Shear strength of unsaturated soils using the borehole shear test

摘要

The borehole shear test (BST) is an in-situ method of assessing the drained shear strength of soil. This test is conducted inside a drilled boring, and uses plates that load the sides of the boring. After applying a normal load and allowing for consolidation, the plates are raised, thus shearing the adjacent soil. The equipment is robust and simple to use, and unlike some other methods, provides a direct measurement of shear strength. The BST has at least theoretical potential for providing high quality in-situ test data at a reasonable cost. This investigation consisted of testing a range of soils in-situ using the BST, conducting laboratory tests on undisturbed samples of the same soils, and comparing the results. All of these soils are unsaturated, but in accordance with customary practice, the saturated shear strength is required for design, so laboratory tests were conducted at both the in-situ and saturated conditions. For the soils evaluated, the research found only modest agreement between the BST shear strength parameters and those obtained from direct shear tests on soaked samples and biaxial tests on backsaturated samples.