Development of an Automated Servo-Controlled Apparatus for Accurate Direct Shear Testing of Rock Joints under Different Boundary Conditions

Precise and accurate measurement of shear strength of rock joints is of great importance in various projects related to rock engineering such as tunnels, dams, surface and underground mining, and oil shafts. In the laboratory, mechanical behavior of rock joints is studied by direct shear testing equipment. Manually controlled devices of direct shear testing are not adequately accurate. In this paper, development of an automated and servo-controlled device for direct shear testing of rock joints has been described. The developed apparatus performs monotonic and cyclic shear tests with different rates. It also allows the correction of the involved area with shear displacement and adjusting the normal load accordingly. In addition to the possibility of terminating the experiment manually, conditions can be set in terms of the test duration, shear displacement, shear stress drop, or their combination to stop the experiment automatically. The data acquired by the displacement and load sensors are constantly transmitted to a personal computer connected to the device, and online graphs can be monitored during the experiment. Furthermore, some measures have been considered to remove sample clearance inside the shear box. Finally, the results of a number of direct shear tests carried out by the apparatus on the joints of known surface morphological characteristics are presented.