Courthouse Commons Pedestrian Tunnel


Holland Partner Group / County of San Diego

Completion Date



Delve Undergound


San Diego, CA

Delivery Method




Contract Value

$45 million
Tunnel interior with smooth concrete finish and domed top

The project was a new Inmate Transfer Tunnel between the San Diego County Jail and the New State Courthouse to securely transport inmates. A 55-foot deep rectangular shaft was supported with a combination of secant piles and solder piles that were internally braced on three levels. The 328-foot long, 27-foot diameter “egg shaped” tunnel was excavated using the sequential excavation method (SEM) through dewatered alluvial soils, crossing an active fault line. Additionally, four short “niches” were excavated perpendicular to the tunnel alignment to create additional space. Ground support consisted of grouted pipe spiling, lattice girders, face wedge, high early strength fiber reinforced shotcrete, and a pipe canopy. Following excavation, the tunnel and shaft were fully waterproofed with a PVC membrane, furnished with a heavily reinforced concrete final lining, and outfitted with eight waterproof seismic seals to accommodate tunnel movement in the event of a seismic event.

The interior buildout scope included three new elevators, MEPF systems, detention ceiling, security systems, total renovation of the County Jail basement, and final finishes. The compressed project footprint occupied a single lane of traffic and sidewalk in downtown San Diego directly in front of the Jail's receiving dock. To maintain access, a moving bridge over the shaft was implemented. Shaft excavation was adjacent to the 22-story Central Jail and tunnel excavation was just 7 feet below the old courthouse foundation, terminating in the new courthouse foundation. This all required significant geotechincal monitoring and coordination with building occupants.


2023 APWA San Diego Project of the Year
2023 ACEC CA Engineering Excellence
2021 ASA Outstanding Underground Project