Coalbed methane(CBM)is a significant factor in triggering coal and gas outburst disaster,while also serving as a clean fuel.With the increasing depth of mining operations,coal seams that exhibit high levels of gas con...Coalbed methane(CBM)is a significant factor in triggering coal and gas outburst disaster,while also serving as a clean fuel.With the increasing depth of mining operations,coal seams that exhibit high levels of gas content and low permeability have become increasingly prevalent.While controllable shockwave(CSW)technology has proven effective in enhancing CBM in laboratory settings,there is a lack of reports on its field applications in soft and low-permeability coal seams.This study establishes the governing equations for stress waves induced by CSW.Laplace numerical inversion was employed to analyse the dynamic response of the coal seam during CSW antireflection.Additionally,quantitative calculations were performed for the crushed zone,fracture zone,and effective CSW influence range,which guided the selection of field test parameters.The results of the field test unveiled a substantial improvement in the gas permeability coefficient,the average rate of pure methane flowrate,and the mean gas flowrate within a 10 m radius of the antireflection borehole.These enhancements were notable,showing increases of 3 times,13.72 times,and 11.48 times,respectively.Furthermore,the field test performed on the CSW antireflection gas extraction hole cluster demonstrated a noticeable improvement in CBM extraction.After antireflection,the maximum peak gas concentration and maximum peak pure methane flow reached 71.2%and 2.59 m^(3)/min,respectively.These findings will offer valuable guidance for the application of CSW antireflection technology in soft and low-permeability coal seams.展开更多
The EGAT Mae Moh Mine is the largest open pit lignite mine in Thailand and it produces lignite about 16 million tons annually. In the near future, the pit limit of the mine will be reached and underground mine will th...The EGAT Mae Moh Mine is the largest open pit lignite mine in Thailand and it produces lignite about 16 million tons annually. In the near future, the pit limit of the mine will be reached and underground mine will then be developed through the open pit in the depth of 400 - 600 m from the surface. However, due to the challenges for underground mining such as poor geological conditions, extra thickness (20 - 30 m) of coal seams, and weak mechanical properties of coal seams and the surrounding rock, the success possibility of underground mining and an applicable underground mining method is being investigated at the present. The paper discusses the applicability of multi-slice bord-and-pillar method for the soft extra thick coal seams in the Mae Moh mine by means of numerical analyses using the 3D finite difference code “FLAC3D”.展开更多
Grouting is an important method to reinforce soft coal roadway,and the presence of primary cracks in the coal body has an important influence on the grouting effect.With the discrete element simulation method,the grou...Grouting is an important method to reinforce soft coal roadway,and the presence of primary cracks in the coal body has an important influence on the grouting effect.With the discrete element simulation method,the grouting process of the soft coal seam was simulated.The mechanism of primary cracks on grouting was revealed,while the influence of fracture characteristics and grouting pressure on the grouting effect was analyzed.The results demonstrated that grouting in the soft coal seam involves the stages of seepage,rapid splitting,slow splitting,and stability.Due to the presence of primary cracks,the grouting diffusion radius increased significantly.Under the slurry pressure,the tensile stress concentration was formed at the crack tip,and the slurry split the coal once the splitting pressure was reached.In addition,the distribution characteristics of fractures are found to have a great influence on the grouting effect.It is observed that smaller fracture spacing is associated with a larger slurry diffusion radius and thus easier penetration of the primary crack tips.The fracture angle affects the direction of fracture propagation.The secondary fracture formed by splitting is a tensile fracture,which is more likely to extend along the direction parallel to the maximum principal stress.Overall,these simulation results have guiding significance for the setting of reasonable spacing of grouting holes in the practice of grouting engineering.展开更多
A number of rockburst accidents occurring in soft coal seams have shown that the rockburst mechanism involved in soft coal seams is significantly different from that involved in hard coal seams. Therefore, the method ...A number of rockburst accidents occurring in soft coal seams have shown that the rockburst mechanism involved in soft coal seams is significantly different from that involved in hard coal seams. Therefore, the method used to evaluate rockburst in hard coal seams is not applicable to soft coal seams. This paper established an energy integral model for the rockburst-inducing area and a friction work calculation model for the plastic area. If the remaining energy after the coal seam is broken in the rockburstinducing area is greater than the friction work required for the coal to burst out, then a rockburst accident will occur. Mechanisms of ‘‘quaking without bursting" and ‘‘quaking and bursting" are clarified for soft coal seams and corresponding control measures are proposed as the optimization of roadway layouts and use of ‘‘three strong systems"(strong de-stressing, strong supporting, and strong monitoring).展开更多
When gob-side entry retaining is implemented in deep coal seams threatened by rockburst, the cementbased supporting body beside roadway will bear greater roof pressure and strong impact load. Then the supporting body ...When gob-side entry retaining is implemented in deep coal seams threatened by rockburst, the cementbased supporting body beside roadway will bear greater roof pressure and strong impact load. Then the supporting body may easily deform and fail because of its low strength in the early stage. This paper established the roadside support mechanical model of gob-side entry retaining. Based on this model,we proposed and used the soft–strong supporting body as roadside support in the gob-side entry retaining. In the early stage of roof movement, the soft–strong supporting body has a better compressibility, which can not only relieve roof pressure and strong impact load, but also reduce the supporting resistance and prevent the supporting body from being crushed. In the later stage, with the increase of the strength of the supporting body, it can better support the overlying roof. The numerical simulation results and industrial test show that the soft–strong supporting body as roadside support can be better applied into the gob-side entry retaining in deep coal seams threatened by rockburst.展开更多
In view of the measurement difficulties of indexes recommended by the 50Items Experience of Coal Mine Gas Prevention in the process of the nonoutburst coalseam upgrade, this paper took the No.8 coal seam of Huainan Mi...In view of the measurement difficulties of indexes recommended by the 50Items Experience of Coal Mine Gas Prevention in the process of the nonoutburst coalseam upgrade, this paper took the No.8 coal seam of Huainan Mining Group as research object. Discussed the suitability of indexes and corresponding critical values, putforward method in determining the indexes and its critical values by analysis and investigation of the gas geological condition and the-spot tracking near position where anoutburst occurred combined with laboratory experiment, and established the indexesand its critical values of nonoutburst coal seam upgrade in No.8 coal seam of HuainanMining Group. The results show that it is suitable to take gas content and tectonic softcoal thickness easily to gain in routine production as primary upgrade indexes that itscritical values are 7.5 m^3/t and 0.8 m, respectively. In addition, takefvalue and Ap valueas auxiliary indexes.展开更多
Based on a shallow roadway with weakly cemented soft strata in western China, this paper studies the range and degree of plastic zones in soft strata roadways with weak cementation. Geological radars were used to moni...Based on a shallow roadway with weakly cemented soft strata in western China, this paper studies the range and degree of plastic zones in soft strata roadways with weak cementation. Geological radars were used to monitor the loose range and level of surrounding rocks. A mechanical model of weakly cemented roadway was established, including granular material based on the measured results. The model was then used to determine the plastic zone radium. The predicted results agree well with measured results which provide valuable theoretical references for the analysis of surrounding rock stability and support reinforcing design of weakly cemented roadways. Finally, a combined supporting scheme of whole section bolting and grouting was proposed based on the original supporting scheme. It is proved that this support plan can effectively control the deformation and plastic zone expansion of the roadway surrounding rock and thus ensure the long-term stable and safe mining.展开更多
In order to study the hypotonic and rheological particularity of “three soft” coal seam in west Henan, China, this paper explored the stress and damage characteristics of crack in coal under condition of water injec...In order to study the hypotonic and rheological particularity of “three soft” coal seam in west Henan, China, this paper explored the stress and damage characteristics of crack in coal under condition of water injection fracturing based on ABAQUS platform;The cohesive element in T-P damage evolution criterion was used to describe the approximately linear relationship between crack width and extending distance in soft coal. The simulation results show that stress evolution and crack damage in soft coal is a gradually developing process under condition of water injection fracturing. When the static pressure is 4 - 10 MPa, and the injection time is about 1 - 2 hours, the damage range of crack in soft coal can basically reach an ideal data of 80 - 100 m, and then greatly improve the hypotonic performance of “three soft” coal seam.展开更多
Injecting external CO_(2) into soft and low-permeability coal seams can improve CH4 extacctinn efficiency, and also benefit in CO_(2) sequestration. However, the distribution law of damage zone around borehole in soft...Injecting external CO_(2) into soft and low-permeability coal seams can improve CH4 extacctinn efficiency, and also benefit in CO_(2) sequestration. However, the distribution law of damage zone around borehole in soft coal seam and its effect on the efficiency of CO_(2) injection promoted CH4 extraction are not clear. In this paper, a multi-physics coupling mathematical model considering damage effect is established for simulating the process of CO_(2) injection promoted CH4 extraction in soft and low-permeability coal seam. The distribution of damage zone and permeability around boreholes under different diameters and coal strengths are analyzed. The gas pressure and gas content in coal seam during CO_(2) injection promoted CH4 extraction when the model considered damage effect are compared with that of ignored. The results show that small borehole diameter corresponds to narrow damage zone around the borehole in coal seam. The damage zone expands with the increase of the borehole diameter. The damage zone increases exponentially with the borehole diameter, while decreases exponentially with the compressive strength of coal seam. The highest permeability in the damage zone has increased by nearly 300 times under the condition of simulated case. CH4 pressure around the extraction borehole reduces, and the reduction area expands with the increase of time. Compared with the result of considering the damage effect, the reduction area of ignoring it is smaller, and the reducing speed is slower. The integrated effect of CO_(2) injection and CH4 extraction leads to rapid decrease of CH4 content in coal seam near the boreholes. The CO_(2) pressure and content increase around the injection borehole, and the increasing area gradually extends to the whole coal seam. In soft coal seams, failure to consider the damage effect will underestimate the efficiency of CH4 extraction and CO_(2) sequestration, resulting conservative layout of boreholes.展开更多
基金supported by the National Natural Science Foundation of China(52074013,52374179)China Huaneng Group Science and Technology Project(HNKJ20-H87)+1 种基金Natural Science Foundation of Anhui Province(2208085ME125)Hefei Comprehensive National Science Center(21KZS216),which are gratefully appreciated.
文摘Coalbed methane(CBM)is a significant factor in triggering coal and gas outburst disaster,while also serving as a clean fuel.With the increasing depth of mining operations,coal seams that exhibit high levels of gas content and low permeability have become increasingly prevalent.While controllable shockwave(CSW)technology has proven effective in enhancing CBM in laboratory settings,there is a lack of reports on its field applications in soft and low-permeability coal seams.This study establishes the governing equations for stress waves induced by CSW.Laplace numerical inversion was employed to analyse the dynamic response of the coal seam during CSW antireflection.Additionally,quantitative calculations were performed for the crushed zone,fracture zone,and effective CSW influence range,which guided the selection of field test parameters.The results of the field test unveiled a substantial improvement in the gas permeability coefficient,the average rate of pure methane flowrate,and the mean gas flowrate within a 10 m radius of the antireflection borehole.These enhancements were notable,showing increases of 3 times,13.72 times,and 11.48 times,respectively.Furthermore,the field test performed on the CSW antireflection gas extraction hole cluster demonstrated a noticeable improvement in CBM extraction.After antireflection,the maximum peak gas concentration and maximum peak pure methane flow reached 71.2%and 2.59 m^(3)/min,respectively.These findings will offer valuable guidance for the application of CSW antireflection technology in soft and low-permeability coal seams.
文摘The EGAT Mae Moh Mine is the largest open pit lignite mine in Thailand and it produces lignite about 16 million tons annually. In the near future, the pit limit of the mine will be reached and underground mine will then be developed through the open pit in the depth of 400 - 600 m from the surface. However, due to the challenges for underground mining such as poor geological conditions, extra thickness (20 - 30 m) of coal seams, and weak mechanical properties of coal seams and the surrounding rock, the success possibility of underground mining and an applicable underground mining method is being investigated at the present. The paper discusses the applicability of multi-slice bord-and-pillar method for the soft extra thick coal seams in the Mae Moh mine by means of numerical analyses using the 3D finite difference code “FLAC3D”.
基金The authors acknowledge the financial support provided by the National Natural Science Foundation of China(No.51604094 and 51674098)the Shandong Provincial Natural Science Foundation(No.ZR2020QE118).
文摘Grouting is an important method to reinforce soft coal roadway,and the presence of primary cracks in the coal body has an important influence on the grouting effect.With the discrete element simulation method,the grouting process of the soft coal seam was simulated.The mechanism of primary cracks on grouting was revealed,while the influence of fracture characteristics and grouting pressure on the grouting effect was analyzed.The results demonstrated that grouting in the soft coal seam involves the stages of seepage,rapid splitting,slow splitting,and stability.Due to the presence of primary cracks,the grouting diffusion radius increased significantly.Under the slurry pressure,the tensile stress concentration was formed at the crack tip,and the slurry split the coal once the splitting pressure was reached.In addition,the distribution characteristics of fractures are found to have a great influence on the grouting effect.It is observed that smaller fracture spacing is associated with a larger slurry diffusion radius and thus easier penetration of the primary crack tips.The fracture angle affects the direction of fracture propagation.The secondary fracture formed by splitting is a tensile fracture,which is more likely to extend along the direction parallel to the maximum principal stress.Overall,these simulation results have guiding significance for the setting of reasonable spacing of grouting holes in the practice of grouting engineering.
基金Financial supports for this work by the National Program on Key Basic Research Project (No.210CB226800)the National Natural Science Foundation of China (Nos.51274022 and 51174016)
文摘A number of rockburst accidents occurring in soft coal seams have shown that the rockburst mechanism involved in soft coal seams is significantly different from that involved in hard coal seams. Therefore, the method used to evaluate rockburst in hard coal seams is not applicable to soft coal seams. This paper established an energy integral model for the rockburst-inducing area and a friction work calculation model for the plastic area. If the remaining energy after the coal seam is broken in the rockburstinducing area is greater than the friction work required for the coal to burst out, then a rockburst accident will occur. Mechanisms of ‘‘quaking without bursting" and ‘‘quaking and bursting" are clarified for soft coal seams and corresponding control measures are proposed as the optimization of roadway layouts and use of ‘‘three strong systems"(strong de-stressing, strong supporting, and strong monitoring).
基金supported by the National Basic Research Program of China (No. 2010CB226805)the Taishan Scholar Construction Project of Shandong Province, China+3 种基金the National Natural Science Foundation of China (No. 51344009)the Research Award Fund for Outstanding Young Scientists of Shandong Province (No. BS2012NJ007)the Ground Pressure and Strata Control Innovative Team Fund of SDUST (No. 2010KYTD105)the Natural Science Foundation of Shandong Province (No. ZR2012EEZ002)
文摘When gob-side entry retaining is implemented in deep coal seams threatened by rockburst, the cementbased supporting body beside roadway will bear greater roof pressure and strong impact load. Then the supporting body may easily deform and fail because of its low strength in the early stage. This paper established the roadside support mechanical model of gob-side entry retaining. Based on this model,we proposed and used the soft–strong supporting body as roadside support in the gob-side entry retaining. In the early stage of roof movement, the soft–strong supporting body has a better compressibility, which can not only relieve roof pressure and strong impact load, but also reduce the supporting resistance and prevent the supporting body from being crushed. In the later stage, with the increase of the strength of the supporting body, it can better support the overlying roof. The numerical simulation results and industrial test show that the soft–strong supporting body as roadside support can be better applied into the gob-side entry retaining in deep coal seams threatened by rockburst.
基金Supported by the National Key Basic Research Development Program of China (973 program) (2005CB221501)the National Key Technologies Research and Development Program of China during the Eleventh Five-Year Plan Period(2006BAK03B01)Program for Changjiang Scholars and Innovative Research Team in University(IRT0618)
文摘In view of the measurement difficulties of indexes recommended by the 50Items Experience of Coal Mine Gas Prevention in the process of the nonoutburst coalseam upgrade, this paper took the No.8 coal seam of Huainan Mining Group as research object. Discussed the suitability of indexes and corresponding critical values, putforward method in determining the indexes and its critical values by analysis and investigation of the gas geological condition and the-spot tracking near position where anoutburst occurred combined with laboratory experiment, and established the indexesand its critical values of nonoutburst coal seam upgrade in No.8 coal seam of HuainanMining Group. The results show that it is suitable to take gas content and tectonic softcoal thickness easily to gain in routine production as primary upgrade indexes that itscritical values are 7.5 m^3/t and 0.8 m, respectively. In addition, takefvalue and Ap valueas auxiliary indexes.
基金provided by the National 973 Programs(No.2014CB046905)the National Natural Science Foundation of China(Nos.51274191 and 51404245)+1 种基金the Doctoral Fund of Ministry of Education(No.20130095110018)China Postdoctoral Science Foundation(No.2014M551699)
文摘Based on a shallow roadway with weakly cemented soft strata in western China, this paper studies the range and degree of plastic zones in soft strata roadways with weak cementation. Geological radars were used to monitor the loose range and level of surrounding rocks. A mechanical model of weakly cemented roadway was established, including granular material based on the measured results. The model was then used to determine the plastic zone radium. The predicted results agree well with measured results which provide valuable theoretical references for the analysis of surrounding rock stability and support reinforcing design of weakly cemented roadways. Finally, a combined supporting scheme of whole section bolting and grouting was proposed based on the original supporting scheme. It is proved that this support plan can effectively control the deformation and plastic zone expansion of the roadway surrounding rock and thus ensure the long-term stable and safe mining.
文摘In order to study the hypotonic and rheological particularity of “three soft” coal seam in west Henan, China, this paper explored the stress and damage characteristics of crack in coal under condition of water injection fracturing based on ABAQUS platform;The cohesive element in T-P damage evolution criterion was used to describe the approximately linear relationship between crack width and extending distance in soft coal. The simulation results show that stress evolution and crack damage in soft coal is a gradually developing process under condition of water injection fracturing. When the static pressure is 4 - 10 MPa, and the injection time is about 1 - 2 hours, the damage range of crack in soft coal can basically reach an ideal data of 80 - 100 m, and then greatly improve the hypotonic performance of “three soft” coal seam.
基金the National Natural Science Foundation of China(Grant No.52104195)the Liaoning Revitalization Talents Program(No.XLYC2008021).
文摘Injecting external CO_(2) into soft and low-permeability coal seams can improve CH4 extacctinn efficiency, and also benefit in CO_(2) sequestration. However, the distribution law of damage zone around borehole in soft coal seam and its effect on the efficiency of CO_(2) injection promoted CH4 extraction are not clear. In this paper, a multi-physics coupling mathematical model considering damage effect is established for simulating the process of CO_(2) injection promoted CH4 extraction in soft and low-permeability coal seam. The distribution of damage zone and permeability around boreholes under different diameters and coal strengths are analyzed. The gas pressure and gas content in coal seam during CO_(2) injection promoted CH4 extraction when the model considered damage effect are compared with that of ignored. The results show that small borehole diameter corresponds to narrow damage zone around the borehole in coal seam. The damage zone expands with the increase of the borehole diameter. The damage zone increases exponentially with the borehole diameter, while decreases exponentially with the compressive strength of coal seam. The highest permeability in the damage zone has increased by nearly 300 times under the condition of simulated case. CH4 pressure around the extraction borehole reduces, and the reduction area expands with the increase of time. Compared with the result of considering the damage effect, the reduction area of ignoring it is smaller, and the reducing speed is slower. The integrated effect of CO_(2) injection and CH4 extraction leads to rapid decrease of CH4 content in coal seam near the boreholes. The CO_(2) pressure and content increase around the injection borehole, and the increasing area gradually extends to the whole coal seam. In soft coal seams, failure to consider the damage effect will underestimate the efficiency of CH4 extraction and CO_(2) sequestration, resulting conservative layout of boreholes.