Reliability Analysis of Allowable Pressure of Strip Footing in Spatially Varying Cohesionless Soil

This paper investigates the probabilistic analysis of bearing capacity of strip footing resting oncohesionless soil deposit. In this study, the cone tip resistance of soil (qc) alone was taken as uncertain pa-rameter. Random field theory was used to analyse the variability of qc. All the three possible phases of uncer-tainty (inherent, measurement and transformation) are considered in the analysis. The results obtained fromthe analysis states that the transformation model plays a major role in the evaluation of variability of designparameter. The effect of spatial variability and averaging distance on the standard deviation of design parame-ter is also studied. The probability that an allowable bearing pressure arrived from the deterministic analysis using an appropriate factor of safety would fall below that defined from probability density function of bear-ing capacity was evaluated, and the corresponding reliability index is calculated. The study shows that the conventional deterministic analysis using factors of safety three overestimates the allowable bearing pressure. For a given target reliability index, the study shows that the simple and traditional probabilistic methodology, which assumes infinite scale of fluctuation and neglects the spatial averaging, results in lower allowable pres-sures than that obtained from advanced probabilistic analysis