Abstract:
Liquefaction and lateral spreading hazards were identified for a water front school building expansion project in New Port Beach Harbor, California. Under the high design earthquake acceleration of 0.5g and shallow water table depth, the top 3 to 15 ft of loose to medium dense silty sand (SM) and clean sand (SP) will be liquefied. To accomplish the liquefaction mitigation, the soil must densified, drained, reinforced, or solidified. Considering the tight site condition, within the operational building, and the shallow liquefiable soil depth, the conventional ground improvement methods, such vibro stone column, compaction grouting, and jet grouting, were not considered as feasible solutions. Instead, a design/built permeation grouting plan was adopted with chemical grouting to form soilcrete grids under the building to mitigate site liquefaction by the shear reinforcement. In order to conform the stringent local environmental requirements in the harbor, we used the colloidal silica grout, the most environment friendly chemical grout in the zones closed to the water front. Due to the low unconfined compressive strength of colloidal silica grouted sands, 53% soilcrete replacement ratio was designed under the building footprint for adequately shear reinforcement and support building loads. This paper provides the site geotechnical investigation, liquefaction analysis, chemical grouting design and site tests, as well as QA/QC.