Reliability Assessment of the Stability of a Working Platform on Very Soft Ground: A Case Study

This paper presents the reliability assessments for a temporary embankment planned to be constructedin Belfast. The case study involves constructing a temporary working platform on very soft groundto support the equipment required to construct a new quay wall by adopting a land-based approach.To ensure the stability of the working platform, the construction of the fill is carried out in lifts with limited thicknesses and hold periods between them. The undrained shear strength of the very soft estuarine deposits making up the subsoil has been identified using field tests and laboratory tests on samples collected during the ground investigation. The undrained shear strength of the underlying ground has a significant impact on the results of the slope stability assessment. To investigate the effects of variability of the strength parameters on the results of the slope stability assessment, a probabilistic approach has been adopted in this paper. In particular, the reliability indices and probabilities of failure of the slope under varying loading conditions have been assessed using the first-order reliability method (FORM) and using Monte Carlo simulations. The slope stability assessments have been carried out using a commercially available limit equilibrium softwaretogether with in-house scripts to perform a significant number of probabilistic calculations. The results of the assessmentshave been compared with those obtained using the deterministic analyses. The results of the probabilistic assessments provide confidence that the proposed land-based methodology meets Eurocode requirements for the probability of failure of the embankment slope and hence is leading to a safe design.

Keywords: Case study, Probabilistic assessments, Reliability, Slope stability, Uncertainty.