Determination of the angle of friction of granular soils in triaxial apparatus and shear devices

Conclusions

1. The orientation of the areas of limiting state is determined by the strain state of the soil, and in the general case differs significantly from prediction on the basis, e.g., of the Mohr-Coulomb theory.

2. The state of limiting equilibrium is described by the Coulomb dry-friction law when φ_C depends on the material composition of the soil. The angle of friction is independent of the initial density of the soil, the load path, or the deformation, and is a physical parameter for a soil of a given material composition.

3. It is established by comparison of test data obtained in triaxial-compression and shear devices that the peak strength is not an objective characteristic of the shear strength of soils.

4. Values of φ_C as determined in triaxial compression and shear devices are in virtual agreement. Data from determination of the shear strength in the shear device, which correspond to the residual strength, are considered in this case. The peak-strength value, which is variable and does not reflect the physical nature of the soil's shear strength in the state of limiting equilibrium, is established during tests in accordance with a scheme of prescribed lateral forces and fixed displacements.

These data indicate the need for changes in the GOST relative to determination of the shear strength of soils in shear devices.