Case Boring Corp. Uses Remotely Controlled Rock Boring Machine with Pinpoint Precision
In the suburbs of Buffalo, New York, a large sewer project was underway. The North Aurora Pump Station Elimination project, for the Erie County Sewer District, was slated to replace the 40-year-old station with a gravity sewer to increase efficiency and save on energy as well as operational costs. But to do that required a particularly difficult crossing below a busy roadway and two houses.
“This was widely considered the most challenging aspect of the entire project,” said Mark Case, President of Case Boring Corp. The company was subcontracted by general contractor Concrete Applied Technologies Corp. (Catco) to bore the 360-ft long hard rock crossing. The location was not the only challenge — the presence of hydrogen sulfide gas, combined with the hard rock geology at a small casing diameter of just 36 in. meant the contractor would need a unique solution.
The Erie County Sewer District began planning the replacement project running through the towns of Cheektowaga and Lancaster due to projected major expenditures to bring the North Aurora Pump Station up to current standards and service levels. The $7.8 million project was determined to be the most cost effective and beneficial solution for ratepayers in the sewer district, and would additionally redirect flows away from infrastructure with limited capacity.
In October 2015, general contractor Catco began installing more than 3,000 ft of 27-in. diameter sanitary sewer pipe, but a roadway crossing in a residential area would require specialized construction. Local contractor Case Boring Corp, specialists in road crossings as well as natural gas pipelines, was called in for the job. The family-owned company, which has been in business since 1962, employs up to 30 people in various crews on specialty construction projects.
The 23-ft deep crossing required accuracy, and went under a house and through a suburban backyard. “We bored from a backyard underneath a three bedroom ranch-style house in sub-development that was purchased by the sewer district. The crossing went 14 ft directly below the basement. Open cut was never a feasible option as the one house would have had to have been demolished, and quite possibly two houses. There were people living in adjacent houses during the construction and we holed through into another backyard-type space that separated a house from an apartment complex. There was no line of sight; it was a blind shot,” explained Case.
Because of the location in a subdivision, there were also active utility lines that made open cut even less of an option. “We had underground electric, gas and water, cable TV lines, you name it,” said Case.
The contractor set up a launch pit in the backyard of the purchased house and prepared for excavation with a four-man work crew. The Robbins Company aided in launch preparations for the contractor’s unique solution.
Selecting the SBU-RC
Case Boring selected the Remote Controlled Small Boring Unit (SBU-RC), a new type of machine for small diameter (36-in. and smaller) utility installations that utilizes a vacuum system connected to a vacuum truck for muck removal.. The SBU-RC was chosen for several reasons, space being only one of them.
“We mainly selected it due to the presence hydrogen sulfide gas. Our other choice would have been 48-in. steel casing and a Robbins manned entry machine, but the larger diameter would have caused a design change that we would need to submit to the owner. Overall, it would have been more expensive and the gas was really bad news. The hydrogen sulfide dissipates naturally in an open trench so it’s not a concern, but in a confined space it could be very dangerous,” said Case. With the remotely operated solution, no one would need to be in the pit and the machine could be steered safely at the surface from an operator’s station.
Limited site space was of course a factor, according to Case. “We were literally in people’s backyards for this project and we found that, as opposed to other methods, the noise level was much less even with the vacuum truck than it would have been with traditional spoil removal and enabled us to work in a smaller footprint. The process of getting rid of spoils was also totally eliminated with the vacuum system, which streamlined operations.” The work site consisted of a 40 ft x 60 ft area — a space that Case says would normally be closer to 100 ft x 120-150 ft.
The selected SBU-RC was equipped with a smart guidance system. The guidance system could show an operator projections of the future bore path so steering corrections could be made before the machine was ever out of line and grade. The feature was critical for the crossing below railroad tracks, which could not be shut down if problems occurred.
During tunneling, an operator in a cabin on the surface is able to adjust the steering within 2 degrees in any direction using an articulating front shield. While not for curved tunnels, the system is able to make necessary adjustments required for a straight, line-and-grade-sensitive tunnel like the Buffalo, N.Y., crossing.
The SBU-RC operates much like other SBUs, with the closest similarity to the Motorized SBU (SBU-M). A circular cutterhead and cutting tools excavates hard rock up to 20,000 psi or mixed ground conditions, while an in-shield drive motor provides torque to the cutterhead of up to 16,000 ft/lbs at 7-10 rpm. An auger boring machine (ABM), or in this case a pipe jacking system, provides thrust.
The machine, with its remote guidance, is able to stay on line and grade and lessen the possibility of an event below residences and a roadway that would require intervention. The entire setup is capable of excavating crossings up to 500 ft long. Due to the vacuum muck removal system, no separation plant is required.
The SBU-RC was launched with Robbins Field Service guiding operation of the machine through shale rock of about 14,000 psi UCS. “During tunneling we had to deal with significant groundwater in the rock. We thought that might prove to be challenging given that the vacuum system doesn’t work too well with water. But we talked with Joe Lechner from Robbins and we were able to work it out with Robbins’ Field Service people. That system actually worked pretty well. It clogged up a couple times but with their help we were able to overcome that,” said Case.
Jeremy Pinkham, Robbins Field Service Manager for The Americas, was at the site. “The shale was very sticky. We couldn’t spray water through the cutterhead as that would cause it to clog. We injected water into the vacuum line and it worked well.” The vacuum system was used along with a 5,250 cfm vacuum truck.
Despite the groundwater, advance rates began to ramp up. “The production rate on the project exceeded by two-fold what I had estimated. From start to finish we averaged 25 to 30 ft per day even with welding 36-in. OD pipe sections,” said Case. The whole crossing took about three weeks to complete, with the machine holing through into a small receiving pit in the second backyard.
“We ended up, after 360 ft, being about 7.5 in. off of line and our elevation was less than 5/8 of an inch low. The result was well within tolerances so it went right where we pointed it. We could easily correct if it went off course,” said Case. After crossing excavation, 21-in. PVC carrier pipe was to be installed inside the casing.
For Case Boring, the performance of the machine made all the difference. “We had a tight tolerance, so coming out of the gate and being able to do something like that, with that type of accuracy in solid rock, was the highlight. The fact that the Robbins equipment could deliver on that was phenomenal,” said Case.
The early completion of the project also had a positive effect. “The owners of the project and general contractor were good to work with and cooperative throughout the project. Everyone was extremely pleased. We finished the bore three weeks ahead of schedule.”
And, while Case Boring doesn’t currently have any other projects like the unique North Aurora Pump Station bore slated, they see a definite use for this type of technology on future utility installations. “This has opened our eyes to the possibilities of what could be done. The equipment exceeded all our expectations of what would be possible.”