Design of support system for bord and pillar workings

Abstract

The estimation of rock load from the strata and its distribution over the underground mine workings is of prime importance. In Indian coalmines, CMRI- RMR and NGI-Q Systems are mostly used for formulating design of support in rock engineering. Support systems are also designed with the help of numerical modeling. The working has been modeled by writing a program code in FLAC5.0. The modeling is done for driving of galleries (development) to form three pillars. The vertical stress contours indicated a maximum stress of about 2.5Mpa on pillars for the depth of 53m with a gallery width of 4.8 m and pillar size of 25 m.
Rock load on the basis of RMR for the development gallery is 2.4 t/m2. Support system consisting of Resin bolt with bolt spacing of 1.5 m row spacing of 1.5 m has a support capacity of 5 t/m2. No of bolts in a row is 3 is for galleries of 4.5m width and area of 4.5m x 1.5m. This support system has a safety factor of 2, which is adequate. Rock load on the basis of RMR for the junction is 3.17t/m2. support system consisting of Resin bolt with bolt spacing of 1.5 m, row spacing of 1.5 m, has a support capacity of 7.4t/m2 No of bolts in a row is 3, No of row 3, is proposed to support junction of 4.5m x 4.5m area which gives a safety factor of 2.33. It shows the junction is well supported & there is no fear of roof fall, so support is adequate.
For depillaring workings, Rock load on the basis of Q is 6.19 t/m2 for Slice, and 7.79 t/m2 for goaf edges. Support system consisting of one chock and 3 steel prop is designed. Goaf edge support is designed with skin to skin chock with a spacing of 1.2 with corner props. The support system for the slice consists of 2 props with spacing of 1.2m having a support capacity of 10 t/m2. The support system gives a factor of safety of 1.61 for slices and safety factor of 1.23 for goaf edge.
Support system can be included in the numerical model for better understanding of the stability of the workings with supports of different types and capacities. These approaches can be followed for many mines and the performance of the support system can be monitored with load cells, and the models can be calibrated accordingly. This will improve the dependability and applicability of the numerical models as a solution for design of support system.