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This article is innovative
Combined with the problems existing in the conventional metal mesh and sprayed concrete protective table in the anchor support, the spraying flexible film (referred to as spray film) technology is proposed and introduced.
(1) The tensile properties of the spray film material were tested, revealing the mechanical characteristics of its fast bearing response and large deformation ability; the normal adhesion performance of the spray film and the red sandstone matrix was tested by direct drawing method, and the results showed that the spray film had good bond strength; the block bearing capacity test was carried out, and the block bearing capacity of the spray film was evaluated.
(2) Based on the characteristics of coal mine roadway engineering, the potential sealing effect of the spray film such as surrounding rock sealing, metal support component sealing, and wall sealing during grouting was discussed, and the specific support performance of the spray film and the net and sprayed concrete was analyzed in detail, and it was believed that the spray film performed excellent in most indicators, especially in construction.
(3) The principle of the application of spray film in the anchor support of coal mine roadway is discussed, and the functional positioning and engineering condition qualification of spray film in anchor support are analyzed, which provides a reference for the application of spray film in anchor support of coal mine roadway.
About the Author
Zhang Nong taught Zhang Nong (1968-), a native of Jinzhai, Anhui. Mining engineering expert, head of intelligent excavation and rock formation control team of China University of Mining and Technology, doctoral supervisor. Vice President of Jiangsu Normal University. He was selected as a leading talent in scientific and technological innovation of the National Ten Thousand Talents Program, a young leading talent in the National Innovative Talents Promotion Plan, a leader of the innovation team of the "Yangtze River Scholars and Innovation Team Development Plan" of the Ministry of Education, and a national candidate for the Million Talents Project in the new century.
Professor Zhang Nong focused on the research of mine pressure and rock formation control theory and application technology, presided over the key projects of the National Natural Science Foundation of China, the national key basic research and development program, more than 10 innovation team projects of the Ministry of Education and the national provincial and ministerial talent funding projects, undertook more than 100 enterprise cooperation research projects, made important progress in the direction of active control principle and technology of coal mine mining roadway, along the empty excavation (stay) lane, anchor support and intelligent fast excavation, and invented the overall control method and dynamic grading strengthening technology of layered roof wedge. Innovative high-performance anchor rods, steel strand pre-tension trusses, flexible anchor rods and other active high-strength prestress support technologies have built a patent group to solve the control of surrounding rock in complex coal mine roadways in mainland China, which has significantly promoted the progress of engineering technology in related fields. He has published 70 SCI search papers and 103 EI search papers, published 6 monographs, and authorized 104 domestic invention patents and 26 foreign patents. It has trained 22 graduate doctors and more than 100 masters. It has won 2 second prizes of national scientific and technological progress, 9 first prizes of provincial and ministerial scientific and technological progress, and more than 20 other provincial and ministerial awards. He has won the China Youth Science and Technology Award (2006), Jiangsu Top Ten Outstanding Youth (2008), the State Council Special Allowance Personnel (2010), the Guanghua Engineering Science and Technology Award Youth Award (2012), the National Advanced Worker (2015) and other honorary titles.
Author
ZHANG Nong1,2,3, WEI Qun4, WU Jiansheng5
Unit
1. State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, 2. School of Mining Engineering, China University of Mining and Technology, 3. Open Laboratory of Jiangsu Normal University, 4. School of Mechanical Engineering, Jiangsu University of Technology, 5. Nanjing Kegong Coal Science and Technology Research Co., Ltd
Combined with the problems existing in the conventional metal mesh and sprayed concrete protective table in the anchor support, the spraying flexible film technology (referred to as spray film) is proposed. The development process of spray film technology and the research status at home and abroad are summarized. The tensile properties of the spray film in different curing periods were tested, the tensile stress-strain relationship of the material was analyzed, and the mechanical characteristics of the spray film material with fast bearing response and large deformation ability were revealed, and a non-reactive polymer cement-based spray film material suitable for coal mine roadway was determined. By direct drawing, the normal adhesion performance of the spray film and the red sandstone matrix was tested, and the results showed that the damage occurred inside the matrix, indicating that there was a good adhesion strength between the spray film and the substrate. The block carrying capacity test of the spray film was carried out, the different stages of the spray film bearing were analyzed, the linear carrying capacity index of the spray film was obtained, and the block carrying capacity of the spray film was evaluated based on the obtained index, and the spray film theoretically had a strong block bearing capacity. Based on the characteristics of coal mine roadway engineering, the potential sealing effect of the spray film such as surrounding rock sealing, metal support component sealing, wall sealing during grouting is discussed, and a detailed comparative analysis of the spray film and the net and sprayed concrete is carried out in terms of bearing timeliness, bearing capacity, deformation capacity, conformability with the surrounding rock surface, construction performance, structural effect, and sealing performance, etc., and it is believed that the spray film has excellent performance in most indicators, especially in construction. The principles of the application of spray film in the anchor support of coal mine roadway are further discussed, and the functional positioning of spray film in anchor support and three typical engineering conditions that cannot be applied are analyzed, which provides a reference for the application of spray film in anchor support of coal mine roadway.
Research background
The role of the net is to diffuse the prestress of the anchor rod with the bracket, steel belt and other components to spread the prestress of the anchor rod to the surrounding rock farther away from the anchor, to prevent the small size loose rock block between the anchor rod from leaving the original position, and then maintain the stability of the support body-surrounding rock system. The effective control of the initial loosening and deformation of the surrounding rock under the anchor support system is very important, but the ordinary metal mesh must play a bearing and supporting role after a considerable amount of deformation (possibly tens of centimeters) of the surrounding rock; it is difficult to ensure good flatness on the surrounding rock surface of the coal mine roadway, and it is difficult to achieve a good fit between the net and the rock surface, and it is difficult to carry it in time. The construction of the anchor rod has basically been mechanized, but the installation of the net is lowly mechanized, which brings challenges to the efficiency and safety of roadway support. Shotcrete is another surface support method, the main role is to close the surrounding rock to prevent weathering, while improving the stress state of the surrounding rock and supporting structure, to prevent the crushing surrounding rock from falling and other mechanical effects. However, the coal mine roadway generally has a large amount of deformation, and the surrounding rock deformation during the excavation of the deep well soft rock roadway is even hundreds of millimeters, while the spray concrete is a brittle material, and the spray layer after the roadway is pressed cannot withstand large tensile stresses, and it is impossible to support the stability of the surrounding rock of the roadway; at the same time, the destruction and shedding of the spray layer itself are also prone to become a safety hazard. In addition, there are still some problems in the construction of shotcrete, such as large construction dust, slow construction speed, high rebound rate, large amount of labor, and huge amount of material transportation. For the anchor support system, it is of great significance to carry out research on new meter protection methods and materials.
Content Overview
1 Technical characteristics of spraying flexible film
Based on the above properties and construction characteristics of the material, from the perspective of engineering characteristics, it is believed that "sprayed flexible film" contains more complete and accurate engineering semantics. Among them, "spraying" reflects the construction characteristics of the technology, including the adhesion of the material and the rock mass, as well as the characteristics of being able to adapt to the uneven rock surface, showing the difference with the coil such as the net; "soft" indicates that the material has the ability to deform, which is different from the brittle shotcrete; "film" reflects the extremely small construction thickness. Based on the above analysis, the re-definition of the spraying flexible film technology is as follows: through the spraying method, the polymer material or polymer composite material is applied to the surface of the surrounding rock, and the curing is formed to form a thin layer with tight bonding with the matrix and deformation ability. Hereinafter referred to as "spray film". Spray film materials are generally divided into reactive and non-reactive types.
2 Research progress of spraying flexible film technology
2.1 Research progress abroad
2.1.1 Mechanical properties test
1) Tensile performance test.
2) Adhesion performance test.
3) Shear resistance test.
2.1.2 Supporting Role
2.2 Domestic research progress
Although scholars have carried out some research work on the support effect of spray film, because the thickness of the spray film is small compared with concrete, and its obvious flexibility, its support effect is still doubtful; when the spray film is used for mine support, it also lacks a widely accepted test, design and construction basis. Under coal mine conditions, there are still relatively few application cases and principle studies, especially as support methods.
3 Selection of mining spray film materials
3.1 Tensile properties
3.2 Normal bonding properties
3.3 Block Carrying Characteristics
Figure 1 Tensile test specimen
Figure 9 Simulates a hemisphere of a loose rock mass
3.4 Potential containment effects
The potential sealing effect of the spray film is first reflected in the sealing of the excavated surrounding rock to prevent weathering. After the underground rock mass is excavated and in contact with the air, the cement between the rock particles is easily weakened by weathering, which in turn forms and aggravates the cracks in the rock mass and reduces the physical and mechanical indicators of the rock mass. After excavation, the surrounding rock surface construction spray film forms a barrier, which can prevent the intrusion of moisture in the air of the roadway and prevent the weakening of the surrounding rock. When used with anchor support, the spray film wraps the metal support member, which can prevent the erosion of the component by water vapor in the air, prevent the corrosion and weakening of the component, and then improve the reliability of the anchor support system. In addition, the sealing of the surrounding rock surface during grouting to prevent running of the pulp is also one of the potential sealing effects of the spray film.
4 Comparison of spray film performance with common watch protection
4.1 Timeliness of carrying
4.2 Carrying Capacity
4.3 Deformability
4.4 Adhesion to the surface of the surrounding rock
4.5 Construction
4.6 Structural effects
4.7 Sealing effect
Figure 10 The state of the watch when it sinks 0.15 units
Fig. 11 Illustration of the carrying capacity of the net and sprayed flexible film
Fig. 13 Conformation of different meter protection methods to the surface of the surrounding rock
Table 1 Performance comparison of different meter protection methods
5 Evaluation of the applicability of spray film
5.1 Application Principles
The subjective acceptance of spray film as a support method at the coal mine site requires a process, and the application of spray film in anchor support should be gradual: first tried under simple engineering conditions
use, then summarize, improve and extend to other conditions.
5.2 Potential Applications
1) Replace thick layers of shotcrete under specific conditions.
2) Replace metal mesh under specific conditions.
5.3 Restricted Conditions of Construction
1) When the surrounding rock of the roadway has been severely broken.
2) When the rock mass has water.
3) Weak rock masses whose surface has weakened or have a large amount of dust accumulation.
Conclusion
1) Typical sprayed flexible film shows timely bearing and large deformation characteristics in tensile test, and can be well bonded with the rock matrix, which is beneficial for timely bearing effect and adapting to the large deformation characteristics of coal mine rock mass.
2) When the block is bearing, the spray film can quickly establish the strength at the beginning of the block movement, and the bearing capacity indicators show that the spray film has a good block bearing potential.
3) The spray film can be carried in time, but the bearing capacity is weaker than that of sprayed concrete and net, and cannot play a structural role; it is obviously better than the existing meter protection method in construction; compared with the net, its superiority is also reflected in the uneven rock surface that can adapt to the coal mine roadway.
4) The application of spray film in coal mine underground should follow the principle of step-by-step, which can first replace shotcrete when there is no need to play a structural role, or partially replace the net when the geological conditions are good. In addition, the spray film can be combined with existing meter protection methods.
Reference format
ZHANG Nong,WEI Qun,WU Jiansheng. Coal Mine Roadway Spraying Flexible Film Technology and Applicability[J].Coal Science and Technology,2022,50(1):78-85. ZHANG Nong,WEI Qun,WU Jiansheng.Spray-on membrane technology and its applicability in coal mine roadways［J］.Coal Science and Technology，2022，50(1）：78-85.
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