A constant normal stiffness direct shear machine

Abstract

When large structural loads are to be supported on rock, particularly soft rock, a common form of foundation is a rock socketed pile. When such a pile is loaded, because of the roughness of the socket walls, vertical displacements can be accompanied by a dilation of the socket walls. This dilation occurs against the constant normal stiffness of the rock mass and consequently, the stresses normal to the sides of the pile will increase until shear failure occurs. This paper describes a direct shear machine which has been developed to simulate side resistance development under constant normal stiffness conditions. The results of a number of tests on specimens consisting of non planar interfaces of a synthetic rock material and concrete are reported to illustrate the mechanisms which take place under a range of constant normal stiffnesses (a).