The Compaction grouting (CPG) method is one of the liquefaction countermeasures to increase the density of improved ground by injecting mortar statically into the ground. CPG is often adopted just below or near the existing structures, and accordingly ground upheaval often becomes a problem. In this study, a series of model and field experiments were conducted for the purpose of developing a new method which has more efficiency than the conventional construction’s upheaval control. The proposed method has proven itself in reducing the ground upheaval quantity by more than 80 %. Furthermore, the results demonstrate that the ground density, K-value and effect of liquefaction countermeasures can be significantly increased by the new Up and Down method (U/D method). Moreover, by using the concept of an equivalent improvement rate, it is possible to predict the upheaval amount and density increase of the improved ground by the new U/D method, thereby facilitating a rational design based on the conventional CPG method. The construction efficiency and upheaval control mechanism of the new method was also examined. It was found that the workability can be improved by using an injection pipe with a tip end tapered shape. The upheaval control mechanism can be explained by the cyclic contraction of the ground due to the up and down of the new CPG method.

Key Words: compaction grouting, liquefaction countermeasure, U/D method