The direct shear test is a laboratory procedure used to determine the shear strength of soil. In this test, a soil sample is placed in a shear box and subjected to a controlled normal load. The box is then pulled apart horizontally, allowing the soil to fail along a predetermined plane. The force required to cause this failure is measured, providing valuable data on the soil's shear strength. This test is essential in geotechnical engineering, as it helps engineers assess the stability of structures like foundations and slopes. The results can inform decisions on soil reinforcement and construction methods, ensuring safety and reliability in civil engineering projects.