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.


Reinforced area of the entrance pit wall directly behind the track.


A ring of steel welded at or near the front of the lead section of casing to cut relief and strengthen the casing.


Proprietary equipment to measure the density of annulus grout.


The vertical section in a manhole between the cone and the benchwall.


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.


The slope or inclination from a vertical plane, as the face or back of a wall.


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.


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.


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.


The space between the toe of a slope and excavation made for intercepting ditches or borrow pits.


The offer or process of the bidder submitted on the prescribed form setting forth the prices for the work to be performed.


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.


Replaceable cutting tools on the cutting head or drill string.


A hard or semi-hard asphaltic residue; often used in construction as a waterproof/barrier layer.