Question

1. A near horizontal 12 m-thick limestone deposit is to be mined using the room and pilar method. The design dimensions consist of 15 m-wide square pillars separated by 12 m- wide entry. The mining will take place in two stages by taking the upper 6 m first and then mining the lower 6 m. The mining depth and overburden specific weight values are given as H- 232 m and 0.0265 MN/m3, respectively. The constants for the linear pillar strength formula used for the design are given as K-40, A0.64 and B 0.36. Calculate the safety factor of the pillars for the following cases: i) first stage mining, ii) final layout, and ii) what if the room width was increased to 14 m but keeping the same extraction ratio (i.e., also increasing pillar width) for the final layout. Comment on the general rock mechanics stability by comparing the case (i) with case (i)

Answer 1