Shear Strength of Cohesionless Soils

The shear strength of cohesionless soils primarily depends on the frictional resistance between soil particles and the effective normal stress. It is described by the formula $\tau = \sigma' \tan\phi'$, where $\tau$ is the shear strength, $\sigma'$ is the effective normal stress, and is the angle of internal friction. Cohesionless soils, such as sands, have negligible true cohesion (), so their shear resistance stems from particle interlocking and friction. The internal friction angle is influenced by particle shape, size distribution, and relative density; denser sands exhibit higher friction angles and greater shear strength. Effective stress governs soil behavior, with pore water pressure reducing effective stress and thus the shear capacity. Peak shear strength can exceed critical state strength due to dilative behavior before failure. Understanding these properties is crucial for safe design of foundations, slopes, and retaining structures, optimizing compaction practices, and assessing groundwater impacts on soil stability.