San Francisco Public Utilities Commission Completes Hand Mined Tunnel for Seismic Resiliency Project

摘要

The San Francisco Public Utilities Commission (SFPUC) recently completed the Peninsula Pipeline Seismic Upgrades (PPSU) Phase 3 Project, a seismic resiliency project with a goal to improve the seismic reliability of high risk sections of the Regional Water System transmission pipelines that run from the Harry Tracy Water Treatment Plant (HTWTP) to the Sunset Reservoir. The project included upgrades to San Andreas Pipeline No. 2 (SAPL2), a 54-inch diameter steel water transmission pipeline located within a steep slope of Stern Grove Park, which was found to be at risk for up to 11-inches of movement during seismically-induced landslides.A portion of the SAPL2 pipeline was replaced using hand mining trenchless installation methods to accommodate the goals of San Francisco Recreation and Parks Department for minimal surface disturbance within the densely vegetated hillside of the park, while providing a reliable source of potable water for the City of San Francisco. The project design included a finite element analysis to verify the suitability of the design’s pipe-wall thickness, miter bend configurations and annular space grouting to meet the seismic design requirements.The project included installation of approximately 680 linear feet of 0.5 to 1-inch thick, butt welded, 54-inch diameter SAPL2 steel pipe, with approximately 140 LF installed in a 72-inch diameter tunnel, using hand mining installation techniques, downhill on a 28-degree slope. The tunnel utilized bolted liner plate construction, with an auger bored pipe in the center for soil removal downslope in the center of the tunnel to the receiving shaft, at the downhill end.