Cyclic Direct Simple Shear and Triaxial Device

Geotechnical Laboratory at Virginia Tec has a Cyclic Direct Simple Shear and Triaxial Device SSH-100 Manufactured by GCTS.

The design of the GCTS Simple Shear System is based on their external cell wall triaxial system. The apparatus has a fixed top and a sliding bottom base mounted on special linear bearings. The system also has a stiff internal support to minimize lateral compliance of the top cap. One of the main advantages of the GCTS Simple Shear System is that it does not require a reinforced membrane as lateral support is provided via the confining pressure. This means that consolidation can be done at K values other than Ko. The system is capable of testing 100 mm (4 in.), 71 mm (2.8 in.), and 50 mm (2 in.) diameter specimens. Because the internal lateral support can be adjusted up or down, various specimen heights can be tested.

The GCTS Simple Shear System operates inside a pressure chamber that allows applying confining pressures to the specimen. The confining pressure can be servo controlled using the volume change, or any other sensor, as feedback. The servo control of the confining pressure enables the user to perform tests at any K value including Ko with the advantage of directly measuring the value of the K ratio. Reinforced membranes can also be used if desired.

The Cyclic Simple Shear Device is designed to achieve the specified loads or displacements at high frequencies. The loading system must be relatively stiff and have sufficient flow capacity to achieve the displacement amplitudes that the specimen is subjected for a given cyclic load. The normal and shear actuators are hydraulically servo controlled providing a very stiff response and loads or deformations can be prescribed.

Liquefaction tests on dry sands can be performed by specifying a zero vertical deformation during cyclic shear loads. The electro-hydraulic loading system proposed for the normal and shear load actuators is capable of applying or maintaining the prescribed loads with a very small compliance. Hydraulic systems are relatively “stiff” systems as compared to pneumatic loaders because of the incompressibility of oils. In addition, GCTS provides a 16-bit resolution Analog-to- Digital high-speed converter to enhance accuracy.

The last consideration to the control precision is the flow capacity of the hydraulic pump system. The Simple Shear systems is designed with a 10 Horse Power / 20 Liters per Minutes (5 GPM) constant pressure/variable volume hydraulic pump as well as a 2,000 cc (122 cubic inches) accumulator. The standard hydraulic system is more than adequate to meet the required cyclic velocity of ±5% strain at 1 hertz. This requirement is greatly surpassed even for a sample height of 100 mm where the peak-to-peak deformation is 5 mm.

More information about this device can be found here.