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PIT SLOPE STABILITY DGMS guidelines to prevent slope failures in opencast mine. Q. 12 B Give the guide lines issued by t
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PIT SLOPE STABILITY
DGMS guidelines to prevent slope failures in opencast mine. Q. 12 B Give the guide lines issued by the DGMS to prevent slope failures in opencast mines. Ans. Following Kawadi opencast coal mine disaster of WCL on 24.6.2000 ( 10 deaths) the DGMS has issued some guidelines for scientific approach towards design of opencast pit sloes as follows : 1.A systematic detailed work needs to be undertaken for solving or understanding the problems of slope failure in opencast mines. The objective of such type of work could be – a) To increase the knowledge of the behavior of mine slopes b) To improve the ability to estimate rock mass strength for such slopes c) To develop an improved design methodology for forward design of rock slopes in the opencast mines and d) To form a detailed slope monitoring protocol for such slopes A geomechanical model needs to be developed based on extensive field work and review of previous studies at the sites. The model may comprise of a detailed description of the geology, joint sets and structures, mechanical properties of intact rock and joints, geo-hydrological conditions and virgin stress state, Form this representative cross sections and parameters needs to be established which could latter to be used as inputs for stability analysis of the pit slopes. 2.Assessment of representative rock mass strength needs to be addressed for the use of appropriate failure criterion in conjunction with rock mass classification by comparing back calculated strengths available from old case studies, a reliable estimate may be established. Failure mechanism needs to be studied by means numerical modeling. For this purpose, the finite difference code FLAG and the distinct element code UDEC can be used. The work must be aimed at investigating failure mechanisms in details, at the same time developing are liable modeling technique for the pit slopes. 3.Effect of ground water. This most import5ant parameter must be fully understood before any attempt is made to model or to study slope stability problems in mines. Rainfall and subsequent movement of ground water greatly affect slope stability. The ground water regime is considered most changeable natural parameter which affects sloe stability in several ways :
By By By By
generating pore positive and negative, which alters stress conditions. changing the bulk density of the material forming the slope. erosion (internal and external) and, changing the mineral constituents of the materials forming the slope.
Ground water in soil may be of two types; occurring above or occurring below the water table ( phreatic surface ). Water above the water table may be transient percolation moving downwards to join the phreatic water below the water table or capillary water held above the water table by surface tension. Phreatic water below the water table is subject to gravitational forces and it saturates the pore space in the material below the water table. Usually three water zones below ground surface can be identified : a) Zone of permanent saturation – where pore spaces are always filled with water b) Zone of intermittent saturation – where pore spaces are filled with water only after heavy rains. c) Zone of no saturation – where pore spaces are never saturated though water may pass through water table in the upper surface of the zone in permanent saturation. Its level changes from season to season. Water flows through soil or rock in different ways depending on the nature of the ground material: Aquifer refers to any water transmitting soil, or rock Aquifers have various modes of ground water flow such as : Homogeneous ( inter granular) flow and Path preferential flow ( either fissure or conduit flow ) which tends to be more rapid and can significantly influence slop stability. Flow in soil is more likely to be inter granular although fissure of conduit flow can also occur via fissures, pipes and draying cracks. Flow in rock can be inter granular, but is more common though joints and discontinuities. It is remarkable that joints in rock may get filled with water during intense rainfall, inducing high hydraulic pressure on the rock mass and therefore adversely affecting stability. While designing an open pit mine slope, all these essential issues must be considered. Moreover, only designing is not enough. Comprehensive design implementation and monitoring protocol needs to be developed by every opencast mine operator in order to achieve safe working conditions in such mines. These guidelines are applicable to coal as well metalliferous mines.
A Schematic Sections Of Failure Jone:
View of Slope Failure
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