DUMP SLOPE STABILITY with special reference to effects

DUMP SLOPE STABILITY with special reference to effects of monsoonal rainfall MINE PORTAL TEAM www. MINEPORTAL. in CALL/WHATSAPP-8804777500 www. fb. com/mineportal. in

INTRODUCTION �Mine dumps and their types (a) internal dump (b) external dump �Mine dump stability - critically important issue �Impact on economics and production of mine �Factors affecting dump slope stability �Methods of slope stability investigations �Impact of rainfall on slope stability - Case study of Goa mine �An empirical formula relating dump parameters and pore water pressure to FOS of slope.

Failure Modes and Failure Mechanism �Surface and edge slides �Shallow flow slide in presence of sufficient water and flowing parallel to the face �Base failure �Block translation- dump on inclined ground �Circular failure- fine grains in dump �Foundation circular failure �Toe spreading

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WASTE DUMP STABILITY: (a) A Geotechnical Perspective �Long and short term stability �Long term stability: (a) Increase in ground water table (b) Decrease in dump material strength �Rainfall Effects: (a) rainfall intensity (b) rainfall duration (c) rainfall pattern

(b) A geo-environmental perspective Waste may contain heavy metals causing many problems in rainy seasons: (a) agricultural canals (b) agricultural yields and fish population (c) heavy siltation and sediment deposits in river beds and creeks.

CASE STUDY �State of Goa- 5% of area(18300 ha) is under mining land �Average annual rainfall- 3000 mm �Open cut mining method in Sesa Goa Iron mines �Annual production: 16 -21 million tonne � 1: 3 ore O/B ratio resulting waste production of 4050 million cubic m �Detailed investigations of mine dump slope stability and geo-environmental issues considering high rainfall �Quantification of soil properties and increase in pore water pressure due to heavy rainfall

LOCATION, GEOLOGY AND CLIMATE OF STUDY AREA �Samples from Sesa Goa Ltd. Codli Mine �Goa is a rising plateau covering an area of 3700 square km and coastline extending over 100 km �Iron, magnese, bauxite and silica sand extraction �Current study area is Sanguem Taluka South. Goa, Goa �South west monsoon: june to september with highest rainfall in june and lowest in feb �Annual rainfall: 3000 to 4000 mm

MATERIALS AND METHODS �Soil sampling and testing: six samples each weighing 3 kgs in plastic bags to retain moisture content were tested in labs. �Ground water analysis: 5 dug-wells were dug in which water level measurement mainly during rainy season for 4 years. �Numerical modeling: general limiting equilibrium method to calculate FOS of slope

RESULTS (a) Material Properties

(b) Ground Water Monitoring

(c) Numerical Modelling

CONCLUSIONS �Optimum dump slope dimensions for safe mining operations �Influence of monsoonal rainfall on FOS is dramatic �Compaction of material plays an important role �Heavy metals presence in dumps is dangerous �Personnel injuries as well as downstream environmental effects �An empirical model to study dump slope failures

REFERENCES � Yelllishetty M, Darlington WJ(2011), Effects of Monsoonal Rainfall on Waste Dump Stability and Respective Geo-environmental Issues-a case study � Cadwell, J. A. , and Moss, A. S. E. (1981)The Simplified Analysis of Mine Waste Embankemennts, Symposium on Design of Non-Impounding Mine Waste Embankements, Denver, USA, AIME Fall Meeting � Chaulya S. K. , Singh R. S. , Chakraborty M. K. and Shrivastava B. K. (2000), Quantification of Stability of Improvement of Dump Stablisation � Juwarkar AA, Singh SK, Dubay K, Nimje M(2003), Reclamation of Iron Mine Spoil Dumps Using Integrated Biotechnological Approach, In: Proceedings of National Seminar on Status of Environmental Management in Mining Industry, IT-BHU, Jan 1718, pp 197 -212 � Yellishetty M, Ranjith PG, Kumar DL(2009), Metal Concentration and Mobility in Unsaturated in Mine Wastes in Mining Areas of Goa, India. Resourbcouserv Recycle 53: 379 -385 � Pathak K. , Rao K. U. M. (2011), Draft Report for Study of Dump Slope Stability of Sukhinda Chromite Mines (Tata Steel) � Geotechnical and Geological Engg 18: 193 -207, 200