MICROTUNNELING TECHNOLOGY USED TO MITIGATE CHALLENGES OF RAILROAD AND UNDERGROUND UTILITIES By Jennifer Martin This fall, the PEC team will complete a project that makes use of microtunneling—an innovative technology that’s only been used once before in the state of Utah.
The Salt Lake City Department of Public Utilities (SLCDPU) awarded PEC the 1500 South Sewer Rehabilitation project in 2017. The project involved plans for microtunneling and trenchless installation—technologies similar to those the engineers used on the Channel Tunnel in England and France.
The sewer rehabilitation project area includes 5,200 linear feet of 30- and 36-inch diameter sewer collection pipe within the 1500 South corridor between 2700 West and Redwood Road; and 1,000 linear feet of 21-inch diameter sewer collection pipe on Industrial Avenue between 1500 South and California Avenue.
Our innovative approach sets the PEC team ahead of the competition as these technologies are not yet commonly used. In fact, the 1500 South Sewer Rehabilitation project will be the second project in the area to incorporate microtunneling plans.
With these plans, the PEC team would resolve significant challenges within the project limitations, including those associated with the multiple Union Pacific Railroad track line crossings and an overlap at Interstate 215.
Joey Willardson, a licensed professional civil and environmental engineer in PEC’s Utah office, worked on the design. He said that the 1500 South project required innovative solutions to best address significant issues of concern at the site near the freeway.
“From our research into its capabilities, we felt that microtunneling beneath I-215 was the best option for the trenchless installation of the sewer main due to the small grade tolerances required and raveling soils beneath the major freeway,” Willardson said.
Other challenges on the 1500 South project included the presence of abandoned utilities beneath I-215 along the microtunnel alignment, the necessity to redesign the grade of the sewer line to avoid large diameter storm drain pipe crossings, and a small sewer grade design window due to existing sewer inverts at either end of the project.
After the SLCDPU sewer rehabilitation project was awarded to PEC in 2017, the project team went to work over the next year to complete the design. As part of that process, PEC prepared a condition assessment to determine the level of deterioration of the existing concrete pipe. The team followed all standards set by the National Associate of Sewer Service Companies (NASSCO) to determine the integrity of the existing pipe and the need for rehabilitation or replacement. The project team also performed pumping tests to estimate the impact of groundwater inflow to excavations during construction.
The design was completed in October 2018. The project is currently in the construction phase, and is scheduled to be completed this fall. The PEC project team for 1500 South includes Leo Florence (Principal), Victor Godfrey (Project Manager), Justin Brewer (Utilities/Transportation), and Joey Willardson (Project Engineer). All have worked together on a number of recent sewer rehabilitation projects for SLCDPU, and are known for their expertise in the area.