Ground Improvement at the Queensway Bay Downtown Harbor, Long Beach, California

Vibro-replacement with stone columns was selected as the optimum ground improvement solution to mitigate liquefaction potential, provide seismic stability, and provide adequate structure foundation support for a proposed harbor/marina development at an oceanfront site. The site is underlain by up to 27 meters of soft/loose hydraulic fills and seafloor sediments. An 18-meter wide ground improvement zone straddling the proposed 600-meter long bulkhead wall alignment was designed to create a non-liquefiable barrier that would prevent flow failures towards the lagoon, limit seismically induced deformations to acceptable levels, and allow the wall to be supported on shallow footings. The construction of a temporary earthfill construction platform served the dual purpose of permitting construction in the dry, and providing a preload that would help accelerate consolidation settlements of the soft cohesive soil layers underlying the bulkhead footing. Stone columns were also used to improve foundation soils below the mud line of a 60- meter long, pile-supported pier, to a level sufficient to provide adequate lateral and uplift capacities during seismic loading. This paper discusses the geotechnical design and field implementation of the ground improvement program