Bennett Trenchless Engineers, as the trenchless subconsultant to CDM, provided trenchless design of seven trenchless crossings for raw and treated water pipelines, including multiple UPRR and levee crossings, for this large water supply project. BTE was responsible for leading the trenchless design effort, evaluating alternative trenchless construction methods and alignment options, preparing trenchless cost estimates and schedules, performing supporting calculations for all trenchless work, providing shaft locations and tunnel profiles, as well as preparing the technical specifications for the trenchless construction.
Microtunneling was selected as the trenchless installation method for most of the crossings due to saturated ground conditions. The total footage of trenchless construction was over 3,100 feet, and the individual drive lengths ranged from 150 to 1,000 feet. Tunnel diameters varied from 48” to 84” to house 36” to 54” water pipelines. The two longest crossings (each > 900’) were required to pass beneath large, levee-supported canals (Bishop Cut and Honker Cut) associated with the San Joaquin River Delta. The designs for these trenchless crossings required specialized design evaluations and mitigation measures, such as fully watertight shoring, subsurface settlement monitoring, and shaft collars rising up the 100-year flood elevation. BTE and CDM coordinated extensively with the local reclamation districts to ensure the safety and stability of the levees during construction.