Bender-element-based penetrometers for measuring shear wave velocity and shear strength

A bender-element-based dynamic penetrometer (BE-DP) was developed for the measurement of shear wave velocity (V_s-hh and V_s-hv) and shear strength parameters (cohesive strength (c) and internal friction angle (ϕ)) of soils. Shear wave velocity was measured through two pairs of bender elements installed in the cone shafts. Small-strain stiffness (G_hh and G_hv) and stiffness anisotropic ratio (G_hh/G_hv) were calculated through the measured shear wave velocity. Shear strength parameters were obtained through a series of theoretical formulas. In-situ tests of fully weathered slate (FWS) and granite residual soil (GRS) by applying BE-DP indicated that FWS had obvious stiffness anisotropy while GRS had slight stiffness anisotropy, which were in consistent with SEM and TEM observations of two kinds of soils. Meanwhile, SEM and TEM observations also showed that soil particle size of FWS was much larger than that of GRS, resulting in a much larger shear wave velocity and small-strain stiffness of FWS than GRS. Due to less disturbance of in-situ tests than laboratory experiments, shear strength measured by BE-DP was a little bit larger than that measured by laboratory experiments for both FWS and GRS. In-situ test results proved that the newly developed BE-DP was feasible, robust, multifunctional and cost-effective.