Rock bolts are subjected to different loading conditions along their lengths such as axial,bending,and/or shear forces,which can cause failure at lower loads than those considered for design purposes.The common existi...Rock bolts are subjected to different loading conditions along their lengths such as axial,bending,and/or shear forces,which can cause failure at lower loads than those considered for design purposes.The common existing methodologies do not consider the actual loading of the rock bolts and assume it is only pure axial or pure shear.This study was conducted to investigate the un-grouted rock bolt performance under combined load conditions.Two loading regimes were evaluated:the effect of initial shear displacement on axial load capacity and displacement,and the effect of axial displacement on the shear load capacity.The first regime was also conducted for shear with a gap,when there is a spacing between the shear interfaces.The results of this study showed that the rock bolt can resist higher axial loads than shear under pure or combined load conditions.Under combined load conditions,the rock bolt capacity decreased significantly for both regimes.However,when applying the shear load with a gap,the rock bolt load capacity was not affected significantly.Also,the total bar deformation was improved for shear and axial.The findings of this study show the need to improve the rock bolt design considering the complex loading conditions in situ with/without a gap.展开更多
The capacity of ground support components which have been affected by corrosion is reduced and may ultimately lead to dynamic failure of the component and the strata. In order to maintain an effective,long-term ground...The capacity of ground support components which have been affected by corrosion is reduced and may ultimately lead to dynamic failure of the component and the strata. In order to maintain an effective,long-term ground support system, significant campaigns of rehabilitation are often required in corrosion affected areas which also expose the workers to hazardous conditions. The most common corrosion protection for steel ground support utilises sacrificial systems such as galvanising. Galvanising has previously been proven to be susceptible to some corrosion processes. Stainless steel is the most effective in resistance to corrosion, but can be cost prohibitive, and its mechanical properties often make it unsuited to use in ground support components. Providing an outer protective plastic coating to bolts has proven to be an effective means of protecting the inner steel bar from corrosion. However, these support systems tend to be susceptible to coating damage, and require post cement grouting to provide full encapsulation. In comparison to a standard bolt/resin system, they can be slow to install and expensive.These systems have also been shown to reduce overall load transfer performance of the bolting system. In order to provide a higher level of corrosion protection whilst maintaining current installation practices and bolting cycle times, Minova has developed the Enduro^(TM)steel ground support range. The Enduro^(TM) range consists of standard Minova steel ground support components which have been treated with a unique coating process. The Enduro^(TM)coating has been tested in the harshest of conditions, in laboratory controlled conditions and in underground trials. It has been proven to effectively resist or completely eliminate the formation of corrosion, even in the most aggressive environments. This paper explains the process and provides the details of the laboratory and underground corrosion performance testing carried out on Enduro^(TM)ground support products.展开更多
Coal burst represented a major hazard for some U.S. mining operations. This paper provides an historical review of the coal burst hazards,identifies the fundamental geological factors associated with these events,and ...Coal burst represented a major hazard for some U.S. mining operations. This paper provides an historical review of the coal burst hazards,identifies the fundamental geological factors associated with these events,and discusses mechanisms that can be used to avoid their occurrences. Coal burst are not common in most underground mines. Their occurrence almost always has such dramatic consequences to a mining operation that changes in practice are required. Fundamental factors influencing coal burst events include strong strata,abnormal strata caving,elevated stresses,critical size pillars and the lack of sufficiently sized barrier pillars during extraction. These factors interact to produce excessive stress,seismic shock and loss of confinement mechanisms. Over the 90 years of dealing with these hazards,many novel prevention controls have been developed including novel mine designs and extraction sequences,most of which are site specific in their application. Without an accurate assessment of the fundamental factors that influence coal burst and knowledge of their mechanisms of occurrence,control techniques may be misapplied and risk inadequately mitigated.展开更多
Stillwater Mining Company is the only U.S. producer of platinum group metals （PGMs） and the largest producer outside of South Afiica and Russia. The company controls a considerable portion of the J-M reef and is cur...Stillwater Mining Company is the only U.S. producer of platinum group metals （PGMs） and the largest producer outside of South Afiica and Russia. The company controls a considerable portion of the J-M reef and is currently developing the ＂Blitz Project,＂ which will provide a main haulage level, ore pass systems, backfill plants, and fiow-through ventilation to increase production and ensure sustainable extraction of this critical strategic mineral. While driving two sub-parallel footwall laterals 8125 m in length, one of the development drifts experienced a massive fall in a geologically disturbed area created by a mafic dike intrusion. Combinations of a void fill material （Tekseal）, polyurethane injection, fore poling coupled with steel arches, and supplemental bolting allow safe and efficient advance through this geologically dis- turbed zone. This paper presents the details of this project.展开更多
Broken and jointed ground is extremely hazardous and requires unique stabilization techniques to protect workers and critical entries.Bolting techniques,even the most advanced pre-load to create roof compression,can l...Broken and jointed ground is extremely hazardous and requires unique stabilization techniques to protect workers and critical entries.Bolting techniques,even the most advanced pre-load to create roof compression,can leave large gaps of unconfined and separated roof.This roof can also be susceptible to water inflows which only exacerbate the support problem.These types of conditions existed on long-term development main entry accessing several future longwall panels.The geotechnical assessment identified well defined jointing systems that also permitted water to flow between the roof separations,which"lubricated"the roof material and minimized any frictional advantages.Chemical injections of polyurethane materials,Minova Carbopur WS,was placed beyond the bolted horizon to move the water to the rib lines and reinforce the fractured and broken roof.The injection materials permitted the effective use of bolting patterns and helped ensure long-term stability of critical entries.The paper describes the evaluation techniques,design patterns,basis for chemical selection and application,and results and recommendations.展开更多
The tensile and shear strength of intrinsic bolting support systems has always been a major concern of designers. A comprehensive laboratory testing program was designed to evaluate the tensile and shear strength of i...The tensile and shear strength of intrinsic bolting support systems has always been a major concern of designers. A comprehensive laboratory testing program was designed to evaluate the tensile and shear strength of individual wires and completely wound PC-strand cables. PC-strand cables with smooth wires and the recent anchorage enhancement innovation of indentation were evaluated and compared. The testing protocol detailed in ISO Standard 15630 utilizes a mandrel system that was investigated at 3different diameters which alters the wire to mandrel ratio from 2:1 to 9:1. The results demonstrate that the difference between smooth and indented wires is statistically insignificant when larger diameter mandrels are used,and that indentation does not adversely affect strand properties and performance.Insight into the shearing mechanism and evaluation techniques are discussed with the introduction of triaxial loading to describe the PC-strand tensile and shearing mechanisms. Another important result indicates that the shear strength of PC-strand cable bolting systems has a greater shear strength value than traditional steel bar bolting systems.展开更多
Impact drop tests are routinely used to examine the dynamic performance of rockbolts.Numerous impact tests have been carried out in the past decades on independently designed,constructed and operated testing rigs.Each...Impact drop tests are routinely used to examine the dynamic performance of rockbolts.Numerous impact tests have been carried out in the past decades on independently designed,constructed and operated testing rigs.Each laboratory has developed testing procedures;thus,the results are often reported in different ways by various laboratories.The inconsistency in testing procedures and reporting formats presents a challenge when comparing results from different laboratories.A series of impact tests of identical rockbolts was carried out using the direct impact method(i.e.the mass free-fall method)on the rigs in four laboratories in different countries.The purpose of these tests was to investigate the level of consistency in the results from the four rigs.Each rig demonstrated a high level of repeatability,but differences existed between the various rigs.The differences would suggest that there is noticeable equipment-dependent bias when test results obtained from different laboratories are compared.It was also observed that the energy dissipated for the plastic displacement of the bolt was smaller than the impact energy in the tests.The average impact load(AIL)and the ultimate plastic displacement(D)of the bolt describe the ultimate dynamic performance of the bolt.In the case where the bolt does not rupture,the specific plastic energy(SPE)is an appropriate parameter in describing the impact performance of the bolt.Two other relevant parameters are the first peak load(FPL)and the initial stiffness(K)of the bolt sample.The information from this test series will guide the formulation of standardised testing procedures for dynamic impact tests of rockbolts.展开更多
Fiber-reinforced spayed concrete has been used for several years in civil and tunneling operations.Research conducted to reduce cure times and increase compressive and flexural strengths resulted in the development of...Fiber-reinforced spayed concrete has been used for several years in civil and tunneling operations.Research conducted to reduce cure times and increase compressive and flexural strengths resulted in the development of Tekcrete Fast~, a cementitious product capable of obtaining 41 MPa compressive strength and 8 MPa flexural strength in only 3 h and reaching 7 d strengths of 62 and 11.7 MPa, respectively.A single bag product that uses conventional shotcrete and gunite application systems makes it a natural crossover product for mining applications.The discovery of incredible adhesion properties and high resistance to chloride permeability helps ensure long-term stability and increases the ease of application.Project results from Disaster City~ in Texas and the application for rehabilitating a coal mine belt entry are presented.The case study illustrates the effectiveness of the product in stabilizing a coal mine beltway and adjacent cross-cuts that were subjected to progressive sloughage due to humidity and cyclical loading.展开更多
基金The authors would like to thank Mining3,Minerals Research Institute of Western Australia,Curtin University and Peabody Energy for funding this research project.They also wish to thank Minova Global and its personnel who assisted in completing all the tests conducted at their facility in Nowra,NSW and for providing the rock bolts for testing.
文摘Rock bolts are subjected to different loading conditions along their lengths such as axial,bending,and/or shear forces,which can cause failure at lower loads than those considered for design purposes.The common existing methodologies do not consider the actual loading of the rock bolts and assume it is only pure axial or pure shear.This study was conducted to investigate the un-grouted rock bolt performance under combined load conditions.Two loading regimes were evaluated:the effect of initial shear displacement on axial load capacity and displacement,and the effect of axial displacement on the shear load capacity.The first regime was also conducted for shear with a gap,when there is a spacing between the shear interfaces.The results of this study showed that the rock bolt can resist higher axial loads than shear under pure or combined load conditions.Under combined load conditions,the rock bolt capacity decreased significantly for both regimes.However,when applying the shear load with a gap,the rock bolt load capacity was not affected significantly.Also,the total bar deformation was improved for shear and axial.The findings of this study show the need to improve the rock bolt design considering the complex loading conditions in situ with/without a gap.
文摘The capacity of ground support components which have been affected by corrosion is reduced and may ultimately lead to dynamic failure of the component and the strata. In order to maintain an effective,long-term ground support system, significant campaigns of rehabilitation are often required in corrosion affected areas which also expose the workers to hazardous conditions. The most common corrosion protection for steel ground support utilises sacrificial systems such as galvanising. Galvanising has previously been proven to be susceptible to some corrosion processes. Stainless steel is the most effective in resistance to corrosion, but can be cost prohibitive, and its mechanical properties often make it unsuited to use in ground support components. Providing an outer protective plastic coating to bolts has proven to be an effective means of protecting the inner steel bar from corrosion. However, these support systems tend to be susceptible to coating damage, and require post cement grouting to provide full encapsulation. In comparison to a standard bolt/resin system, they can be slow to install and expensive.These systems have also been shown to reduce overall load transfer performance of the bolting system. In order to provide a higher level of corrosion protection whilst maintaining current installation practices and bolting cycle times, Minova has developed the Enduro^(TM)steel ground support range. The Enduro^(TM) range consists of standard Minova steel ground support components which have been treated with a unique coating process. The Enduro^(TM)coating has been tested in the harshest of conditions, in laboratory controlled conditions and in underground trials. It has been proven to effectively resist or completely eliminate the formation of corrosion, even in the most aggressive environments. This paper explains the process and provides the details of the laboratory and underground corrosion performance testing carried out on Enduro^(TM)ground support products.
文摘Coal burst represented a major hazard for some U.S. mining operations. This paper provides an historical review of the coal burst hazards,identifies the fundamental geological factors associated with these events,and discusses mechanisms that can be used to avoid their occurrences. Coal burst are not common in most underground mines. Their occurrence almost always has such dramatic consequences to a mining operation that changes in practice are required. Fundamental factors influencing coal burst events include strong strata,abnormal strata caving,elevated stresses,critical size pillars and the lack of sufficiently sized barrier pillars during extraction. These factors interact to produce excessive stress,seismic shock and loss of confinement mechanisms. Over the 90 years of dealing with these hazards,many novel prevention controls have been developed including novel mine designs and extraction sequences,most of which are site specific in their application. Without an accurate assessment of the fundamental factors that influence coal burst and knowledge of their mechanisms of occurrence,control techniques may be misapplied and risk inadequately mitigated.
文摘Stillwater Mining Company is the only U.S. producer of platinum group metals （PGMs） and the largest producer outside of South Afiica and Russia. The company controls a considerable portion of the J-M reef and is currently developing the ＂Blitz Project,＂ which will provide a main haulage level, ore pass systems, backfill plants, and fiow-through ventilation to increase production and ensure sustainable extraction of this critical strategic mineral. While driving two sub-parallel footwall laterals 8125 m in length, one of the development drifts experienced a massive fall in a geologically disturbed area created by a mafic dike intrusion. Combinations of a void fill material （Tekseal）, polyurethane injection, fore poling coupled with steel arches, and supplemental bolting allow safe and efficient advance through this geologically dis- turbed zone. This paper presents the details of this project.
文摘Broken and jointed ground is extremely hazardous and requires unique stabilization techniques to protect workers and critical entries.Bolting techniques,even the most advanced pre-load to create roof compression,can leave large gaps of unconfined and separated roof.This roof can also be susceptible to water inflows which only exacerbate the support problem.These types of conditions existed on long-term development main entry accessing several future longwall panels.The geotechnical assessment identified well defined jointing systems that also permitted water to flow between the roof separations,which"lubricated"the roof material and minimized any frictional advantages.Chemical injections of polyurethane materials,Minova Carbopur WS,was placed beyond the bolted horizon to move the water to the rib lines and reinforce the fractured and broken roof.The injection materials permitted the effective use of bolting patterns and helped ensure long-term stability of critical entries.The paper describes the evaluation techniques,design patterns,basis for chemical selection and application,and results and recommendations.
文摘The tensile and shear strength of intrinsic bolting support systems has always been a major concern of designers. A comprehensive laboratory testing program was designed to evaluate the tensile and shear strength of individual wires and completely wound PC-strand cables. PC-strand cables with smooth wires and the recent anchorage enhancement innovation of indentation were evaluated and compared. The testing protocol detailed in ISO Standard 15630 utilizes a mandrel system that was investigated at 3different diameters which alters the wire to mandrel ratio from 2:1 to 9:1. The results demonstrate that the difference between smooth and indented wires is statistically insignificant when larger diameter mandrels are used,and that indentation does not adversely affect strand properties and performance.Insight into the shearing mechanism and evaluation techniques are discussed with the introduction of triaxial loading to describe the PC-strand tensile and shearing mechanisms. Another important result indicates that the shear strength of PC-strand cable bolting systems has a greater shear strength value than traditional steel bar bolting systems.
文摘Impact drop tests are routinely used to examine the dynamic performance of rockbolts.Numerous impact tests have been carried out in the past decades on independently designed,constructed and operated testing rigs.Each laboratory has developed testing procedures;thus,the results are often reported in different ways by various laboratories.The inconsistency in testing procedures and reporting formats presents a challenge when comparing results from different laboratories.A series of impact tests of identical rockbolts was carried out using the direct impact method(i.e.the mass free-fall method)on the rigs in four laboratories in different countries.The purpose of these tests was to investigate the level of consistency in the results from the four rigs.Each rig demonstrated a high level of repeatability,but differences existed between the various rigs.The differences would suggest that there is noticeable equipment-dependent bias when test results obtained from different laboratories are compared.It was also observed that the energy dissipated for the plastic displacement of the bolt was smaller than the impact energy in the tests.The average impact load(AIL)and the ultimate plastic displacement(D)of the bolt describe the ultimate dynamic performance of the bolt.In the case where the bolt does not rupture,the specific plastic energy(SPE)is an appropriate parameter in describing the impact performance of the bolt.Two other relevant parameters are the first peak load(FPL)and the initial stiffness(K)of the bolt sample.The information from this test series will guide the formulation of standardised testing procedures for dynamic impact tests of rockbolts.
文摘Fiber-reinforced spayed concrete has been used for several years in civil and tunneling operations.Research conducted to reduce cure times and increase compressive and flexural strengths resulted in the development of Tekcrete Fast~, a cementitious product capable of obtaining 41 MPa compressive strength and 8 MPa flexural strength in only 3 h and reaching 7 d strengths of 62 and 11.7 MPa, respectively.A single bag product that uses conventional shotcrete and gunite application systems makes it a natural crossover product for mining applications.The discovery of incredible adhesion properties and high resistance to chloride permeability helps ensure long-term stability and increases the ease of application.Project results from Disaster City~ in Texas and the application for rehabilitating a coal mine belt entry are presented.The case study illustrates the effectiveness of the product in stabilizing a coal mine beltway and adjacent cross-cuts that were subjected to progressive sloughage due to humidity and cyclical loading.
