This study investigates the influence of lithological discontinuities in the slope behavior of an open pit mine located in Peru. According to surveys of structural geology, the region of the mine has two large main systems of faults, separated from distances greater than 200m, and several secondary fractures, separated from distances greater than 20m. These faults can affect the stability of the slopes and turn themselves into preferred channels of water infiltration to the mining area. Field tests were carried out to obtain the properties of the intact rock, the quality of the rock mass and spatial orientation of the fault systems. The behavior of rock slopes, in terms of stability as well as the occurrence of displacements caused by excavations, is investigated using two and three dimensional numerical models based on the finite element method, considering the Mohr-Coulomb constitutive model for mechanical representation of the rock mass. Comparisons with the obtained numerical results show the effects of the presence of discontinuities on the slope behavior.

1. Introduction

The region of Jinzao Mining mine covers an area of 5,900 km2, located in the province of Arequipa, Peru, 50 km south of the city of Nazca and 550 km from the capital Lima. The local geology is formed by metamorphic rocks of Mesoproterozoic, limestone and conglomerate rocks of Paleozoic, volcano-sedimentary rocks of the Mesozoic, aeolian and marine deposits of the Quaternary and intrusive rocks of the Cretaceous. Metamorphic rocks were deformed regionally, with the occurrence of folds and faults during the formation of the Andes. Figure 1 shows a system of longitudinal faults parallel to the direction of the mineralized body, marked as West fault, East fault and faults A, B, C, D, with dip direction N40° and dip above 65°E. In the same figure are shown the transverse North fault (dip direction N140° and dip 65°E/W) and the cross sections 1, 2, 3 and 4 considered in the slope stability analyses of the open pit mine.

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