VO NGOC BAU

Effects of shear strain rate on deformation characteristics in various soils

TOYOTA Hirofumi

Soil of each type shows different mechanical properties. Therefore, in geotechnical engineering, soils are roughly divided into sandy soil, cohesive soil, and clay. In this study, a hollow cylindrical torsional shear apparatus was used to investigate the effects of shear rate on mechanical properties of soils. Undrained shearing was conducted with different shear strain rate of 0.002 %/min, 0.02 %/min, 0.22 %/min, and 2 %/min under major principal stress direction of α=45o and intermediate principal stress coefficient of b=0.5. Toyoura sand, Yoneyama silt, and NZ kaolin were used corresponding to sandy soil, cohesive soil, and clay, respectively. 
Major findings obtained through the study are summarize as follows:
1.	In the case of Toyoura sand, the stress-strain relations exhibit almost no effect of the shear strain rate. The effects of shear rate on secant shear modulus are also slight.
2.	In the case of Yoneyama silt, the deviator stress increases with the strain rate in the shear strain less than 1%. However, this trend is not apparent in the shear strain greater than 1%. The secant shear modulus increases with increased shear strain rate.
3.	Although NZ kaolin shows the same behavior with Yoneyama silt in the shear strain less than 1%, this tendency continues up to the shear strain of 5%. The secant shear modulus increases with increased shear strain rate.
4.	The shear strain rate dependency on the secant shear modulus is the strongest in NZ kaolin, followed in order by Yoneyama silt and Toyoura sand.