Slope Stability in Open Pit Mines in Clayey Rock Mass
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Slope Stability in Open Pit Mines in Clayey Rock Mass N. F. Nizametdinova*, R. F. Nizametdinovaa, A. A. Nagibina, and A. R. Estaevaa a
Karaganda State Technical University, Karaganda, 100000 Republic of Kazakhstan *e-mail: [email protected] Received November 22, 2019 Revised February 18, 2020 Accepted April 10, 2020
Abstract—Justification of slope parameters for benches and pit walls in clayey rock mass bases on studies into geological structure and physical and mechanical properties of rocks of various lithological varieties. The upper layers of pit walls occur in weak clayey overburden, in the crust of weathering and in transition zone with conglomerates, up to 150 m in total thickness. In this case, it is required to calculate accurately angles of clayey slopes, to undertake cutback at recommended angles and to eliminate heavy flow of melt water and rain water from ground surface to the slopes. Mining within the design pit wall limits should be accompanied by continuous instrumental monitoring of pit wall slopes. Keywords: Clayey rocks, stability, bench, pit wall, open pit mine, internal friction angle, cohesion, crust of weathering, rock mass, stability factor. DOI: 10.1134/S1062739120026649
INTRODUCTION
Slope stability in open pit mines in clayey rock mass is of higher concern as strength of clayey overburden varies in the course of mining as moisture content of rocks increases under the action of rainfall and stream rises. Local slope stability in clayey overburden to 50 m thick can be improved by means of making hard rock buttresses. In soft overburden more than 100 m thick, it is required to undertake pit slope design, pit slope cutback of recommended geometry using a shovel and to remove overburden by layers to 5 m high. During excavation of clayey rocks, is necessary to carry out continuous instrumental monitoring over pit slope stability using digital laser technologies [1]. Reliable clayey slope design is based on all-inclusive analysis of rocks strength by means of labscale (exploratory drilling core samples) and field tests [1–4]. The tests aim to determine density γ, compressive strength σ c , tensile strength σ t , cohesion K and internal friction angle ρ of rocks, as well as cohesion K ′ and friction angle ρ ′ of interfaces [1, 2, 5]. Exploratory drilling and coring is carried out at different depths. The test cohesion and friction angle values need scrutinizing as measurements can be inaccurate due to water content of rocks and micro cracks. The inaccurate values are eliminated by averaging over main types of rocks (Table 1). Sometimes clayey overburden and residuum samples are subjected to tests in integrated triaxial shear/compression K m (monolith) and in-plane she
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