ABSTRACT

The paper deals with geotechnical study and slope stability analyses of the final slope at Lanjiberna Limestone open cast mine. The Lanjiberna open cast mine is mainly characterized top soil, dolomite, dolomitic limestone and limestone. The bulk density and direct shear tests were conducted at Rock Mechanics Laboratory of CIMFR on the samples collected from the field. The geotechnical mapping was done on the exposed benches of the quarry as per the norms of International Society of Rock Mechanics (ISRM 1978). The kinematic analysis was done to determine the critical orientation of structural discontinuities. After identifying kinematically possible failure modes, detailed slope stability analysis was carried out by GALENA software based on limit equilibrium method. The present study reveals that the 96m high final slope could be designed with 58 degree overall slope angle. The sensitivity analysis shows that the influence of water is also alarming. It was recommended that the slope should be kept in drained geomining condition by providing suitable drainage and keeping drainage effectively maintained

1 INTRODUCTION

The Lanjiberna Limestone open cast mine is located in the Orissa state of India. There are three nos. of quarries in this mine namely Q-1_3,Q-4_5 and Q-2_6 respectively. The study was conducted at quarry no. 2–6. Presently quarry no. 2 and 6 are named as two different quarries. The mine management is going to join and merge these two quarries and proposed to work as a single pit by removing the ramp centrally located and by shifting the road towards north. The purpose of study was to suggest optimum slope design of quarry2–6. Presently the pit is being mined with 45 degree overall slope angle.

The present Limestone production is 1.70 million tonne from the captive mines, which had been planned to increase to 4.20 million tones per annum. With the proposed enhanced production of mines from 1.70 million tones to 4.20 million tones per year, the total deposit will last for more than 27 years.

The rock discontinuities were mapped at the exposed benches of the pit as per the norms of International Society of Rock Mechanics (ISRM 1978). Geotechnical mapping was undertaken to determine the critical orientation of structural discontinuities. After identifying kinematically possible failure modes, detailed slope stability analysis is carried out by limit equilibrium method. Sensitivity analysis was done to determine the most effective remedial measure for any critical slope.

2 GEOLOGY

The slopes of the quarry are mainly characterized by topsoil, dolomite, dolomitic limestone and limestone, which are well jointed. Geologically, Langiberna limestone area belongs to Birmitrapur stage of the gangpur series of Indian Dharwars. In Lanjiberna, there are two, almost parallel, bands of limestone running East West separated by a band of dolomitic limestone of about 200 to 300m width.

3 GEOHYDROLOGY

The climate of the area is sub-tropical. The average annual is around 1200 mm. The area of the quarry area does not have top-aquifer, as the weathered mantle is not developed below soil profile.

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