Reliability-based analysis and design of foundations resting on a spatially random soil

International audienceThis paper presents the effect of the spatial variability of the soil shear strength parameters on the reliability analysis and design of a vertically loaded shallow strip footing against bearing failure. The deterministic model used is based on the upper-bound method of limit analysis. The Hasofer-Lind reliability index based on the most critical probabilistic failure surface is calculated for the assessment of the footing reliability. The random fields used in the analysis are the soil shear strength parameters. Normal and non-normal anisotropic random fields with or without cross correlation are considered. The two random fields are averaged along the potential slip lines of the failure mechanism. It was found that the assumption of negative cross correlation, soil heterogeneity and anisotropy regarding the autocorrelation distance gives a higher reliability index than the hypothesis of no cross correlation, homogeneous and isotropic soil respectively. These assumptions merely allow the reliability to be more accurately estimated and thus lead to an economic design. The failure probability was found more sensitive to the variability of the angle of internal friction than the cohesion. For design, an iterative procedure is performed to determine the breadth of the footing for a target failure probability