situ composite pipe structure.
Pipeline Rehabilitation - The in situ repair of an existing pipeline, which has become corroded or abraded, by insert renewal of a liner which rehabilitates the bore of the pipeline but does not contribute significantly to increased pressure capability or increased structural strength, yet does improve flow efficiency/hydraulics.
Pipeline System - Interconnecting pipe network for the conveyance of fluids.
Pitch - The upward or downward angle of the MTBM, measured from a theoretical horizontal plane passing through the longitudinal axis of the MTBM.
Pitting - Highly localized corrosion resulting in deep penetration at only a few spots.
Pitting Factor - The depth of the deepest pit divided by the "average penetration" as calculated from weight loss.
Planner - Individual who defines and schedules maintenance (including inspection) activities and provide coordination between operations and work groups.
Planting Piping - Installation procedure that digs a trench and lays the pipe in one step.
Plastic - Any of a variety of thermoplastic and thermoset material used in sewer construction (e.g., high-density polyethylene, polypropylene, PVC, fiberglass reinforced plastics, polyester felt reinforced pipe, epoxy and polyester mortars, etc).
Plasticizer - An admixture to cement to make a mix more fluid without the addition of more water.
Plate - A flat-rolled iron or steel product.
Plough-In Piping - Installation procedure that splits the earth and pulls the pipe into position.
Point Source Repair - See Localized Repair.
Pointing - Method of repairing a brick sewer or manhole by the application of cement mortar where loss has occurred.
Polyester - Resin formed by condensation of polybasic and monobasic acids with polyhydric alcohols.
Polyethylene - A ductile, durable, virtually inert thermoplastic composed by polymers of ethylene. It is normally a translucent, tough solid. In pipe grade resins, ethylene-hexene copolymers are usually specified with carbon black pigment for weatherability.
Polyolefin - A family of plastic material used to make pipes.
Polypropylene - A type of plastic pipe from the polyolefin family. (abbrev. PP)
Ponding - Jetting or the use of water to hasten the settlement of an embankment - requires the judgment of a soils engineer. In hydraulics, pending refers to water backed up in a channel or ditch as the result of a culvert of inadequate capacity or design to permit the water to flow unrestricted.
Pore Water Pressure - The pressure of the groundwater held within a soil or rock: in gaps (pores) between particles.
Potholing - Small, carefully dug, nonmechanized excavation, used to locate a utility or other subsurface feature.
Power Package - The engine and drive section of a split boring machine or the remote engine and hydraulic pumps of a power unit.
Power Requirements - Manufacturer’s recommend maximum flow and pressure.
PPI (Plastic Pipe Institute) - A division of The Society of the Plastics Industry, Inc.
PRC - Polyester Resin Concrete
Precipitation - Process by which water in liquid or solid state (rain, sleet, snow) is discharged out of the atmosphere upon a land or water surface.
Preconditioning Work - That part of a project, usually before renovation work, which includes preparatory cleaning and internal inspection.
Preparatory Cleaning - Internal cleaning of pipelines, particularly sewers, prior to inspection, usually with water jetting and removal of material where appropriate.
Pressure - Changes the drilling fluid pressure.
Pressure Rating - Estimated maximum internal pressure that allows a high degree of certainty that failure of the pipe will not occur.
Pressurized - To pump or force a liquid at a higher rate than that achievable under normal open channel or free surface conditions.
Preventative - Routine maintenance designed to prevent sewer system maintenance problems.
Primary Pipe - The basic conduit when used in conjunction with a "protective liner"; when inspected and evaluated it is the basic or primary pipe which must meet the fit-for-use criteria. When a sewer section is upgraded with a structural, monolithic liner, the liner becomes the primary pipe; subsequent inspection and evaluation is then performed with respect to that liner.
Primary Properties - The properties used to classify polyethylene materials.
Prioritization - To list in descending order of urgency/action.
Priority Classification, Priority Rating - A rating system based on the characteristics of the wastewater conveyed in any sewer structure; sewers carrying hazardous waster have higher priorities ( lower numbers); sewers with special process or location risks carry higher priorities.
Privatize - To take out of public operation or ownership; to instigate private sector participation in the financing and/or operation and/or maintenance and/or ownership of public assets, such as treatment plants and collection systems, for example.
Proactive - To adopt a positive role towards ensuring effective solutions. To anticipate and control events; the opposite of reactive. Probing by auger or coring tool, usually vertically, at the site to determine soil conditions.
Product Pipe - See Carrier Pipe.
Profile - Anchor pattern on a surface produce by abrasive, blasting or acid treatment.
Project - The entire construction to be performed as provided in the contract documents.
Protruding - To be projecting outward.
PSI - Pounds per Square Inch. US customary unit for pressure. One PSI equals 6.896 Kilonewtons per square meter.
Pull Back - That part of a guided boring or directional drilling operation in which the drill string is pulled back through the bore to the entry pit or surface rig, usually installing the product pipe at the same time.
Pull Back Force - The tensile load applied to a drill string during the pull back process. Guided boring and directional drilling rigs are generally rated by their maximum pull-back force.
Pull-In Piping - Also referred to as insert renewal; installation procedure whereby pipe is pulled inside old mains and service lines to provide the new main or service line.
Pump, Sewage Ejector - See Sewage Ejector Pump.
Pump, Sewage Grinder - See Sewage Grinder Pump.
Push Bar - See Thrust Block.
Push Block - See Thrust Block.
Push Package - See Thrust Package.
Push Ring Adapter - Mechanical component mounted on the thrust ring to prevent the thrust ring from coming into contact with and damaging the pipe collar.
PVC - Polyvinyl Chloride; a form of thermoplastic pipe.

Radian - An arc of a circle equal in length to the radius; or the angle at the center measured by the arc.
Radius of Gyration - The distance from the reference at which all of the area can be considered concentrated that still produces the same moment of inertia. Numerically it is equal to the square root of the moment of inertia, divided by the area.
Rainfall - Precipitation in the form of water (usage includes snow).
Ramming - A percussive hammer is attached to an open end casing, which is driven through the ground. The spoil within the casing is removed to leave an open casing.
Ranking - To assign a relative position to competing items.
Ratepayers - Terminology used by lawmakers to refer to utility customers responsible for paying for service.
Re-Engineering - All aspects of upgrading the performance of existing collection systems. Structural re-engineering includes repair, rehabilitation and renewal. Hydraulic reengineering covers replacement, reinforcement, flow reduction or attenuation and occasionally rehabilitation.
Receiving Pit - (1) See exit pit. (2) An opening in the earth located at the expected exit of the cutting head or casing. (3) Come out hole, come out pit; The pit that is dug at the end of the bore, opposite the jacking pit.
Receiving Shaft - See Reception Shaft.
Reception Shaft - Excavation into which the microtunneling equipment is driven and recovered.
Reception/Exit Shaft/Pit - Excavation into which trenchless technology equipment is driven and recovered following the installation of the product pipe, conduit, or cable.
Reduction - Gain of electrons, as when copper is electro-plated on steel from a copper sulfate solution (opposite of "Oxidation").
Reference Groundwater Level - The reference groundwater elevation.
Regression Analysis - An evaluation of the long-term hoop stress data. A linear curve is calculated using the least Squares method to fit the logarithm of hoop stress versus the logarithm of the resulting hours-to-failure.
Regulator - A device for controlling the quantity of sewage and storm water admitted from a combined sewer collector line into an interceptor, pump station or treatment facility, thereby determining the amount and quality of the flow discharged through an overflow device to receiving waters or other points of disposal.
Rehabilitation - (1) All methods for restoring or upgrading the performance of an existing pipeline system. (2) Methods by which the performance of a length of sewer is improved by incorporating the original sewer fabric, but excluding maintenance operations such as tree root or silt removal. Or rehabilitation In situ renovation to improve the performance and extend the life of a defective pipeline, incorporating the fabric of that pipeline. Rehabilitation may be to address structural and/or hydraulic weakness.
Reinforcement - The provision of an additional sewer which in conjunction with an existing sewer increases overall flow capacity.
Reinstatement - Method of backfilling, compaction and re-surfacing of any excavation in order to restore the surface and underlying structure to enable it to perform its original function.
Remote Control System - The remote control system monitors and controls the MBTM, the automated transport system, and the guidance system from a location not in the MTBM.
Renewal - Construction of a new sewer, on or off the line of an existing sewer. The basic function and capacity of the new sewer being similar to the original.
Renovation - Methods of rehabilitation in which all or part of the original fabric of a pipeline are incorporated and its current performance improved.
Repair - Rectification of damage to the structural fabric of the sewer, or the reconstruction of short lengths, but not the reconstruction of a whole pipeline.
Replacement - Construction of a new sewer, on or off the line of an existing sewer. The function of the new sewer will incorporate that of the old, but may also include other improvements or development work.
Rerounding - A preparatory process which involves the insertion of an expansion device into a distorted pipe to return it to a circular cross section. This is usually carried out prior to the insertion of a permanent liner or supporting band.
Rescue Shaft - An unplanned additional shaft required to remove obstacles/obstructions and/or retrieve or repair the MTBM. The rescue shaft may need to function as a jacking shaft to complete the drive.
Resin Impregnation (Wet-Out) - A process used in cured-in-place pipe installation where a plastic coated fabric tube is uniformly saturated with a liquid thermosetting resin while air is removed from the coated tube by means of vacuum suction.
Resin Injection - The localized repair of pipes, usually sewers, by injection of a resin formulation into cracks or cavities which subsequently cures to prevent leakage and further deterioration. It may also increase the structural strength of the pipeline.
Resins - An organic polymer, solid or liquid; usually thermoplastic or thermosetting.
Restoration - The backfilling, compaction and re-surfacing of any excavation in order to restore the surface and underlying structure to enable it to perform its original function.
Retract - The motion of the machine away from the face of the entrance pit.
Return Line - Pipeline that transports slurry from the face of the MTBM to the slurry separation plant. Also known as an outlet line or discharge line.
Reverse - The counter-clockwise rotation of the auger as viewed from the machine end.
Reversing Procedure - Procedure for reversing, if applicable.
Revetment - A wall or a facing of wood, willow mattresses, steel units, stone or concrete placed on stream banks to prevent erosion.
Reynolds Number - A dimensionless quantity named after Osbourne Reynolds who first made know the difference between laminar and turbulent flow. The practical value of the Reynolds Number is that it indicated the degree of turbulence in a flowing liquid. It depends on the hydraulic radius of the conduit, the viscosity of the water and the velocity of flow. For a conduit of a given size, the velocity is generally the major variable and the Reynolds Number will increase as the velocity of flow increases.
Rider - A shallow collection line that runs along the microtunneled trunk sewer to a drop manhole.
RII - Rainfall Induced Infiltration; is a particular form of infiltration which is similar to stormwater inflow. RII generally occurs during and immediately after rainfall events.
Ring Compression - The principal stress in a confined thin circular ring subjected to external pressure.
Rip Rap - Rough stone of various sizes placed compactly or irregularly to prevent scour by water or debris.
Riser - A thin ring located between the frame and cone of a manhole. Used to bring the frame and cover final grade. Commonly, several riser are present in a manhole.
Robot - Remote control device with closed circuit television (CCTV) monitoring, used mainly in localized repair work, such as cutting away obstructions, re-opening lateral connections, grinding and re-filling defective areas and injecting resin into cracks and cavities.
Rock - Per ASTM D653 and ISRM, any naturally formed aggregate of mineral matter occurring in large masses or fragments.
Rod Pushing - Method of forming a pilot bore by driving a closed pipe head with rigid attachment from a launch pit into the soil which is displaced. Limited steering and monitoring capability may be provided, usually in conjunction with a locator. See Thrust Boring.
Rods - Either flexible poles, fiberglass or wood for example, for removing blockages in sewers; or graduated measuring devices for estimating internal sewer dimensions.
Roll - The angle of rotation about the theoretical longitudinal centerline of the MTBM, measured from the 12 o’clock position.
Roller Cone Bit or Reamer - A bit or reamer in which the teeth rotate on separate, internal shafts that are usually aligned perpendicular to line. Used for boring rock.
Roof Leader - A drain or pipe that conducts storm water from the roof of a structure downward and thence into a sever for removal from the property, or onto the ground for runoff or seepage disposal.
Rotary Rod Machine - A machine used to drill earth horizontally by means of a cutting head attached to a rotating rod (not an auger). Such drilling may include fluid injected to the cutting head through a hollow rod.
Rotation Controls - Those controls that control the direction and/or the rotation of the tool.
Rotation Speed - The speed at which the rod turns.
Roughness Coefficient - A factor in the Kutter, Manning, and other flow formulas representing the effect of channel (or conduit) roughness upon energy losses in the flowing water.
RPM - Reinforced Plastic Mortar; a form of thermoset plastic pipe.
RTR - Reinforced Thermosetting Resin; a form of thermoset plastic pipe within the GRP family.
Runoff - That part of precipitation carried off from the area upon which it falls. Also, the rate of surface discharge of the above. That part of precipitation reaching a stream, drain or sewer. Ratoride; a form of thermoplastic Pipe.

Saddle - A vertical support mechanism to hold the casing in position while starting (collaring) the bore.
Saddle Machine - See Cradle Machine.
Safety Factor - As used in determining reinspection interval; a fractional multiplier, based on priority rating, to ensure sewer segment reinspection prior to becoming not fit for use.
Safety Glasses - Eye protection to be worn at all times.
Safety Sign - A notice attached to the machine which advises the nature and severity of a potential hazard which can cause injury or death. It can also provide instructions to reduce or eliminate the hazard.
Samples - Physical examples which illustrate materials, equipment or workmanship and establish standards by which the work will be judged.
Sanitary Sewer - A sewer that conveys the wastewater from two or more properties.
Scaling - High temperature corrosion resulting in formation of thick corrosion product layers. Deposition of insoluble materials on metal surfaces, usually inside water boilers or heat exchanger tubes.
SDR - See Standard Dimension Ratio
Seal - A water-tight bond.
Secondary Stress - Forces acting on the pipe in addition to the internal pressure such as those forces imposed due to soil loading and dynamic soil conditions.
Section Modulus - The moment of inertia of the area of a section of a member divided by the distance from the center of gravity to the outermost fiber.
Sectional Properties - End area per unit of widths, moment of inertial, section modulus, and radius o gyration.
Sediment - Particles that settles on the pipe invert, causing a reduction in cross sectional area.
Sediment Debris - Specifies the extent of the problem (defect) based on the judgment of the field crew.
Seepage - Water escaping through or emerging from the ground along rather extensive line or surface, as contrasted with a spring, the water of which emerges from a single spot.
Seeper - Applied to infiltration during the first stages to quantify the slow ingress of water into a sewer through a defect or faulty joint.
Segmental Concrete Tunnel Liner - Used the same way as Liner Plate except that they are tunnel liners made of concrete.
Segmental Lining - The use of prefabricated segments in Man-Entry work to form a new lining within a defective pipe. The segments are usually sealed at the joints and the annulus is grouted. See Lining with Pipe Segments.
Segmental Sliplining - See Sliplining. See Lining with Discrete Pipes.
Self-Cleansing - A consequence of good hydraulic design when the pipe invert is kept relatively free of sediments by ensuring adequate flow velocities.
Separate System - A system that uses sanitary sewers to convey the wastewater and stormwater sewers to carry the stormwater.
Serviceability of the Piping System - Continued service life with a high degree of confidence that a failure will not occur during its long-term service.
Settlement - Measurable downward movement of the ground or of an overlying utility or other structure as the result of excavation or dewatering.
Settlement Point or Marker - An instrument installed at ground surface or driven into the ground to monitor vertical ground deformations before, during, and after construction.
Sewage - Wastewater transported in a sewer.
Sewage Ejector Pump - A sewage ejector pump is used to pump wastewater to an elevation whereby the wastewater can flow by gravity to the sewer.
Sewage Grinder Pump - A sewage grinder pump will discharge a finely ground slurry into a small diameter pressure pipe. In a low pressure sewer system (LPSS) all the piping downstream of the grinder pump will normally be under low pressure, 60psi or less.
Sewer - An underground pipe or conduit for transporting stormwater and/or wastewater.
Sewer Building - The conduit which connects building wastewater sources to the public or street sewer, including lines serving homes, public buildings, commercial establishments and industry structures. In this specification, the building sewer is referred to in two sections: (1) the section between the building line and the property line, frequently specified and supervised by plumbing or housing officials; and (2) the section between the property line and the street sewer, including the connection thereto, frequently specified and supervised by sewer, public works, or engineering officials (Referred to also as "house sewer", "building connection", or "service connection").
Sewer Cleaning - The utilization of mechanical or hydraulic equipment to dislodge, transport, and remove debris from sewer lines.
Sewer Inspection - Computer database used to store information about the Information Center sewer system.
Sewer Inspection Information System Group (SIIC) - Location where inspectors store and maintain inspection results, etc.
Sewer Interceptor - A sewer which receives the flow from collector sewers and conveys the wastewaters to treatment facilities.
Sewer Lateral - A building sewer (sometimes referred to as a sewer lateral or house lateral) is the pipeline between the County sanitary sewer line, which is usually located in the street, and the indoor plumbing. County sanitary sewer lines have a pipe inside diameter of 8" or greater while building sewers have a pipe inside diameter of less than 8". Generally, residential building sewers have a pipe inside diameter of 4" while building sewers for business establishments have a pipe inside diameter of either 4" or 6". The residential building sewer is owned and maintained by the property owner even if it extends into the street or public right of way.
Sewer Pipe - A length of conduit, manufactured from various materials and in various lengths, that when joined together can be used to transport wastewaters from the points of origin to a treatment facility. Types of pipe are: Acrylonitrile-butadiene-styrene (ABS); Asbestos-Cement (AC); Brick Pipe (BP); Concrete Pipe (CP); Cast Iron Pipe (CIP); Polyethylene (PE); Polyvinylchloride (PVC); Vitrified Clay (VC).
Sewer Structure - Any portion of the industrial sewer system including pipeline segments, trap tanks, sumps and other structures; each are assigned a unique number.
Shaft - A pit or wall sunk from the ground surface into a tunnel for the purpose of furnishing ventilation or access to the tunnel.
Shank - A hardened male hex bar, containing one or more transverse holes, to couple and hold in a female hex connector.
Sheet Piling - See Piling.
Sheeting - A wall of metal plates or wood planking to keep out water, soft or runny materials.
Shield - A steel cylinder at the face of a utility tunnel or casing, which may sometimes employ the use of a mechanical excavator and may be steerable, and provide hazard protection from the area covered.
Shield Cut - The theoretical difference between the radial measurement of the MTBM shield and the jacking pipe and is equal to (MTBM OD - Pipe OD)/2.
Shield Tunneling Method - Method of excavation in the front of a tunnel or pipe jack using a shield.
Shop Drawings - All drawings, diagrams, illustrations, brochures, schedules, and other data which are prepared by the contractor, a subcontractor, manufacturer supplier or distributor and which illustrate the equipment, materials or some portion of the work as required by the contract documents.
Shoring - See Piling.
Single Ring Brick Sewer - A brick sewer which consists of a single layer of bricks.
Siphon - A pressurized length within a gravity sewer pipeline driven by a higher liquid elevation at the upstream end. Often used to traverse below rivers, for example, and avoid the use of pumps.
Site - Any location where work has been or will be done.
Site Access - An adequately clear area of a size sufficient to accommodate personnel and equipment required at the location where work is to be performed, including roadway or surface sufficiently,, unobstructed to permit conveyance of vehicles from the nearest paved roadway to the work location.
Skew (or Skew Angle) - The acute angle formed by the intersection of the line normal to the centerline of the road improvement, with the centerline of a culvert or other structure.
Skin Friction - Resistance to thrust caused by soil pressure around the casing.
Skinning - The act of fitting a steel cylinder over the MTBM shield body to increase the diameter of an existing MTBM with the use of an appropriately upsized cutter wheel. Also referred to as upsizing or shimming.
Sleeve Pipe - A pipe installed as external protection to a product pipe.
Slide - Movement of a part of the earth under force of gravity.
Slime Shield - Earth pressure balance shield with soil conditioning additives to facilitate the excavation of the ground.
Slipline - A rehabilitation technique covering the insertion of one pipe inside an existing pipe.
Sliplining - (1) General term used to describe methods of lining with continuous pipes and lining with discrete pipes. (2) Insertion of a new pipe by pulling or pushing it into the existing pipe and grouting the annular space. The pipe used may be continuous or a string of discrete pipes. This latter is also referred to as Segmental Sliplining.
Slurry - A mixture of drilling fluid and spoils.
Slurry Chamber - A chamber in which excavated material is mixed with slurry for transport through the discharge line to the separation plant at the surface. The slurry chamber is located behind the cutter wheel of a slurry microtunneling machine.
Slurry Lines - Parallel hoses or pipes that transport spoils and slurry from the face of a slurry microtunneling machine through the discharge line to the ground surface for separation, and then return the slurry to the face for reuse through the charge line (the charge line is also known as a feed line or inlet line).
Slurry Separation - A process where excavated material is separated from the circulation slurry. Mechanical separation is typical, although gravity separation in pits or tanks is possible with coarse-grained soils.
Slurry Shield Method - Method using a mechanical tunnelling shield with closed face which employs hydraulic means for removing the excavated material and balances the ground water pressure. See also Earth Pressure Balance Machine.
Smooth Radius Bend - A contoured sweep or bend with no sharp or angular sections.
Social Costs - Costs incurred by society as a result of collection system works. These include business losses due to road closures, and the cost of extended journey times due to traffic delays and diversions.
Socket - See Female Hex Connector.
Soft Lining - See Cured-In-Place Pipe (CIPP) or Lining with Cured-In-Place Pipes.
Softening Temperature - There are many ways to measure the softening temperature of a plastic. The commonly reported Vicat Softening Temperature method is to measure the temperature at which penetration of a blunt needle through a given sample occurs under conditions specified in ASTM D 1525.
Solar Radiation - The emission of light from the suns, including very short ultraviolet wavelengths, visible light and very long infrared wavelengths.
Solubility - The amount of one substance that will dissolve in another to produce a saturated solution.
Sonde Housing - This integral unit is the direction drill head which also houses the sonde radio sending unit.
Spacer Block - Device used to extend the distance that the hydraulic rams within a jacking system can propel the pipeline.
Spacers - Mechanical structures used to transfer the jacking force from the jacking thrust ring to the pipe and to accommodate lengths of pipe that are longer than the stroke length of the jacks.
Spalling - (1) A process that describes the flaking, or slitting away of the surface layer. (2) The spontaneous chipping, fragmentation, or separation of a surface or surface coating.
Span - Horizontal distance between supports, or maximum inside distance between the sidewall of culverts.
Special Conditions - When included as a part of the contract documents. Special conditions refer only to the work under this contract.
Specials - Pipe sections immediately ahead of and behind the IJS. Specials have ends that are specifically manufactured to physically accommodate the IJS.
Specific Gravity - The density of a material divided by the density of water usually at 4 degrees Celsius. Since the density of water is nearly 1 g/cm3 and the density of water is very nearly 1 g/cm3, the density of any substance in g/cm is nearly the same numerically as its specific gravity relative to water.
Specifications - Those portions of the contract documents consisting of written technical descriptions of materials, equipment, construction systems, standards and workmanship as applied to the work.
Speed Controls - Those controls that control the speed of the engine, rotation of the tool, travel of tool, and forward or lateral movement of the machine.
Speed Reducer - See Final Drive.
Spelter - Zinc or galvanized coating on steel products.
SPG - Structural Performance Grade; used to generate a final structural condition classification for sewer lengths. Recognizes the impact of external factors: surrounding soil conditions; frequency of surcharging, for example, and relates these to the Internal Condition Grade (ICG).
Spillway - A low-level passage serving a dam or reservoir through which surplus water may be discharged; usually an open ditch around the end of a dam, a gateway, or a pipe in a dam. - An outlet pipe, flume or channel serving to discharge water from a ditch, ditch check, gutter or embankment protector.
Spiral Lining - A technique in which a ribbed plastic strip is spirally wound by a winding machine to form a liner which is inserted into a defective pipeline. The annular space may be grouted or the spiral liner expanded to reduce the annulus and form a Close-Fit liner.
Spiral Weld Pipe (Casing) - Pipe made from coils of steel plate by wrapping around a mandrail in such a manner that the welds are a spiral helix.
Split Design - A boring machine having the capability of being broken down into two or more elements to reduce the lifting weight.
Spoil Chamber - See Casing Pusher.
Spoil Ejector - A set of paddles, rotating in close proximity to the inside of the casing pusher.
Spoil Ejector Door - A door that partially or completely closes the spoil opening when at rest.
Spoils (Muck) - Earth, rock, and other materials excavated during the installation process. Also referred to as cuttings.
Spot Repair - See Localized Repair.
Spray Lining - A technique for applying a lining of cement mortar or resin by rotating a spray head which is winched through the existing pipeline.
Springline - (1) Also Springing. An imaginary horizontal line across the sewer that passes between the points where the sewer has its greatest cross sectional width. (2) Midpoint of sewer pipe. (The line equal distance between the crown and the invert of the pipe).
Spun Lining - A bituminous lining in a pipe, made smooth or uniform by spinning the pipe around its axis.
SRPC - Sulfate Resisting Portland Cement; customarily used for making concrete, mortar and grout in aggressive conditions where sulfates concentrations may be high.
SSBS - Sanitary Sewer Bypasses; structures to relieve hydraulic overload on nominally sanitary sewers, leading to flooding and or pollution of a watercourse. Typically occurring during wet weather.
SSES - Sewer System Evaluation Survey; mainly for inflow and infiltration (I/I) surveys to determine the degree and location of flows entering the collection system.
Stabilization - See Chemical Stabilization.
Stabilizer - An ingredient used in the formulation of some plastics to assist in maintaining the physical and chemical properties of the materials at their initial values throughout the processing service life of the material.
Stakedown Plate - A plate staked to the ground to stabilize the forward end of the drill rack.
Standard Dimension Ratio - SDR, Standard Dimension Ratio is defined as the ratio of the outside pipe diameter to wall thickness.
Steerable moling - Method similar to impact moling with a limited steering capability.
Steering Head - A moveable lead section of casing that can be adjusted to steer the bore.
Stepwise - A logical process carried out in sequence.
Stoppage - A blockage in the sewer line that prevents the passage of wastewater.
Storm - A rainfall event. (See also - catastrophic rainfall event.)
Storm Mains - Primary collector pipelines in the storm water collection system.
Storm Sewer - A sewer intended to carry only storm waters, surface runoffs, street washwaters, and drainage.
Stormwater Sewer - A sewer that conveys stormwater runoff from two or more properties and stormwater runoff from roofs, paved areas and roads within the catchment area of the sewer.
Strain Rate - The rate of lineal change per unit length.
Street Access - Areas normally used for public vehicular traffic (including roads, streets, or rights-of-way) to which safe access is required for performance of work.
Stress - The load applied per unit area of material. Often expressed as pounds of force per square inch (psi).
Stress Corrosion Cracking (SCS) - Cracking of a metal produced by the combined action of corrosion and tensile stress (residual or applied).
Stress Life Curves - Graphic representations showing the extrapolation to 100,000 hours of applied hoop stress versus hours to failure data on logarithmic scales per ASTM D 2837.
Stress Relieve - The decrease in imposed stresses at a constant strain. In thermoplastic materials it occurs as a property of the material with time.
Stringing - Process by which a line is floated through a sewer segment for later use to pull a cable for video inspection or cleaning equipment.
Structural - Physical adequacy to support imposed loads.
Structure ID - A number that defines a component of the sewer system.
Subcontractor - An individual, firm or corporation having a direct contract with contractor or with any other subcontractor for the performance of a part of the work at the site - or - An individual, firm or corporation having direct contract with the contractor or with a lower-tier subcontractor for performance of part of the work.
Subdrain - A pervious backfilled trench containing a pipe with perforations or open joints for the purpose of intercepting ground water or seepage.
Subgrade - The surface of a portion of the roadbed on which paving, or railroad track ballast, or other structure is placed.
Subsidence - The settlement of the ground, pipeline or other structure. The effects may not be evenly distributed and differential settlement may occur.
Substantial Completion - The stage in construction when a project can be utilized for the purposes for which it was intended. At substantial completion, minor items and items that are seasonally restricted need not be completed, but the items that affect operational integrity and function of the facility must be capable of continuous use.
Sulfide Stress Cracking (SSC) - Brittle failure by cracking under the combined action of tensile stress and corrosion in the presence of water and hydrogen sulfide.
Sump - A depression in the pit to allow for the collection of water and the installation of a pump for water removal.
Sump Pump - A device placed at the base of a shaft or in an MTBM to collect and remove fluids incidental to the construction process and resulting from shaft leakage, and to prevent the excavation equipment from flooding.
Supplementary General Conditions - Federal conditions in effect at time at submission of bid.
Supplier - Any person or organization who supplies materials or equipment for the work, inducing that fabricated to a special designs, but who does not perform labor at the site.
Surcharge - When the sewer flow exceeds the hydraulic carrying capacity of the sewer line.
Surcharge Condition - When the sewer flow depth equals or exceeds the diameter of the discharging sewer line.
Surcharged Sewer - A gravity sewer that is overloaded beyond its pipe full flow capacity such that the flow becomes pressurized.
Surety - The corporate body which is bound with the contractor and which engages to be responsible for the contractor and his acceptable performance of the work.
Surface Hardness - A measure of the net increase in depth as an indented load is increased from a minor load to a major load and then returned to a minor load. This is used as an indication of relative hardness among like materials.
Survey Tools - Downhole equipment and instruments used to determine the position of a bore in directional drilling or in site investigation.
Swab (Bull Plug) - A steel plug which is pulled through a horizontal bore to remove the cuttings.
Swageing - The reduction in diameter of a polyethylene pipe by passing it through one or more dies. The die may be heated if necessary.
Swagelining - A method of sliplining whereby the diameter of the PE pipe is temporarily reduced by swageing prior to insertion in the defective pipe. After insertion, the pipe is expanded by means of steam or a rerounding device.
Swale (DIP, SAG) - A significant deviation In pipe grade such as to cause entrapment of solids, semisolids, and liquids, thereby impeding the accuracy and/or effectiveness of flow measurements, cleaning, and internal inspection.
Swivel Pulling - Used to attach service (to be pulled into drilled hole) to drill pipe.

Tailwater - The water just downstream from a structure.
Target Shaft/Pit - See Reception/Exit Shaft/Pit.
Taxpayer - Contributions through taxation to utilities to fund supplied services.
TBM - See Tunnel Boring Machine.
Teeth - See Bits.
Televise - Process by which a sewer line or lateral is inspected with a closed-circuit television camera.
Tensile Strength - The pulling stress in psi that is required to elongate a given specimen to the breaking point.
Tensile Strength At Yield - The measured tensile stress required to initiate permanent deformation in a sample under the conditions described in ASTM D 638.
Test Medium - The fluid or gas inside the main being tested.
Thermal Conductivity - The Thermal conductivity is the property of a material to conduct heat. It is evaluated primarily in terms of Fourier's Law for heat conduction. Heat transfer occurs at a lower rate across materials of low thermal conductivity than across materials of high thermal conductivity. These variables are mass, length, time, and temperature.
Thermal Expansion/Contraction - The fractional change in length of a material subjected to a unit change in temperature.
Thermal Stabilizers - Compounds added to the plastic resins when compounded that prevent degradation of properties due to elevated temperatures.
Thermography - The recording of temperature variations; a technique to assist in the detection of voids around pipelines.
Thermoplastic - A material, such an polyethylene, that will repeatedly soften when heated and harden when cooled.
Thermoset - A material, such as epoxies, that will undergo or has undergone a chemical reaction by the action of heat, chemical catalyst, ultraviolet light, etc., leading to an infusible state.
Threading - The process of installing a slightly smaller pipe or arch within a failing drainage structure.
Throttle - Controls power, speed.
Thrust - Force applied to a pipeline or drill string to propel it through the ground.
Thrust Block - An engineered structure, located between the jacking frame and the shaft wall, that distributes the jacking force developed by the hydraulic jacking frame over a large surface area to the ground behind the back wall of the shaft.
Thrust Block Pin - See Dogs.
Thrust Boring - A method of forming a pilot bore by driving a closed pipe or head from a thrust pit into the soil which is displaced. Some small diameter models have steering capability achieved by a slanted pilot-head face and electronic monitoring. Back reaming may be used to enlarge the pilot bore. Also loosely applied to various trenchless installations methods. See Rod Pushing.
Thrust Jacking Method - Method in which a pipe is jacked through the ground without mechanical excavation of material from the front of the pipeline.
Thrust Package - The bottom section of a split boring machine containing the cylinders and thrust block.
Thrust Pit - See Drive Pit.
Thrust Ring - A fabricated ring that is mounted on the face of the jacking frame. It is intended to transfer the jacking force from the jacking frame to the thrust-bearing area of the pipe section being jacked.
Thrust/Travel Controls - Those controls that control the advance and retraction of the tool.
Tile (VT) - Used to describe products (sewer pipe and block) manufactured from fired hydrous alumina silicate clay.
Tool Diameter (d) - Maximum diameter of tool body.
Tool Length - Distance between tip and end of tool, not including whip hose.
Tooling - Ground-engaging elements of the cutter wheel designed to excavate and penetrate the ground.
Top Hat - A steel can with a faceplate bolted to a reception shaft wall to receive the arriving MTBM.
Torque - The rotary force available at the drive chuck.
Torque Limiter - A rotary slip clutch used to protect the final drive.
Track - A set of longitudinal rails mounted on cross members that support and guide a boring machine.
Track Brake - A mechanical device to provide a limited resistance to movement between the machine and the track.
Track Pins - Steel pins to be driven through holes in the track into the base of the pit.
Track Roller - See Cam Follower.
Transmission - A gear reduction unit located between the power source and final drive.
Transportation System - The excavated spoil from the tunnel face to the surface.
Travel - Changes travel speed.
Trench Box - A preconstructed set of side plates and adjustable cross members to prevent the walls of the pit from collapsing.
Trenching - See open cut or conventional trenching.
Trenchless Technology - A family of construction techniques for installing or rehabilitating underground infrastructure with minimal disruption to surface traffic, businesses, and residents. Also includes technologies for inspection, leak location, and leak detection with minimal disruption and minimal excavation from the ground surface.
Trunk Sewer - A sewer into which at least two branch sanitary, combined or stormwater sewers connect. It conveys the flow to the Interceptor sewer. The trunk sewer is the longest connection sewer in any drainage basin. Also sometimes known as a "main" sewer.
Tuberculation - Localized corrosion at scattered locations resulting in knob like mounds.
Tunnel - An underground conduit, often deep and expensive to construct, which provides conveyance and/or storage volumes for wastewater, often involving minimal surface disruption.
Tunnel Boring Machine (TBM) - (1) A full-face circular mechanized shield machine, usually of Man-Entry diameter, steerable and with a rotary cutting head. For pipe installation it leads a string of jacked pipes. It may be controlled from within the shield or remotely. (2) (Mole, Tunneling Head) A mechanical excavator used in a tunnel to excavate the front face of the tunnel.
Tunnel Horizon - The vertical band within the ground where the tunnel is excavated. Includes one tunnel diameter above the crown and one tunnel diameter below the invert.
Tunneling - A construction method of excavating an opening beneath the ground without continuous disturbance of the ground surface and of large-enough diameter to allow individuals access and erection of a ground support system at the location of material excavation.
Two-Pass - A procedure by which the carrier pipe is installed within a casing.
Two-Speed Control - A hydraulic valve that increases the flow of oil to the cylinders to provide rapid low power motion of the machine.
Type "K" Barrier Rail - A portable concrete fence or barrier that is made in the vague shape of the letter "K".

Ultraviolet Absorbers (Stabilizers) - Compounds that when mixed with thermoplastic resin selectively absorb ultraviolet rays protecting the resins from ultraviolet attack.
Unanticipated Return - See inadvertent return.
Uncased Bore - Any bore without a lining or pipe inserted, i.e. self-supporting, whether temporary or permanent.
Underdrain - See subdrain.
Underground Utility - Active or inactive services or utilities below ground level.
Uniform Corrosion - Corrosion that results in an equal amount of material loss over an entire pipe surface.
Upset - The inadvertent action of a boring machine that rotates the machine and track from its normal and upright position to another position.
Upsizing - Process of creating a larger diameter MTBM than a machine with the original factory configuration. Also, any method that increases the cross-sectional area of an existing pipeline, replacing it with a larger cross-sectional area pipe.
Utility Corridor - Duct in which two or more different utility services are installed with access for maintenance. Commonly referred to as a Utilidor in North America.
Utility Monitoring Point (UMP) - An instrument designed to measure movement of an individual utility when exposed to construction activities.
Utility Tunneling - A construction method for excavating an opening beneath the ground without continuous disturbance of the ground surface. The excavation is of sufficient diameter to permit personnel access, and allow excavation, transport of spoils, and erection of a ground support system.

Valve - Mechanism that controls the volume or direction of flow can be closed, partially open, or fully open.
VCP - Vitrified Clay Pipe
VCT - Vitrified Clay Tile or Vitrified Clay Tile Pipe
Velocity Head - For water moving at a given velocity, the equivalent head through which it would have to fall by gravity to acquire the same velocity.
Virgin Soils - Soils which have not previously been excavated.
Voids - (1) Holes on the outside of the pipe in the surrounding soil or material. (2) A term generally applied to paints to describe holidays, holes, and skips in the film. Also used to describe shrinkage in castings or welds.
Volume - The amount of drilling fluid flow.

Wale - Guide or brace of steel or timber, used in trenches and other construction.
Walkover System - See Locator.
Wall - Also riser. The vertical section between the bench and the cone of a manhole.
Washover Pipe - A rotating drill pipe of larger diameter than the pilot drill pipe and placed around it with its leading edge less far advanced. Its purpose is to provide stiffness to the drilling pipe in order to maintain steering control over long bores, to reduce friction between the drill string and the soil and to facilitate mud circulation. See Directional Drilling.
Waste Ejector - See Spoil Ejector.
Wastewater - The liquid conveyed in sewer system.
Water Jetting - Process of using the internal cleansing mechanism of the cutterhead, by which high-pressure water is sprayed from nozzles to help remove cohesive soils.
Water Level - An instrument that uses a tube filled with water to indicate the elevation of the lead section of casing.
Water Table - (1) The elevation of the ground water. (2) The upper limit of the portion of ground wholly saturated with water.
Watercourse - A flowing water body: ranging in size from a creek to a river, for example.
Waterline - Maximum liquid level in a sewer pipe/structure during normal operating cycles.
Watershed - (1) A defined geographical area, usually delineated by high ground, that drains to a watercourse. (2) Region or area contributing to the supply of a stream or lake; drainage area, drainage basin, catchment area.
Weatherability - The properties of a plastic material that allows it to withstand natural weathering; hot and cold temperatures, wind, rain and ultraviolet rays.
WEF - Water Environment Federation
Weir Manhole - A manhole that contains a weir used to measure flow.
Wetout - The process of injecting resin into, and distributing it throughout, a hose or tube which will then be installed into the pipeline and cured in place.
Wetted Perimeter - The length of the perimeter in contact with the water. For a circular pipe of inside diameter "d", flowing full, the wetted perimeter is the circumference, d. The same pipe flowing half full would have a wetted perimeter of d/2.
Winch - Mechanical device used to pull the CCTV cameras or cleaning tools through a sewer pipe.
Wing Cutters - Appendages on cutting heads that will open to increase the cutting diameter of the head when turned in a forward direction, and close when turned in a reverse direction. They are used to cut clearance for the casing pipe.
Work - Any and all obligations, duties and responsibilities necessary to the successful completion of the project assigned to or undertaken by contractor under the contract documents, including all labor, materials, equipment and other incidentals, and the furnishing thereof.
WQS - Water Quality Standard; prescribed attainment targets to ensure suitably clean water.
Wrapped Casing - A coating on pipe for protection from corrosion, usually composed of asphalt and asphalt coated paper. Some coatings may contain plastic, fiberglass, coal tar, or other materials.
Written Notice - The term "notice" as used herein shall mean and include all written notices, demands, instructions, claims, approvals, and disapproval required to obtain compliance with contract requirements. Written notice shall be deemed to have been duly served if delivered in person to the individual or to a member of the firm or to an officer of the corporation for whom it is intended, or to an authorized representative of such individual, firm or corporation, or if delivered at or sent by registered mail to the last business address known to him who gives the notice. Unless otherwise stated in writing, any notice to or demand upon the owner under this contract shall be delivered to the owner though the engineer.
WWTP - Wastewater Treatment Plant

Yaw - The angle of the MTBM to the left or right of a theoretical vertical plane passing through the MTBM’s longitudinal axis.

Zone of Influence - Volume of ground that could possibly be impacted by settlement or heave from tunnel mining, shaft excavation, pile driving, or other construction activities.
Zones - Different areas in manholes and other structures which are used for defect evaluation.

Trenchless 101

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