Coal Pillar Strength Study. (The Design of Production Pillars in Coal Mines).

摘要

Laboratory tests for unconfined compressive strength and Young's modulus on 371test cylinders of coal at length to diameter ratios of 1/2, 1, 1-1/2,and 2,and nominal diameters of 1, 2, 4, 6, 8,and 12inches are reported. Linear regression of ultimate strength Cu on diameter to height ratio D/L results in the equation Cu(psi) = 4219(0.422(D/L) + 0.578). Finite elements analyses of the laboratory tests using flaw-free geologic materials result in C = C1(0.61D/L + 0.39) and C = C1(0.04D/L + 0.96) using linear and quadratic failure criteria. Field measurements at 117closure pin stations and 119vibrating wire stress gage sites in the vicinity of two 60-by 60-foot test pillars separated by 20-foot entries and crosscuts show approximately 1to 2inches closure and 2,000to 4,000psi stress change prior to mining of the pillars to failure. Finite element analysis of the test section from development through pillar mining and retreat using laboratory rock properties as input shows good agreement with the measured closures. (Portions of this document are not fully legible)