Geophysical Characterization of Shear Zone in Direct Shear Test

Shear behavior of granular soils largely affects the safety and stability of underground and earth structures. This study presents the characteristics of the shear zone in a direct shear test using shear wave and electric resistivity measurements. An innovative direct shear box made of transparent non-conductive acrylic material has been developed to prevent electrical interference. Bender elements and electric resistivity probes are embedded in the wall of the direct shear box to estimate the shear wave velocities and the electric resistivity at the shear and non-shear zones. Experimental results show that, at the shear zone, the shear wave velocity increases and the electric resistivity increases and decreases in the loose and dense specimens during shearing. At the non-shear zone, the shear wave velocity and electric resistivity remain constant regardless of the relative density. The results demonstrate correlation among the shear stress, vertical strain, small strain shear modulus, and void ratio at shear zone. This study suggests that the application of the modified direct shear box including shear wave and electric resistivity measurements may become an effective tool for analyzing soil behavior at the shear zone.