A Constant Normal Stiffness Direct Shear Device for Static and Cyclic Loading
A device has been designed and built to carry out both static and cyclic direct shear tests on specimens of soil and rock and on interfaces of soil or rock and construction materials. The device has the special capability of allowing the shear deformation to proceed under conditions of constant normal stiffness. This is in contrast to the more conventional direct shear devices, which permit shearing under conditions of constant normal stress. It is expected that the constant normal stiffness conditions will be more representative of many in-situ conditions of shear deformation; an important example occurs at the interface of a pile and the formation in which it is placed (particularly those piles that are grouted into the formation). When used with a servo-controlled testing machine the device is capable of applying either static or cyclic shear loading to the test specimens utilizing either load or displacement control. The device is described in this paper, and typical results are presented for static and cyclic loading of a variety of interfaces including some that dilate on shearing and others that collapse as they are sheared.