Internal Friction Angle of Soil

07/28/26

“How can we quantify how well soil particles resist shear failure?”

Soil particle bodies will collapse and fail when there’s a large enough shear stress applied to them. But how can we quantify this? Well, what if we were to take the soil body, place it on a theoretical inclined plane, and tilt the platform until the soil body collapses? The angle at which the body collapses is known as the Internal Friction Angle of Soil, and is the most widely used way to measure how well soil particles resist shear failure. The internal friction angle of soil is governed by the equation internal friction angle of soil = tan((shear stress due to friction)/(normal stress acting on soil))^-1. The higher the normal stress on the soil, the more it can resist shear stresses.