As a subconsultant to GTS, Inc., Bennett Trenchless provided trenchless design assistance on the relocation of three large PG&E gas transmission lines, 16- to 24-inches in diameter. The relocation of the existing lines was required due to modifications to the I-680/I-80/SR-12 Interchange. The design required twin guided boring crossings of I-80, twin HDD crossings of I-680, and a single guided boring crossing of I-680. Bennett Trenchless conducted a trenchless feasibility analysis to determine the most appropriate methods for the crossings, evaluated potential bore alignments, estimated settlement and hydrofracture risks, conducted pipe stress calculations for the HDD bores, prepared technical specifications and drawings.
Challenges included restricted work areas for all of the crossings, numerous major existing utilities, abandoned foundations near the exit point, lenses of loose sand beneath the highway, and crossing beneath 30-inch and 39-inch diameter water mains. Profiles and alignments were chosen to manage settlement and hydrofracture risk to the interstates and utilities, and a settlement monitoring program was designed to protect Caltrans and private facilities. The project was completed within budget and schedule with no claims.