Limitations and potential design risks when applying empirically derived coal pillar strength equations to real-life mine stability problems
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摘要
The method of determining coal pillar strength equations from databases of stable and failed case histories is more than 50 years old and has been applied in different countries by different researchers in a range of mining situations. While common wisdom sensibly limits the use of the resultant pillar strength equations and methods to design scenarios that are consistent with the founding database, there are a number of examples where failures have occurred as a direct result of applying empirical design methods to coal pillar design problems that are inconsistent with the founding database. This paper explores the reasons why empirically derived coal pillar strength equations tend to be problem-specific and should be considered as providing no more than a pillar strength ‘‘index." These include the non-consideration of overburden horizontal stress within the mine stability problem, an inadequate definition of supercritical overburden behavior as it applies to standing coal pillars, and the non-consideration of overburden displacement and coal pillar strain limits. All of which combine to potentially complicate and confuse the back-analysis of coal pillar strength from failed cases. A modified coal pillar design representation and model are presented based on coal pillars acting to reinforce a horizontally stressed overburden, rather than suspend an otherwise unstable self-loaded overburden or section, the latter having been at the core of historical empirical studies into coal pillar strength and stability.
The method of determining coal pillar strength equations from databases of stable and failed case histories is more than 50 years old and has been applied in different countries by different researchers in a range of mining situations. While common wisdom sensibly limits the use of the resultant pillar strength equations and methods to design scenarios that are consistent with the founding database, there are a number of examples where failures have occurred as a direct result of applying empirical design methods to coal pillar design problems that are inconsistent with the founding database. This paper explores the reasons why empirically derived coal pillar strength equations tend to be problem-specific and should be considered as providing no more than a pillar strength ‘‘index." These include the non-consideration of overburden horizontal stress within the mine stability problem, an inadequate definition of supercritical overburden behavior as it applies to standing coal pillars, and the non-consideration of overburden displacement and coal pillar strain limits. All of which combine to potentially complicate and confuse the back-analysis of coal pillar strength from failed cases. A modified coal pillar design representation and model are presented based on coal pillars acting to reinforce a horizontally stressed overburden, rather than suspend an otherwise unstable self-loaded overburden or section, the latter having been at the core of historical empirical studies into coal pillar strength and stability.
The method of determining coal pillar strength equations from databases of stable and failed case histories is more than 50 years old and has been applied in different countries by different researchers in a range of mining situations. While common wisdom sensibly limits the use of the resultant pillar strength equations and methods to design scenarios that are consistent with the founding database, there are a number of examples where failures have occurred as a direct result of applying empirical design methods to coal pillar design problems that are inconsistent with the founding database. This paper explores the reasons why empirically derived coal pillar strength equations tend to be problem-specific and should be considered as providing no more than a pillar strength ‘‘index." These include the non-consideration of overburden horizontal stress within the mine stability problem, an inadequate definition of supercritical overburden behavior as it applies to standing coal pillars, and the non-consideration of overburden displacement and coal pillar strain limits. All of which combine to potentially complicate and confuse the back-analysis of coal pillar strength from failed cases. A modified coal pillar design representation and model are presented based on coal pillars acting to reinforce a horizontally stressed overburden, rather than suspend an otherwise unstable self-loaded overburden or section, the latter having been at the core of historical empirical studies into coal pillar strength and stability.
引文
[1]Galvin JM.Considerations associated with the application of the UNSW and other pillar design formulae.Proceedings of the 41st U.S.symposium on rock mechanics.Alexandria(VA):American Rock Mechanics Association;2006.pp.9.
[2]Esterhuizen GS.Extending empirical evidence through numerical modelling in rock engineering design.J South Afr Inst Min Metall 2014;114(10):755-64.
[3]Galvin JM.Ground engineering:principles and practices for underground coal mining.Switzerland:Springer International Publishing;2016.p.684.
[4]Frith R,Reed G.Coal pillar design when considered a reinforcement problem rather than a suspension problem.Int J Min Sci Technol 2017;28(1):11-9.
[5]Esterhuizen GS,Mark C,Murphy M.The ground response curve and its impact on pillar loading in coal mines.In:Proceedings of the 3rd international workshop on coal pillar mechanics and design.Pittsburgh(PA):National Institute for Occupational Safety and Health;2010.p.121-9.
[6]Ditton S,Sutherland T.Management of subsidence at the Tasman and Abel mines-issues and outcomes.In:Proceedings of the coal operators’conference.Wollongong(Australia):University of Wollongong;2013.p.86-98.
[7]McTyer K,Sutherland T.The Duncan method of partial pillar extraction at tasman mine.In:Proceedings of the coal operators’conference.Wollongong(Australia):University of Wollongong;2011.p.8-15.
[8]Salamon MDG,Munro AH.A study of the strength of coal pillars.J South Afr Inst Min Metall 1967;68(2):56-67.
[9]Shirley A,Fagg S.Subsidence events,investigations&litigation:the need for a forensic approach.In:Proceedings of the 10th triennial conference on mine subsidence.Barton(ACT):Mine Subsidence Technology Society;2017.p.283-301.
[10]Vasundhara..Geomechanical behaviour of soft floor strata in underground coal mines PhD thesis.Sydney(Australia):UNSW;1998.p.609.
[11]Seedsman R.Awaba-understanding soft floors and massive conglomerates.Proceedings of the general meeting of the mine managers association of Australia.Toronto(NSW):MMAA;2008.
[12]Mills K,Edwards J.Review of pillar stability in claystone floor strata.In:Proceedings on the symposium on safety in mines-the role of geology.Sydney,NSW.p.161-8.
[13]Frith RC,McKavanagh B.Optimisation of longwall mining layouts under massive strata conditions and management of the associated safety and ground control problems Project C7019.Brisbane(Queensland):ACARP;2000.
[14]Van Der Merwe JN.Beyond coalbrook:critical review of coal strata control developments in South Africa.In:Proceedings of the 25th international conference on ground control in mining.Morgantown(WV):West Virginia University;2006.p.335-46.
[15]Mills K,O’Grady P.Impact of longwall width on overburden behaviour.In:Proceedings of the coal operators’conference.Wollongong(Australia):University of Wollongong;1998.p.147-55.
[16]Ditton S,Frith R.Influence of overburden lithology on subsidence and subsurface fracturing on groundwater Project C10023.Brisbane(Queensland):ACARP;2003.
[17]Salamon MDG,Ozba MU,Madden BJ.Life and design of bord-and-pillar workings affected by pillar spalling.J S Afr Min Metall 1998;98(3):135-45.
[18]Mills K.Observations of ground movements within the overburden strata above longwall panels and implications for groundwater impacts.Proceedings of the 38th symposium on the advances in the study of the Sydney Basin.Wollongong(Australia):Strata Control Technology;2012.
[19]UNSW.Strata control graduate diploma course notes.Sydney(Australia):School of Mining Engineering,University of New South Wales;2010.
[20]Colwell M,Frith R.ALTS 2009-a ten year journey.In:Proceedings of the coal operators’conference.Wollongong(Australia):University of Wollongong;2009.p.37-53.
[21]Colwell M,Frith R.Analysis and design of faceroad roof support(ADFRS).In:Proceedings of the coal operators’conference.Wollongong(Australia):University of Wollongong;2013.p.74-85.
[22]Mo S,Canbulat I,Zhang C,Oh J,Shen B,Hagan P.Numerical investigation into the effect of backfilling on coal pillar strength in highwall miningInternational.J Min Sci Technol 2018;28(2):281-6.
[23]Hill D.Coal pillar design criteria for surface protection.In:Proceedings of the coal operators’conference.Wollongong(Australia):University of Wollongong;2005.p.31-7.
[24]Bieniawski ZT.The effect of specimen size on compressive strength of coal.Int J Rock Mech Min Sci Geomech Abstr 1968;5(4):325-35.
[25]Madden B.A re-assessment of coal-pillar design.J S Afr Inst Min Metall1991;91(1):27-37.
[26]Van Der Merwe JN.Revised strength factor for coal in the Vaal basin.J S Afr Inst Min Metall 1993;93(3):272-5.
[27]Canbulat I.Life of coal pillars and design considerations.In:Proceedings of the2nd Australasian ground control in mining conference.Victoria(Australia):AusIMM;2010.p.57-66.
[28]Senate US.Report on the August 6,2007 disaster at Crandall canyon mine.Washington DC:Health,Education,Labor and Pensions Committee;2008.pp.75.
[2]Esterhuizen GS.Extending empirical evidence through numerical modelling in rock engineering design.J South Afr Inst Min Metall 2014;114(10):755-64.
[3]Galvin JM.Ground engineering:principles and practices for underground coal mining.Switzerland:Springer International Publishing;2016.p.684.
[4]Frith R,Reed G.Coal pillar design when considered a reinforcement problem rather than a suspension problem.Int J Min Sci Technol 2017;28(1):11-9.
[5]Esterhuizen GS,Mark C,Murphy M.The ground response curve and its impact on pillar loading in coal mines.In:Proceedings of the 3rd international workshop on coal pillar mechanics and design.Pittsburgh(PA):National Institute for Occupational Safety and Health;2010.p.121-9.
[6]Ditton S,Sutherland T.Management of subsidence at the Tasman and Abel mines-issues and outcomes.In:Proceedings of the coal operators’conference.Wollongong(Australia):University of Wollongong;2013.p.86-98.
[7]McTyer K,Sutherland T.The Duncan method of partial pillar extraction at tasman mine.In:Proceedings of the coal operators’conference.Wollongong(Australia):University of Wollongong;2011.p.8-15.
[8]Salamon MDG,Munro AH.A study of the strength of coal pillars.J South Afr Inst Min Metall 1967;68(2):56-67.
[9]Shirley A,Fagg S.Subsidence events,investigations&litigation:the need for a forensic approach.In:Proceedings of the 10th triennial conference on mine subsidence.Barton(ACT):Mine Subsidence Technology Society;2017.p.283-301.
[10]Vasundhara..Geomechanical behaviour of soft floor strata in underground coal mines PhD thesis.Sydney(Australia):UNSW;1998.p.609.
[11]Seedsman R.Awaba-understanding soft floors and massive conglomerates.Proceedings of the general meeting of the mine managers association of Australia.Toronto(NSW):MMAA;2008.
[12]Mills K,Edwards J.Review of pillar stability in claystone floor strata.In:Proceedings on the symposium on safety in mines-the role of geology.Sydney,NSW.p.161-8.
[13]Frith RC,McKavanagh B.Optimisation of longwall mining layouts under massive strata conditions and management of the associated safety and ground control problems Project C7019.Brisbane(Queensland):ACARP;2000.
[14]Van Der Merwe JN.Beyond coalbrook:critical review of coal strata control developments in South Africa.In:Proceedings of the 25th international conference on ground control in mining.Morgantown(WV):West Virginia University;2006.p.335-46.
[15]Mills K,O’Grady P.Impact of longwall width on overburden behaviour.In:Proceedings of the coal operators’conference.Wollongong(Australia):University of Wollongong;1998.p.147-55.
[16]Ditton S,Frith R.Influence of overburden lithology on subsidence and subsurface fracturing on groundwater Project C10023.Brisbane(Queensland):ACARP;2003.
[17]Salamon MDG,Ozba MU,Madden BJ.Life and design of bord-and-pillar workings affected by pillar spalling.J S Afr Min Metall 1998;98(3):135-45.
[18]Mills K.Observations of ground movements within the overburden strata above longwall panels and implications for groundwater impacts.Proceedings of the 38th symposium on the advances in the study of the Sydney Basin.Wollongong(Australia):Strata Control Technology;2012.
[19]UNSW.Strata control graduate diploma course notes.Sydney(Australia):School of Mining Engineering,University of New South Wales;2010.
[20]Colwell M,Frith R.ALTS 2009-a ten year journey.In:Proceedings of the coal operators’conference.Wollongong(Australia):University of Wollongong;2009.p.37-53.
[21]Colwell M,Frith R.Analysis and design of faceroad roof support(ADFRS).In:Proceedings of the coal operators’conference.Wollongong(Australia):University of Wollongong;2013.p.74-85.
[22]Mo S,Canbulat I,Zhang C,Oh J,Shen B,Hagan P.Numerical investigation into the effect of backfilling on coal pillar strength in highwall miningInternational.J Min Sci Technol 2018;28(2):281-6.
[23]Hill D.Coal pillar design criteria for surface protection.In:Proceedings of the coal operators’conference.Wollongong(Australia):University of Wollongong;2005.p.31-7.
[24]Bieniawski ZT.The effect of specimen size on compressive strength of coal.Int J Rock Mech Min Sci Geomech Abstr 1968;5(4):325-35.
[25]Madden B.A re-assessment of coal-pillar design.J S Afr Inst Min Metall1991;91(1):27-37.
[26]Van Der Merwe JN.Revised strength factor for coal in the Vaal basin.J S Afr Inst Min Metall 1993;93(3):272-5.
[27]Canbulat I.Life of coal pillars and design considerations.In:Proceedings of the2nd Australasian ground control in mining conference.Victoria(Australia):AusIMM;2010.p.57-66.
[28]Senate US.Report on the August 6,2007 disaster at Crandall canyon mine.Washington DC:Health,Education,Labor and Pensions Committee;2008.pp.75.