San Francisco’s new Public Safety Building (PSB) is located on 3rd Street in Mission Bay. The 300,000-sq-ft state-of-the-art building combines the 110,000-sq-ft San Francisco Police Department (SFPD) Police Command Center, the 20,000-sq-ft Southern District Police Station, the 17,000-sq-ft San Francisco Fire Department (SFFD) Fire Station, 25,000 sq ft of community space and a 128,000-sq-ft parking structure, including adaptive reuse of a historic, red brick fire house.
In the event of a major earthquake, this building was not expected to be operational and it is essential that the police command structure be fully operational immediately after the “Big One” and the facility was designed to meet a green building certification rating of LEED (Leadership in Energy and Environmental Design) Gold and create a seismically safe building that will be fully operational after a major earthquake.
Raito Soil Mixing Wall (RSW) was adopted to install soil-cement-bentonite walls for excavation support of the parking structure basement and groundwater control. Steel H-piles and Tie Backs were installed for excavation support walls to resist the lateral forces. Triple-shaft DSM equipment was used for the excavation support wall installation to a maximum depth of 36 ft. The drilling depth, penetration/withdrawal speed, shaft rotation and slurry injection rate were monitored on a real time basis for accurate mixing control and a uniformly mixed product. The construction started in February 2012 and completed in May 2012.
Test specimens from the soil-cement-bentonite excavation support wall for strength and permeability testing were retrieved by wet sampling. Acceptance criteria for unconfined compressive strength required an average of 100 psi at 28 days. hydraulic conductivity of the excavation support wall required a maximum permeability coefficient of 1×10-6 cm/sec.
Quality Control (QC) data collected for each element were processed and recorded on the daily drill rig and batch plant reports. All values were meet the requirements of the design and specifications. The batch plant operator had been reviewed the data of each element to verify compliance.
RSW uses multiple augers, paddle shafts rotating in alternating directions to mix in-situ soil with cement grout, bentonite slurry, clay slurry, or other stabilizing reagent slurries to install continuous subsurface soil-cement walls for excavation support and groundwater or underground pollutants control, or ground reinforcement; column blocks, lattice, or areal patterns for stabilization.