Direct shear test

The direct shear test, also known as shear box test, is used to determine the shear strength parameters of a soil sample and evaluate the response to shearing forces. This test provides information about the shear strength, deformation characteristics, and stress-strain behavior of the soil. Similarly, the results of the direct shear test are used to determine the soil’s resistance to shearing and its ability to withstand applied forces. Here, soil sample is placed in shear box, and shearing force is applied at the top horizontally which induces shear stress in the soil sample, causing it to deform and eventually fail along a predetermined shear plane within the sample.
The direct shear test can be performed for both disturbed and undisturbed samples. The major difference for disturbed and undisturbed sample is the sampling technique. For disturbed samples, soil is obtained via excavation and drilling. Most of the time, undisturbed samples are preferred due to its more accurate representation of the soil behavior. However, due to difficulty in sampling, disturbed samples are also adopted. The selection of the sample type generally depends on the location, soil type, soil conditions, groundwater conditions etc.
Direct shear test can also be applied on cohesive soil such as clay. Clay soils exhibit unique characteristics due to their fine-grained nature and high-water content, making the direct shear test an important method for understanding their mechanical properties. The test results help in assessing the stability of slopes, designing foundations, and evaluating the performance of geotechnical structures in clayey soil environments.