Reliability analysis of reinforced embankments on soft ground

Abstract

A limit equilibrium stability model of reinforced embankments on soft ground is formulated and a practical reliability evaluation procedure is proposed. The stability model allows for a tension crack in the embankment, tensile reinforcement at the base of embankment, and a nonlinear undrained shear strength profile in the soft ground. The proposed reliability evaluation procedure derives from an intuitively obvious ellipsoidal perspective. It obtains the same reliability index as the current first-order reliability method (FORM), but is more practical and transparent because the spreadsheet-automated search is in the original space of the variables. The proposed method deals with correlations without orthogonal transformation of the covariance matrix. The versatility of the proposed method is demonstrated in an example reinforced embankment that has 12 random variables, including six autocorrelated strength values, and a performance function that is nonexplicit due to the need to search for the critical slip surface and to integrate numerically the depth-dependent shear strength. The probability of failure compares well with Monte Carlo simulation. Reliability-based design is also discussed, and comparisons with case histories are made. The ease of implementation, conceptual clarity, and versatility of the Proposed method should enhance the wider use of the more rational reliability-based analysis and design over the conventional factor-of-safety approach.