Lessons Learned: Sanitary Sewer Project Converted to Pilot Tube Method of Guided Boring

The Pilot Tube Method (PTM) of Guided Boring is not typically top of mind as a value engineering option. But in this project in Burton, MI, PTM was used to change the originally specified installation method from open excavation crossing a two-lane asphalt roadway. In the end, the method change was economically advantageous, it avoided a good deal of collateral damage, and it was more efficient. We will dissect the project and review the Lessons Learned. The project was specified as an open-cut installation of approximately 308 linear feet of 8-inch PVC between two existing maintenance holes, at a maximum slope of 0.13%. The Burton sewer project was converted to a vitrified clay pipe (VCP) PTM installation due to ground conditions and a necessity to limit the size of the working footprint. The sewer was close to 30' deep and was routed under a popular two-lane road and between two houses. The contractor proposed using PTM so that the road was not disturbed and the massive disruption of an open trench between those houses was avoided. The contractor also proposed adding a maintenance hole in the middle of the run such that the laterals could enter this new maintenance hole. This was more efficient than tapping the pipe 30' deep for those laterals. The soils were worse than expected based on the Geotechnical Report. The soils actually encountered were a running, silty clay with little support. The contractor used a 60,000 lb. Link Belt 235 with a custom-built extendable stick capable of digging 31'. The jacking and receiving shafts were lined with sheet piling. Pulling a trench box through those soils would have been even more difficult than originally anticipated and would result in a lot of collateral damage. Due to space constraints of the project footprint, the contractor used shorter pipe lengths for installation of the sewer. This allowed the shafts (jacking and reception) to be limited to 13-feet diameter and avoided disruption of the two-lane street. The Lessons Learned on this Trenchless project will be beneficial for many Designers, Municipalities and Contractors.