Shoji Kato

Application of suction stress for estimating unsaturated shear strength of soils using direct shear testing under low confining pressure

The primary objective of this study is to evaluate effects of suction on shear strength of unsaturated soils under low confining pressure and to examine the relationships between suction, shear strength behavior, and volumetric deforma- tion using newly developed direct shear testing equipment for compacted weathered granite soils. The soil-water retention curves (SWRCs) of unsaturated soils were obtained under various overburden pressures. To analyze test results from the direct shear test under unsaturated conditions, a new method, suction stress-SWRC method (SSM), is proposed to deter- mine the suction value for each overburden pressure and the suction stresses. As a result, it has been found that the stress states at the peak shear strength point are on the same failure line for the saturated state when the suction stress is treated as a component of confining pressure. The relationship between stress ratio and dilatancy for the saturated state can be ex- tended to the unsaturated state. It is also noted that the estimated unsaturated shear strengths using the SSM agree well with the measured values from laboratory testing.

Effect of Suction Stress on Critical State of Compacted Silty Soils under Low Confining Pressure

AbstractThe critical-state behavior of an unsaturated dilative specimen under low confining pressure from 0 to 50 kPa was examined by conducting a constant water content–compression (CWCC) test on unsaturated compacted silty soil. Trends in the compressive strength and deformation of specimens were measured from each testing condition. The experimental results were analyzed by assuming that the effective confining stress can be calculated through the use of suction stress, which is defined as the product of the effective degree of saturation and the matric suction. It was found that the postpeak shear-strength states are arranged on the critical-state line for saturated conditions by considering the suction stress as a stress component in the (pnet + ps, q) plane. The state boundary surface was observed in the relationship between the stress ratio [q/(pnet + ps)], considering the suction stress, and referential specific volume (νλ). It can be concluded, therefore, that the existence of a critical state fo...

DISTINCT ELEMENT METHOD SIMULATION ON DEFORMATION MODE AND STRESS STATE FOR SPECIMEN SHAPE IN DIRECT SHEAR TEST

In order to examine the deformation mode and the stress state according to the specimen shape in the direct shear test (DST), a series of the three-dimensional DEM (distinct element method) simulations of the DST for sandy soils were carried out with the circular and the rectangular specimens. From the obtained results, the deformation mode of the rectangular specimen was under the plane strain condition, while the deformation mode of the circular specimen could not be explained as a plane strain condition. In addition, the principal stress states around the potential shear plane were analyzed and discussed by means of the analysis of the soil particle level.

Effects of Grain Shape on Mechanical Behaviors of Granular Material under Plane Strain Condition in 3D DEM Analyses

In this paper, we carried out the true triaxial test simulation under plane strain condition with three dimensional DEM analyses (3D DEM) to study behavior and development of shear band. The maximum mobilized internal friction angle corresponds to the shape factor, FU, on a linear relationship, and the inclination of the linear relationship seems to become larger with the microscopic angularity of the grain. The thickness of the shear band increased with the grain size. Also the grain shape affects on the relationship of residual stress ratio to relative shear displacement along the shear band.