Shear Characteristics and Constitutive Model of Interface Between Coral Sand and Geogrid

Abstract:

Large direct shear tests were conducted on the in-situ graded coral sand in the South China Sea and the interface between the coral sand and polypropylene biaxial geogrid under different normal stresses. The test results show that the shear stress-shear displacement curves of coral sand and reinforcement-soil interface show obvious strain softening characteristics. The peak shear strength lines of both show a bilinear form， and the residual shear strength lines of both show a good linear relationship. The average interface friction ratio between coral sand and geogrid at all levels of normal stress is about 1.37， which is much higher than that between siliceous sand and geogrid， indicating that the reinforcement effect can be mobilized in the reinforced coral sand. During the shearing process of coral sand and reinforcement-soil interface， the samples generally experienced a “relative shear shrinkage-relative shear dilatancy-relative shear shrinkage”， and reinforced coral sand can significantly reduce the shear shrinkage deformation. The relative breakage rates of the samples in the direct shear test and the reinforcement-soil interface direct shear test are close and increase with the increase of the normal stress. The Duncan-Chang model and shear softening model are used to respectively describe the pre peak and post peak of shear stress-displacement curves of the South China Sea and polypropylene biaxial geogrid interface. The interface constitutive model established can well reflect its shear characteristics.

Key words:coral sand;geogrid;large-scale direct shear test;gradation;constitutive model