Liquefaction Mitigation by Chemical Grouting-Paper

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A waterfront school expansion in Newport Beach, California, faced liquefaction and lateral-spreading hazards from shallow loose-to-medium-dense sands, with groundwater near the surface and a design earthquake peak acceleration of 0.5 g. Analysis predicted about 64 mm of earthquake-induced settlement and potential loss of foundation bearing capacity and increased pressure on the seawall.<br /><br />Conventional methods were unsuitable because of tight access, nearby buildings and utilities, vibration concerns, and the need to keep classrooms operating. The project therefore used permeation grouting to create interconnected, load-bearing soil grids beneath the building. Environmentally compatible colloidal silica mixed with salt-based brine was used near the seawall; sodium silicate grout, which produces stronger treated soil, was used farther inland. A high treatment ratio—about 53% of the liquefiable soil volume—compensated for the relatively low strength of colloidal-silica-treated sand. Design analyses predicted near-zero post-treatment liquefaction settlement.<br /><br />Grouting was carried out through sleeve-port pipes using controlled injection volumes, low pressures, and low flow rates to limit ground heave, soil fracturing, and seawall movement. Quality assurance included grout sampling and gel-time checks, post-treatment penetration tests, verification borings, and field strength testing. Because conventional penetration tests and coring did not reliably demonstrate the improvement, excavation, pocket-penetrometer readings, and block samples were also used. A localized weak silty-sand layer received supplementary compaction grouting.<br /><br />The project treated 154 grout holes with 466 m³ of chemicals. Testing of excavated colloidal-silica-treated soil confirmed strengths above the design target in observed areas. Monitoring recorded no building heave or seawall movement. The project demonstrated that chemical grouting could mitigate liquefaction beneath an occupied building in a constrained, environmentally sensitive waterfront setting.

Keywords

liquefaction mitigation

permeation grouting

waterfront school

Newport Beach

colloidal silica

sodium silicate

groundwater

seawall

soil stabilization

earthquake settlement