24 – Design of Coal Pillar Arrays and Chain Pillars

Publisher Summary This chapter focuses on design of coal pillar arrays and chain pillars. Pillar formation in underground coal mining is either done as a requirement of the method of extraction itself, that is, in bord and pillar mining, or for fulfilling various functions such as panel isolation, protection of roadways, shafts or surface features, protection of current mine workings from dangers of water inundation, and as a guard against roof collapses in the face area while depillaring. Pillars for panel isolation, commonly termed as chain pillars, and those for protection against the goaf in depillaring, called ribs, are generally required for temporary stability and can have lower safety factors than the remaining pillar types, which must be permanent in nature. Design of pillar arrays is commonly required under shallow covers when subsidence at the surface or at an upper coal seam cannot be induced within the permissible limits specified. As in any design of structures, the pillar design procedure essentially consists of estimating the pillar strength and the load on pillars and linking the two through a proper safety factor. The following factors influence pillar strength: (1) uniaxial and triaxial coal strength, (2) width to height ratio of pillar, (3) pillar size or volume, (4) shape in plan, (5) pre-excavation horizontal stresses, (6) end conditions or conditions at the roof-pillar and/or floor-pillar contact and also presence of bands in the seam, (7) water and weathering underground, and (8) method of road drivage such as with road headers or with blasting.

[1]  M. U. Ozbay.  The stability and design of yield pillars located at shallow and moderate depths , 1989 .

[2]  V. E. Hooker,et al.  Laboratory and in situ mechanical behavior studies of fractured oil shale pillars , 1975 .

[3]  Syd S. Peng,et al.  Chain pillar design for U.S. longwall panels , 1985 .

[4]  M. N. Das.  Influence of width/height ratio on post-failure behaviour of coal , 1986 .

[5]  P. R. Sheorey,et al.  Considerations for the Stability of Longwall Chain Pillars and Adjacent Roadway , 1981 .

[6]  Bhawani Singh,et al.  Schmidt hammer rebound data for estimation of large scale in situ coal strength , 1984 .

[7]  Charles T. Holland,et al.  The Strength Of Coal In Mine Pillars , 1964 .

[8]  P. R. Sheorey,et al.  Coal pillar strength estimation from failed and stable cases , 1987 .

[9]  Bhawani Singh,et al.  A Numerical Procedure for Rock Pressure Problems in Level Seams , 1981 .

[10]  M.D.G. Salamon,et al.  Stability, instability and design of pillar workings , 1970 .

[11]  P. R. Sheorey.  A theory for In Situ stresses in isotropic and transverseley isotropic rock , 1994 .

[12]  G. J. Chekan,et al.  Loading characteristics of pillars in multiple-seam mining operations. Report of Investigations/1988 , 1988 .

[13]  A. H. Salamon,et al.  A study of the strength of coal pillars , 1967 .

[14]  Z. T. Bieniawski,et al.  The effect of specimen size on compressive strength of coal , 1968 .

[15]  B. Singh,et al.  Subsidence research in India , 1986 .

[16]  P. R. Sheorey.  Support pressure estimation in failed rock conditions , 1985 .

[17]  A. H. Wilson.  A method of estimating the closure and strength of lining required in drivages surrounded by a yield zone , 1980 .

[18]  W. A. Hustrulid.  A review of coal pillar strength formulas , 1976 .

[19]  Horst Wagner,et al.  Use of Ash to Improve Strata Control in Bord and Pillar Workings , 1981 .

[20]  P. R. Sheorey,et al.  Pillar strength approaches based on a new failure criterion for coal seams , 1986 .

[21]  P. R. Sheorey.  Estimation of gain in pillar strength due to bolting: technical note : Int J Rock Mech Min SciV25, N5, Oct 1988, P321–326 , 1989 .

[22]  Robert Peele,et al.  Mining engineers' handbook , 1945 .

[23]  P. R. Sheorey.  Estimation of gain in pillar strength due to bolting , 1988 .

[24]  J. F. T. Agapito,et al.  Effect of pillar reinforcement on long-term stability of an oil shale mine , 1985 .