Showing papers by "Yun Wook Choo published in 2006"

Cyclic threshold shear strains of sands based on pore water pressure buildup and variation of deformation characteristics

Abstract: The cyclic threshold shear strain c th is defined as the cyclic strain amplitude above which the pore water pressure in saturated sandy soil increases and/or the modulus and damping values vary with the number of loading cycles during cyclic loadings. In this paper, the cyclic threshold shear strains are thoroughly investigated on sands using torsional shear tests. Toyoura sand is tested at various densities, drainage conditions (dry, saturated drained, and saturated undrained), and effective confining pressures. Based on the test results, the cyclic threshold strains above which the excess pore water pressure increases and/or shear modulus and damping ratio vary with the number of cycles are determined. Cyclic hardening in dry and saturated drained conditions, and cyclic degradation in an undrained condition, are observed for the same sample, using identical testing equipment. c th for cyclic degradation is compared with c th for cyclic hardening. The variation of damping ratio with the number of cycles is observed at different drainage conditions, and c th for damping ratio is also investigated.

Development of Torsional Shear Testing System to Measure P-wave Velocity, S-wave Velocity and Pore Water Pressure Buildup on Fully and Partially Saturated Sands

Abstract: Laboratory tests have revealed that the liquefaction resistance of sands depends strongly upon the degree of saturation, which is expressed in terms of the pore pressure coefficient, B. The velocity of compression waves(i.e. P-waves), which have been known to be influenced largely by the degree of saturation and can be measured conveniently in the field, appears as an indicator of saturation. In this paper, the Stokoe type torsional shear(TS) testing equipment is modified to saturate the specimen and measure the velocities of P-wave and S-wave and pore pressure buildup. The velocities of P-wave and S-wave for Toyoura sand from Japan is measured and compared at the various B-value (degree of saturation) which are partially saturated to fully saturated conditions. Additionally, the variation of the pore water pressure induced during undrained TS tests at the various B-value is measured and analyzed.