2019 Vol. 45, No. 8

  Previous Issue | Next Issue 
Display Method:
Cover Catalogue
Mine emergency communication system
Mine emergency communication system
2019, 45(8): 1-5. doi: 10.13272/j.issn.1671-251x.17483
<Abstract>(167) <HTML> (33) <PDF>(30)
Abstract:
Feasibility of using existing mine communication system as emergency communication system was analyzed. Leakage communication system, inductive communication system, multi-base station mobile communication system, broadcast communication system and rescue communication system cannot be used as emergency communication system. Mine wired dispatching communication system can be used as mine emergency communication system. Through-the-earth communication system can be used as emergency communication system, but the accidents can cause more than 100 meters of underground transmission antenna damage and affect underground communication to the ground. A wireless relay mine emergency communication system was put forward which adopts multi-stage wireless relay and the wireless transmission distance is not less than 10 km. Backup power supply should be provided after undereground power cut or an accident. Base stations, base station power, and base station cable should be set in an electromechanical chamber or protected. Antenna feeders are buried in laneway, and use an arc or streamline structure to flattened itself against the laneway wall or roadway roof. Antenna, base station and its power supply, antenna feeder, cable, etc. are designed with waterproof, high temperature and shock resistance. Base stations adopt redundant arrangement. Mine emergency communication system based on wireless and wired dual links was put forward which has the function of automatic routing for wired and wireless lines. The wired network structure is recommended to use a structure with strong anti-fault capability, such as star network structure, double tree network structure or tree network structure. Double-tree cables or optical cables should be installed in different roadways, or different cables or optical cables should be used. Between the base station and the ground dispatching room, there is no equipment that needs to be powered. Passive optical networks should be selected for optical cables with tree or double tree network structures.
Design of data transmission system in coal mine underground based on 6LowPA
TIAN Hao, ZHAO Xiaohu, ZHANG Kai, WANG Kuan, LI Yichen
2019, 45(8): 6-12. doi: 10.13272/j.issn.1671-251x.2019040003
<Abstract>(58) <HTML> (9) <PDF>(7)
Abstract:
In view of the problems of the existing data transmission system in coal mine underground, such as limited data transmission distance, inconvenient node deployment, limited sensor address and delayed data transmission, a data transmission system in coal mine underground based on 6LowPAN was designed. The system adopts combination with Ethernet and 6LowPAN protocol, and SPI, RS485 and other interfaces are reserved in data acquisition nodes to realize sensor data acquisition. Data acquisition nodes are wireless network nodes and can effectively select appropriate routing paths through the routing system to send sensor data to the data sink nodes. Wired connections can be built between the sink nodes and the boundary routes, and data can be uploaded to the ground server via Ethernet to achieve stable and reliable data transmission. The test results show that the system is obviously superior to the traditional data transmission system in terms of transmission delay, packet loss rate and throughput, and can efficiently and reliably transmit underground data of coal mine with good real-time performance, high communication rate and stability.
Research on coal mine fusion monitoring system based on Internet of things
HE Yaoyi, WANG Haibo
2019, 45(8): 13-18. doi: 10.13272/j.issn.1671-251x.17458
<Abstract>(64) <HTML> (14) <PDF>(16)
Abstract:
According to multi-system fusion requirements of monitoring system in Technology Schemes of Upgrading of Coal Mine Safety Monitoring and Control System, a coal mine fusion monitoring system based on Internet of things was designed, and solutions for underground data fusion and ground data fusion were put forward respectively. In underground data fusion, fusion substation provides comparatively independent data acquisition channel and service processing unit for each service subsystem in a region, and sends each kind of fusion data to corresponding service subsystem. Multi-service fusion gateway dispatches multi fusion substations to realize data fusion of across-region service subsystems. In ground data fusion, multi-system fusion software platform realizes sorted data storage, analysis, mining, comprehensive utilization and integrated display. Key technologies of coal mine fusion monitoring system were researched including main data, message service bus and "one map" model display. The system can provide unified and consistent data source support for intelligent mine, so as to realize integrated fusion and emergency linkage of monitoring systems.
Intelligent prevention and control method of deep rock burst and its development path
PAN Junfeng, LIU Shaohong, MA Wentao, FENG Meihua, WANG Shuwen, GAO Jiaming
2019, 45(8): 19-24. doi: 10.13272/j.issn.1671-251x.17469
<Abstract>(74) <HTML> (13) <PDF>(13)
Abstract:
In order to solve the safety problem of deep intelligent mining and prevention and control personnel threatened by rock burst, an intelligent prevention and control method of deep rock burst was put forward. Based on the key role of foundational static load inducing rock burst initiation, theoretical basis of intelligent prevention and control of deep rock burst was proposed, which was to automatically detect the foundational static load of surrounding rock in mining space, and achieve intelligent and precise decrease of its concentration degree, so as to improve threshold of acquiring static load or dynamic load increment in later stage for achieving purpose of rock burst prevention and control. Development paths of researching intelligent prevention and control of deep rock burst in the future were put forward, which included active schedule theory and method of multi-source information of rock burst disaster, expert database of disaster prevention scheme based on multi-source information fusion, rapidly interactive and intelligent robot and informationized equipment, intelligent control of rock burst disaster and compound disaster self-adaption technology and effect self-evaluation technology of major disaster prevention and control.
Research status of early warning technology of coal and gas outburst and its development trend
NING Xiaoliang
2019, 45(8): 25-31. doi: 10.13272/j.issn.1671-251x.17464
<Abstract>(132) <HTML> (10) <PDF>(14)
Abstract:
Research achievements of early warning technology of coal and gas outburst were summarized and analyzed in detail from four aspects: early warning theory of coal and gas outburst, acquisition means of early warning information, early warning index and model and early warning software system. The main problems of existing early warning technology of coal and gas outburst were pointed out, for example, timeliness and reliability of part early warning information acquisition needed to be further improved, early models could not realize effective and deep data mining, etc. Development trend of early warning technology of coal and gas outburst was put forward, including development of early warning information monitoring and acquisition technology and equipment with high automation level and precision, research of early warning index and model based on big data, and development of early warning software system based on cloud technology.
Design of signal generator for mine-used mud pulse wireless measurement while drilling
LI Quanxin, CHU Zhiwei
2019, 45(8): 32-37. doi: 10.13272/j.issn.1671-251x.17466
<Abstract>(57) <HTML> (9) <PDF>(12)
Abstract:
For working conditions of small pump capacity and low pressure of directional drilling in coal mine underground, a mine-used mud pulse wireless measurement while drilling (MWD) device was developed, and technique requirements, structure composition and application conditions of the MWD device were analyzed. Design scheme of signal generator in the MWD device, namely signal generator for mine-used mud pulse wireless MWD, was focused on. Structure design of explosion-proof driving section and its solenoid valve in the signal generator as well as pulse generator, and design of liquid passageway control valve and its valve head parameters in the pulse generator were introduced. The field test results show that the signal generator can generate mud pressure pulse signals stably and reliably with the maximum signal transmission depth of 2 570 m and low mud pressure pulse attenuation rate of 5.8%/100 m, which has ability to apply to deeper boreholes.
Research on multi-source data fusion positioning algorithm for coal mine roadway
BAO Jianjun
2019, 45(8): 38-42. doi: 10.13272/j.issn.1671-251x.17462
<Abstract>(101) <HTML> (15) <PDF>(13)
Abstract:
In the non-line-of-sight condition of coal mine roadway, the use of time of flight(TOF) positioning algorithm or received signal strength（RSS） algorithm alone has problems such as inaccurate direction judgement and large positioning errors; TOF positioning algorithm combined with RSS positioning algorithm, although accuracy of direction judgement is improved compared with the single TOF algorithm, the judgement of tags in non-line-of-sight motion scenes is still not accurate enough, and the positioning track is not smooth enough.In view of the above problems, a multi-source data fusion positioning algorithm based on TOF, RSS and polynomial interpolation prediction(PIM) was proposed. The algorithm first measures TOF between label and positioning base station and calculates RSS, then uses PIM to fit and forecast label position at the current moment combined with historical location data, and according to the combination of predicted position, TOF and RSS, the direction of the tag relative to the base station is determined. Finally, the positioning result is optimized by weighted data fusion, so as to improve positioning stability and accuracy. The experimental results show that compared with the single TOF positioning algorithm or RSS algorithm, the proposed algorithm can effectively improve accuracy and stability of the positioning system, and can more accurately determine direction of the tag relative to the base station, and direction determination accuracy is above 99%.
Information security risk assessment of industrial Internet of coal mine
MENG Qingyong, GU Chuang
2019, 45(8): 43-47. doi: 10.13272/j.issn.1671-251x.17381
<Abstract>(179) <HTML> (12) <PDF>(19)
Abstract:
For problems that information security protection measures of industrial Internet of coal mine were mostly applied to small areas and it was difficult to assess the whole information security risk, an information security risk assessment method of industrial Internet of coal mine was proposed which was based on static and dynamic dimensions. In the method, security protection regulations carried out in coal mine information systems are feature-transformed according to Information Security Technology-baseline for Classified Protection of Cybersecurity and GB/T 34679-2017 General Technical Specifications for Smart Mine Information Systems, and a correlation coefficient matrix of security protection requirements for each system is established, so as to calculate the number of security protection regulations which are actually carried out in the system. Then, a security risk assessment model is established by combining with risk number and probability of higher risk category, so as to assess information security risk of industrial Internet of coal mine. The test result shows that the method can effectively assess information security status of industrial Internet of coal mine, and guide coal mine enterprise to analyze information security risk and design and carry out security protection plan, so as to decrease information security risk of industrial Internet of coal mine.
Research on risk assessment of coal mine safety hidden dangers
HE Qiao, XU Jin, CHEN Qing
2019, 45(8): 48-53. doi: 10.13272/j.issn.1671-251x.2018100063
<Abstract>(76) <HTML> (7) <PDF>(9)
Abstract:
The existing risk rating of coal mine safety hidden dangers is simply superposition of hidden dangers, risk evaluation of hidden dangers does not consider time factor, so it cannot achieve purpose of real-time early warning, nor reflect state of hidden dangers at different times. Moreover, risk evaluation is not closely integrated with closed-loop management process of hidden dangers identification, and it cannot reflect dynamic changes of risks. For the above problems, the life cycle of coal mine safety hidden dangers was analyzed, including its formation, development and evolved into an accident, the single hidden dangers risk and regional hidden dangers risk were comprehensively evaluated combing with the process of hidden dangers identification and warning management, and corresponding emergency treatment mechanism was established. Using evaluating-point approach, the single hidden dangers risk was evaluated from the difficulty of identification, vulnerability and controllability, the duration of hidden dangers rectification is included in the hidden dangers risk evaluation, so as to reflect hidden dangers status at different times in real time, which is more in line with the development law of hidden dangers. According to restrictive relationship between identification and management ability and dynamic dominant hidden dangers, the regional hidden dangers risk was evaluated comprehensively, on the basis of risk value and characteristics of region, different early warning levels can be set to realize comprehensive early warning of regional hidden dangers. Considering factors of hidden dangers identification and management ability in the regional hidden dangers risk evaluation, can more accurately reflect the risk degree and risk trend of regional hidden dangers.
Design of mine-used audio and video linkage software
DU Zhigang, CHEN Kang, WANG Wei
2019, 45(8): 54-59. doi: 10.13272/j.issn.1671-251x.2018090042
<Abstract>(65) <HTML> (6) <PDF>(7)
Abstract:
In view of the lack of effective linkage between audio communication and video communication in current mine integrated dispatching communication system, it cannot support dispatcher to proceed efficient audio and video linkage communication, a mine-used audio and video linkage software was designed. The software middleware obtains status of terminal of scheduling communication host in real time through OCP protocol, the data processing module judges the phone status, and sends the linked video information to the client through the message queue RabbitMQ. The client receives the legitimate instructions sent by the data processing module and controls the opening and closing of the video terminal.The test results show that the software is stable and easy to install; through the Web configuration management platform, users can easily manage the telephone and video information, and configure the corresponding relationship between the two;for each scheduling phone bounded by client, when the phone is calling party or called, the camera information of phone of the other party can be displayed on the screen. The video information can be displayed smoothly and the response can be made within 1 s,which meets real-time requirements of users.
Architecture design of coal mine data center based on Hadoop
HAN An
2019, 45(8): 60-64. doi: 10.13272/j.issn.1671-251x.17436
<Abstract>(145) <HTML> (5) <PDF>(23)
Abstract:
According to business requirements of coal mine safety production and development requirements of smart mine, the new coal mine data center needs to meet efficient processing, caching, calculation, storage and release of massive and multivariate data of coal mine under the same space-time coordinate system. In view of problems of discrete data storage and difficulties in data integration, business application and data analysis of traditional coal mine data center, an architecture of coal mine data center based on Hadoop was designed. Real-time data stream engine storm is adopted for real-time data calculation, and MapReduce and Spark are applied to implement batch processing and memory calculation to solve high-frequency time-series data storage and massive data calculation problems. Hadoop distributed file system (HDFS) is used for files reliable storage, and distributed storage database HBase is used for persistent storage of historical data, which can meet data analysis needs of the same space-time coordinate system by its modeless sparse design. Redis is used as a real-time database storage data snapshot for the latest data retrieval. Coal mine data center based on Hadoop makes full use of high-speed data access and compression performance of big data technology, complexity of data application in coal enterprises and daily operation and maintenance difficulty of data center are effectively reduced through unified cloud computing data center, which can lay a data foundation for the construction of smart mine.
Strapdown inertial navigation curve measurement system of full-section roadheader in coal mine
LIU Yu, CHEN Genlin, LIU Yongzhong
2019, 45(8): 65-69.. doi: 10.13272/j.issn.1671-251x.2018120061
<Abstract>(47) <HTML> (7) <PDF>(8)
Abstract:
In view of problems of bad visibility and difficulty in real-time measurement existed in deviation curve measurement system of coal mine tunneling roadway, a strapdown inertial navigation curve measurement system of full-section roadheader in coal mine was designed. The strapdown inertial navigation system uses strapdown attitude update algorithm to acquire attitude angle of the roadheader in real time.The travel sensor is installed on the roadheader and used to measure travel value pushed forward by each cutting section. The attitude angle and travel value were plug into the actual roadway curve algorithm to get the actual roadway tunneling curve, and tunneling deviation curve can be obtained by comparing with the design axis of roadway, the deviation of roadway tunneling is corrected in time according to the tunneling deviation curve, so as to ensure engineering quality. The experimental results show that the system can realize fast and real-time high-precision curve monitoring, and can accurately calculate and measure the curve deviation of full-section roadheader in coal mine. When the tunneling is 5 m, the maximum deviation is about 23.2 mm, which meets requirements of coal mine tunneling curve accuracy.
Inertial navigation positioning method of roadheader based on zero-velocity update
TIAN Yuan
2019, 45(8): 70-73. doi: 10.13272/j.issn.1671-251x.2019010033
<Abstract>(73) <HTML> (10) <PDF>(8)
Abstract:
Aiming at problems of poor environmental adaptability of photoelectric navigation and low accuracy of long-term positioning of inertial navigation adopted in roadheader positioning, an inertial navigation positioning method of roadheader based on zero-velocity update was put forward based on analysis of movement characteristics of roadheader. In short stopping time interval of roadheader, velocity error curve of inertial navigation system is fitted by quadratic curve, and position error curve is obtained by integration, so as to correct position measurement value of inertial navigation system. The test results show that the inertial navigation positioning accuracy of roadheader based on zero-speed update can reach centimeter-level, fluctuation range of positioning error is small, and accumulated positioning error has no obvious increasing trend with the increase of time, which meets positioning requirements of roadheader.
Bearing residual life prediction based on principal component feature fusion and SVM
MA Hailong
2019, 45(8): 74-78. doi: 10.13272/j.issn.1671-251x.2019010085
<Abstract>(85) <HTML> (9) <PDF>(9)
Abstract:
In order to solve the problem that using single feature quantity for bearing residual life prediction had large error and it was difficult to estimate bearing residual life under the condition of limited data samples, a bearing residual life prediction method based on principal component feature fusion and support vector machine(SVM) was proposed. This method collects data samples of vibration acceleration signals and extracts the characteristic indexes such as RMS, peak value and wavelet entropy to characterize the degradation trend of bearings. The principal component analysis is used to fuse multiple feature indexs to eliminate the redundancy and correlation between features, and construct regressive feature quantities with relative multi-feature; the regressive feature quantities are input into SVM model for bearing residual life prediction. The field engineering application results show that the bearing residual life prediction method based on principal component feature fusion and SVM can screen out the principal components which contain most of the information under small sample condition, thus reducing the calculation amount while ensuring the prediction accuracy.
Present situation and development trend of control and protection technology for mine-used combined switch
YANG Fan, CHEN Jiang
2019, 45(8): 79-82. doi: 10.13272/j.issn.1671-251x.17408
<Abstract>(58) <HTML> (5) <PDF>(6)
Abstract:
Present situation of control and protection technology for mine-used combined switch was introduced from aspects of short circuit protection, overload protection, leakage lockout and leakage protection, transient overvoltage protection and temperature protection. Problems of control and protection technology for mine-used combined switch such as incomplete relay protection, protection misoperation, complicated control mode and simple self-diagnosis were pointed out. Development trend of control and protection technology for mine-used combined switch were put forward, including improvement of relay protection method and software filtering method, control intensification, intelligent self-diagnosis and remote diagnosis.
Technology of gas extraction by deep hole directional drilling in underground coal mine and its applicatio
MA Xiaomin
2019, 45(8): 83-87. doi: 10.13272/j.issn.1671-251x.2019010058
<Abstract>(120) <HTML> (10) <PDF>(13)
Abstract:
In order to solve problems of slow tunneling and tension of mine excavation replacement in test mine using traditional extraction technology, a scheme of using deep hole directional drilling with long directional drilling instead of conventional drilling to carry out coal seam gas extraction was proposed. Directional drilling has a large effective area on coal seam, which can change distribution of original coal stress in a large range, thus breaking dynamic balance of gas adsorption and desorption in coal seam and transforming a large number of adsorbed gas into free state; Under the action of pressure gradient formed by drilling negative pressure and coal ground stress and gas pressure, free gas flow continuously to drilling space, make the surrounding coal gas emission effectively, cause shrink deformation of coal, permeability coefficient increases significantly, ground stress and gas pressure gradient are reduced, so as to make the long drilling directional extraction influence range expanded, realize the effective gas extraction from coal seam in a large area. The test results show that using deep hole directional drilling with long directional drilling can get a well formed hole and has obvious effect in gas extraction. Total drilling footage of the test hole is 2 213 m,the maximum drilling depth reaches 523 m, and the average daily extraction pure quantity is 3 528 m3. The average volume fraction of gas extraction is up to 88.3%, and the highest value is 98.0%. The average single-hole gas extraction pure quantity is 1.23 m3/min, and the maximum value exceed 2 m3/min. Compared with conventional drilling extraction, the pure quantity of single-hole gas extraction of directional drilling is increased by more than 16 times, the volume fraction of single-hole gas extraction is increased by 2-4 times, and monthly average footage of roadway is increased by more than1 times.
Design of cavity drill bit while drilling for gas drainage of crossing borehole
GAO Xiaoliang, ZHANG Xianzhen, LU Qianhai
2019, 45(8): 88-91. doi: 10.13272/j.issn.1671-251x.17453
<Abstract>(77) <HTML> (7) <PDF>(6)
Abstract:
In order to improve gas drainage effect of crossing borehole, cavity drilling technology is often used to increase part borehole diameter of coal seam section, which avoids invalid footage of hole section in rock layer. However, due to limitation of structure of cavity drill bit, it is generally necessary to to lift the drill after the pilot drilling is completed, then the cavity drilling bit is put into the hole to carry out cavity drilling, which need more procedures, long auxiliary operation time. In order to solve the above problems, a mechanical cavity drill bit while drilling was designed with rack and pinion structure. The wing is retracted when the cavity drill bit is drilling in the rock layer. After entering coal seam, axial movement of the piston with rack is driven by change of hydraulic parameters, which drives the pinion blade to rotate and open to ream drilling. After caving drilling is finished, the wing is retracted, the drill bit is pull out from the drilling hole, and the hole is sealed and the gas is pumped. The field test results show that the drill bit can construct pilot hole when rock is closed, and can open smoothly and carry out hole cutting drilling after entering coal seam and the pump volume is increased, which increases the diameter of borehole in coal seam, reduces auxiliary operation time of crossing borehole,improves construction efficiency of crossing borehole.
Error analysis and compensation of north-seeking system of drilling orientation device in underground coal mine
YAN Bin, CHENG Jianyuan, CAI Yuanli, LI Ping, FENG Hong
2019, 45(8): 92-96. doi: 10.13272/j.issn.1671-251x.2019030034
<Abstract>(85) <HTML> (10) <PDF>(7)
Abstract:
In view of problem that existing drilling orientation device for drilling rig can not meet actual demand in terms of measurement accuracy, cost and operability, a drilling orientation device for drilling rig was designed which combines north-seeking system based on single-axis fiber optic gyroscope with tracking system based on micro-inertial measurement unit. Basic principle of north-seeking system was introduced taking four-position north-seeking method as an example, and various errors and their resources of the north-seeking system were introduced from aspects of output error of fiber optic gyroscope, installation error, inclination error, inversion error and geophysical quantity error. A nonlinear acceleration error compensation model was established for installation error and inclination error. Kalman filter method was used to correct random drift error of fiber optic gyroscope. The experimental results show that the reduction of inclination angle, random drift error of fiber optic gyroscope, mechanism rotation error and installation error can effectively improve north-seeking accuracy of drilling orientation device and meet drilling requirements of underground coal mine.
Research of weight on bit transmission law of ultra-long directional borehole along coal seam
LIU Fei, XU Chao, WANG Xian, JIANG Lei, BI Zhiqi
2019, 45(8): 97-100. doi: 10.13272/j.issn.1671-251x.17456
<Abstract>(108) <HTML> (8) <PDF>(6)
Abstract:
In order to further increase directional borehole depth along coal seam and improve drilling efficiency of ultra-long directional borehole, influencing factors of weight on bit(WOB) transmission of ultra-long directional borehole along coal seam were analyzed, including borehole trajectory, borehole depth, sediment in borehole and drilling strata. Based on engineering background of 2 570 m ultra-long directional borehole along coal seam in Baode Coal Mine, law of WOB transmission under compound directional drilling was researched. The research results show that with the increase of borehole depth, feed pressure of sliding directional drilling increases exponentially, and finally reaches rated feed pressure of drilling rig, which leads to decrease of transmission efficiency of WOB. Under condition of compound drilling, feed pressure of compound drilling keeps at a low level with the increase of borehole depth, which is far lower than rated feed pressure of drilling rig. Rotary pressure of drilling rig almost increases linearly with the increase of borehole depth, but it is lower than rated rotary pressure of drilling rig, which leads to high transmission efficiency of WOB. The higher the pump pressure and pump volume of mud pump are, the higher the slag discharge efficiency is, the lower the friction resistance of drilling tool is, and the higher the transmission efficiency of WOB is. Conversely, the lower the transmission efficiency of WOB is.
Design of electric control system for coalbed methane truck-mounted drilling rig
ZHAO Liang
2019, 45(8): 101-104. doi: 10.13272/j.issn.1671-251x.2019020021
<Abstract>(65) <HTML> (10) <PDF>(14)
Abstract:
Aiming at problem that traditional mechanical instrumens and hydraulic control modes cannot meet requirements of safe, accurate and efficient construction of coalbed methane truck-mounted drilling rig, an electric control system for coalbed methane truck-mounted drilling rig was designed. The system is composed of sensors, sub-console, control box and main console. The sub-console collects parameters of diesel engine and realizes control functions such as diesel engine starting and stopping, throttle adjustment and throttle switching. The control box drives solenoid valve of hydraulic system for logical control. The main console is used for driller to observe drilling parameters and operate drilling operations. The field application results show that the system can monitor and display drilling parameters of diesel engine and drilling rig in real time and accurately, and realize logical control of diesel engine operation and drilling rig, which provides guarantee for auxiliary drilling construction and improving drilling quality.
Application of 3D inversion of audio-frequency electric perspective in detection of water-containing/water-conductive collapse colum
WANG Cheng, LU Jingji
2019, 45(8): 105-108. doi: 10.13272/j.issn.1671-251x.2019010028
<Abstract>(95) <HTML> (6) <PDF>(6)
Abstract:
In order to accurately detect water-containing/water-conductive collapse column and realize 3D interpretation of water-containing/water-conductive collapse column, based on electrical properties difference between water-containing/water-conductive collapse column and surrounding rock, water-rich strata of rock-seam in working face floor are explored by use of audio-frequency electric perspective. 3D inversion imaging of audio-frequency electric perspective observation data is carried out to obtain resistivity variation. The results show that 3D inversion of audio-frequency electric perspective can accurately identify spatial position and distribution range of water-containing/water-conductive collapse column, which provides reliable reference for coal mine water prevention.

苏ICP备 05016349号-2

Supported by: Beijing Renhe Information Technology Co. Ltd.  Visits：