Mine dump slope classification

Rahul (2010) proposed a dump classification system for coal mine waste dump slope. The parameters which have been taken for the classification are overall dump height, overall slope angle, number of benches, density of dumped material, cohesion, angle of internal friction, foundation type, slope of foundation, degree of confinement, method of construction, piezometric and climatic condition and seismicity. Numerical modeling and limit equilibrium methods are used to establish the classification system. DSR value of a given rock mass is obtained after summation of the rating values of all the parameters, as illustrated in Table 4.7.

Explain the basis of these rating values

Whether DSR performance has been validated?

Table: 4.1 Proposed DSR system for coal mine

 Key factors affecting stability Range of conditions and description Rating Overall dump height, m Up to 40m 20 41-80 m 15 81-120 m 10 121-160m 5 >160m 0 Overall slope angle(θ), degree θ <18 30 18 QUOTE   22 25 22 QUOTE   26 20 26 QUOTE   30 15 30 QUOTE   34 10 34 QUOTE   37 5 >37 0 Number of Benches 2-4 5 >4 10 Hydrological condition Most Favourable No groundwater table is generated 15 Favourable Ground water table is up to 15% of overall height of dump 10 Intermediate Ground water table up to 15 to 30 % of overall height of dump. 5 Unfavourable Ground water table up to 30 to 40 % of overall height of dump. 0 Most unfavourable Ground water table is more than 40% of overall height of dump. -5 Dump material quality Cohesion Rating=  QUOTE  +3 Internal angle of friction Rating= 0.5  QUOTE  Internal angle of friction – 7.5

Dumps are divided into dump stability classes on the basis of calculated factor of safety and DSR value of dump. Table 4.2 shows which type of failure hazard is expected in which dump stability class. It also explains the level of investigation required by particular class and the design and construction of the dump slope.

Table: 4.2 Dump stability classes and recommendations

 Dump stability class Failure hazard Range of dump rating Recommended level of effort for investigation, design and construction A Negligible >75 •      Minimum lab testing is required •      Minimal restriction on construction •      Visual monitoring is sufficient B Low 61-75 •      Thorough site investigation •      Limited lab index testing •      Basic stability analysis is required •      Limited restrictions on construction •      Routine visual and instrumental monitoring C Moderate 46-60 •      Detailed site investigation •      Undisturbed samples may be required •      Detailed lab testing, including shear strength and durability test •      Detailed stability analysis is required including parametric study •      Moderate restriction on construction •      Detailed instrumental monitoring is required D High <45 •      Detailed and phased site investigation •      Undisturbed sampling probably required •      Detailed stability analysis is required, including parametric studies and full evaluation of alternatives •      Severe restrictions on construction •      Detailed and continuous instrument monitoring is required