Reliability Study of the Stability of a Retaining Wall for Underground Parking Type Structures with Two-storey Basement

The aim of this work is to see whether supports defined as stable by deterministic calculations can automatically be reliable in the geotechnical sense, as is often considered in Senegal. The analysis was carried out on an building project that had to rest on a two-level subsoil in a site requiring underpinning. A deterministic calculation of the project is carried out to verify the stability of the retaining wall with a safety factor. Then, a probabilistic calculation is made to take into account the variability of the characteristics of the soils that will house the retaining structure, with a coefficient of variation of 10%. The reliability index is determined by considering a safety factor threshold value of 1.5. The length of the sheet with reliable stability is then determined. The results show that for a plug length of 1.8 m, both the secant pile wall and the cast wall are stable with a safety factor greater than 1.7. However, the probabilities of failure and the reliability index remain below their thresholds for both the secant pile wall and the cast wall when the plug is 1.8 m long. The supports are stable and reliable when the plug length is 2.8 m for the same materials. In conclusion, a safety factor greater than the limit does not guarantee a reliable structure in deterministic studies.