A room and pillar operation is planned for a depth of 300
m (984 ft) in a stratum that has a compressive strength
13.57 MPa (1,968 psi) determined from laboratory
testing on cylinders of L/D (length/diameter) of one.
Entries and crosscuts are planned at 6 m (20 ft). Square
pillars of 4 m high (seam thickness) are anticipated.
Determine the pillar dimensions and extraction ratio
associated with a pillar safety factor of 1.5.
For a pre, pre-feasibility study the Hedley-Grant pillar strength equation can be used in conjunction with the tributary area theory, TAT. The results obtained for the strength and dimensions given is a 6 by 6 m pillar the percentage extraction is 75% and the safety factor 1,65 with the laboratory strength is reduced to 75 MPa for the rock mass.
This result is subject to the orebody overall geometry, mainly regional extent, the geological strength index GSI, of the ore body.
For a bankable feasibility study the procedures described in the listed articles should definitely be taken into consideration.
"A brief review of the Hedley-Grant Pillar design formula and a proposed alternative pillar design methodology" Rudiger Kersten, 2022. Aspects Min Miner Sci 8(4) AMMS 000694.
"An alternative pillar design methodology" R W O Kersten, 2019, SAIMM, volume 119, May 2019.
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