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