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We are proud to spotlight NASTT’s 2017 No-Dig Show Gold Sponsor and Corporate Member Hammerhead.
During the 1980’s, two pioneering engineers had a vision to create equipment and tools that would efficiently and effectively install utilities in a trenchless manner. The company’s first offering, a three-inch piercing tool, built in their garage helped change the way utilities are installed.
Hammerhead is a global leader in the design and manufacture of piercing tools, bursting systems, pneumatic hammers and horizontal directional drill tooling. Hammerhead products are recognized throughout the industry as one of the most reliable and productive trenchless tools in the market. For decades Hammerhead has led the industry in bringing innovative trenchless solutions to customers. No project is the same, so their dedicated team of industry experts creates customized solutions to meet your needs. And with a global network of dealers, they are there to support you after the sale — whether it’s in the in the field, on the phone or in your office — you can count on Hammerhead to be your trusted partner.
If you’d like to visit with one of NASTT’s Gold Sponsors, head to booth #701 at NASTT’s No-Dig Show in Washington, DC! For more information, go to nodigshow.com
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Recently, 12 students from NASTT’s Student Chapter at UMASS Lowell attended a Horizontal Directional Drilling (HDD) site visit on location with Liberty Utilities in Somerset, Massachusetts. The students observed an HDD river crossing project. A safety briefing was held and all the necessary PPE was donned prior to the students entering the job site.
Everyone in attendance thoroughly enjoyed the visit and found it to be very educational on the HDD process and how trenchless technology is used in utility work.
Many thanks to Liberty Utilities for hosting the students and helping to educate the future of trenchless!
Blog, Industry News, trenchless projects
Rock Machine surmounts challenges on High-Cover Los Condores HEPP
Project officials and Robbins team members celebrate the impending launch of the Double Shield TBM on 10.4 km (6.4 mi) of tunnels for the Los Condores Hydroelectric Project.
Chile’s Los Condores HEPP is a high cover, hard rock challenge, with 500 m (1,640 ft) of rock above the tunnel and a high-altitude jobsite 2,500 m (8,200 ft) above sea level. As of January 2017, a 4.56 m (15.0 ft) Robbins Double Shield TBM had completed boring its 900 m (2,950 ft) long access tunnel and was well on the way to boring the first section of headrace tunnel. The machine embarked on its journey on May 27, 2016, and has since excavated over 1,300 m (4,270 ft) of tunnel in total.
The journey to machine launch was an arduous one, requiring shipment of TBM components and vehicle transport on unpaved, mountainous roads. Contractor Ferrovial Agroman is responsible for the intake tunnel at the Los Condores Hydroelectric Project, and was well aware of the challenges associated with machine launch: “The location of the work is a big constraint due to its rugged terrain and geographical location in the Andes. With all this, we are anxious to perform work in an efficient manner,” said Pello Idigoras, Tunnel Production Manager for Ferrovial Agroman.
As of January 2017 the Robbins TBM had completed the 900 m (2,950 ft) long access tunnel and was boring its first section of headrace tunnel at rates of up to 25 rings per day.
The jobsite, located 360 km (224 mi) south of Santiago, Chile, is part of a new 150 MW power plant and intake tunnel. The Robbins Double Shield TBM is boring two sections of the intake tunnel, the first measuring 6 km (3.7 mi) and the second measuring 4.4 km (2.7 mi). A section between the two tunnels will be excavated by drill and blast to connect them, making the intake tunnel about 12 km (7.5 mi) in length. “This project brings an increase in energy production in the country, thus contributing to the overall improvement in the welfare of its citizens,” said Idigoras of the effect the completed hydropower project will have on surrounding areas.
The tunnel, located in the mountainous Maule Region of Chile, is being bored in two types of rock: sedimentary and volcanic. The rock has been tested at strengths up to 100 MPa (14,500 psi) UCS, with at least two fault zones—the first of which has already been traversed in rhyolite, andesite, tuff, and breccia. For Idigoras, the conditions are well-suited to Double Shield tunneling: “We have good quality medium to hard rock for Double Shield excavation overall,” he said. Despite that, some areas of challenging ground persist. To cope with the conditions, including steadily increasing water inflows at rates of up to 3,500 l/min (925 gal/min), the contractor is utilizing cementitious grouting and chemical grouting with polyurethane and foam. Such ground conditioning techniques were anticipated and the Robbins Double shield was designed to effectively apply these techniques.
The challenging launch of the Robbins TBM at the remote jobsite 2,500 m (8,200 ft) above sea level.
As the TBM excavates, it is lining the tunnel with 250 mm (10 in) thick, 1.2 m (3.9 ft) long concrete segments in a 4+1 arrangement. The machine is currently progressing at a rate of up to 25 rings per 20 hours of boring. Crews are operating in two 10-hour shifts with one 4-hour shift dedicated to maintenance. Idigoras sees the TBM performance and completion of the access tunnel as huge project milestones, though much work remains to be done. “After many months working in engineering, manufacturing, installation, and commissioning, we are proud to see this result. It would be impossible to name all the people who participated in this project thus far but they, as a whole, have managed to get the TBM started digging and boring well.”
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Swiftly-Assembled Machine to bore Emergency Water Supply Tunnel
After an Onsite First Time Assembly (OFTA) lasting just 2.5 months, Atlanta Georgia, USA’s newest TBM, dubbed “Driller Mike”, made its initial startup on October 13, 2016 and ramped up to full production two weeks later. Atlanta’s Mayor Kasim Reed and city officials gathered with local and national media to celebrate the occasion. The 3.8 m (12.5 ft) diameter Robbins Main Beam TBM is now boring the 8.0 km (5.0 mi) Bellwood Tunnel after being walked forward 100 ft into a starter tunnel. The Bellwood Tunnel path will travel from an inactive quarry and run below a water treatment plant and reservoir before ending next to the Chattahoochee River.
The project was green-lighted by the City of Atlanta’s Department of Watershed Management due to the city’s 
current emergency water supply shortage. The PC/Russell JV, the project’s construction manager at risk, sub-contracted with the Atkinson/Technique JV to operate the TBM and will oversee construction of various intake and pumping shafts as well as final lining operations. The project is of utmost importance for the City of Atlanta, explained Bob Huie, Sr. Project Manager for the PC/Russell JV. “Right now, the downtown area’s emergency water supply is approximately three days. With the tunnel the supply will increase to between 30 and 90 days. To be a part of the city’s emergency water supply solution is huge. This tunnel will protect the city for a very long time.”
With the tunnel on the fast track, swift TBM assembly was key. The OFTA process involved coordination by multiple
crews at the large quarry site. “The OFTA went very well. The overall assembly process was well organized and supervised by the Atkinson/Technique JV and Robbins. We had a good team of folks to put it all together,” said Huie. He continued: “This is a unique job where there’s a lot of people with a variety of backgrounds, but everyone came together to make the OFTA happen.”
The Robbins TBM is now excavating in granite, with at least 300 m (1,000 ft) of zones in three separate areas that will require continuous probing. In a section directly below an existing reservoir, monitoring will be particularly crucial to ensure no water inflows occur. The Robbins machine will also be required to negotiate several curves: “We have one curve in the first 300 m (1,000 ft) and the main 370 m (1,200 ft) radius curve is 1,800 m (6,000 ft) in. We plan to do short TBM strokes in this section—about 20 cm (8 inches) to 30 cm (1 ft) shorter than normal to get through the curves,” said Larry Weslowski, Tunneling Superintendent for the PC/Russell JV.
Excavation is scheduled to be completed in the first quarter of 2018. After final lining, the tunnel will be filled with 
water and the quarry site will become Atlanta’s largest reservoir and park, totaling hundreds of acres. While the park site is a bonus for residents, the water storage capacity it will provide is critical. Nearly 1.2 million customers, including 200,000 passengers who pass through the world’s busiest airport every day, count on the water supply each time they turn on the tap. “If the city were to lose water supply for a day, the estimated economic impact would be at least USD $100 million per day. If you consider that this is a USD $300 million project, that seems a pretty good investment in comparison to what could happen,” said Huie.
Image 1: The Robbins Main Beam TBM, dubbed “Driller Mike”, was launched on Atlanta, Georgia, USA’s Bellwood Tunnel in October 2016.
Image 2: Robbins Field Service stand proudly in front of the completed Main Beam TBM after an Onsite First Time Assembly lasting just 2.5 months.
Image 3: The 3.8 m (12.5 ft) diameter Robbins Main Beam TBM will bore the 8.0 km (5.0 mi) Bellwood Tunnel through granite rock with potential zones of water inflows.
Image 4: Atlanta Mayor Kasim Reed (left) and Atlanta City Councilman Andre Dickens (right) attend the TBM’s launch ceremony to kick off the Bellwood Tunnel excavation.
Desiree Willis
Technical Writer
Email: willisd@robbinstbm.com
Direct: 253.872.4490
Blog, Industry News, trenchless people, trenchless products, trenchless projects
Highly Anticipated Photo Finish wraps up Tunneling at Massive Metro
On September 28, 2016, Bangalore’s last TBM for the city’s metro rail project broke through, marking the end of 
TBM tunneling on the Namma Metro phase 1. The Robbins-operated machine, known as “Krishna”, bored a 750 m (2,460 ft) drive through challenging conditions between Chickpet and Majestic stations. Cleanup and final commissioning of the tunnel will be completed in 2017, and is the last obstacle before owner Bangalore Metro Rail Corporation Ltd. (BMRCL) can open the Malleswaram-Majestic link. The TBM’s sister machine, “Kaveri”, completed a parallel tunnel in June 2016.
The success follows a gauntlet of challenges on the two tunnel sites. Due to severe delays on the original tunnel drives, Robbins was approached and asked to take over the operations of the remaining two competitor-manufactured TBMs in February 2015. After obtaining agreement from the project owner and the contractor, Robbins took over the responsibility for all aspects of the underground operations. “We provided a team of over 60 staff including TBM operators, TBM technicians, ring builders, a grouting team, and more. We were also responsible for running surface installations and equipment such as the grout batching plant, gantry cranes and power supply. Contractor Coastal Projects Ltd. (CPL) provided a team of people including surveyors, QC engineers, and loco operators who reported directly to our site management team,” explained Jim Clark, Projects Manager for Robbins India. 
The Robbins crew carried out tunneling operations while the Chickpet station was being constructed around them to mitigate delays incurred before they took over project operations. The project’s most difficult challenges included a low overburden and unconsolidated ground along the alignment, and the discovery of several uncharted wells directly on the alignment. Difficult ground frequently prevented proper pressurization during cutting tool replacement, requiring a grout solution to be pumped in to fill voids and left to cure. Initially the curing process took up to 36 hours, but with improved application methods this was reduced to a 12-hour curing time.
Another challenge involved the sensitive building structures along the tunnel path. Issues with surface vibration, explained Clark, required that cutterhead speed be limited to 1.8 RPM during the day shift and 1.2 RPM during the night shift. Despite the obstacles, the TBMs advanced at rates of up to 50mm (2 in)/min in highly weathered rock.
“This is an industry first, wherein a TBM manufacturer has utilized their in-house expertise and knowledge to take on this level of responsibility for a project,” said Clark, addressing the magnitude of the successful breakthroughs. “The fact that it was ‘a first’ and we were successful in bringing this high-profile project back on track is a great achievement for The Robbins Company.”
Now that tunneling is complete, the North and South runs of the Namma metro will be connected–a line that, once in service, will carry an estimated 40,000 passengers daily. It is anticipated that Phase One of the metro will be opened in its entirety in 2017.
Blog, Industry News, trenchless projects
Real time information on asphalt density and uniformity is a boon to construction quality efforts
By Roger Roberts, GSSI
Properly compacted asphalt is a major factor in the lifespan of roads, since inadequately compacted asphalt deteriorates at a more rapid rate than properly compacted material. With the billions spent on road construction and repairs each year, it has become a matter of urgency to find new technologies that can ensure the integrity of asphalt on newly paved roads. New radio wave technology is now available to nondestructively determine asphalt density during application.
Asphalt installation and compaction basics
The air void content within asphalt varies based on the amount of compaction during asphalt emplacement and variations in the asphalt mix composition. Asphalt with too many air voids (often considered to be more than 8 percent) deteriorates at a more rapid rate. Too few air voids (less than 3 percent) results from over-compacted asphalt, which is also undesirable. In either case, the asphalt is subject to early failure and the road’s lifetime is less than asphalt that contains the optimal air void content.
Construction engineers are looking for that “sweet spot” where the compaction of the asphalt when it is laid down is optimal. They typically assess asphalt by measuring density variations, which can be used to calculate the air void content.
To ensure optimal compaction, asphalt should be kept at a specific temperature range as it is being laid down. If the paving machine and transfer vehicles do not do a good job keeping the material uniformly hot, there can be “cold patch” areas. When the roller rolls over areas not within the optimal temperature range, it cannot properly compact the material. For example, such cold patches may occur if the asphalt paver is refilled from end-dump trucks, which cool the asphalt more near the metal sides and end of the truck than in the middle. Some poorly-paved roads have regularly spaced defects associated with end-dump truck refills.
One may not be able to notice these areas at first, but they may become obvious later. In fact, there are many roads where one can observe a cold patch every several hundred feet that is starting to deteriorate – turning into a raveled section in the road. If the work crew does not catch the problem during paving, the road may need to be repaved far sooner than if the material was properly applied.
Another compaction issue occurs when the established “rolling pattern” is not properly followed. The rolling pattern refers to the number of times, speed, and lap pattern rollers should employ when rolling new asphalt to achieve the optimum compaction. If the paving crew misses a section and does not compact the material with the proper number of rolls, they can create areas where compaction is faulty.
Discovering and correcting any rolling pattern issues during the first few days of a paving job benefits both the owner and contractor, since contract specifications may include requirements on how asphalt is laid down in terms of acceptable void content. Contracts may also include a bonus for getting to the specific asphalt void content range – or a penalty if the crew goes outside the specified void content range.
Options for measuring asphalt density and void content
There are several available methods that can be used to measure asphalt density variations, which are then used to calculate void content variation. One non-destructive testing (NDT) method is the nuclear density gauge, which consists of a radiation source that emits a cloud of particles and a sensor that counts the received particles that are scattered back by the test material. By calculating the percentage of particles that return to the sensor, the gauge can be calibrated to measure the density and inner structure of the test material. [1]
While quite accurate, the nuclear gauge has several disadvantages. The gauge is placed on asphalt and measurements are taken over a specific period of time, usually a few minutes or less. The method requires contact, with the device required to remain stationary at the measurement point. Due to the length of time required for the measurement, nuclear gauge measurements are taken sparsely, on the order of a few measurements per 100 lane feet. Collection of only these “spot” measurements does not adequately capture all the asphalt’s variability. Also, because it uses radioactive material, the nuclear gauge requires user training and secure storage. There are also special transportation requirements. Re-licensing, maintenance, and recalibration fees run about $2000 per year.
Similar to a nuclear gauge, the non-nuclear density gauge measures electrical impedance; a calibration procedure is then performed to correlate it to density [2]. Like the nuclear density gauge, the method is quite limited, because it samples only very small portions of the asphalt.
Because the nuclear and non-nuclear density gauges may collect only one value over a large area, they are unable to catch all the variations in void content that may be important to ensuring a quality paving job.
Another NDT option is the use of radio waves, which can be used to obtain real time measurements over a large swath of pavement in short periods of time. Radio wave reflections from the asphalt can be used to directly calculate the asphalt dielectric values, which are then correlated with the new pavement’s void content, a relative indication of density.
One other method that should be mentioned is “coring,” a destructive method in which one physically extracts a core from the asphalt and measures its properties. Coring is used as a primary asphalt compaction evaluation method and is always used to “ground truth” measurements from other methods. Coring is done on a very limited basis, so it often under-represents the true variability in asphalt void content.
New radio wave technology used to help improve asphalt mixture quality
The initial relationship between void content and road condition has been known for a long time. In the late 1990s, researchers at the Texas Transportation Institute (TTI) discovered the relationship between the dielectric calculated by ground penetrating radar (GPR), an application-specific use of radio waves, and void content.
Researchers later developed a working methodology for use of infrared and radio wave technologies for improving the assessment of asphalt mixture and compaction quality. They then looked for a way to commercialize it so it could be easily used by state departments of transportation.
Previously, use of the GPR technique required specialized equipment, a great deal of data interpretation, and a number of manual steps. In 2013, TTI began working with GSSI to package the device components into a streamlined and operator-friendly device that would provide real time profiling of asphalt mixture uniformity. The work was done as part of the Federal Highway Administration’s Strategic Highway Research Program (SHRP 2). [3]
Over the next few years, GSSI developed the technology into the PaveScan RDM, which TTI used in several pilot studies. The non-contact PaveScan technology uses a sensor that typically outputs a measurement each half-foot along the lane traveled, so a mile’s worth of data includes roughly 10,000 measurements for each sensor used.
TTI found that the new PaveScan system overcomes hardware, data processing, and staff expertise hurdles that existed in the past. According to TTI, “The utility of GPR was realized on all pilot projects, where the radar results provided quantitative assessment of density and uniformity.”[3]
GSSI later developed a three-channel system that can be vehicle-mounted to obtain moving void content measurements in one pass, covering both wheel paths and between the wheel paths. One sensor is located in one wheel path, one in the middle and one in the other wheel path – so three measurements are output for each half-foot along the lane traveled. In this way, a mile’s worth of data includes roughly 30,000 measurements – all collected in a mere 20 minutes.
The PaveScan RDM system has a number of benefits. First of all, it is a way of ensuring asphalt integrity of newly paved roads. Now, when a contractor lays down a new road, the asphalt void content over the entire area paved is accurately calculated, so both contractors and the owner of the road are satisfied. Secondly, the system is easy to use, bringing down the level of expertise needed to a manageable level. Thirdly, it is a very rapid method, adaptable to being put on a vehicle. The safety benefits of not having someone standing in a lane next to moving traffic are huge.
Previously, the prototype PaveScan unit developed by GSSI was used in the evaluations done as part of the SHRP 2 project. This year, GSSI delivered a production 3-channel unit to TTI, which is being used to further its research. Additional production units have been purchased with SHRP 2 funding by the Minnesota Department of Transportation, the Maine Department of Transportation, and the Nebraska Department of Transportation. By June 2016, there will be four units in the field, working to ensure that tax dollars allocated for road construction are being used wisely.
References
[1] Nuclear density gauge, https://en.wikipedia.org/wiki/Nuclear_density_gauge#cite_ref-Radioisotope_Gauges_for_Industrial_1-0, retrieved 4/26/16.
[2] Non-Nuclear Methods for HMA Density Measurements, MBTC 2075 Final Report, Williams, Stacey, G., 2008, http://arkansastrc.com/MBTC%20REPORTS/MBTC%202075.pdf
[3] Pre-Implementation of Infrared and Ground-Penetrating Radar Technologies for Improving Asphalt Mixture Quality, Strategic Highway Research Program, Transportation Research Board of the National Academies, Stephen Sebesta and Tom Scullion, Texas A&M Transportation Institute, The Texas A&M University System, College Station, Texas, © 2014 National Academy of Sciences. All rights reserved.
We are proud to spotlight NASTT’s 2017 No-Dig Show Gold Sponsor and Corporate Member Hammerhead.
