Behavior and Critical Failure Modes of Strip Foundations on Slopes under Seismic and Structural Loading

This paper presents a numerical study on capacity envelopes of strip foundations placed on the top and the face of two typical soil slopes at different offset distances and subjected to earthquake effects using the pseudostatic method. The capacity is estimated using nonlinear two-dimensional (2D) finite-element limit analysis (FELA). Modified swipe and probe analyses are performed to develop vertical force-moment (V-M) and vertical force-shear force (V-H) capacity envelopes. Characteristic features of these capacity envelopes and critical failure modes of foundations on slopes are identified and compared with the foundations on flat ground. Relative influence of the soil and structure inertia on the capacity envelope of the foundation is also explored. The critical failure mode of a foundation on slope, subjected to gravity and seismic action, depends on the effective column height of the structure. A comparison of the capacity envelopes of typical foundations with the corresponding RC columns indicates that the foundation design methods of the current building codes cannot avoid premature failure of foundations on slopes, prior to columns.