Vacuum-assisted consolidation of a hydraulic landfill

As part of the Pier 300 42-acre site ground modification project, a field test of vacuum-assisted preconsolidation of hydraulic fill was studied. The objective of the test was to assess the feasibility of this technology as an alternative or supplement to conventional surcharge techniques for ground improvement of future hydraulic fill sites at the port of Los Angeles. The test section was about 30×30 m² consisting of prefabricated wick drains capped with a geomembrane, a slotted pipe collector system embedded in a sand blanket beneath the geomembrane, an anchor trench and protective cover medium for the membrane, and a vacuum pump. Instrumentation included high air-entrainment piezometers to measure negative pore pressures, monitoring of the ground surface settlement and multi-point borehole extensometers for deep settlement measurements. Results indicate that, due to less than optimum site conditions, the efficiency of vacuum consolidation was about 50 percent, or equivalent to about 3 meter of surcharge fill at the test site. Under better conditions or with a more effective membrane seal, higher efficiency and greater equivalent surcharge heights can be achieved, making vacuum-assisted consolidation an economically viable alternative or supplement to mechanical surcharges.