Undrained stability of unsupported conical slopes in two-layered clays

A conical slope is widely used in many constructions of in situ piles, piers, footings, mat foundations, raft foundations, energy storages, or water tanks since this unsupported excavation is much cheaper than an excavation with supports. This paper presents new plasticity solutions for undrained stability of unsupported conical slopes in two-layered clays by using axisymmetric finite element limit analysis. Four parametric studies were performed on the slope height ratio, the slope inclination angle, the thickness ratio of two-layered clay, and the strength ratio of two-layered clay, where the stability factor of this problem is investigated. In all the cases, the exact stability factors are accurately bracketed by lower and upper bound solutions within 1%. The design charts for estimating the stability of conical slopes in two-layered clays are proposed. Three failure mechanisms, i.e., toe, based, and face failures are observed and discussed in the paper. The predicted failure mechanisms of the unsupported conical slopes in two-layered clays are presented in order to portray the impact of all considered dimensionless parameters.