Design approach for deeply embedded circular caisson foundations under combined loading.

Abstract

Deeply embedded caissons with a significantly large diameter, widely used as bridge foundation elements, are generally subjected to the complex combinations of several environmental and operational forces. The undrained capacities of rigid caisson foundations embedded in soils with increasing strength with depth and under combined loading are investigated using finite-element analyses. Estimation of uniaxial capacities followed by biaxial failure envelopes is carried out to capture the effect of vertical load on ultimate transverse capacities. Two-dimensional failure envelope in H-M loading space is presented to define the combined ultimate loading state of the circular caissons where the shape of the envelope is illustrated by a series of closed form expressions. The trajectory of the V-H-M failure envelope obtained from numerical analysis is validated by the mechanisms of upper bound limit analysis. Finally an example problem is provided to showcase the applicability of the expressions proposed to execute the design approach.