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

Conclusion

The state of limiting equilibrium of a granular soil of the material composition under consideration is characterized by a constant ϕk. In this case, this quantity can be obtained with satisfactory accuracy in testing on various experimental apparatus. The differences in the ϕk values that have been established at the present time are a result of imperfection in the methods employed to interpret the experimental data.

Together with the positive conclusion that we have indicated, let us stress that the orientation of the slip areas depends on the loading path and the initial density of the soil. In the general case, consequently, it is necessary to describe additionally the relation between soil stresses and strains both in the sublimiting state, and in the state of limiting equilibrium for practical utilization of the result obtained in solving edge problems of soil mechanics. In this case, the solution of practical problems of foundation engineering can be based on numerical methods of computer-aided design.

In soil mechanics, purely practical problems are approximately solved, and the configuration of the slip surface is not determined as a result of computation in these solution, but is assigned on the basis of codification of full-scale observations. In these computations, data on the state of the soil's limiting equilibrium are used precisely in the form of the Coulomb dry-friction law, and the ϕk value obtained should be used in them.

In using the ϕk value, correspondence between computed and actual data is determined only by the degree of approximation of the assigned configuration of the collapse surface to its actual position, and not by the angle of internal friction, where a definitiveness necessary for practice is established.