What factor influences soil shear strength?

The factor that directly influences soil shear strength is the cohesion and internal friction angle. Shear strength of soil is primarily determined by its cohesive properties and the friction between soil particles. Cohesion refers to the attraction between soil particles, which can provide strength even when the soil is saturated. The internal friction angle represents how well the soil particles resist sliding over each other when subjected to shear forces.

These two parameters are critical in geotechnical engineering as they help in analyzing the stability of slopes, the bearing capacity of foundations, and the prediction of soil behavior under various loading conditions. The combination of cohesion and the frictional forces present determines the overall ability of the soil to withstand shear stress without failing.

While moisture content, depth of soil, and the presence of vegetation can affect various soil properties, they do not fundamentally define the shear strength of the soil in the same direct manner as cohesion and the internal friction angle do. Moisture content can influence cohesion and friction but is not a standalone measure of shear strength. The depth of the soil can impact loads but again does not measure shear strength directly. Vegetation might help in soil stabilization due to root systems, but its effect is indirect compared to the fundamental properties of cohesion and internal friction.