Estimating K0-Value of In-Situ Gravelly Soils

Abstract

ABSTRACT Hatanaka and Uchida (1996) developed a simple method (named G0-equal method) for estimating K0-value of cohesionless soils by equalizing the initial shear modulus calculated from the shear wave velocity measured in the field (GOF) and that measured in laboratory (GO l ) for high-quality undisturbed samples. It is clear that to directly equalize the shear wave velocity obtained both in the laboratory and the field is more convenient. As a result, the G0-equal method was modified as a VS-equal method in the present study. In the VS-equal method, the K0-value can be described in Eq. (1) . (1) K 0 = 3 / σ v ′ ⋅ V SF / a ′ 1 / n ′ − 1 / 2 (2) V SL = a ′ σ m ′ n ′ where, K0 is the coefficient of earth pressure at rest, σ'v is the effective vertical stress at depth for measuring the shear wave velocity, VSF is the shear wave velocity measured in the field, σ'm is the effective mean principal stress, and a' and n' are the soil constants in Eq. (2) . In order to examine the validity of the Vs-equal method, the effects of the principal stress ratio and the stress history on the VsL-σ′m correlation were verified by performing a series of laboratory tests on undisturbed and reconstituted sand and gravel samples. The K0-value of in-situ gravelly soils was measured by using the Vs-equal method. High-quality undisturbed gravelly samples for the determination of the K0-value were recovered at six sites. Based on the test results and discussion, the following were concluded. 1. A simple testing method was successfully created for reliably measuring the shear wave velocity of gravel samples in the laboratory. This method has the following advantages; ① without bedding error, ② little personal error, ③ easy to use and ④ adjustable to specimen height. 2. The effect of the principal stress ratio (R = σ3′/σ1′, σ3′ : radial stress, σ1′: axial stress) on the VSL − σm′ relation was found to be negligibly small in the range of R tested (R = 0.5 ~ 1.5). The effect of the stress history on the VSL − σm′ relation was also found to be very small. These results indicate that the Es-equal method modified from the G0-equal method is a useful tool to determine the K0-value for sandy and gravelly soils. 3. The K0-values measured by the VS-equal method were 0.19 to 0.40 for untreated gravelly fill, 0.55 to 1.0 for compacted gravelly fill, and 0.83 to 1.14 for Holocene gravelly soils. Test results indicate that the K0-value of compacted gravelly soils almost correspond to the range of the K0-value usually adopted in practical use (K0 = 0.5 to 1.0). However, the K0-values for gravelly fill are much lower than that for common use. Holocene gravel has relatively high K0-values. 4. Based on the test results, a simple equation (Eq. (3) ) is newly proposed for the estimation of the K0-value for in-situ gravelly soils by only using the shear wave velocity measured in the field (VSF). (3) K 0 = 0.0058 V S F − 0.53 ( 150 ≤ V S F ≤ 350 ( m / s ) )