Contra Costa Water District constructed a new Alternative Intake Project (AIP) near its existing pumping facilities in the San Joaquin Delta region of California, east of the San Francisco Bay. The new AIP project was designed to divert raw water from the new intake pumping plant through a new 72 inch pipeline. An approximate 900-foot section of this new pipeline crossed under the Old River. Construction of this crossing required the installation of a 96-inch steel casing using micro-tunnel pipe-jacking techniques. The micro-tunneling operation required a 90-foot deep jacking shaft and a 70-foot deep receiving shaft. Malcolm designed and built these access shafts utilizing the Cutter Soil Mix (CSM) method.
Malcolm installed CSM panels at the receiving shaft first and then moved over the jacking shaft. Slurry from the CSM process was pumped to a temporary storage basin and then relocated to the final on-site disposal area. Wet grab samples were obtained from each panel during construction to allow compressive strength testing. Excavation and shotcrete proceeded on an approximate 3 day cycle for each 5-foot lift. When the bottom of the shaft elevation was reached, a reinforced concrete seal slab was installed followed by more heavily reinforced shotcrete structures to accommodate the tunnel penetrations and the MTBM jacking forces.