The saturated GDS Back Pressured Shearbox (GDSBPS) is used for direct shear testing on soil specimens with control of sample pore pressures. Two versions of the GDS back pressured shearbox exist (Saturated and Unsaturated). Both versions allow the pore pressures within the sample to be controlled. The control of pore pressure during direct shear testing allows real-world situations to be modelled in the laboratory. GDS back pressure shearboxes have been used in the past to recreate landslide conditions in soils and to test pre-existing failure plains in rock samples. The unsaturated GDSBPS is based on a standard, saturated device but modified to allow the measurement and control of matric suction (the difference between the pore air and water pressures). Matric suction is applied to the soil specimen by maintaining air pressure in the test chamber and a water pressure below the high-air-entry porous disks in the base pedistal. The measurement and control of matric suction during shearing is critical for simulating the behavior of partially saturated soils. As such the GDSBPS provides a realistic model of many real-world geotechnical problems, such as slope stability in semi-saturated conditions.

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