Cylinder Direct Shear: A New Test Method

Abstract

The Cylinder Direct Shear is a new test method that has been developed for determining large displacement interfacial shear strengths of geosynthetics. The significance of the new test method is that many geosynthetics interfaces lose shear strength with increasing displacement. The new method is patented and is designed around the current 0.3-m (12-in.) direct shear per ASTM D-5321. It consists of testing the geosynthetic interface mounted on a cylinder instead of on a flat plate. The Cylinder Direct Shear has one geosynthetic mounted on the surface of the rigid cylinder and the second geosynthetic anchored to a stationary anchor bar and contained within a latex rubber membrane. The test assembly is mounted within a pressure chamber and a normal force is applied using the chamber pressure acting on the latex rubber membrane. Friction resistance is measured by recording the torque to rotate the cylinder while the normal force is applied and displacement is determined by measuring the rotation of the cylinder relative to the stationary anchor bar. Comparable results have been obtained using the same geosynthetic interfaces at similar displacements when compared with current 0.3-m direct shear testing. The primary difference of the Cylinder Direct Shear with the 0.3-m direct shear has been the ability to measure interface shear strengths using continuous unlimited displacement testing in the machine direction to displacements far beyond the 7.5 to 10 cm limitation of the current 0.3-m direct shear. Interface shear strengths of geosynthetics have been measured at displacements in excess of 6 m using the Cylinder Direct Shear Test.