Reliability of a Soil-Nailed Slope Considering Regional Shear Strength Information

This paper presents a reliability case study of a soil-nailed slope, considering probability distributions of shear strength parameters based on a regional database of triaxial test results for different soil types in Hong Kong. In particular, the distributions of colluvium and saprolitic soil parameters were each derived using data from hundreds of soil specimens retrieved from various projects across the city. The probability of failure for the slope is evaluated by Monte Carlo simulations, which were implemented through the limit equilibrium analysis software, SLOPE/W, together with a tailor-made Microsoft Excel spreadsheet. Probabilistic analyses were performed for the slope with and without the soil nails, and the results offer another perspective to assess the effectiveness of upgrading works in reducing failure probability in the face of significant uncertainty associated with the soil properties. The hazard levels associated with various combinations of c'-ø' parameters and potential slip surfaces are extracted from the analyses and presented on two-dimensional 'contour' plots of factor of safety, which also change with the installation of soil nails to upgrade the slope.

Keywords: triaxial test database, completely decomposed granite, colluvium, soil-nailed slope, slope reliability.