San Diego Courthouse Commons Shaft Shoring and Tunnel Canopy Tubes-PPT Presentation

PPT Presentation

Pdf Summary

The Courthouse Commons Tunnel project in downtown San Diego connected the County Central Jail to the State Courthouse. The work included a three-story underground transfer shaft and a 320-foot-long, 23-foot-diameter modified horseshoe tunnel, excavated about 60 feet below ground using the sequential excavation method. The tunnel passed through sandy deposits and an active fault zone, with groundwater managed through dewatering wells.<br /><br />Construction began in April 2020. The 18-by-52-foot shaft was shored with 41 deep piles—23 secant piles beside the jail and 18 soldier piles—with three levels of internal bracing. Crews excavated in four-foot lifts, installing bracing as they progressed. Restricted access required different equipment at upper and lower shaft levels, and a temporary sliding bridge maintained truck access to the jail.<br /><br />Three arrays of grout-filled canopy tubes supported tunnel excavation. The project used 7⅝-inch-diameter tubes, installed in reaches up to 99 feet long, with alignment monitored by an inertial-sensing gyro. A testing program assessed tube bending strength, and crews followed specified grout-volume and pressure criteria during installation.<br /><br />To mitigate settlement beneath the old jail, cement grout was injected under strip footings and grade beams through drilled holes or sleeve ports. The project was completed without settlement or collapse. The presentation identifies teamwork, technical expertise, workforce, equipment, and support as key factors in its success.

Keywords

Courthouse Commons Tunnel

San Diego

sequential excavation method

underground transfer shaft

secant piles

soldier piles

canopy tubes

dewatering wells

cement grouting

settlement mitigation