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: Increase in ground water table 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- 3000mm 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 40-50 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 100km 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 4000mm

MATERIALS AND METHODS Soil sampling and testing: six samples each weighing 3kgs 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 4years. 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 17-18,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 Recycle53: 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 Environmental Earth Science(2011) 63: 1169-1177 http://www.springerlink.com/content/b31q62767n244162/fulltext.pdf (13/08/20111) http://www.springerlink.com/content/w417305613052445/fulltext.pdf (14/08/2011)