Development and Preliminary Field Testing of Cyclic Borehole Shear Soil Test Device

To help advance capabilities for measuring the in situ cyclic response of soils at chosen depths under controlled cyclic loading, a new prototype cyclic borehole shear test (CBST) device was developed in this study. Based on the monotonic BST device, the new CBST applies controlled normal and cyclic shear stresses to soil through serrated steel plates in contact with the wall of a 3-in. diameter borehole, while measuring the displacement of the shear plates as well as the shear stresses applied to the soil. Pore pressure is measured using a sintered porous disk embedded in one shear plate and hydraulically connected to a pressure transducer. Using the hardware and software control programs developed in this study, the capability of the prototype CBST device to measure the monotonic shear strength of soil is demonstrated, and preliminary results on the measured in situ soil behavior under cyclic loading conditions are presented.