Reduction of liquefaction hazards by deep soil mixing

Abstract

One of the most promising technologies for site improvement involves deep soil mixing (DSM), whereby cements and hardening agents are mixed in situ with native soil to increase strength and stiffness properties. This method proved to be effective in stabilizing potentially liquefiable soil at several sites during the Kobe earthquake, including the Oriental Hotel, where partial coverage by DSM columns was successful not only in controlling lateral spread but in preventing liquefaction. This paper describes a simplified analytical approach for modeling the dynamic response of DSM at liquefiable sites. The approach combines two-dimensional models of DSM panels oriented both parallel and perpendicular to the direction of strongest ground motion to account for three-dimensional distortion of the DSM grid. Maximum and average soil shear strains from the analysis are used to estimate the ratio of excess pore pressure to effective overburden stress on the basis of published laboratory data. Analytical results compare very favorably with two separate sets of centrifuge test data. The analytical model correctly predicts the observed behavior of DSM-reinforced soil at the Oriental Hotel during the Kobe earthquake. DSM is effective in reducing liquefaction potential because it provides reinforcement to restrict shear strain in the soil mass. The proposed analytical approach correctly accounts for observed performance and provides a means of assessing the appropriate DSM grid dimensions for effective site improvement.