This study aims to determine if large-scale choked panel destress blasting can provide sufficient beneficial stress reduction in highly-stressed remnant ore pillar that is planned for production. The orebody is divide...This study aims to determine if large-scale choked panel destress blasting can provide sufficient beneficial stress reduction in highly-stressed remnant ore pillar that is planned for production. The orebody is divided into 20 stopes over 2 levels, and 2 panels are choke-blasted in the hanging wall to shield the ore pillar by creating a stress shadow around it. A linear-elastic model of the mining system is constructed with finite difference code FLAC3 D. The effect of destress blasting in the panels is simulated by applying a fragmentation factor(α) to the rock mass stiffness and a stress reduction factor(β) to the current state of stress in the region occupied by the destress panels. As an extreme case, the destress panel is also modeled as a void to obtain the maximum possible beneficial effects of destressing and stress shadow.Four stopes are mined in the stress shadow of the panels in 6 lifts and then backfilled. The effect of destress blasting on the remnant ore pillar is quantified based on stress change and brittle shear ratio(BSR) in the stress shadow zone compared to the base case without destress blasting. To establish realistic rock fragmentation and stress reduction factors, model results are compared to measured stress changes reported for case studies at Fraser and Brunswick mines. A 1.5 MPa immediate stress decrease was observed 20 m away from the panel at Fraser Mine, and a 4 MPa immediate stress decrease was observed 25 m away at Brunswick Mine. Comparable results are obtained from the current model with a rock fragmentation factor α of 0.2 and a stress reduction factor α of 0.8. It is shown that a destress blasting with these parameters reduces the major principal stress in the nearest stopes by 10-25 MPa.This yields an immediate reduction of BSR, which is deemed sufficient to reduce volume of ore at risk in the pillar.展开更多
Induced seismicity is strongly related to various engineering projects that cause anthropogenic in-situ stress change at a great depth.Hence,there is a need to estimate and mitigate the associated risks.In the past,va...Induced seismicity is strongly related to various engineering projects that cause anthropogenic in-situ stress change at a great depth.Hence,there is a need to estimate and mitigate the associated risks.In the past,various simulation methods have been developed and applied to induced seismicity analysis,but there is still a fundamental diference between simulation results and feld observations in terms of the spatial distribution of seismic events and its frequency.The present study aims to develop a method to simulate spatially distributed on-fault seismicity whilst reproducing a complex stress state in the fault zone.Hence,an equivalent continuum model is constructed,based on a discrete fracture network within a fault damage zone,by employing the crack tensor theory.A fault core is simulated at the center of the model as a discontinuous plane.Using the model,a heterogeneous stress state with stress anomalies in the fault zone is frst simulated by applying tractions on the model outer boundaries.Subsequently,the efective normal stress on the fault plane is decreased in a stepwise manner to induce slip.The simulation result is validated in terms of the b-value and other seismic source parameters,hence demonstrating that the model can reproduce spatially and temporally distributed on-fault seismicity.Further analysis on the parameters shows the variation of frequency-magnitude distribution before the occurrence of large seismic events.This variation is found to be consistent with feld observations,thus suggesting the potential use of this simulation method in evaluating the risk for seismic hazards in various engineering projects.展开更多
Thermal shocking effect occurs when the coalbed methane(CBM)reservoirs meet liquid nitrogen(LN2)of extremely low temperature.In this study,3D via X-ray microcomputer tomography(μCT)and scanning electron microscope(SE...Thermal shocking effect occurs when the coalbed methane(CBM)reservoirs meet liquid nitrogen(LN2)of extremely low temperature.In this study,3D via X-ray microcomputer tomography(μCT)and scanning electron microscope(SEM)are employed to visualize and quantify morphological evolution characteristics of fractures in coal after LN2 thermal shocking treatments.LN2 thermal shocking leads to a denser fracture network than its original state with coal porosity growth rate increasing up to 183.3%.The surface porosity of theμCT scanned layers inside the coal specimen is influenced by LN2 thermal shocking which rises from 18.76%to 215.11%,illustrating the deformation heterogeneity of coal after LN2 thermal shocking.The cracking effect of LN2 thermal shocking on the surface of low porosity is generally more effective than that of high surface porosity,indicating the applicability of LN2 thermal shocking on low-permeability CBM reservoir stimulation.The characteristics of SEM scanned coal matrix in the coal powder and the coal block after the LN2 thermal shocking presented a large amount of deep and shallow progressive scratch layers,fracture variation diversity(i.e.extension,propagation,connectivity,irregularity)on the surface of the coal block and these were the main reasons leading to the decrease of the uniaxial compressive strength of the coal specimen.展开更多
One of the most serious mining disasters in underground mines is rockburst phenomena.They can lead to injuries and even fatalities as well as damage to underground openings and mining equipment.This has forced many re...One of the most serious mining disasters in underground mines is rockburst phenomena.They can lead to injuries and even fatalities as well as damage to underground openings and mining equipment.This has forced many researchers to investigate alternative methods to predict the potential for rockburst occurrence.However,due to the highly complex relation between geological,mechanical and geometric parameters of the mining environment,the traditional mechanics-based prediction methods do not always yield precise results.With the emergence of machine learning methods,a breakthrough in the prediction of rockburst occurrence has become possible in recent years.This paper presents a state-ofthe-art review of various applications of machine learning methods for the prediction of rockburst potential.First,existing rockburst prediction methods are introduced,and the limitations of such methods are highlighted.A brief overview of typical machine learning methods and their main features as predictive tools is then presented.The current applications of machine learning models in rockburst prediction are surveyed,with related mechanisms,technical details and performance analysis.展开更多
The geotechnical slope design of an open pit wall starts at the bench scale configuration.At this scale,the rock slope stability is governed primarily by the geological discontinuities within the rock mass and as a re...The geotechnical slope design of an open pit wall starts at the bench scale configuration.At this scale,the rock slope stability is governed primarily by the geological discontinuities within the rock mass and as a result,structurally-controlled failures(e.g.planar,wedge or toppling)are most likely to occur.The probabilistic approach offers a major advantage over the traditional deterministic method in that it accounts for the different degrees of variability and uncertainty often encountered in rock properties.This paper presents a bench slope stability assessment for an open pit mine in Peru using a probabilistic-based approach by coupling a kinematic analysis based on stereographic projection techniques followed by a kinetic analysis by means of the limit equilibrium method.Finally,these two probabilities are combined to provide an overall measure of the probability of failure(PoF)of the bench slope system.The case study is characterized by significant scatter in the geometrical and mechanical properties of the joints.Extensive surface mapping was conducted at 36 different sites following the ISRM suggested procedures.Several direct shear tests were carried out.It is shown that by combining field and laboratory measurements and engineering judgment,the probability density functions(PDF)of the discontinuity parameters can be obtained.These are then used in a Monte Carlo simulation process to compute both kinematic and kinetic probabilities of failure.The overall probability of failure aims to provide the design engineer with a tool to critically evaluate the bench performance from a geotechnical risk perspective and to provide a basis for future bench design optimization.展开更多
This paper examines the stability condition of a jointed rock slope in the south western region of Saudi Arabia using deterministic and probabilistic approaches,under both dry and wet conditions.The study area is char...This paper examines the stability condition of a jointed rock slope in the south western region of Saudi Arabia using deterministic and probabilistic approaches,under both dry and wet conditions.The study area is characterized by complex geology in rugged terrains.The stability analysis is carried out using the code FLAC3D to generate a 3-dimensional,ubiquitous joint model,to determine the influence of the dominant,unfavourable discontinuity orientation with respect to the slope face.The deterministic analysis is first implemented using the mean values of the selected random variables,namely the dip,dip direction and friction angle of the dominant discontinuity set,and the stability condition is assessed with a factor of safety based on the classical frictional joint constitutive model.A Box-Behnken design(BBD)approach is then adopted to create the surface response function as a second order polynomial for the factor of safety.To do so,fifteen FLAC3D models are generated in accordance with the BBD.Based on this,10,000 simulations of different slope realizations are carried out using Monte-Carlo simulation technique,and the probability of unsatisfactory of performance of the rock slope is assessed.It is shown that the probabilistic approach provides more insight and confidence in the stability condition of the rock slope,both under dry and steady state heavy rainfall conditions.A discussion is presented on the significance of accepting lower safety factors when heavy rainfall conditions are encountered.展开更多
Destress blasting is a rockburst control technique where highly stressed rock is blasted to reduce the local stress and stiffness of the rock,thereby reducing its burst proneness.The technique is commonly practiced in...Destress blasting is a rockburst control technique where highly stressed rock is blasted to reduce the local stress and stiffness of the rock,thereby reducing its burst proneness.The technique is commonly practiced in deep hard rock mines in burst prone developments,as well as in sill or crown pillars which become burst-prone as the orebody is extracted.Large-scale destressing is a variant of destress blasting where panels are created parallel to the orebody strike with a longhole,fanning blast pattern from cross cut drifts situated in the host rock.The aim of panel destressing is to reduce the stress concentration in the ore blocks or pillars to be mined.This paper focuses on the large-scale destress blasting program conducted at Vale's Copper Cliff Mine(CCM)in Ontario,Canada.The merits of panel destressing are examined through field measurements of mining induced stress changes in the pillar.The destressing mechanism is simulated with a rock fragmentation factor(a)and stress reduction/dissipation factor(b).A 3D model is built and validated with measured induced stress changes.It is shown that the best correlation between the numerical model and field measurements is obtained when the combination of a and b indicates that the blast causes high fragmentation(a=0.05)and high stress release(b=0.95)in the destress panel.It is demonstrated that the burst proneness of the ore blocks in the panel stress shadow is reduced in terms of the brittle shear ratio(BSR)and the burst potential index(BPI).展开更多
Coal seam gas content is frequently measured in quantity during underground coal mining operation and coalbed methane(CBM)exploration as a significant basic parameter.Due to the calculation error of lost gas and resid...Coal seam gas content is frequently measured in quantity during underground coal mining operation and coalbed methane(CBM)exploration as a significant basic parameter.Due to the calculation error of lost gas and residual gas in the direct method,the efficiency and accuracy of the current methods are not inadequate to the large area multi-point measurement of coal seam gas content.This paper firstly deduces a simplified theoretical dynamic model for calculating lost gas based on gas dynamic diffusion theory.Secondly,the effects of various factors on gas dynamic diffusion from coal particle are experimentally studied.And sampling procedure of representative coal particle is improved.Thirdly,a new estimation method of residual gas content based on excess adsorption and competitive adsorption theory is proposed.The results showed that the maximum error of calculating the losing gas content by using the new simplified model is only 4%.Considering the influence of particle size on gas diffusion law,the particle size of the collected coal sample is below 0.25 mm,which improves the measurement speed and reflects the safety representativeness of the sample.The determination time of gas content reduced from 36 to 3 h/piece.Moreover,the absolute error is 0.15–0.50 m^3/t,and the relative error is within 5%.A new engineering method for determining the coal seam gas content is developed according to the above research.展开更多
The paper presents the influence of varying immediate roof thickness on the lower strong roof strata movement and failure pattern in longwall coal mining with large mining height. The investigation is based on 58 geol...The paper presents the influence of varying immediate roof thickness on the lower strong roof strata movement and failure pattern in longwall coal mining with large mining height. The investigation is based on 58 geological drill holes and hydraulic shield pressure measurements around the longwall Panel 42105 of the Buertai Mine in Inner Mongolia Autonomous Region, China. The longwall Panel 42105 is characterized by relatively soft immediate roof strata of varying thickness superposed by strong strata,herein defined as lower strong roof. A voussoir beam model is adopted to interpret the structural movement of the lower strong roof strata and shield pressure measurements. It is shown that when the immediate roof is relatively thick, the broken overlying lower strong roof tends to form a stable voussoir beam with previously broken layer, thus not exerting high pressure on the hydraulic shield and working face. When the immediate roof is relatively thin, the broken overlying lower strong roof tends to behave as a cantilever beam, thus exerting higher pressure on the hydraulic shield and working face. Comparison of model predictions with measured time-weighted average shield pressure(TWAP) shows good agreement.展开更多
The stability of rock slopes is considered crucial to public safety in highways passing through rock cuts, as well as to personnel and equipment safety in open pit mines. Slope instability and failures occur due to ma...The stability of rock slopes is considered crucial to public safety in highways passing through rock cuts, as well as to personnel and equipment safety in open pit mines. Slope instability and failures occur due to many factors such as adverse slope geometries, geological discontinuities, weak or weathered slope materials as well as severe weather conditions. External loads like heavy precipitation and seismicity could play a significant role in slope failure. In this paper, several rock mass classification systems developed for rock slope stability assessment are evaluated against known rock slope conditions in a region of Saudi Arabia, where slopes located in rugged terrains with complex geometry serve as highway road cuts. Selected empirical methods have been applied to 22 rock cuts that are selected based on their failure mechanisms and slope materials. The stability conditions are identified, and the results of each rock slope classification system are compared. The paper also highlights the limitations of the empirical classification methods used in the study and proposes future research directions.展开更多
Expansive cements are powdery materials which produce expansive stresses during the moist curing process. These cements are classified as shrinkage-compensated or self-stressing cements. The shrinkage compensated is u...Expansive cements are powdery materials which produce expansive stresses during the moist curing process. These cements are classified as shrinkage-compensated or self-stressing cements. The shrinkage compensated is used in the construction industry and will not be investigated in this paper. Self-Stressing cement is widely used in the demolition & fragmentation industry and will be the main focus of this report. The objective of this paper is to discuss the relationship between Sulfate-compounds on the expansion time and degree of expansion of Betonamit expansive cement. Based on literature [1], expansion time is directly proportional to sulfate content when mixed with Portland cement. Hence, as the sulfate content of the cement mixture increases, expansion time increases. However, in this research project the effect of Portland cement was removed to further examine the effect of sulfate on Betonamit only. This phenomenon was investigated using various concentrations of 4 different Sulfate-compounds. The results proved the possibility of decreasing the expansion time of Betonamit and, quite remarkably, a much greater degree of expansion was obtained.展开更多
The method of drilling and blasting with explosives is widely used in rock fragmentation applications in the mining industry for mine development and ore production.However,the use of explosives is associated with rig...The method of drilling and blasting with explosives is widely used in rock fragmentation applications in the mining industry for mine development and ore production.However,the use of explosives is associated with rigorous safety and environmental constraints as blasting creates toxic fumes,ground vibrations,and dust.This study is focused on the use of Soundless Chemical Demolition Agents(SCDA)as a more environmentally friendly method for rock breakage and a potential replacement of explosives.In this paper,the results of a series of experimental tests are reported to identify the efect of SCDA on hard rock breakage under no load and under uniaxial loading conditions.Stanstead granite prismatic specimens of 152.4 mm(6″)×152.4–203.2 mm(6–8″)×406.4 mm(16″)are used to test the infuence of borehole size on the time to fracturing with SCDA borehole size of 25.4 mm(1″),31.75 mm(1.25″)and 38.1 mm(1.5″).It is shown that the fracturing time decreases with increasing borehole size.It is also shown that specimens subjected to uniaxial compression of 5 MPa fracture as early as 7 h after SCDA mixing.A borehole spacing to borehole diameter ratio of 12.8 to 14.6 is suggested for practical applications.展开更多
基金financially supported by a joint grant from MITACS Canada and Vale Canada Ltd
文摘This study aims to determine if large-scale choked panel destress blasting can provide sufficient beneficial stress reduction in highly-stressed remnant ore pillar that is planned for production. The orebody is divided into 20 stopes over 2 levels, and 2 panels are choke-blasted in the hanging wall to shield the ore pillar by creating a stress shadow around it. A linear-elastic model of the mining system is constructed with finite difference code FLAC3 D. The effect of destress blasting in the panels is simulated by applying a fragmentation factor(α) to the rock mass stiffness and a stress reduction factor(β) to the current state of stress in the region occupied by the destress panels. As an extreme case, the destress panel is also modeled as a void to obtain the maximum possible beneficial effects of destressing and stress shadow.Four stopes are mined in the stress shadow of the panels in 6 lifts and then backfilled. The effect of destress blasting on the remnant ore pillar is quantified based on stress change and brittle shear ratio(BSR) in the stress shadow zone compared to the base case without destress blasting. To establish realistic rock fragmentation and stress reduction factors, model results are compared to measured stress changes reported for case studies at Fraser and Brunswick mines. A 1.5 MPa immediate stress decrease was observed 20 m away from the panel at Fraser Mine, and a 4 MPa immediate stress decrease was observed 25 m away at Brunswick Mine. Comparable results are obtained from the current model with a rock fragmentation factor α of 0.2 and a stress reduction factor α of 0.8. It is shown that a destress blasting with these parameters reduces the major principal stress in the nearest stopes by 10-25 MPa.This yields an immediate reduction of BSR, which is deemed sufficient to reduce volume of ore at risk in the pillar.
文摘Induced seismicity is strongly related to various engineering projects that cause anthropogenic in-situ stress change at a great depth.Hence,there is a need to estimate and mitigate the associated risks.In the past,various simulation methods have been developed and applied to induced seismicity analysis,but there is still a fundamental diference between simulation results and feld observations in terms of the spatial distribution of seismic events and its frequency.The present study aims to develop a method to simulate spatially distributed on-fault seismicity whilst reproducing a complex stress state in the fault zone.Hence,an equivalent continuum model is constructed,based on a discrete fracture network within a fault damage zone,by employing the crack tensor theory.A fault core is simulated at the center of the model as a discontinuous plane.Using the model,a heterogeneous stress state with stress anomalies in the fault zone is frst simulated by applying tractions on the model outer boundaries.Subsequently,the efective normal stress on the fault plane is decreased in a stepwise manner to induce slip.The simulation result is validated in terms of the b-value and other seismic source parameters,hence demonstrating that the model can reproduce spatially and temporally distributed on-fault seismicity.Further analysis on the parameters shows the variation of frequency-magnitude distribution before the occurrence of large seismic events.This variation is found to be consistent with feld observations,thus suggesting the potential use of this simulation method in evaluating the risk for seismic hazards in various engineering projects.
基金Project(2017XKQY012)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Thermal shocking effect occurs when the coalbed methane(CBM)reservoirs meet liquid nitrogen(LN2)of extremely low temperature.In this study,3D via X-ray microcomputer tomography(μCT)and scanning electron microscope(SEM)are employed to visualize and quantify morphological evolution characteristics of fractures in coal after LN2 thermal shocking treatments.LN2 thermal shocking leads to a denser fracture network than its original state with coal porosity growth rate increasing up to 183.3%.The surface porosity of theμCT scanned layers inside the coal specimen is influenced by LN2 thermal shocking which rises from 18.76%to 215.11%,illustrating the deformation heterogeneity of coal after LN2 thermal shocking.The cracking effect of LN2 thermal shocking on the surface of low porosity is generally more effective than that of high surface porosity,indicating the applicability of LN2 thermal shocking on low-permeability CBM reservoir stimulation.The characteristics of SEM scanned coal matrix in the coal powder and the coal block after the LN2 thermal shocking presented a large amount of deep and shallow progressive scratch layers,fracture variation diversity(i.e.extension,propagation,connectivity,irregularity)on the surface of the coal block and these were the main reasons leading to the decrease of the uniaxial compressive strength of the coal specimen.
文摘One of the most serious mining disasters in underground mines is rockburst phenomena.They can lead to injuries and even fatalities as well as damage to underground openings and mining equipment.This has forced many researchers to investigate alternative methods to predict the potential for rockburst occurrence.However,due to the highly complex relation between geological,mechanical and geometric parameters of the mining environment,the traditional mechanics-based prediction methods do not always yield precise results.With the emergence of machine learning methods,a breakthrough in the prediction of rockburst occurrence has become possible in recent years.This paper presents a state-ofthe-art review of various applications of machine learning methods for the prediction of rockburst potential.First,existing rockburst prediction methods are introduced,and the limitations of such methods are highlighted.A brief overview of typical machine learning methods and their main features as predictive tools is then presented.The current applications of machine learning models in rockburst prediction are surveyed,with related mechanisms,technical details and performance analysis.
基金supported by a scholarship from the Peruvian Institute of Mining Engineers
文摘The geotechnical slope design of an open pit wall starts at the bench scale configuration.At this scale,the rock slope stability is governed primarily by the geological discontinuities within the rock mass and as a result,structurally-controlled failures(e.g.planar,wedge or toppling)are most likely to occur.The probabilistic approach offers a major advantage over the traditional deterministic method in that it accounts for the different degrees of variability and uncertainty often encountered in rock properties.This paper presents a bench slope stability assessment for an open pit mine in Peru using a probabilistic-based approach by coupling a kinematic analysis based on stereographic projection techniques followed by a kinetic analysis by means of the limit equilibrium method.Finally,these two probabilities are combined to provide an overall measure of the probability of failure(PoF)of the bench slope system.The case study is characterized by significant scatter in the geometrical and mechanical properties of the joints.Extensive surface mapping was conducted at 36 different sites following the ISRM suggested procedures.Several direct shear tests were carried out.It is shown that by combining field and laboratory measurements and engineering judgment,the probability density functions(PDF)of the discontinuity parameters can be obtained.These are then used in a Monte Carlo simulation process to compute both kinematic and kinetic probabilities of failure.The overall probability of failure aims to provide the design engineer with a tool to critically evaluate the bench performance from a geotechnical risk perspective and to provide a basis for future bench design optimization.
基金financially supported by the Saudi Geological Survey through a doctoral fellowship at McGill University
文摘This paper examines the stability condition of a jointed rock slope in the south western region of Saudi Arabia using deterministic and probabilistic approaches,under both dry and wet conditions.The study area is characterized by complex geology in rugged terrains.The stability analysis is carried out using the code FLAC3D to generate a 3-dimensional,ubiquitous joint model,to determine the influence of the dominant,unfavourable discontinuity orientation with respect to the slope face.The deterministic analysis is first implemented using the mean values of the selected random variables,namely the dip,dip direction and friction angle of the dominant discontinuity set,and the stability condition is assessed with a factor of safety based on the classical frictional joint constitutive model.A Box-Behnken design(BBD)approach is then adopted to create the surface response function as a second order polynomial for the factor of safety.To do so,fifteen FLAC3D models are generated in accordance with the BBD.Based on this,10,000 simulations of different slope realizations are carried out using Monte-Carlo simulation technique,and the probability of unsatisfactory of performance of the rock slope is assessed.It is shown that the probabilistic approach provides more insight and confidence in the stability condition of the rock slope,both under dry and steady state heavy rainfall conditions.A discussion is presented on the significance of accepting lower safety factors when heavy rainfall conditions are encountered.
基金This work is financially supported by a joint grant from MITACS Canada and Vale Canada Ltdthe MEDA fellowship program of the McGill faculty of Engineering.
文摘Destress blasting is a rockburst control technique where highly stressed rock is blasted to reduce the local stress and stiffness of the rock,thereby reducing its burst proneness.The technique is commonly practiced in deep hard rock mines in burst prone developments,as well as in sill or crown pillars which become burst-prone as the orebody is extracted.Large-scale destressing is a variant of destress blasting where panels are created parallel to the orebody strike with a longhole,fanning blast pattern from cross cut drifts situated in the host rock.The aim of panel destressing is to reduce the stress concentration in the ore blocks or pillars to be mined.This paper focuses on the large-scale destress blasting program conducted at Vale's Copper Cliff Mine(CCM)in Ontario,Canada.The merits of panel destressing are examined through field measurements of mining induced stress changes in the pillar.The destressing mechanism is simulated with a rock fragmentation factor(a)and stress reduction/dissipation factor(b).A 3D model is built and validated with measured induced stress changes.It is shown that the best correlation between the numerical model and field measurements is obtained when the combination of a and b indicates that the blast causes high fragmentation(a=0.05)and high stress release(b=0.95)in the destress panel.It is demonstrated that the burst proneness of the ore blocks in the panel stress shadow is reduced in terms of the brittle shear ratio(BSR)and the burst potential index(BPI).
基金the National Natural Science Foundation of China(51774119,51374095,and 51604092)the primary research projects of critical scientific research in Henan Colleges and Universities(19zx003)+1 种基金Program for Innovative Research Team in University of Ministry of Education of China(IRT_16R22)State Key Laboratory Cultivation Base for Gas Geology and Gas Control(Henan Polytechnic University)(WS2018A02)。
文摘Coal seam gas content is frequently measured in quantity during underground coal mining operation and coalbed methane(CBM)exploration as a significant basic parameter.Due to the calculation error of lost gas and residual gas in the direct method,the efficiency and accuracy of the current methods are not inadequate to the large area multi-point measurement of coal seam gas content.This paper firstly deduces a simplified theoretical dynamic model for calculating lost gas based on gas dynamic diffusion theory.Secondly,the effects of various factors on gas dynamic diffusion from coal particle are experimentally studied.And sampling procedure of representative coal particle is improved.Thirdly,a new estimation method of residual gas content based on excess adsorption and competitive adsorption theory is proposed.The results showed that the maximum error of calculating the losing gas content by using the new simplified model is only 4%.Considering the influence of particle size on gas diffusion law,the particle size of the collected coal sample is below 0.25 mm,which improves the measurement speed and reflects the safety representativeness of the sample.The determination time of gas content reduced from 36 to 3 h/piece.Moreover,the absolute error is 0.15–0.50 m^3/t,and the relative error is within 5%.A new engineering method for determining the coal seam gas content is developed according to the above research.
基金the fund supported by the National Natural Science Foundation of China(Grant No.U1261207)
文摘The paper presents the influence of varying immediate roof thickness on the lower strong roof strata movement and failure pattern in longwall coal mining with large mining height. The investigation is based on 58 geological drill holes and hydraulic shield pressure measurements around the longwall Panel 42105 of the Buertai Mine in Inner Mongolia Autonomous Region, China. The longwall Panel 42105 is characterized by relatively soft immediate roof strata of varying thickness superposed by strong strata,herein defined as lower strong roof. A voussoir beam model is adopted to interpret the structural movement of the lower strong roof strata and shield pressure measurements. It is shown that when the immediate roof is relatively thick, the broken overlying lower strong roof tends to form a stable voussoir beam with previously broken layer, thus not exerting high pressure on the hydraulic shield and working face. When the immediate roof is relatively thin, the broken overlying lower strong roof tends to behave as a cantilever beam, thus exerting higher pressure on the hydraulic shield and working face. Comparison of model predictions with measured time-weighted average shield pressure(TWAP) shows good agreement.
基金financially supported by the Saudi Geological Survey through a doctoral fellowship at McGill University
文摘The stability of rock slopes is considered crucial to public safety in highways passing through rock cuts, as well as to personnel and equipment safety in open pit mines. Slope instability and failures occur due to many factors such as adverse slope geometries, geological discontinuities, weak or weathered slope materials as well as severe weather conditions. External loads like heavy precipitation and seismicity could play a significant role in slope failure. In this paper, several rock mass classification systems developed for rock slope stability assessment are evaluated against known rock slope conditions in a region of Saudi Arabia, where slopes located in rugged terrains with complex geometry serve as highway road cuts. Selected empirical methods have been applied to 22 rock cuts that are selected based on their failure mechanisms and slope materials. The stability conditions are identified, and the results of each rock slope classification system are compared. The paper also highlights the limitations of the empirical classification methods used in the study and proposes future research directions.
文摘Expansive cements are powdery materials which produce expansive stresses during the moist curing process. These cements are classified as shrinkage-compensated or self-stressing cements. The shrinkage compensated is used in the construction industry and will not be investigated in this paper. Self-Stressing cement is widely used in the demolition & fragmentation industry and will be the main focus of this report. The objective of this paper is to discuss the relationship between Sulfate-compounds on the expansion time and degree of expansion of Betonamit expansive cement. Based on literature [1], expansion time is directly proportional to sulfate content when mixed with Portland cement. Hence, as the sulfate content of the cement mixture increases, expansion time increases. However, in this research project the effect of Portland cement was removed to further examine the effect of sulfate on Betonamit only. This phenomenon was investigated using various concentrations of 4 different Sulfate-compounds. The results proved the possibility of decreasing the expansion time of Betonamit and, quite remarkably, a much greater degree of expansion was obtained.
基金supported by a research grant from Natural Resources Canada,Clean Growth Program,Grant No.CGP-17-1003 and industry partner Newmont Corporation。
文摘The method of drilling and blasting with explosives is widely used in rock fragmentation applications in the mining industry for mine development and ore production.However,the use of explosives is associated with rigorous safety and environmental constraints as blasting creates toxic fumes,ground vibrations,and dust.This study is focused on the use of Soundless Chemical Demolition Agents(SCDA)as a more environmentally friendly method for rock breakage and a potential replacement of explosives.In this paper,the results of a series of experimental tests are reported to identify the efect of SCDA on hard rock breakage under no load and under uniaxial loading conditions.Stanstead granite prismatic specimens of 152.4 mm(6″)×152.4–203.2 mm(6–8″)×406.4 mm(16″)are used to test the infuence of borehole size on the time to fracturing with SCDA borehole size of 25.4 mm(1″),31.75 mm(1.25″)and 38.1 mm(1.5″).It is shown that the fracturing time decreases with increasing borehole size.It is also shown that specimens subjected to uniaxial compression of 5 MPa fracture as early as 7 h after SCDA mixing.A borehole spacing to borehole diameter ratio of 12.8 to 14.6 is suggested for practical applications.
