The Effect of Partial Drainage on the Short-Term Bearing Capacity of Saturated Clay Foundations

Abstract

Disregarding the partial drainage of saturated clay foundations during staged construction of a building would underestimate the calculated short-term bearing capacity of foundations, resulting in imposing an extra burden on clients due to prescribing soil improvement. This paper aims to investigate the effect of partial drainage of saturated clay foundations subjected to different loading patterns on the mechanical response. Therefore, two main stages, including determination of shear strength parameters from triaxial simulations and foundation analysis based on the acquired shear parameters, were considered. In triaxial models, a change in the consolidation phase was proposed to determine more realistic shear strength parameters in a way that reflects the partial consolidation through the staged construction. It was found that drainage during construction could significantly increase the short-term bearing capacity up to 70% in comparison with the unconsolidated undrained triaxial test condition. Moreover, a well-justified equation and stepwise method were proposed to estimate the short-term bearing capacity of clay foundations with respect to the partial drainage during construction. In civil engineering, there are several cases in which superstructures should be constructed over saturated clay foundations. Therefore, the bearing capacity of these foundations should be determined and controlled in short-term (end of construction) and long-term (during service life of the structure) conditions. Owing to the fact that during staged construction of superstructures, a sort of partial drainage occurs, estimating the short-term bearing capacity of saturated clay foundations using the parameters derived from the undrained unconsolidated triaxial test could be very conservative, resulting in imposing an extra burden on clients due to prescribing unnecessary soil improvement. This paper by a combination of triaxial and foundation analysis investigated the effect of partial drainage of saturated clay foundations subjected to different loading patterns on the mechanical response. An attempt was made to provide engineers and designers with an appropriate relationship and a stepwise method so that they could determine the short-term bearing capacity of foundations considering the partial drainage in the common geotechnical practices. The proposed approach is applicable for clayey foundations in which taking undisturbed samples is possible.