Microstructural investigation on mechanical behavior of soil-geosynthetic interface in direct shear test

Interface shear strength between soil and geosynthetics mainly depends on the mechanical and physical properties of soil, geosynthetics and the normal stress acting at the interface. This paper presents results of an extensive experimental investigation carried out on sand-geosynthetic interface using modified large direct shear box. The study focusses on the shearing mechanism at the sand-geosynthetic interface and the effect of different parameters on the shearing mechanism. Smooth HDPE geomembrane, nonwoven needle punched geotextile and two types of sand having different mean particle size, have been used in the present study. Microstructural investigation of deformed specimen through Field Emission Scanning Electron Microscope (FESEM) reveals the shearing mechanism which includes interlocking and fiber stretching for sand-geotextile while sliding, indentation and plowing for sand-geomembrane interface. The shearing mechanism for sand-geomembrane interface highly depends on the normal stress and degree of saturation of sand. The critical normal stress that demarcates the sliding and plowing mechanism for sand-geomembrane interface is different for dry and wet sand. The amount of scouring (or plowing) of the geomembrane surface reduces with increase in the mean particle size of sand. FESEM images revealed that the sand particles get adhered to the geotextile fibers for tests involving wet sands. The present microstructural study aided in understanding the shearing mechanism at sand-geosynthetic interface to a large extent.