Evaluation of Interface Shear Strength of Soil and Structures

Retaining walls, deep foundations, and reinforced soil/nailed structures involve interaction between structural elements and soil. Experimental investigation of interface characteristics such as adhesion, the angle of interface friction, compression/dilation behavior, and normal and shear stiffness forms an essential prerequisite in the design and numerical modeling of these structures. In the present work, direct shear tests are conducted to quantify the shear strength and interface characteristics between two soils, namely red clayey sand and black clay in contact with different continuums such as cement mortar, steel, jute geotextile, woven, and nonwoven geotextile. Direct shear test is conducted with one half of box filled with soil and contact with a structural surface glued to a wooden block placed in the other half. The ratio of interface friction angle to the internal friction angle of soil ranged from 0.73 to 0.95 depending on the roughness of the surface. Volume change of soil depends on the roughness and hardness of the continuum surface. Vertical inclusion of reinforcement in soil increased the shear strength of soil from 11 to 39%, and the improvement in shear strength of soil depends on the extensibility of reinforcement and its resistance to rotation.