Wave velocities depending on shear strain, directionality, and excess pore water pressure from wildlife liquefaction array

Data from the Wildlife Liquefaction Array, which is located at southern California’s Imperial Valley in the USA, are analyzed. Variations in shear wave (V_s) and compression wave (V_p) velocities are identified during strong motions. Shear strains (γ) are computed from recorded acceleration time series between the sensors. All these variables are compared with the ground-surface accelerations and excess pore water pressure ratio (R_u) at different depths. Results show that R_u starts to accumulate when γ exceeds the threshold strain of 0.01–0.015%. V_s is negatively correlated to R_u and γ. Further investigation shows that V_s degradation depends on maximum horizontal shear strain with the different azimuthal angles at the same time window. By contrast, V_s reduction with R_u is caused by the decrease in effective stress; hence R_u reduces V_s regardless of the azimuthal angles. V_p degradation is limited compared with that of V_s under strong shaking, indicating that the constrain modulus is determined by the combination of soil skeleton and pore fluid.