Study on monotonic direct shear characteristics of geosynthetics-calcareous sand interface

The investigation of shear behavior on geosynthetics-calcareous sand interface is significant to internal stability design of reinforced revetment structure. A series of large-scale monotonic direct shear tests were performed to study the interface shear characteristics of geotextile-calcareous sand (GT-CS), geogrid-calcareous sand (GG-CS), and unreinforced calcareous sand (URCS). The interface shear behavior was investigated by considering the effects of interface types including URCS, GT-CS, and GG-CS interfaces, and normal stresses ranging from 25 to 100 kPa. The interface interaction mechanism for different interface types is disclosed. The results indicate that embedding geotextiles and geogrids into calcareous sand filler changes the interface dilatancy behavior of calcareous sand, and is obviously affected by normal stress. The dilatancy curves of GT-CS and GG-CS interfaces exhibit predominantly contraction-dilation and contraction, while the dilatation curves of URCS interface primarily display contraction-dilation-contraction and contraction. The shear softening behavior of GT-CS and GG-CS interfaces is primarily influenced by interface interaction mechanisms at the hardening stage and post-peak softening stage. Additionally, the use of geogrid/geotextile has a reinforcing effect on calcareous sand filler, resulting in an increase of 1.22-1.44 times in interface peak cohesion. This increase falls within the range observed for geosynthetics-siliceous sand and geosynthetics-soil.