ESTIMATING K_0-VALUE OF IN-SITU GRAVELLY SOILS

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Hatanaka and Uchida (1996) developed a simple method (named G_0-equal method) for estimating K_0-value of cohesionless soils by equalizing the initial shear modulus calculated from the shear wave velocity measured in the field (G_<OF>) and that measured in laboratory (G_<OL>) 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 G_0-equal method was modified as a V_S-equal method in the present study. In the V_S-equal method, the K_0-value can be described in Eq. (1). K_0={(3/σ'_v)・(V_<SF>/a')^<1/n'>-1}/2 (1) V_<SL>=a'(σ'_m)^<n'> (2) where, K_0 is the coefficient of earth pressure at rest, σ'_v is the effective vertical stress at depth for measuring the shear wave velocity, V_<SF> is the shear wave velocity measured in the field, σ'_m is the effective mean principal stress, and α' and n' are the soil constants in Eq. (2). In order to examine the validity of the V_S-equal method, the effects of the principal stress ratio and the stress history on the V_<SL>-σ'_m correlation were verified by performing a series of laboratory tests on undisturbed and reconstituted sand and gravel samples. The K_0-value of in-situ gravelly soils was measured by using the V_S-equal method. High-quality undisturbed gravelly samples for the determination of the K_0-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=σ'_3/σ'_1,σ'_3 : radial stress, σ'_1 : axial stress) on the V_<SL>-σ'_m 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 V_<SL>-σ'_m relation was also found to be very small. These results indicate that the V_S-equal method modified from the G_0-equal method is a useful tool to determine the K_0-value for sandy and gravelly soils. 3. The K_0-values measured by the V_S-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 K_0-value of compacted gravelly soils almost correspond to the range of the K_0-value usually adopted in practical use (K_0=0.5 to 1.0). However, the K_0-values for gravelly fill are much lower than that for common use. Holocene gravel has relatively high K_0-values. 4. Based on the test results, a simple equation (Eq. (3)) is newly proposed for the estimation of the K_0-values for insitu gravelly soils by only using the shear wave velocity measured in the field (V_<SF>). K_0=0.0058V_<SF>-0.53 (150≤V_<SF>≤350 (m/s)) (3)
社団法人地盤工学会の論文
1999-10-15

ESTIMATING K_0-VALUE OF IN-SITU GRAVELLY SOILS

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