Stability of infinite slopes investigated with elastoplasticity and hypoplasticity

It is commonly assumed that the maximum slope angle β of an infinite cohesionless slope is equal to the friction angle of the soil ϕ. However, this relation only holds for a dilatancy angle ψ equal to the friction angle if the Mohr‐Coulomb failure criterion is employed. This article demonstrates that the increase in the soil strength due to the plane strain conditions in an infinite slope allows for using β = ϕ as a conservative approximation for ϕ < 35° and ψ > ϕ/3. Further, the calculations presented here support the common practice in geotechnical engineering of using the strength parameters obtained from triaxial tests in limit state calculations such as Bishop's method without further consideration of the dilatancy. However, it seems to be more appropriate to use direct shear tests wherever possible, i.e. for fine‐grained soils.