With the depletion of easily minable coal seams,less favorable reserves under adverse conditions have to be mined out to meet the market demand.Due to some historical reasons,large amount of remnant coal was left unre...With the depletion of easily minable coal seams,less favorable reserves under adverse conditions have to be mined out to meet the market demand.Due to some historical reasons,large amount of remnant coal was left unrecovered.One such case history occurred with the remnant rectangular stripe coal pillars using partial extraction method at Guandi Mine,Shanxi Province,China.The challenge that the coal mine was facing was that there is an ultra-close coal seam right under it with an only 0.8–1.5 m sandstone dirt band in between.The simulation study was carried out to investigate the simultaneous recovery of upper remnant coal pillars while mining the ultra-close lower panel using longwall top coal caving(LTCC).The remnant coal pillar was induced to cave in as top coal in LTCC system.Physical modelling shows that the coal pillars are the abutments of the stress arch structure formed within the overburden strata.The stability of overhanging roof strata highly depends on the stability of the remnant coal pillars.And the gob development(roof strata cave-in)is intermittent with the cave-in of these coal pillars and the sandstone dirt band.FLAC3D numerical modelling shows that the multi-seam interaction has a significant influence on mining-induced stress environment for mining of lower panels.The pattern of the stress evolution on the coal pillars with the advance of the lower working face was found.It is demonstrated that the stress relief of a remnant coal pillar enhances the caveability of the pillars and sandstone dirt band below.展开更多
A roadway within ultra-close multiple-seams(RUCMSs) is one of the most difficult supported coal roadways to deal with in underground coal mines. This is usually due to the unknown stress distributions, improper roadwa...A roadway within ultra-close multiple-seams(RUCMSs) is one of the most difficult supported coal roadways to deal with in underground coal mines. This is usually due to the unknown stress distributions, improper roadway layout, and unreasonable support parameters. In order to solve this support problem and effectively save RUCMSs from frequent and abrupt disasters(such as serious deformation of the surrounding rock, roof cave ins, and coal side collapse), a comprehensive method is adopted here which includes theoretical analysis, numerical simulation, and field monitoring. A mechanical model was constructed to determine the stress distribution in the coal pillar after two sides of a longwall panel had been mined. Based on this model, the horizontal, vertical, and tangential stress equations for the plane below the floor of the upper-left coal pillar were deduced. In addition, a typical coal mine(the Jinggonger colliery, located in Shuozhou city, Shanxi province, China) with an average distance between its 9# and 11# coal seams of less than 8.0 was chosen to conduct research on the proper layout and reasonable support required for a typical coal roadway located within coal seam 11#. Using FLAC3D(Fast Lagrangian Analysis of Continua in 3-Dimensions) numerical software, eight schemes were designed with different horizontal distances(d) between the center lines of the coal pillar and the roadway in the lower coal seam(RLCS). The simulations and detailed analysis indicate that the proper distances required are between 22.5 and 27.5 m. A total of 20 simulation schemes were used to investigate the factors influencing the support provided by the key bolts(bolt length, spacing, distance between two rows, installation angle, and pre-tightening force). The results were analyzed and used to determine reasonable values for the support parameters. Field results show that the stability and strength of the RLCS can be effectively safeguarded using a combination of researched stress distribution characteristics, proper layout of the RLCS, and correct support parameters.展开更多
The roof of a roadway under goaf with ultra-close separation consists of thin rock strata and rocks caving in upper goaf. Influenced by the mining of the upper coal seam, the roof is loose and broken, and its integrit...The roof of a roadway under goaf with ultra-close separation consists of thin rock strata and rocks caving in upper goaf. Influenced by the mining of the upper coal seam, the roof is loose and broken, and its integrity is poor. Resin anchored bolts cannot provide an effective anchoring force in such roof conditions. By conducting free expansion tests and field pull-out tests on a hydraulic expansion bolt, this study has analyzed the influencing factors and laws of radial expansion and anchoring force changes in the rod body.This has revealed the anchoring mechanism of such bolts, and has obtained reasonable water injection pressures and suitable drilling diameters(which are 20–25 MPa and 32–35 mm respectively) for the hydraulic expansion bolt(u28 mm) used in these tests. Based on pull-out tests at different interlayer spacing, the applicability of hydraulic expansion bolts had been verified for controlling the roof of roadways under goaf with ultra-close distance. Combined with the deformation and failure characteristics of the test roadway roof, this paper proposes a united roof-control technology based on the use of hydraulic expansion bolts and advancing intubation for the roof. Engineering practice indicated that the roof of the test roadway did not generate leaking and caving phenomenon, and the amount of roof deformation was controlled to within 150 mm. Maintenance of the roadway roof has been improved significantly, which ensures safe mining in coal seams with ultra-close separation.展开更多
以风电为代表的新能源发电装机容量占比逐年增长,精确的风电功率超短期预测对提高风能利用率、助力双碳实现有重要意义。该文提出一种基于多元注意力框架与引导式监督学习的闭环风电功率超短期预测策略,从特征筛选、模型优化、策略改良...以风电为代表的新能源发电装机容量占比逐年增长,精确的风电功率超短期预测对提高风能利用率、助力双碳实现有重要意义。该文提出一种基于多元注意力框架与引导式监督学习的闭环风电功率超短期预测策略,从特征筛选、模型优化、策略改良3个角度全面提高预测准确性与模型智能性。首先,采用动态权重特征选择算法、孤立森林算法以及最邻近节点算法筛选并处理数据,便于预测模型更好把握其中特征;其次,对长短期记忆(long short term memory,LSTM)基模型多角度优化,并根据基模型中不同信息的特点,构建关于LSTM的多元注意力框架(Multielement-attention-LSTM),将此框架用于对LightGBM集成学习模型的引导,并通过多种可视化方法提高了模型可解释性;最后,将Bland-Altman应用于模型输出与实际风电出力一致性检验,在预测数据与实际数据交互的基础上实现训练–预测闭环机制。仿真结果表明,所构建的Multielement-attention-LSTM框架具有提高模型预测精度的作用,且闭环更新机制具备合理性。展开更多
基金This study was funded by the National Natural Science Foundation for Young Scientists of China(No.51804209)National Natural Science Foundation of China-Shanxi Joint Fund for Coal-Based Low-Carbon Technology(No.U1710258)Applied Basic Research Programs,Science and Technology Foundation for Youths of Shanxi Province,China(No.201801D221363).
文摘With the depletion of easily minable coal seams,less favorable reserves under adverse conditions have to be mined out to meet the market demand.Due to some historical reasons,large amount of remnant coal was left unrecovered.One such case history occurred with the remnant rectangular stripe coal pillars using partial extraction method at Guandi Mine,Shanxi Province,China.The challenge that the coal mine was facing was that there is an ultra-close coal seam right under it with an only 0.8–1.5 m sandstone dirt band in between.The simulation study was carried out to investigate the simultaneous recovery of upper remnant coal pillars while mining the ultra-close lower panel using longwall top coal caving(LTCC).The remnant coal pillar was induced to cave in as top coal in LTCC system.Physical modelling shows that the coal pillars are the abutments of the stress arch structure formed within the overburden strata.The stability of overhanging roof strata highly depends on the stability of the remnant coal pillars.And the gob development(roof strata cave-in)is intermittent with the cave-in of these coal pillars and the sandstone dirt band.FLAC3D numerical modelling shows that the multi-seam interaction has a significant influence on mining-induced stress environment for mining of lower panels.The pattern of the stress evolution on the coal pillars with the advance of the lower working face was found.It is demonstrated that the stress relief of a remnant coal pillar enhances the caveability of the pillars and sandstone dirt band below.
基金Project(2014QNA50)supported by Fundamental Research Funds for the Central UniversitiesChina+1 种基金Project(51404248)supported by National Natural Science Foundation of the Youth Science Foundation of ChinaProject(PAPD)supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘A roadway within ultra-close multiple-seams(RUCMSs) is one of the most difficult supported coal roadways to deal with in underground coal mines. This is usually due to the unknown stress distributions, improper roadway layout, and unreasonable support parameters. In order to solve this support problem and effectively save RUCMSs from frequent and abrupt disasters(such as serious deformation of the surrounding rock, roof cave ins, and coal side collapse), a comprehensive method is adopted here which includes theoretical analysis, numerical simulation, and field monitoring. A mechanical model was constructed to determine the stress distribution in the coal pillar after two sides of a longwall panel had been mined. Based on this model, the horizontal, vertical, and tangential stress equations for the plane below the floor of the upper-left coal pillar were deduced. In addition, a typical coal mine(the Jinggonger colliery, located in Shuozhou city, Shanxi province, China) with an average distance between its 9# and 11# coal seams of less than 8.0 was chosen to conduct research on the proper layout and reasonable support required for a typical coal roadway located within coal seam 11#. Using FLAC3D(Fast Lagrangian Analysis of Continua in 3-Dimensions) numerical software, eight schemes were designed with different horizontal distances(d) between the center lines of the coal pillar and the roadway in the lower coal seam(RLCS). The simulations and detailed analysis indicate that the proper distances required are between 22.5 and 27.5 m. A total of 20 simulation schemes were used to investigate the factors influencing the support provided by the key bolts(bolt length, spacing, distance between two rows, installation angle, and pre-tightening force). The results were analyzed and used to determine reasonable values for the support parameters. Field results show that the stability and strength of the RLCS can be effectively safeguarded using a combination of researched stress distribution characteristics, proper layout of the RLCS, and correct support parameters.
基金supports from the National Natural Science Foundation of China (Nos. 51204166 and 51174195)the Advantage Disciplines Construction Fund Program of Jiangsu Universities (No. SZBF2011-6-B35)
文摘The roof of a roadway under goaf with ultra-close separation consists of thin rock strata and rocks caving in upper goaf. Influenced by the mining of the upper coal seam, the roof is loose and broken, and its integrity is poor. Resin anchored bolts cannot provide an effective anchoring force in such roof conditions. By conducting free expansion tests and field pull-out tests on a hydraulic expansion bolt, this study has analyzed the influencing factors and laws of radial expansion and anchoring force changes in the rod body.This has revealed the anchoring mechanism of such bolts, and has obtained reasonable water injection pressures and suitable drilling diameters(which are 20–25 MPa and 32–35 mm respectively) for the hydraulic expansion bolt(u28 mm) used in these tests. Based on pull-out tests at different interlayer spacing, the applicability of hydraulic expansion bolts had been verified for controlling the roof of roadways under goaf with ultra-close distance. Combined with the deformation and failure characteristics of the test roadway roof, this paper proposes a united roof-control technology based on the use of hydraulic expansion bolts and advancing intubation for the roof. Engineering practice indicated that the roof of the test roadway did not generate leaking and caving phenomenon, and the amount of roof deformation was controlled to within 150 mm. Maintenance of the roadway roof has been improved significantly, which ensures safe mining in coal seams with ultra-close separation.
文摘以风电为代表的新能源发电装机容量占比逐年增长,精确的风电功率超短期预测对提高风能利用率、助力双碳实现有重要意义。该文提出一种基于多元注意力框架与引导式监督学习的闭环风电功率超短期预测策略,从特征筛选、模型优化、策略改良3个角度全面提高预测准确性与模型智能性。首先,采用动态权重特征选择算法、孤立森林算法以及最邻近节点算法筛选并处理数据,便于预测模型更好把握其中特征;其次,对长短期记忆(long short term memory,LSTM)基模型多角度优化,并根据基模型中不同信息的特点,构建关于LSTM的多元注意力框架(Multielement-attention-LSTM),将此框架用于对LightGBM集成学习模型的引导,并通过多种可视化方法提高了模型可解释性;最后,将Bland-Altman应用于模型输出与实际风电出力一致性检验,在预测数据与实际数据交互的基础上实现训练–预测闭环机制。仿真结果表明,所构建的Multielement-attention-LSTM框架具有提高模型预测精度的作用,且闭环更新机制具备合理性。
