ABSTRACT
It appeared that the loose sand from a depth of 6 m to a depth of 11 m has a potential of liquefaction during an earthquake of the maximum horizontal groundsurface acceleration of 200 Gal, according to the simplified method of liquefaction potential evaluation recommended by Tokimatsu and Yoshimi (1983) or AIJ (2001). To cope with the liquefiable sand layer, a grid-form ground improvement (TOFT method) was introduced. In the method the grid-form soil-cement walls are constructed by deep mixing method as illustrated in Fig. 2. They confine a loose sand layer by the high-modulus walls with an unconfined compressive
strength of 2000-4000 kPa, so as not to cause large shear deformation in the loose sand layer during a strong earthquake. The effectiveness of the grid-form ground improvement has become evident at the 1995 Kobe earthquake (Tokimastu et al. 1996).
