| The factor-of-safety approach has traditionally been used for assessing internal and external stability of MSE walls. Acceptable factors of safety incorporate uncertainty and variability in the soil properties, reinforcement properties, and geometric characteristics of the MSE wall. The factor-of-safety approach, however, does not explicitly account for uncertainties. Thus, it may lead to instability if the uncertainty is greater than anticipated. Alternatively, the probabilistic approach, which explicitly accounts for uncertainties employing probability of failure rather than factor of safety, can result in more consistent designs.;A two-phase approach was used to develop a reliability-based design (RBD) method for internal and external stability of MSE walls. In the first phase, a parametric study was conducted using Monte Carlo simulation to identify parameters that affect the probability of failure. Parameters that were found to have a significant effect on the probability of internal failure were the mean and coefficient of variation of the backfill friction angle, the mean and coefficient of variation of the tensile strength of reinforcement, the mean unit weight of the backfill, the mean surcharge, the mean reinforcement vertical spacing, and the mean reinforcement length. The mean and coefficient of variation of the backfill friction angle are significant parameters for sliding mode of failure, the mean and coefficient of variation of the backfill friction angle and coefficient of variation of the backfill unit weight are significant parameters for overturning mode of failure, and the mean and coefficient of variation of the foundation soil friction angle and the mean of the backfill friction angle are significant parameters for bearing capacity mode of failure. In the second phase, RBD charts were developed by determining the required reinforcement length and reinforcement tensile strength for each target probability of failure (0.01, 0.001, and 0.0001) using all combinations of parameters found to be significant.;The probability of failure of an MSE wall system incorporates probabilities of failure obtained using RBD methods for internal stability and external stability. The system probability of failure was calculated by summing the probabilities of failure obtained from all modes of failure. |
