Ultimate and serviceability limit states of large shallow foundations under combined loading
Abstract
Estimation of the bearing capacity and deformations of large shallow foundations under combined loadings can be of great significance. Some geotechnical design guidelines recommend the failure load envelope method for ultimate limit state analysis. Since many investigations of this method focus primarily on undrained failure envelopes using unlimited-tension interfaces, zero-tension interfaces have not been well investigated. In addition, less work is available on drained failure envelopes. For serviceability limit states, the majority of approaches used are based on uncoupled, isotropic assumptions. Further work needs to be done on more appropriate elastic solutions for combined loadings.
General VHMT failure envelopes for circular foundations under undrained and drained soil conditions have been investigated using finite element analysis. The effects of soil strength heterogeneity, foundation embedment and surficial crustal layer have been examined for undrained soil conditions. In addition, cohesive-frictional soils have been considered for drained soil conditions. In comparison, classical bearing capacity theories appear to be rather conservative for combined loadings.
To estimate the deformations of large shallow foundations under combined loadings, researchers have proposed many analytical isotropic elastic solutions based on idealized soil conditions. However, many natural soils will be anisotropic or at least transversely isotropic due to their complex deposition history. This research has investigated the coupled elastic stiffnesses for circular foundations founded in cross-anisotropic soils. Gibson and embedment correction factors have been derived to account for the effects of soil stiffness non-homogeneity and foundation embedment.