A Discussion on Numerical Modeling of Fault for Large Open Pit Mines

Azarfar, B. (University of Nevada Reno) | Peik, B. (University of Nevada Reno) | Abbasi, B. (University of Nevada Reno) | Roghanchi, P. (New Mexico Institute of Mining and Technology)

OnePetro 

ABSTRACT: The interaction of lithology and different geological units (e.g., joints, beds, faults, and alteration) and their impacts on rock slope stability can impose significant challenges for a mining operation. Numerical modeling is a powerful tool for simulating fault response. This paper attempts to highlight the challenges in simulating faults in numerical modeling using FLAC3D software and ways to overcome these problems. A case history for a fault slip was used to assess the performance of present methods (weak zone, ubiquitous-joint, and interface) for fault modeling. Strength reduction method was used to evaluate the stability of the slope. A sensitivity analysis was conducted to investigate the impact of fault geometry and thickness on the overall stability of the slope. It is found that the fault responds differently using each method. The lowest FOS value were observed in weak zone method, whereas the ubiquitous-joint technic showed the highest FOS value. Furthermore, the mechanism of slope failure was slightly different using each simulation method. The reason for this is whether the fault is modeled, so tight that has no reaction to mining or alternatively, is moving in an uncontrolled manner. Therefore, it is important to calibrate the model for correct fault movements.

1. INTRODUCTION

Determining slope stability is a critical part of the design stage of mining and civil engineering projects. This is especially important in large open-pit mines and dam construction. In an open pit mine, a slope failure not only results in a delay in production, also may cause fatality and equipment loss (Fellenius, 1936; Duncan & Goodman, 1968; Mahtab & Goodman, 1970; Stacey, 1970; Stacey, 1972; Stacey, 1973; Duncan & Wright, 1980; Hoek & Bray, 1981). Nowadays, with the growth of the global demand for minerals and advancements in technology, the depth of open-pit mines has increased significantly. This has imposed several design challenges in slope engineering and has exponentially increased the possibility of large slope failures (Kalkani, 1975; Stacey, 1996; Sjoberg & Norstrom, 2001; Wines & Lilly, 2002; Wyllie & Mah, 2004; Franz, 2009; Tutluoglu, et al., 2015)

The factor of safety (FOS) is a common approach for evaluating the stability of a slope. Bishop defined the FOS as the ratio of actual shear strength to the minimum shear strength required to maintain equilibrium, Fig. 1). (Bishop, 1955; Matsui & San, 1992; Fleurisson, 2012; Abderrahmane & Abdelmadjid, 2016). Hence, the FOS value of one (FOS=1) shows that the failure is imminent.