It is arguable that the development of reinforcing roof bolting systems has largely stagnated in recent times, primarily due to the prevailing industry view that few, if any, further improvements can be made to what c...It is arguable that the development of reinforcing roof bolting systems has largely stagnated in recent times, primarily due to the prevailing industry view that few, if any, further improvements can be made to what currently exists.However, this paper contends that reinforcing roof bolting systems can be further refined by considering both the specific manner by which horizontally bedded roof strata loses its natural self-supporting ability and the specific means by which reinforcing roof bolts act to promote or retain this natural self-supporting ability.The Australian coal industry has insisted on minimising bolt-hole diameter to maximise load transfer and on targeting full-encapsulation by any means necessary for many years.This has led to a significant, albeit unintended, consequence in terms of overall roof bolting effectiveness, namely increased resin pressures during bolt installation and the associated potential for opening bedding planes that may have, otherwise, remained closed during the bolt installation process.Given that the natural self-supporting ability of roof strata is strongly linked to whether bedding planes are open or closed, logically, minimising resin pressures should be a significant benefit.This paper focuses primarily on three key issues that relate directly to the function of the roof bolting system itself:(1) the importance of proper resin mixing in the context of maximising load transfer strength and stiffness,(2) the importance of minimising resin pressures developed during bolt installation, and(3) the importance of maximising the effectiveness of the available bolt pre-tension.All mine operators should be invested in improving the individual effectiveness of each installed roof bolt, even by relatively small incremental amounts, so this is an important topic for discussion within the mining community.展开更多
In the past decades,the intense excavation of coal resources in China has induced a series of severe waterrelated disasters or problems,such as water burst accidents,severe groundwater depletion and contamination.All ...In the past decades,the intense excavation of coal resources in China has induced a series of severe waterrelated disasters or problems,such as water burst accidents,severe groundwater depletion and contamination.All of these problems were caused by the structural changes of roof rocks or bed rocks induced by coal excavation.The structure of collapsed roof rocks is generally classified into three zones：falling zone.展开更多
Broken coal structure and low permeability are the main reasons for the difficult production of coalbed methane(CBM)in broken-soft coal seams.In this paper,No.8 coal seam in the Luling Mine of the Huaibei Coal Field w...Broken coal structure and low permeability are the main reasons for the difficult production of coalbed methane(CBM)in broken-soft coal seams.In this paper,No.8 coal seam in the Luling Mine of the Huaibei Coal Field was taken as an example to study the way to improve CBM production of broken-soft coal reservoirs.First,drilling,fracturing and production of horizontal wells were considered comprehensively.Then,based on the idea of exploiting CBM through horizontal wells in roof strata close to the broken-soft coal seams,the propagation laws of fractures created by layer-penetrating fracturing of horizontal wells in roof strata were studied,and accordingly the location of horizontal well was optimized.Finally,the CBM horizontal well exploitation technology for the roof strata close to coal seams was developed and tested on site.And the following research results were obtained.First,the vertical fractures created during layer-penetrating fracturing of horizontal wells in roof strata can propagate from the roof strata with high stress values downward to the coal seam with low stress values.In addition,the location of horizontal well has an important influence on the effect of layer-penetrating fracturing.The closer the horizontal well is to the coal seam,the better the fracture propagation effect of layer-penetrating fracturing.Second,the horizontal well should be arranged in the roof strata 1.5 m away from the top of coal seam,so that fracturing stimulation requirements of horizontal wells in roof strata can be satisfied to the uttermost.Third,three key technologies are formed,including the“high-quality,fast and safe”drilling technology,the deep-penetration oriented perforating technology and the“large displacement,large scale,high pad ratio and moderate proppant concentration”active water fracturing technology.Fourth,the gas production with this technology in engineering practice is remarkable.In conclusion,the CBM development technology of horizontal wells in roof strata close to broken-soft coal seams is feasible.The research results provide a new technical method for the development of CBM in broken-soft coal seams.展开更多
A water-resistant key strata model of a goaf floor prior to main roof weighting was developed to explore the relationship between water inrush from the floor and main roof weighting. The stress distribution,broken cha...A water-resistant key strata model of a goaf floor prior to main roof weighting was developed to explore the relationship between water inrush from the floor and main roof weighting. The stress distribution,broken characteristics, and the risk area for water inrush of the water-resistant key strata were analysed using elastic thin plate theory. The formula of the maximum water pressure tolerated by the waterresistant key strata was deduced. The effects of the caved load of the goaf, the goaf size prior to main roof weighting, the advancing distance of the workface or weighting step, and the thickness of the waterresistant key strata on the breaking and instability of the water-resistant key strata were analysed.The results indicate that the water inrush from the floor can be predicted and prevented by controlling the initial or periodic weighting step with measures such as artificial forced caving, thus achieving safe mining conditions above confined aquifers. The findings provide an important theoretical basis for determining water inrush from the floor when mining above confined aquifers.展开更多
To reduce the cost of backfilling coal mining and utilize the underground space of coal mines,a new backfilling mining method with low backfilling rate called constructional backfilling coal mining(CBCM)is proposed.Th...To reduce the cost of backfilling coal mining and utilize the underground space of coal mines,a new backfilling mining method with low backfilling rate called constructional backfilling coal mining(CBCM)is proposed.The "backfilling body-immediate roof" cooperative bearing structure of CBCM is analyzed by establishing the model of the medium thick plate on an elastic foundation.The influence of the backfilling rate on the stability of overlying strata is analyzed by the numerical simulation experiment.The control effect of CBCM is verified by a physic similar simulation test.The economic benefit of CBCM is analyzed.The conclusions are:the deformation characteristics of the immediate roof and critical backfilling spacing in CBCM can be analyzed based on the Hu Haichang’s theory.Exerting the bearing capacity of the immediate roof is beneficial to the stability of the overlying strata.The CBCM has a good control effect on the overburden in Xinyang Mine when the backfilling rate is lower than 25%.The backfilling cost of per ton coal is 37.39 yuan/t when the backfilling rate is 13.7%,with a decrease rate of 56.63%than the full-filling.The research results can provide theoretical support for the application of CBCM in coal mining.展开更多
This paper analyzed the deformation mechanism in lateral roof roadway of the Ding Wu-3 roadway which was disturbed by repeated mining of close coal seams Wu-8 and Wu-10 in Pingdingshan No. 1 Mine. To determine the str...This paper analyzed the deformation mechanism in lateral roof roadway of the Ding Wu-3 roadway which was disturbed by repeated mining of close coal seams Wu-8 and Wu-10 in Pingdingshan No. 1 Mine. To determine the strata disturbance scope, the strata displacement angle was used to calculate the protection pillar width. A numerical model was built considering the field geological conditions. In simulation, the mining stress borderline was defined as the contour where the induced stress is 1.5 times of the original stress. Simulation results show the mining stress borderline of the lateral roadway extended 91.7 m outward after repeated mining. Then the original stress increased, deforming the road- way of interest. This deformation agreed with the in situ observations. Moreover, the strata displacement angle changed due to repeated mining. Therefore, reselection of the displacement angle was required to design the protective pillar width. Since a constant strata displacement angle was used in traditional design, the orooosed method was beneficial in field cases.展开更多
文摘It is arguable that the development of reinforcing roof bolting systems has largely stagnated in recent times, primarily due to the prevailing industry view that few, if any, further improvements can be made to what currently exists.However, this paper contends that reinforcing roof bolting systems can be further refined by considering both the specific manner by which horizontally bedded roof strata loses its natural self-supporting ability and the specific means by which reinforcing roof bolts act to promote or retain this natural self-supporting ability.The Australian coal industry has insisted on minimising bolt-hole diameter to maximise load transfer and on targeting full-encapsulation by any means necessary for many years.This has led to a significant, albeit unintended, consequence in terms of overall roof bolting effectiveness, namely increased resin pressures during bolt installation and the associated potential for opening bedding planes that may have, otherwise, remained closed during the bolt installation process.Given that the natural self-supporting ability of roof strata is strongly linked to whether bedding planes are open or closed, logically, minimising resin pressures should be a significant benefit.This paper focuses primarily on three key issues that relate directly to the function of the roof bolting system itself:(1) the importance of proper resin mixing in the context of maximising load transfer strength and stiffness,(2) the importance of minimising resin pressures developed during bolt installation, and(3) the importance of maximising the effectiveness of the available bolt pre-tension.All mine operators should be invested in improving the individual effectiveness of each installed roof bolt, even by relatively small incremental amounts, so this is an important topic for discussion within the mining community.
文摘In the past decades,the intense excavation of coal resources in China has induced a series of severe waterrelated disasters or problems,such as water burst accidents,severe groundwater depletion and contamination.All of these problems were caused by the structural changes of roof rocks or bed rocks induced by coal excavation.The structure of collapsed roof rocks is generally classified into three zones：falling zone.
基金supported by National Natural Science Foundation of China“Propagation mechanism and morphology control of fractures created by layer-penetrating fracturing of horizontal wells in roof strata in broken-soft coal seams”(No.:51874349)National Major Science and Technology Project“Development of large-scale oil/gas fields and coalbed methane”(No.:2016ZX05045002-004).
文摘Broken coal structure and low permeability are the main reasons for the difficult production of coalbed methane(CBM)in broken-soft coal seams.In this paper,No.8 coal seam in the Luling Mine of the Huaibei Coal Field was taken as an example to study the way to improve CBM production of broken-soft coal reservoirs.First,drilling,fracturing and production of horizontal wells were considered comprehensively.Then,based on the idea of exploiting CBM through horizontal wells in roof strata close to the broken-soft coal seams,the propagation laws of fractures created by layer-penetrating fracturing of horizontal wells in roof strata were studied,and accordingly the location of horizontal well was optimized.Finally,the CBM horizontal well exploitation technology for the roof strata close to coal seams was developed and tested on site.And the following research results were obtained.First,the vertical fractures created during layer-penetrating fracturing of horizontal wells in roof strata can propagate from the roof strata with high stress values downward to the coal seam with low stress values.In addition,the location of horizontal well has an important influence on the effect of layer-penetrating fracturing.The closer the horizontal well is to the coal seam,the better the fracture propagation effect of layer-penetrating fracturing.Second,the horizontal well should be arranged in the roof strata 1.5 m away from the top of coal seam,so that fracturing stimulation requirements of horizontal wells in roof strata can be satisfied to the uttermost.Third,three key technologies are formed,including the“high-quality,fast and safe”drilling technology,the deep-penetration oriented perforating technology and the“large displacement,large scale,high pad ratio and moderate proppant concentration”active water fracturing technology.Fourth,the gas production with this technology in engineering practice is remarkable.In conclusion,the CBM development technology of horizontal wells in roof strata close to broken-soft coal seams is feasible.The research results provide a new technical method for the development of CBM in broken-soft coal seams.
基金supported by the National Natural Science Foundation of China (Nos. 51404013 and 51674008)the Open Projects of State Key Laboratory of Coal Resources and Safe Mining at the China University of Mining and Technology (No. 13KF01)the Natural Science Foundation of Anhui Province (Nos. 1508085ME77 and 1508085QE89)
文摘A water-resistant key strata model of a goaf floor prior to main roof weighting was developed to explore the relationship between water inrush from the floor and main roof weighting. The stress distribution,broken characteristics, and the risk area for water inrush of the water-resistant key strata were analysed using elastic thin plate theory. The formula of the maximum water pressure tolerated by the waterresistant key strata was deduced. The effects of the caved load of the goaf, the goaf size prior to main roof weighting, the advancing distance of the workface or weighting step, and the thickness of the waterresistant key strata on the breaking and instability of the water-resistant key strata were analysed.The results indicate that the water inrush from the floor can be predicted and prevented by controlling the initial or periodic weighting step with measures such as artificial forced caving, thus achieving safe mining conditions above confined aquifers. The findings provide an important theoretical basis for determining water inrush from the floor when mining above confined aquifers.
基金supported by the Youth Funds of National Natural Science Foundation of China(No.52004173)the Distinguished Youth Funds of National Natural Science Foundation of China(No.51925402)+2 种基金the Science and Technology Innovation Project of Colleges and Universities in Shanxi Province(No.2020L0066)the China Postdoctoral Science Foundation(No.2022M712922)the Shanxi-Zheda Institute of Advanced Materials and Chemical Engineering(Nos.2021SX-TD001 and 2022SXTD008).
文摘To reduce the cost of backfilling coal mining and utilize the underground space of coal mines,a new backfilling mining method with low backfilling rate called constructional backfilling coal mining(CBCM)is proposed.The "backfilling body-immediate roof" cooperative bearing structure of CBCM is analyzed by establishing the model of the medium thick plate on an elastic foundation.The influence of the backfilling rate on the stability of overlying strata is analyzed by the numerical simulation experiment.The control effect of CBCM is verified by a physic similar simulation test.The economic benefit of CBCM is analyzed.The conclusions are:the deformation characteristics of the immediate roof and critical backfilling spacing in CBCM can be analyzed based on the Hu Haichang’s theory.Exerting the bearing capacity of the immediate roof is beneficial to the stability of the overlying strata.The CBCM has a good control effect on the overburden in Xinyang Mine when the backfilling rate is lower than 25%.The backfilling cost of per ton coal is 37.39 yuan/t when the backfilling rate is 13.7%,with a decrease rate of 56.63%than the full-filling.The research results can provide theoretical support for the application of CBCM in coal mining.
基金Financial supports from the National Natural Science Foundation of China (No. 51204160)the Priority Academic Program Development of Jiangsu Higher Education Institutions of China(No.SZBF2011-6-B35)+1 种基金the National Science and Technology Support Program of China(No.2012BAK04B06)the Project Funded by State Key Laboratory of Coal Resources and Safe Mining of China(No.SKLCRSM11X03)
文摘This paper analyzed the deformation mechanism in lateral roof roadway of the Ding Wu-3 roadway which was disturbed by repeated mining of close coal seams Wu-8 and Wu-10 in Pingdingshan No. 1 Mine. To determine the strata disturbance scope, the strata displacement angle was used to calculate the protection pillar width. A numerical model was built considering the field geological conditions. In simulation, the mining stress borderline was defined as the contour where the induced stress is 1.5 times of the original stress. Simulation results show the mining stress borderline of the lateral roadway extended 91.7 m outward after repeated mining. Then the original stress increased, deforming the road- way of interest. This deformation agreed with the in situ observations. Moreover, the strata displacement angle changed due to repeated mining. Therefore, reselection of the displacement angle was required to design the protective pillar width. Since a constant strata displacement angle was used in traditional design, the orooosed method was beneficial in field cases.
