The design method of the sand compaction pile method (SCP) and compaction grouting method (CPG) is studied in this paper. SCP is a countermeasure against liquefaction densifying the ground by installing sand piles. CPG is also a liquefaction countermeasure densifying the ground by injecting mortars into the ground with a high pressure. A prediction method of the SPT N-value of ground after the compaction by SCP and CPG, and a prediction method of ground deformations due to the CPG work are proposed considering the mechanical behaviors of soils during the compaction. The outlines of the paper follow.
　Accuracy of a conventional method on the prediction of the SPT N-value after the compaction is examined by using field data on the N-value. It is found that the prediction by the conventional method and the field data are contradicted each other, because the method does not consider the mechanical behaviors of soils during the compaction.
　The behaviors of soils during the compaction are studied by using the field data and model tests on the compaction. And the densification mechanism of soils is proposed on the basis of the soil behaviors under cyclic shear, where it is hypothesized that the densification of the ground is the accumulation of the negative dilatancy of the soils due to the cyclic shear caused by the installation of the compaction piles or grout mortars.
　The new prediction method on the SPT N-value after the compaction is proposed using the bowl model which is the constitutive model for soils under cyclic shearing. The accuracy of the new method is examined with the filed data and it is shown that the new one has accuracy better than the conventional one.
　The prediction method on the ground deformations due to the CPG injection is proposed using the prediction method on the N-value and hypothesis that the defomations of surrounding soils of the mortars occurs spherically. The predicted deformations are compared with the observed ones in the field and the proposed method is veified.