Direct Shear Test Laboratory
Celtest have the capability to carry out large volumes of 300mm shear box tests, with five machines in operation.
For more information in regards to our testing capabilities, please contact us.
How does the direct shear test work?
In the direct shear test a square prism of soil is restrained in a 300mm x 300mm steel box. The box is split into two square sections, the sections sit one on top of the other on a steel base. The sample is then compacted into the box and, the assembly is then lifted into the shearing machine using an electrical winch. A vertical force (normal load) is then applied to the top of the sample.
While the top section of the steel box is clamped in place, a load is applied to the bottom section, which is free to move. As the sideways force is increased, the sample will eventually fail or ‘shear’ along the horizontal plane and the force required results in the shear strength of the material.
By carrying out tests on a set of three specimens of the same sample under different normal pressures, the relationship between measured shear stress at failure and normal applied stress is obtained and the angle of internal friction can be determined from these results.
Why test for shear strength properties?
The laboratory direct shear test is used by geotechnical engineers to measure the shear strength properties of unbound aggregates or soil. This information can be used to either confirm compliance with a specification or predict the failure of materials on site when subjected to external forces such as bridge structures, buildings, embankments etc.
How long does a direct shear test take?
The test can take as little as one day for granular materials and up to three weeks for clay materials.
Which standards are followed to perform the test?
BS 1377-7 1990 (UK)
ASTM D3080 (USA)
AASHTO T 236 (USA)
(Information correct at time of publishing)