Past finite element analysis of pillar mining effects on the Ross Shaft at the Homestake Mine in Lead, SD, indicated stability of the shaft during mining on both sides of a central pillar that was defined within a much larger original shaft pillar. Experience with pillar mining that began in 1988 verified the earlier forecast of stability. Mining of the remaining central portion of the original pillar began in early 1995. A "cave" occurred in 1996 that led to a temporary cessation of pillar mining; pillar mining began anew in 1997 and continued for a short period. A relatively small portion of the central pillar remains. Previous pillar mining on north and south sides of the central pillar and mining between the central pillar and the Ross Shaft as well as top and bottom sill development have isolated the ore remaining. Thus, one intuitively expects little effect of final mining on the Ross Shaft. Results of the present study confirm this expectation and show very little change in shaft stability as a consequence of mining the ore remaining in the central portion of the original shaft pillar. Comparisons of three-dimensional finite element model displacements with borehole extensometer measurements that began in June, 1944, reinforce this conclusion.
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