What is the primary purpose of the shear test in geotechnical engineering?

The primary purpose of the shear test in geotechnical engineering is to determine the friction angle of soil. This test assesses the soil's strength by evaluating how much shear stress the soil can withstand before failure occurs. The friction angle is a crucial parameter in soil mechanics, as it reflects the resistance to sliding along internal surfaces within the soil mass under load.

Understanding the friction angle helps engineers predict how soils will behave under various loading conditions, which is essential for designing foundations, retaining structures, and other civil engineering projects. The shear test directly measures the soil's shear strength, allowing for the calculation of the friction angle based on stress conditions at failure.

Permeability, soil density, and compaction are important factors in soil analysis but are assessed through different testing methods and techniques. Therefore, while they are relevant in broader soil evaluation, they are not the focus of shear tests, which center specifically on shear strength and the corresponding friction angle.