In-situ direct shear tests on shear strength indices of pebble and gravelly soil

As an effective method to determine strength indices of pebble and gravelly soil, the field large-scale direct shear test on four typical samples of pebble and gravelly soil in the area of low mountains and hills Southern to the Yangtze River is conducted. At the same time, the particle size analysis test on pebble and gravelly soil is done in laboratory by sampling in the failure surface after shear failure. The test results show that there are obvious peak strength and steady residual strength at the relation curve between shear stress and shear displacement by direct shear test on well graded pebble and gravelly soil. The cohesive strength is lower and the internal friction angle is higher for pebble and gravelly soil in test site. The strength characteristics of pebble and gravelly soil are different from those of common homogeneous soil and cataclastic rock mass, which are related to many factors such as property of component materials, particle size, size grading, coarseness degree, cementation of cement and dense degree.