Stability Analysis of Dump Slope in Open Cast Mines

Author Name(s): B. Shruthi, Vaishali J. Rajurkar, Sumit S. Geete
Author Email: megastructure1857@gmail.com

Abstract

This paper present a case study of dump slope stability of Makardhokra – II open cast mine of western coalfield limited. This mine spread over the area of 289.0 hectares. Dump slope instability is the prime concern of proposed mine site. Depth of Black Cotton Soil is extended up to a depth of 20m from the natural ground level. To assess the stability of the OBD slope, samples of dump material were collected from benches of OBD slope. Geotechnical parameters of dump material were evaluated mainly for black cotton soil and white soil. From the geotechnical and geometrical parameters, numerical models were created in software GEO5 for stability analysis and calculation of FoS. GEO5 worked on the Limit Equilibrium Method. The optimal and economical solution for dump slope management and for safety analysis, Geo5 software is used by considering three methods namely Bishop Method, Fellenius method and Spencer method. To check the suitability of improvement the stability of the OBD slope, cantilever wall of 2.75m and 3.0m with variation of backfilling from the inner face of the wall at distance of 0, 0.5m, 1m and 1.5m were evaluated through LEM. Feasibility of gabion wall for improvement of the stability of OBD was also checked. FoS was calculated by varying the slope angle of dump and replacement of black cotton soil with white soil. It is seen that as the angle of the slope increases then FoS decreases. Provision of gabbion wall and replacing black cotton soil of dump with white soil indicate the improved value of Fos. Because of restriction of land, feasibility of construction of retaining wall provision is discarded. Provision of cantilever wall and gabion wall increase the FoS of OBD slope. From cost analysis, cost of provision of cantilever wall is about 70% more than const of provision of gabion wall. Gabion wall proposed to be economical, suitable, easily workable and sustainable method for stability of OBD slope of Makardhokra – II open cast mine.

Introduction

Open Cast mining of coal activity increases day by day to fulfill the demand of the coal for power generation sector. As the depth of the coal mines goes downwards from the existing ground level then the extracted material quantity increases. This extracted quantity of the material called as overburden dump material (OBD) and it is stored in the form of dump. OBD are of two types namely Internal Pit Dump (IPD) and External Over Burden Dump. Dumping of large quantity of extracted material is major problem in the mining industry and again it relates to the optimum use of land for the dump material storage [11]. Stability of the OBD slope is depends on shear strength of the material. Shear strength of soil correlated to the cohesion and angle of internal friction. Stability of the OBD slope is mainly governed by the geotechnical parameters of the OBD material [3,10]. Stability of the dump slope is govern by geological, geometrical, hydraulic and physico-mechanical factors of dump slope material [9]. Pore pressure is main critical factor to reduce the Stability of the OBD slope through reduction in the shear strength of the OBD material [10]. Stability of OBD slope is improved through plantation of the vegetation on the external surface of the OBD slope. Penetrated roots of the plantation increases the cohesion of small thickness of dump slope [6]. Stability analysis methods mainly find out probable failure envelope and factor of safety (FoS). Limit equilibrium methods (LEM) are mainly used to calculate the FoS of the OBD slope and LEM mainly consider failure envelope as circular [4,8]. Strength reduction method based on the numerical modeling also very useful to calculate the probable failure surface and calculation of the FoS.

Conclusion

The following conclusions can be drawn from the work done: 1. As the flattering of slope is safe and considered to the economical solution due to filling of dump from the site is used in above case, but not suggested to use due to restricted space is available over the site. 2. As the construction of 2.75 m cantilever retaining wall shows fare results but the construction cost of such wall comes out to be 43.05 lakhs ( Calculated as per CSR 2016-17) 3. The other alternative for the stability of slope is gabion wall; the cost of Gabion wall comes out to be 24.96 lakhs. (Calculated as per CSR 2016-17). This makes the gabion wall method more economical. The cost of Cantilever wall is nearly around 70% higher than the cost Gabion wall. 4. Gabion wall also has some other advantages like it can be removed and reused if needed. As the mine life is very less, it is generally advisable to use temporary construction Moreover as the mine is not permanent; gabion wall is more advisable for temporary construction. Gabion wall doesn’t allow developing hydrostatic pressure and pore water pressure is easily dissipated in this case. 5. Construction of Gabion wall is very fast, On other side cantilever wall is very expensive, requires more construction time, skilful workmanship and it is a permanent kind of structure. Whereas Gabion construction is very eco friendly as it allows the growth of vegetation. 6. As the existing soil available is the Umrer region is black cotton soil which is subjected to swelling in rainy season which leads to increase in earth pressure due to increase in unit weight. Also the soil is subjected to pore water pressure. The use of Gabion wall provided drainage to disperse the pressure of water flowing through backfill soil which also allows good natural drainage. Therefore, it is suggested to use Gabions for the stability of dump

646 total views, no views today

Download PDF File

About the author: admin