Summary:
The publication of the new generation of Eurocodes opens the door to a general use of probabilistic methods in the field of geotechnics. In particular, the reliability analyses described in the accompanying document make it possible to define probabilities of failure explicitly, offering an interesting alternative to conventional design methods based on a deterministic approach and partial safety factors.
This contribution illustrates the potential benefits of using the probabilistic approach, coupled with numerical modelling using finite elements, on a simple design example of a superficial footing. First, the numerical approach is validated against the analytical approach by comparing the load-bearing capacity of the footing for characteristic values of resistance, for several values of the soil’s friction angle.
Subsequently, the deterministic verification formats described in the current Swiss standards (SIA) and in the Eurocodes 2.0 are applied to the analytical approach and to the numerical approach, making it possible to define the relationship between the friction angle and the vertical load that can be applied to the footing for each approach.
Finally, the probabilistic approach is used on the numerical model, using mean values of cohesion and angle of friction calculated on the basis of the coefficients of variation proposed in [1], and a target probability of failure compatible with the assumptions made to define partial safety factors for the deterministic approach. It is shown that the value of the design load resulting from this approach is higher than that resulting from the deterministic approach, and that the use of a Bayesian approach - based on additional tests and therefore making it possible to reduce the coefficients of variation of the resistance parameters - increases this gain. It has thus been shown that overdesigning of our geo-structures can be potentially avoided by using the probabilistic approach.
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