Water Content and Soil Strength

Summary The strength of beds of soil aggregates, saturated and unsaturated, has been measured with a ring shear machine. For saturated loose soil with free drainage the cohesion and friction components and, therefore, total strength are proportional to the applied normal load. When sheared under load the soil compresses to an ultimate voids ratio after which there is negligible change. This ultimate state differs from the critical voids ratio for saturated clay in that it appears to depend on the strength of the individual aggregates as well as on the nature of the soil material. In unsaturated soil, as the aggregates are strained, suction in the pore water increases. This suction acts as an equivalent applied load on the water‐filled fraction of the soil, and increases its potential resistance to strain by an amount determined by the apparent coefficient of friction of the saturated soil. The ultimate voids ratio for the unsaturated soil at any load is higher than that for the saturated soil.