This system features electro-hydraulic closed-loop digital servo control of the shear and normal loads for test automation. 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. soilpile interaction).
The top shear box has the horizontal translation 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 although the top shear box is suspended on springs that balance its own weight allowing for different shear gaps settings and the precise measurement and control of the normal stress. Included with this system are loading plates with square grid of retractable pins spaced at 25 mm in both directions to grab different type of samples such as soils, asphalt and other materials. Also included is a water reservoir to submerge specimens during testing.