Pacific Gas & Electric (PG&E) has more than 42,000 miles of gas pipeline throughout California. Some sections, like one of the main lines in Fremont, California, cross major interstates and railroad lines. PG&E opted to replace this section of pipeline using a micro-tunneling technique – with a jacking shaft at one end and receiving shaft at the other.
Malcolm installed the 42-foot deep access shafts using the Cutter Soil Mixing (CSM) method for the shaft walls and jet grouting to seal the shaft floor. For the excavation to be performed in dry conditions without the need for dewatering, the bottom seal needed to be tightly tied into the walls. The bottom seal was 35 feet below groundwater level. To verify effectiveness of the jet grouting, Malcolm conducted a test program utilizing geophones to measure the jet grout column diameter in real time.