Anisotropic Stress-Strain Behavior at Small Strains of Clay by Triaxial and Bender Element Tests

Abstract

In this study, to examine the effect of the fabric anisotropy on elastic moduli (shear and Young's moduli), the bender element, cyclic and monotonic triaxial tests were performed on reconstituted clay specimens with different fabric characteristics. The specimens with the angle between the axial direction of the triaxial specimen and the bedding direction of 0 and 90 degrees were cut from the pre-consolidated clay block. These specimens were isotropically consolidated under several kinds of confining pressures. The shear wave velocities in three different directions (VH, HH, HV-wave) were measured by bender element tests, and the stiffness under wide ranges of strain levels up to failure were measured by cyclic and monotonic triaxial tests. Test results showed that; 1) the shear modulus obtained from the shear wave for propagating and vibrating horizontal to the bedding plane is higher than the others two kinds of moduli, 2) the horizontal Young's modulus at small strain is also higher than the vertical one, 3) the anisotropy of the elastic modulus of clay is larger than that with sand, but becomes lower with the increase in strain level and consolidation stress.

Effects of inherent anisotropy on G0 of unsaturated sand

“…This trend tend to be reversed when the shear strain is greater than 10 -1 %. These results are in agreement with observation conducted by Yamashita et al (2003 and2005). The authors made specimen as pluviation direction of 0 o (V-specimen) and 90 o (H-specimen).…”

“…The ratios of (G0(a=90°)/G0(a=0°)) are 1.14 and 1.12 for unsaturated sand and saturated sand, respectively. Bellotti et al (1996), Pennington et al (1997), Yamashita et al (2005), Hight et al (2007), and Teng et al (2013) demonstrated that the shear moduli in the horizontal plane were higher than those in vertical plane. Ng and Yung (2008) proved that the increase of matric suction from 0 kPa to 50 kPa induced the increase of the shear modulus ratio (G0(hh)/G0(hv)) from 1.03 to 1.05.…”

“…According to the equation 1, G0 is varied with the changing of the void ratio e. Thus, the effect of the heterogeneous specimen can generate the difference between LSS and BE tests. Yamashita et al (2005) assumed that the higher results on elastic modulus obtained from BE test than those results from triaxial test might be affected by the different strain level in 10 -3 % (triaxial test) and smaller than 10 -3 % (BE test). The bedding error in triaxial test also might be taken account for the difference between LSS and BE tests.…”

“…The inherent anisotropy on shear strength has been investigated widely in much previous research employed a variety of laboratory tests (Oda et al, 1972; Aurthur and Menzies, 1972; Lam and Tatsuoka, 1986;Guo, 2008;Tong et al, 2014;Razeghi and Romiani, 2015). On the other side, the inherent anisotropy on the shear modulus at small strain was also carried out by means of shear wave velocity Vs determination (Pennington et al, 1997;Jovičić et al, 1998;Gasparre et al, 2007;Escribano and Nash, 2015) and direct measurement of G0 using the local strain measuring instruments incorporated to testing apparatus (Hoque and Tatsuoka, 1998;Yamashita et al, 2003;Yamashita et al, 2005).…”