GROUND IMPROVEMENT OF INTERMEDIATE RECLAIMED LAND BY COMPACTION THROUGH CAVITY EXPANSION OF SAND PILES

The crushed Tertiary Period mudstone used as the geomaterial for the artificial reclaimed land in the Joetsu Region of Japan consists of coarse and fine fractions of about 50% each and is classified as an “intermediate soil.” Unlike sand or clay soils, no constitutive equations or sufficiently established design methods have been available until now for evaluating intermediate soils. This paper first utilizes the SYS Cam-clay model (Asaoka et al., 2002) to identify the soil profile of intermediate reclaimed land through comparison of laboratory test results with the calculated responses of the constitutive equation. Next, the soil profile obtained is used to carry out various soil-water coupled finite deformation analyses. The main conclusions reached are as follows: 1) The rates of decay/collapse of the soil structure, loss of overconsolidation, and evolution of anisotropy of the soil materials that constitute the Joetsu reclaimed land lie midway between those of typical sand and clay. 2) Ground improvement by cavity expansion of sand piles is effective in converting the reclaimed land from a highly structured ground having heavier overconsolidation to a lightly overconsolidated ground with a low degree of structure by increasing the confining pressures within the ground. In particular, the reduction in the specific volume of the soil elements in the vicinity of the sand piles becomes large. 3) In the case of small vertical displacement, the composite ground containing the sand piles exhibits a bearing capacity of about 1.5 times that of an unimproved ground, and in the case of large displacement, the bearing capacity is about 2 times larger.