Unsaturated Back Pressured Shear Box

Product Code : Unsat BPS

The Unsaturated Back Pressure Shearbox (Unsat BPS) has the ability to perform direct shear tests with precise control over the pore water and the pore air pressure, for the recreation and measurement of realistic slope failure conditions in unsaturated or saturated soil. The BPS range also includes a dedicated saturated version (control of pore water pressure only) and a dynamic version.
Key features Benefits to the user
Internal loadcell: Internal loadcell for shear and optionally normal force for load measurements as close to the sample as possible for greater accuracy.
Optional low-cost version: Low-cost version available which uses hanging weights for axial load.
Rigid aluminium cell body: To reduce system compliance.
Real-world situations to be modelled in the laboratory: All 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.

L= 875mm x W = 350mm

Displacement Accuracy

<0.1% FSO

Displacement Resolution

axial = +/- 15mm, shear = +/- 25mm


240V or 110V 50/60Hz single phase

Resolution of Measurement and Control

16 bit (± 25mm = ± 0.7μm(shear), ±10mm = ±0.3μm (axial)

Sample Sizes

75mm x 75mm (alternative sizes available on request)

he GDSBPS apparatus can be specified with many different options, some are listed below but many more are available. Please contact GDS if the required specification is not listed here or if higher pressures / forces are required.