A Simple Method for the Determination of Ko-Value in Sandy Soils

Abstract

A laboratory test method for the determination of the coefficient of earth pressure at rest, Ko, in sandy soils is presented. In this method, initially, a series of undrained cyclic triaxial tests were made on high-quality undisturbed sand samples recovered by the in-situ freezing sampling method (FS sample), in order to obtain the relationship between the shear modulus at very small strain, Go, and the effective confining stress, σ'c. Next, the Go was also calculated based on elastic wave theory by using the shear wave velocity measured at a depth from which the undisturbed samples were recovered. By equalizing the Go values obtained from these two independent methods, the coefficient of earth pressure at rest, Ko, in the sandy soils, can be determined using the proposed simple method. The Ko-value of a diluvial sand obtained using this method is 0.84. Based on the test results on the sand samples obtained by the rotary type triple tube sampling method (TS sample), recovered from the same soil layer and the same depth, however, the Ko value obtained with this method was 1.44, which is considerably larger than that obtained from the FS sample. The larger Ko value of the TS sample compared with that of the FS sample is because the initial shear modulus of the TS sample is much lower than that of the FS sample for the same level of confining stress due to sample disturbance.