The GCTS Direct Shear Systems feature electro-hydraulic closed-loop digital servo control of the shear and normal load actuators. This allows for complete automation of the testing procedure, making performance of the test simple and accurate. The systems can easily perform both constant normal stiffness and constant normal stress tests. All SDS systems are hydraulically-powered, which eliminates vibrations caused by motorized systems that can disrupt granular specimens. The top shear box can be horizontally translated and the bottom shear box is mounted on pre-loaded sliding bearings to minimize horizontal friction. Set screws with nylon tips are used to adjust the shear gap and the top shear box is suspended on springs that balance its own weight. This allows for different shear gap settings and the more precise measurement and control of the normal stress. Also included is a water reservoir to submerge specimens during testing.
Loads or deformations for both the shear and normal actuators can be prescribed for automatically performing conventional direct shear tests as well as more advanced tests. This system can be easily programmed to perform tests such as the constant normal stiffness test where the normal load is a function of a prescribed stiffness for simulating actual compressibility of a ground shear plane (e.g. soil-pile interaction). All tests are set up in the software and carried out automatically, without any need for user intervention.