To ensure safe and effective productive operations in an open-pit limestone quarries, measurements and continuous monitoring of rock slope displacement is essential in order to assess slope stability. This is because instability of rock slopes may results in slope failures, consequently, leads to economic risks and fatal accidents in the quarries. Therefore, understanding the mechanism of rock slope deformation and factors that influence the rock slope stability is extremely important. In the previous study, the effects of regional rock stress on elastic deformation due to excavation and backfilling has been cleared. Furthermore, the effects of changes in temperature, rainfall and snow melt have also been investigated. Although past works provided valuable information on characterization of rock slope deformation by analysis of 3D displacement data; however, none of them has addressed the influence of geological formation including deterioration of clay zone existing on rock slope in the quarries, which could exhibit reduction in the strength and deformability of the rock slopes due to its high plasticity, weak strength and high sensitivity to the variation in water content. Therefore, this paper discusses a numerical investigation on the effects of deterioration of the existing clay on deformation of a cut rock slope formed in the quarries using 2D finite element method in terms of reduction in Young's modulus of the clay. The deformation mechanism is discussed, including the analysis of rock slope displacement measured by automated polar system (APS). This shows that change in distance which lies between 20-100mm decreases gradually with time for 5 years. The simulated results reveal the characteristics of deformation modes as forward and downward displacement of the cut rock slope. This resulted from deterioration effects of the clay rock existing at the foot wall of the rock slope.

1. Introduction

In Japan, There are large reserves of limestone, quarried for cement productions, construction aggregates, and consumption in iron and steel industries (Kuo, 2012). Therefore, large-scale limestone quarries, mostly open-pit limestone quarries are still in operation. To improve productivity of the quarry, rock mass are being excavated by bench cut method with increasing height and width, demanding continuous monitoring of rock slope in order to ensure its stability. Rock slope instability may consequently; result in slope failure, causing loss of production, unexpected expense to restore a quarry and probably loss of life (Yamaguchi and Shimotani, 1986). The priority in ensuring the stability of rock slope may also be attributed to the fact that the exact geological and mechanical properties of the cut slope are uncertain, mostly for rock slope formed by alternating complex geological formation of limestone and clay rock. In Japan, there have been several cases of rock slope failures in limestone quarries (Yamaguchi and Shimotani, 1986).

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