A subterranean in-custody transfer tunnel will extend between the existing San Diego Central Jail and the New San Diego Central Court. The tunnel will beapproximately 323 feet in length. The tunnel alignment extends between portal structures on the west face of the existing jail and on the east face of the new court foundation wall. The existing jail portal structure is outside the property line of the San Diego Central Jail. The west transfer structure occurs at the B3 basement level of the New San Diego Central Court.
The tunnel will be constructed of sprayed shotcrete and formed reinforced concrete and extends beneath the foundations of the existing The County Courthouse. In custody transfer movements through the tunnel between new court and existing jail require elevators and stairs for vertical circulation. The Sequential Excavation Method (SEM) will be utilized to a construct the tunnel. This involves a process of sequentially excavating a series of smaller headings and drifts, which are ultimately interconnected to create the required tunnel cross section. The SEM method is appropriate for tunnels with varying geometries and where the internal clearance requirements are not well suited to a circular profile generated by a Tunnel Boring Machine. The SEM cross-section will accommodate a 9-feet wide by 8-feet 9-inch high internal walking corridor. The SEM method enables close control of the ground to minimize ground loss and limit settlement induced damage to structures. Approximately 20 strategically placed dewatering wells along the tunnel alignment are required to facilitate excavation and control the adjacent soil settlement. These wells will be placed in advance of the start of excavation and will continue to operate until the
tunnel is in place and fully waterproofed.

Develop 2 Construction SWPPPs and QSD/QSP Services

San Diego, CA

State of California Department of Transportation