A comparative deterministic and probabilistic stability analysis of rock-fill tailing dam

Abstract

This paper presents a comparative study between simple deterministic stability analysis and probabilistic analysis, considering the case of an existing rock-fill tailing dam of 51 m height located in Rajasthan, India. A detailed seismic stability analysis was carried out considering the pseudostatic approach. All the analyses were carried out in CAD-based 2-D limit equilibrium program SLIDE 2D. In order to integrate the soil heterogeneity, stochastic Monte Carlo Simulation (MCS) technique was used. A minimal random number generator developed by Park and Miller (Association for Computing Machinery 31(10):1193–1201, 1988) was used in the analysis. The factor of safety values were calculated using Spencer’s method by considering circular failure surfaces. The cohesive strength (c), the angle of friction (φ) and the acceleration (αh) due to earthquakes were considered as the random variable in the study. For the critical geometry of the slope, the observed factor of safety values in case of upstream slope (1.67) and downstream slope (1.15) were found to be higher than the values specified in the IS 7894 (Code of practice for the stability analysis of the earth dams. Indian Standard, New Delhi, 1975) (reaffirmed in 1997) and ANCOLD (Guidelines on tailings dam design, construction and operation. Australian National Committee on Large Dam, 1999). The seismic deformation analysis was also carried for the downstream slope using the Newmark displacement method. Permanent displacement of the slope was found within the tolerable limits. Further, the results revealed that the spatial variability of the soil significantly influences the factor of safety values. Hence, the present study recommends the probabilistic stability analysis over the deterministic stability analysis for the rock-fill tailing dams.