Déthié Sarr^1,, Hamed Fall¹, Mouhamedine Wade¹

The aim of this work is to understand the behaviour of foundations on the heterogeneous basalts of Dakar. The methodology consists of collecting field and laboratory data and then processing them by Monte Carlo simulation to study the variability of the Rci, mi and GSI characteristics. The Hoek-Brown and Goodman methods are used for the probabilistic calculation of the bearing capacity and the settlement as well as their probability of failure for footings of dimensions 1x1 m², 1x2 m² and 2x2 m² considering a safety factor of 2. The respective average settlements of these footings are 0.523 mm, 0.343 mm and 0.261 mm with a coefficient of variation of the settlements of 15.5% around the average value. For the Hoek-Brown method, we have a probability of failure of 2.5.10^-4 for the 1x1 m footing above the reference limit. Whereas the 1x2 m² and 2x2 m² footings show reliability indices and failure probabilities of 3.9 and 4.8.10^-5 and 4.28 and 9.3.10^-6 respectively, which are admissible for the target values. For the Goodman method, the probabilistic values of all the footings studied are admissible for the target values. The probabilities of failure of the footings are given as 7.1.10^-8 for the 1x1 m²; 4.9.10^-12 for the 1x2 m² and 1.7.10^-14 for the 2x2. A probabilistic calculation guarantees better reliability for the foundations than a deterministic calculation.

foundations, safety factor, probabilities of failure, reliability index, rock