Abstract
Onjaku soil is the weathering product of basalt distributed in Uwaba area, the north western part of Saga Prefecture. The Onjaku soil compacted below optimum water content exhibits collapse-induced settlement when the soil is soaked under an overburden pressure. The present paper describes the changes in the compressibility and shear strength of the Onjaku soil compacted below optimum water content due to soaking under various pressure applied. A decrease of the compression yield stress and compression index, and an increase of the coefficient of volume compressibility were brought about by the release of suction. After soaking the shear strength of Onjaku soil samples below optimum water content dropped to the strength of the samples initially soaking. It is experimentally certified that the suction affects the cohesion of Onjaku soil.
