San Diego Courthouse Commons Shaft Shoring and Tunnel Canopy Tubes-Paper

Paper

Pdf Summary

The San Diego Courthouse Commons project created a secure underground route for transporting inmates between the County Jail and the new State Courthouse. Condon-Johnson & Associates (CJA) installed temporary shaft shoring, tunnel canopy pipes, and grout treatment to support construction and limit settlement near the existing Old Jail.<br /><br />The 56-foot-deep access shaft was supported by 41 piles, including secant piles beside the County Jail and soldier piles with lagging elsewhere. Three levels of internal bracing stabilized the excavation. A sliding bridge, designed for 80,000 pounds, maintained truck access to the jail. Groundwater was lowered during excavation, and a reinforced concrete slab was installed at the shaft base.<br /><br />For sequential excavation of the tunnel, CJA installed three overlapping reaches of 7⅝-inch canopy pipes: 24 pipes at 99 feet long, followed by 21 pipes at 80 feet and 21 at 75 feet. Testing confirmed the pipes’ bending capacity, and an inertial sensing gyro verified alignment. The pipes were grouted internally and externally, with installation and grout records maintained for quality control.<br /><br />To reduce the risk of settlement as the tunnel passed beneath the Old Jail, CJA installed sleeve-port grout pipes through the basement floor and footings. Grout was injected into treatment zones below the foundations, with pressure, flow, and volume monitored.<br /><br />The authors report that shaft movements remained within design tolerances and that the canopy-pipe and void-filling systems supported tunneling while mitigating the potential for settlement and collapse. They identify collaboration, technical expertise, workforce, and equipment quality as key contributors to meeting project requirements.

Keywords

San Diego Courthouse Commons

underground inmate transport

temporary shaft shoring

canopy pipes

grout treatment

secant piles

soldier piles

ground settlement control

Old Jail

tunnel excavation