To establish the movement relationship for the roof breaking under shallow mining conditions, the mechanical model of the roof rock beam was built, then the structure instability process of the roof rock beam was anal...To establish the movement relationship for the roof breaking under shallow mining conditions, the mechanical model of the roof rock beam was built, then the structure instability process of the roof rock beam was analyzed. The changing criterion of the vertical displacement was established and the relationship between the deflection and the rotary motion of roof block was determined. Regarding a mining face in Shangwan Mine, the responsing laws of the deflection and horizontal thrust of the roof rock beam were obtained through FLAC3D numerical analysis. The results show that the structure instability of the cracked roof rock beam depends on the interaction between the vertical load and the horizontal thrust.For the roof rock beam, when the vertical load keeps constant, the horizontal thrust fluctuating rises with increasing deflection. The horizontal thrust increases constantly with the deeper buried depth and the smaller span.展开更多
With the excavation of underground opening,the roof rock block may fall under external dynamic disturbance.In this paper,the roof rock mass was simplified as a rock block system composed of trapezoidal rock blocks.A s...With the excavation of underground opening,the roof rock block may fall under external dynamic disturbance.In this paper,the roof rock mass was simplified as a rock block system composed of trapezoidal rock blocks.A series of experiments and numerical simulations were performed to study the sliding process of the key block under the horizontal static clamping load and vertical impact disturbance.The propagation of stress wave in the block system were captured and analyzed by using high-speed camera and digital image correlation technique.The results reveal that a pendulum-type wave was generated due to the propagation and superposition of stress waves in the block system.Therefore,the governing mechanism of the sliding displacement of the key block was clarified based on the propagation of incident stress waves or pendulum-type waves.Meanwhile,it is found that the sliding distance of the key block decreases in a power function with the increasing friction coefficient,or decreases in a parabolic function with the increasing trapezoid internal angle.Finally,a case study on the roof block sliding of the roadway at a gold mine was conducted,and it is concluded that the sliding of the key block resulted from the coupled effects of"shear driving"and"low friction"driven by stress wave propagation,regardless of a single or multi-layer rock block system.These results may provide technical guideline for preventing rock-falling accidents caused by blasting distur-bances in underground mining.展开更多
In order to reveal the dynamic process of hard-thick roof inducing rock burst, one of the most common and strongest dynamic disasters in coal mine, the numerical simulation is conducted to study the dynamic loading ef...In order to reveal the dynamic process of hard-thick roof inducing rock burst, one of the most common and strongest dynamic disasters in coal mine, the numerical simulation is conducted to study the dynamic loading effect of roof vibration on roadway surrounding rocks as well as the impact on stability. The results show that, on one hand, hard-thick roof will result in high stress concentration on mining surrounding rocks; on the other hand, the breaking of hard-thick roof will lead to mining seismicity, causing dynamic loading effect on coal and rock mass. High stress concentration and dynamic loading combination reaches to the mechanical conditions for the occurrence of rock burst, which will induce rock burst. The mining induced seismic events occurring in the roof breaking act on the mining surrounding rocks in the form of stress wave. The stress wave then has a reflection on the free surface of roadway and the tensile stress will be generated around the free surface. Horizontal vibration of roadway surrounding particles will cause instant changes of horizontal stress of roadway surrounding rocks; the horizontal displacement is directly related to the horizontal stress but is not significantly correlated with the vertical stress; the increase of horizontal stress of roadway near surface surrounding rocks and the release of elastic deformation energy of deep surrounding coal and rock mass are immanent causes that lead to the impact instability of roadway surrounding rocks. The most significant measures for rock burst prevention are controlling of horizontal stress and vibration strength.展开更多
Despite recent advances in mine health and safety, roof collapse and instabilities are still the leading causes of injury and fatality in underground mining operations. Improving safety and optimum design of ground su...Despite recent advances in mine health and safety, roof collapse and instabilities are still the leading causes of injury and fatality in underground mining operations. Improving safety and optimum design of ground support requires good and reliable ground characterization. While many geophysical methods have been developed for ground characterizations, their accuracy is insufficient for customized ground support design of underground workings. The actual measurements on the samples of the roof and wall strata from the exploration boring are reliable but the related holes are far apart, thus unsuitable for design purposes. The best source of information could be the geological back mapping of the roof and walls, but this is disruptive to mining operations, and provided information is only from rock surface.Interpretation of the data obtained from roof bolt drilling can offer a good and reliable source of information that can be used for ground characterization and ground support design and evaluations. This paper offers a brief review of the mine roof characterization methods, followed by introduction and discussion of the roof characterization methods by instrumented roof bolters. A brief overview of the results of the preliminary study and initial testing on an instrumented drill and summary of the suggested improvements are also discussed.展开更多
Based on the research on rock burst phenomenon induced by the breakage of thick and hard roof around roadways and working faces in coal mines,a criterion of rock burst induced by roof breakage(RBRB) was proposed and t...Based on the research on rock burst phenomenon induced by the breakage of thick and hard roof around roadways and working faces in coal mines,a criterion of rock burst induced by roof breakage(RBRB) was proposed and the model was built.Through the model.a method calculating the varied stresses induced by roof breakage in support objects and coal body was proposed and a unified formula was derived for the calculation of stress increment on support objects and coal body under different breaking forms of roof.Whilst the formula for calculating dynamic load was derived by introducing dynamic index Kd.The formula was verified in Huating Mine by stress measurement.According to the formula for stress increment calculating,the sensitivities of dynamic load parameters were further studied.The results show that the thickness and breaking depth of roof,width of support object are the sensitive factors.Based on the discussion of the model,six associated effective methods for rock burst prevention are obtained.展开更多
Described the outcomes of a comprehensive numerical modeling on the rock bolting performance for preventing the deformation of stratified, composite roof structure of drift in a coal mine. The investigation was undert...Described the outcomes of a comprehensive numerical modeling on the rock bolting performance for preventing the deformation of stratified, composite roof structure of drift in a coal mine. The investigation was undertaken in the adverse geological condi- tions, with variation of bolt parameters, including length, density, distribution, pretension, as well as the geometry of opening,so as to determine the effect of bolting parameter variation on roof deformation and stability. The outcomes clearly demonstrated that a sig- nificant improvement of roof stability can be achieved associating with bolting parameters optimization, and indicated the importance of flexible geotechnical designation of rock bolting reinforcement in mining practice.展开更多
The damage process of fractured rock mass showed that the fracture in rocks induced roof collapse in Yangchangwan Coal Mine, China. The rock mass was particularly weak and fractured. There occurred 6 large-scale dynam...The damage process of fractured rock mass showed that the fracture in rocks induced roof collapse in Yangchangwan Coal Mine, China. The rock mass was particularly weak and fractured. There occurred 6 large-scale dynamical roof falls in the excavation disturbed zone (EDZ) with the collapsing volume of 216 m^3. First, the field detailed geological environment, regional seismic dynamics, and dynamic instability of roadways were generally investigated. Second, the field multiple-index monitoring measurements for detecting the deep delamination of the roof, convergence deformation, bolt-cable load, acoustic emission (AE) characteristic parameters, total AE events, AE energy-releasing rate, rock mass fracture, and damage were arranged. Finally, according to the time-space-strength relations, a quantitative assessment of the influence of rock-mass damage on the dynamic roof instability was accomplished.展开更多
Based on the developing degree of structure planes in coal roof, whole, blocky and heavily fractured structure models are built up. Through simulation test of similar materials, the distribution of deformation, failur...Based on the developing degree of structure planes in coal roof, whole, blocky and heavily fractured structure models are built up. Through simulation test of similar materials, the distribution of deformation, failure and underground pressure induced by coal mining in coal roof with different rock mass structures are analyzed. The test results indicate that the distances of first and periodic weighting of main roof and the height of caving and fracture zone decrease with the increment of fractures in roof rock mass. From whole to blocky and heavily fractured structures, abutment pressure ahead of working face reduces and the peak value of abutment pressure migrates to inside of roof rock mass.展开更多
The effective reinforcement of two or more overlying layers of mine openings in a single installation is usually done by coupling of two standard rock bolts mainly during the extraction of medium-thick coal seams.Howe...The effective reinforcement of two or more overlying layers of mine openings in a single installation is usually done by coupling of two standard rock bolts mainly during the extraction of medium-thick coal seams.However,field observations show that the couplers of multiple bolts often degrade or break mostly at their connections.These types of failures can be avoided by strengthening the couplers of such multi-bolts assemblies.To achieve this,a novel threaded coupler system with an expansion shell was suggested in this paper.The newly designed coupler consists of a threaded tapered-plug-cumconnector with an expansion shell for connecting and tightening two standard rock bolts.An analytical model for evaluating the load distribution along the coupler subject to axial load was derived.Numerical analysis was performed to analyse the load transfer,deformation,and strains across the coupler including the factor of safety for the bolt-coupler-resin and bolt-coupler-expansion shell.The results validated the analytical model of the proposed coupler design,which provides better anchorage near the interface of the host rock mass.Thus,the developed coupler design would reduce the failures of the proposed coupler and stabilize laminated roof strata above the medium-thick coal seams in underground mines.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 51474188, 51074140, and 51774112)the Natural Science Foundation of Hebei Province of China (No. E2014203012)+4 种基金the International Cooperation Project of Henan Science and Technology Department (No. 182102410060)International Cooperative Talent Project of Henan Province (No. 2016GH22)the Doctoral Fund of Henan Polytechnic University of China (No. B2015-67)the Research Fund of State and Local Joint Engineering Laboratory for Gas Drainage & Ground Control of Deep Mines (Henan Polytechnic niversity)of China (No. G201614)Taihang Scholars Program
文摘To establish the movement relationship for the roof breaking under shallow mining conditions, the mechanical model of the roof rock beam was built, then the structure instability process of the roof rock beam was analyzed. The changing criterion of the vertical displacement was established and the relationship between the deflection and the rotary motion of roof block was determined. Regarding a mining face in Shangwan Mine, the responsing laws of the deflection and horizontal thrust of the roof rock beam were obtained through FLAC3D numerical analysis. The results show that the structure instability of the cracked roof rock beam depends on the interaction between the vertical load and the horizontal thrust.For the roof rock beam, when the vertical load keeps constant, the horizontal thrust fluctuating rises with increasing deflection. The horizontal thrust increases constantly with the deeper buried depth and the smaller span.
基金supported by National Natural Science Foundation of China(Grant Nos.U1906208,51874069,51904056)Liaoning Revitalization Talents Program,China(Grant No.XLYC1802031)+1 种基金Fundamental Research Funds for the Central Universities,China(Grant Nos.N180115009,N2101028)China Postdoctoral Science Foundation(Grant No.2020M670782).
文摘With the excavation of underground opening,the roof rock block may fall under external dynamic disturbance.In this paper,the roof rock mass was simplified as a rock block system composed of trapezoidal rock blocks.A series of experiments and numerical simulations were performed to study the sliding process of the key block under the horizontal static clamping load and vertical impact disturbance.The propagation of stress wave in the block system were captured and analyzed by using high-speed camera and digital image correlation technique.The results reveal that a pendulum-type wave was generated due to the propagation and superposition of stress waves in the block system.Therefore,the governing mechanism of the sliding displacement of the key block was clarified based on the propagation of incident stress waves or pendulum-type waves.Meanwhile,it is found that the sliding distance of the key block decreases in a power function with the increasing friction coefficient,or decreases in a parabolic function with the increasing trapezoid internal angle.Finally,a case study on the roof block sliding of the roadway at a gold mine was conducted,and it is concluded that the sliding of the key block resulted from the coupled effects of"shear driving"and"low friction"driven by stress wave propagation,regardless of a single or multi-layer rock block system.These results may provide technical guideline for preventing rock-falling accidents caused by blasting distur-bances in underground mining.
基金Project(51404243)supported by the National Natural Science Foundation of ChinaProject(2014QNB26)supported by the Fundamental Research Funds for the Central Universities,China
文摘In order to reveal the dynamic process of hard-thick roof inducing rock burst, one of the most common and strongest dynamic disasters in coal mine, the numerical simulation is conducted to study the dynamic loading effect of roof vibration on roadway surrounding rocks as well as the impact on stability. The results show that, on one hand, hard-thick roof will result in high stress concentration on mining surrounding rocks; on the other hand, the breaking of hard-thick roof will lead to mining seismicity, causing dynamic loading effect on coal and rock mass. High stress concentration and dynamic loading combination reaches to the mechanical conditions for the occurrence of rock burst, which will induce rock burst. The mining induced seismic events occurring in the roof breaking act on the mining surrounding rocks in the form of stress wave. The stress wave then has a reflection on the free surface of roadway and the tensile stress will be generated around the free surface. Horizontal vibration of roadway surrounding particles will cause instant changes of horizontal stress of roadway surrounding rocks; the horizontal displacement is directly related to the horizontal stress but is not significantly correlated with the vertical stress; the increase of horizontal stress of roadway near surface surrounding rocks and the release of elastic deformation energy of deep surrounding coal and rock mass are immanent causes that lead to the impact instability of roadway surrounding rocks. The most significant measures for rock burst prevention are controlling of horizontal stress and vibration strength.
基金supported by the funding of the National Institute for Occupational Safety and Health under a contract with the Pennsylvania State University as part of the capacity building in ground supportthe funding from TüBITAK of Turkey has been used to support the sabbatical leave of Dr.Kahraman who made some contributions to this study
文摘Despite recent advances in mine health and safety, roof collapse and instabilities are still the leading causes of injury and fatality in underground mining operations. Improving safety and optimum design of ground support requires good and reliable ground characterization. While many geophysical methods have been developed for ground characterizations, their accuracy is insufficient for customized ground support design of underground workings. The actual measurements on the samples of the roof and wall strata from the exploration boring are reliable but the related holes are far apart, thus unsuitable for design purposes. The best source of information could be the geological back mapping of the roof and walls, but this is disruptive to mining operations, and provided information is only from rock surface.Interpretation of the data obtained from roof bolt drilling can offer a good and reliable source of information that can be used for ground characterization and ground support design and evaluations. This paper offers a brief review of the mine roof characterization methods, followed by introduction and discussion of the roof characterization methods by instrumented roof bolters. A brief overview of the results of the preliminary study and initial testing on an instrumented drill and summary of the suggested improvements are also discussed.
基金Project(2010CB226805) supported by the National Basic Research Program of ChinaProjects(30370412,30670558) supported by the National Natural Science Foundation of ChinaProject(SKLCRSM10X05) supported by the Self-research Program of the Key Laboratory of Coal Resources and Safe Mining,China
文摘Based on the research on rock burst phenomenon induced by the breakage of thick and hard roof around roadways and working faces in coal mines,a criterion of rock burst induced by roof breakage(RBRB) was proposed and the model was built.Through the model.a method calculating the varied stresses induced by roof breakage in support objects and coal body was proposed and a unified formula was derived for the calculation of stress increment on support objects and coal body under different breaking forms of roof.Whilst the formula for calculating dynamic load was derived by introducing dynamic index Kd.The formula was verified in Huating Mine by stress measurement.According to the formula for stress increment calculating,the sensitivities of dynamic load parameters were further studied.The results show that the thickness and breaking depth of roof,width of support object are the sensitive factors.Based on the discussion of the model,six associated effective methods for rock burst prevention are obtained.
文摘Described the outcomes of a comprehensive numerical modeling on the rock bolting performance for preventing the deformation of stratified, composite roof structure of drift in a coal mine. The investigation was undertaken in the adverse geological condi- tions, with variation of bolt parameters, including length, density, distribution, pretension, as well as the geometry of opening,so as to determine the effect of bolting parameter variation on roof deformation and stability. The outcomes clearly demonstrated that a sig- nificant improvement of roof stability can be achieved associating with bolting parameters optimization, and indicated the importance of flexible geotechnical designation of rock bolting reinforcement in mining practice.
基金supported by the National Natural Science Foundation of China (No.10402033 and No.10772144)
文摘The damage process of fractured rock mass showed that the fracture in rocks induced roof collapse in Yangchangwan Coal Mine, China. The rock mass was particularly weak and fractured. There occurred 6 large-scale dynamical roof falls in the excavation disturbed zone (EDZ) with the collapsing volume of 216 m^3. First, the field detailed geological environment, regional seismic dynamics, and dynamic instability of roadways were generally investigated. Second, the field multiple-index monitoring measurements for detecting the deep delamination of the roof, convergence deformation, bolt-cable load, acoustic emission (AE) characteristic parameters, total AE events, AE energy-releasing rate, rock mass fracture, and damage were arranged. Finally, according to the time-space-strength relations, a quantitative assessment of the influence of rock-mass damage on the dynamic roof instability was accomplished.
基金Supported by the National Natural Science Foundation of China(5 97740 0 3 and 49872 0 5 3 )
文摘Based on the developing degree of structure planes in coal roof, whole, blocky and heavily fractured structure models are built up. Through simulation test of similar materials, the distribution of deformation, failure and underground pressure induced by coal mining in coal roof with different rock mass structures are analyzed. The test results indicate that the distances of first and periodic weighting of main roof and the height of caving and fracture zone decrease with the increment of fractures in roof rock mass. From whole to blocky and heavily fractured structures, abutment pressure ahead of working face reduces and the peak value of abutment pressure migrates to inside of roof rock mass.
文摘The effective reinforcement of two or more overlying layers of mine openings in a single installation is usually done by coupling of two standard rock bolts mainly during the extraction of medium-thick coal seams.However,field observations show that the couplers of multiple bolts often degrade or break mostly at their connections.These types of failures can be avoided by strengthening the couplers of such multi-bolts assemblies.To achieve this,a novel threaded coupler system with an expansion shell was suggested in this paper.The newly designed coupler consists of a threaded tapered-plug-cumconnector with an expansion shell for connecting and tightening two standard rock bolts.An analytical model for evaluating the load distribution along the coupler subject to axial load was derived.Numerical analysis was performed to analyse the load transfer,deformation,and strains across the coupler including the factor of safety for the bolt-coupler-resin and bolt-coupler-expansion shell.The results validated the analytical model of the proposed coupler design,which provides better anchorage near the interface of the host rock mass.Thus,the developed coupler design would reduce the failures of the proposed coupler and stabilize laminated roof strata above the medium-thick coal seams in underground mines.