Bay Division Pipeline 3 and 4 Hayward Fault Crossing Seismic Upgrade

These pipelines cross a highly active branch of the San Andreas Fault and are the main water supply conduit for nearly 2 million people in the San Francisco Bay Area. They also cross underneath Interstate Hwy. 680 which is one of the main transportation corridors.

Due to the underlying geology, the various parts of the fault zone transmit forces differently. The heavy wall was designed to resist distortion and using minimum 60 ksi yield strength steel for all the sections in the specific fault zone. Under normal conditions, the creep in the fault zone will compress the pipe over time and in the section under Interstate Hwy. 680 a large vault contains a 78″ pressure balanced expansion joint, two 78″ ball joints and a conventional 78″ expansion joint. The pipe also had to roll and slide in the tunnels underneath the interstate highway.

All pipe sections within the fault zone were butt welded to transmit the forces along the axis of the pipe. This required extremely close tolerances on the fabricated sections in order to maintain the exact alignment. In addition, the right of way was extremely narrow and crowded, requiring a precise delivery schedule with the correct end positions as the pipe could not be turned around. There were also many emergency bypass connections to feed or draw water from the local utility systems that required close coordination with additional agencies.

All pipe was urethane lined and coated with a cement mortar overcoat. Pipe section lengths varied from 20 ft. to 50 ft.