Compaction Grouting to Mitigate Liquefaction for a New Medical Retail Building

This paper presents a case study of compaction grouting used as a mitigation measure for soil liquefaction beneath a proposed two-story retail building with integral parking structure. The site is in an area that experienced significant seismic shaking, liquefaction, and structural damage during the 1994 "Northridge" earthquake. Analysis suggested potential for a lateral spreading hazard into the adjacent Los Angeles River. Compaction grouting was used to treat loose to medium dense saturated alluvium to a depth of 17.1 m. A test grout section was conducted prior to production to help determine optimum spacing of grout injection locations. Records of injected grout quantities were maintained in order to provide an indication of relative soil displacement with respect to treatment depth. A grout flow logger was used periodically to acquire real-time pressure and flow data during production grouting. Evaluation of these data provided a means of detecting soil response, providing a basis for establishing practical quantity limits when working near a buried storm drain pipe and a concrete-lined embankment. Comparison of pre-grouting and post-grouting soil test data showed significant improvement in liquefaction resistance, and estimated total and differential settlement was reduced from approximately 280 to 35 mm. Ground improvement was sufficient to allow the local building department to approve a previously infeasible project and to allow an alternate (more conventional) foundation system, representing significant project economy.