Foundation System for a New Grain Export Terminal

摘要

A new grain export terminal will be constructed on a 4.0 ha (10-acre) parcel adjacent to Pier T on the Navy Mole in the Port of Long Beach. The mole was likely constructed by infilling monolithic quarry rock dikes with hydraulic and/or mechanically placed fill. Terminal improvements include grain silos, a grain elevator tower, a surge tank, rail receiving facilities, and a loadout building. The design of the terminal facilities must consider the effects of strong ground motions and liquefaction because the project site is located in a seismically active region and underlying soils are liquefiable. Typically, foundations for many of these improvements would involve piles embedded in competent soils well below the liquefiable soils, but designing piles to resist downdrag loads from liquefaction was determined to be very costly and could impact the overall project budget structure. Alternative foundation systems that will meet project budgetary requirements were examined. The selected foundation system, which is more cost effective than pile supported foundations, consists of shallow foundations overlying soils improved with cement deep soil mixing (CDSM) technique. The CDSM was designed to mitigate the liquefaction potential, provide a suitable bearing surface for proposed foundations, and reduce potential settlements to tolerable levels. Finite difference methods were employed to design the idealized CDSM layout in terms of minimum area replacement ratio and minimum depth of improvement under the design level ground motions.