Importance of 3D analyses on static and seismic stability of jointed open-pit mine slopes

Amin Azhari, PhD Alireza Yarahmadi Bafghi, PhD Lohrasb Faramarzi, PhD Ramin Salamat Mamakani, MSc

Assistant Professor, Department of Mining Engineering, Isfahan University of Technology, Isfahan, Iran 

Professor, Department of Mining and Metallurgical Engineering, Yazd University, Yazd, Iran

Associate Professor, Department of Mining Engineering, Isfahan University of Technology, Isfahan, Iran

Graduate student, Department of Mining Engineering, Isfahan University of Technology, Isfahan, Iran

Doi:10.1680/jgeen.21.00030

Abstract

Most studies on open-pit mine stability have been performed in two-dimensional (2D) mode, which neglects the effect of the circular shape and thus the effect of third-direction boundary conditions. The aim of this work was to study the effect of the third dimension on static and dynamic stability analyses of pit slopes by comparing results from two- and three-dimensional (3D) numerical and limit equilibrium analyses. Geomechanical data from Choghart open-pit mine, located in the seismically active area of central Iran, were considered under a historical earthquake (M = 6.4). Kinematic analyses showed that two tectonic blocks of the mine – BL1 and BL2 – are susceptible to wedge and planar failures, respectively. The 2D and 3D static analyses showed that both blocks are stable, with higher safety factors (SFs) obtained using numerical 3D analyses. In the dynamic analyses, both 2D and 3D analyses showed wedge instability for BL1. However, for BL2, the 2D numerical analyses showed instability whereas the 3D numerical and pseudo-static analyses indicated block stability. The results revealed that the 3D SFs are generally 20–40% greater than those from 2D analyses. This can be explained by the consideration of the third-direction effect, verifying the importance of 3D analyses.

Keywords: earthquakes numerical modelling pseudo-static analysis slopes static analysis three-dimensional analysis two-dimensional analysis