Undrained capacity of two rigidly connected rectangular foundations under general V-H-M loading

Analytical and numerical solutions of the undrained load-carrying capacity of shallow foundations are mainly available for single foundations. This paper investigates the undrained limit states of two-spaced rectangular foundations with rigid connections. Three-dimensional finite-element analyses are carried out to systematically examine the coupled interaction of foundation spacing and degree of soil strength heterogeneity on the loadcarrying capacity of the foundation systems under general loading. Results are presented in the form of ultimate limit states under pure vertical (V), horizontal (H), and moment (M) loads, and the failure envelopes under combined V-H, V-M, H-M and V-H-M loading. Soil failure mechanisms obtained from the finite-element analyses are shown for the representative loading paths of the two-foundation systems. Based on the failure mechanisms, the methods are established for calculating the undrained load-carrying capacity of the two-foundation systems to assist the foundation design in practice.