ABSTRACT:

The optimum slope design in open cast mine is of great importance, lf the designed slope is steeper than the optimum limit, the slope may fail and if it is too gentle, the volume of waste removed increases. In any case, it is uneconomical. This research analyses the stability of Angouran open cast mine. There are 3 major faults in the area which divide the mine into 3 parts. Field investigation indicates 3 joint sets of dip/dip direction of 82/180°, 27/130° and 76°/273° respectively. Shear strength parameters of discontinuities were determined. These parameters were utilized for slope stability analysis. Limit equilibrium and numerical methods were used. The study shows that block No. 1 (west of mine) and block No. 3(east of mine) possess inclination of individual bench and overall slope of the open cast mine are 83° and 51°respectively and for block No. 2(north of mine) there arc 81° and 48° respectively.

I.
INTRODUCTION

There are four methods for studying stability analysis and design of optimum slope. These are limit equilibrium, numerical, empirical and physical methods (Giani 1992). Initially the failure mode is evaluated by stenographic method. Then with respect to the failure mode a suitable analytical method is chosen. Among of these methods, the limit equilibrium and numerical methods were selected to design the optimum dip of Angouran open cast mine. Many numerical methods are available such as finite element, boundary element and finite difference methods (Pande 1990). "FLAC" software which is based on the finite difference was used in slope stability analysis. Using limit equilibrium method, "SWEDGE" software was adopted to study the stability. The limit equilibrium method takes into account the structural setting of the area where as the 2D finite difference method can not model the structural setting. The local geology is governed by the effect of discontinuities and this has to be taken into consideration. Therefore the properties or the discontinuities are to be evaluated as an input parameters in the analyses.

2.
CASE STUDY

The Angouran lead-zinc mine is located at 130 kilometers south west of Zanjan city. The mine is located 2950m above sea level. Average relative moisture is 60% and 40% for winter and summer respectively. Average annual rainfall is 280 mm, Geographical coordinates are 47.20% eastern longitude and 36.40° northern latitude.

3.
GEOLOGICAL CONDITION

The ore body consists of two main parts, the upper part is sulfide and the lower part is oxidized (carbonate and silicate). The carbonate part is possessing mainly a schistose structure and in some places is dense. The sulfide part has located in deep, as a result just the carbonate part is exploited. (Calsimin Co. 1995) Surrounding rock in the mine is limestone. Field investigation Was carried out and the data were analysed by "DIPS" software. The analysis shows that there are 3 major joint sets in the area. Their dip and dip directions arc presented in Table I.

4.
GEOTECHNICAL PARAMETERS

Laboratory tests were carried out on intact and jointed rocks for determining physical.

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