Development of a New In-Situ Direct Shear Test

An in-situ direct shear test apparatus, in both small and large sizes, and its testing techniques have been developed. This test is performed simply by pulling horizontally a latticed shearing frame, embedded in the ground, with a flexible rope or chain under the application of a constant vertical load on the sample. In the new test, the real normal and shear stresses acting on the shear plane can be exactly measured. A number of the large-sized in-situ direct shear tests have been performed on eight kinds of coarse-grained granular materials including rockfills at different construction sites of embankments. The measured shear strengths approximate those of large-sized triaxial compression tests on samples with parallel grain-size distributions. The smaller version of this new test has been used successfully for testing sands and clays. For clays, artificially produced or in-situ, the measured undrained shear strengths are nearly equal to qu/2 by unconfined compression tests on the same clays. The extreme simplicity and high accuracy of this newly developed test are emphasized.