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تعداد صفحات این فایل: ۲۵ صفحه

بخشی از مقاله انگلیسیعنوان انگلیسی:Longwall mining “cutting cantilever beam theory” and 110 mining method in ChinadThe third mining science innovation~~en~~

Abstract

With the third innovation in science and technology worldwide, China has also experienced this marvelous progress. Concerning the longwall mining in China, the “masonry beam theory” (MBT) was first proposed in the 1960s, illustrating that the transmission and equilibrium method of overburden pressure using reserved coal pillar in mined-out areas can be realized. This forms the so-called “۱۲۱ mining method”, which lays a solid foundation for development of mining science and technology in China. The “transfer rock beam theory” (TRBT) proposed in the 1980s gives a further understanding for the transmission path of stope overburden pressure and pressure distribution in high-stress areas. In this regard, the advanced 121 mining method was proposed with smaller coal pillar for excavation design, making significant contributions to improvement of the coal recovery rate in that era. In the 21st century, the traditional mining technologies faced great challenges and, under the theoretical developments pioneered by Profs. Minggao Qian and Zhenqi Song, the “cutting cantilever beam theory” (CCBT) was proposed in 2008. After that the 110 mining method is formulated subsequently, namely one stope face, after the first mining cycle, needs one advanced gateway excavation, while the other one is automatically formed during the last mining cycle without coal pillars left in the mining area. This method can be implemented using the CCBT by incorporating the key technologies, including the directional pre-splitting roof cutting, constant resistance and large deformation (CRLD) bolt/anchor supporting system with negative Poisson’s ratio (NPR) effect material, and remote real-time monitoring technology. The CCBT and 110 mining method will provide the theoretical and technical basis for the development of mining industry in China.

۱ Introduction

In the 1960s, Prof. Minggao Qian proposed the “masonry beam theory” (MBT) (Qian, 1981, 1982) for the first time in China, and presented a full discussion on the transmission and equilibrium method of overburden pressure in mined-out areas by using reserved coal pillar. On this basis, the “۱۲۱ mining method” was established, namely one stoping face needs two advanced excavation tunnels and one reserved coal pillar before the next mining cycle. The MBT and mining system based on the 121 mining method laid a sound foundation for the development of mining science in China. The second mining innovation started in the 1980s, which was characterized by the “transfer rock beam theory” (TRBT) (Song, 1979, 1982) proposed by Prof. Zhenqi Song. This illustrated a further transmission path of stope overburden pressure and the pressure distribution in high-stress areas. Then the advanced “۱۲۱ mining method” was raised with smaller coal pillar in terms of field excavation design, making important contributions to development of the coal recovery rate in that era.

At the beginning of the 21st century, large deformation failure problems in coal mines became more challenging with increasing mining depth, and the accidents in risk-prone gateway and deep gob-side gateway accounted for 80%e90% of total accidents in working face gateways (He, 2004, 2005; He et al., 2005). It is basically considered that the traditional 121 mining method was not suitable for the deep mining purpose (Zhai and Zhou, 1999; Li, 2000; Liu and Shi, 2007; Fei, 2008). In 2008, the theory of “cutting cantilever beam theory” (CCBT) was first put forward. In this theory, it can be noted that the ground pressure was used for the purpose of advanced roof caving by precutting to form a cantilever beam above the gob-side gateway. When the precutting was performed on the roof of gateway, the transmission of overburden pressure was cut off, which mitigated the periodic pressure when using the 121 mining method, and part of roof rock mass was driven down, forming one side of the gateway for the next stope mining cycle. The CCBT provides a new basis for the non-pillar mining, under which the 110 mining method was developed (He et al., 2007; Zhang et al., 2011; Song and Xie, 2012; Wang and Wang, 2012; Liu and Zhang, 2013; Sun et al., 2014), namely one stope face, after the first mining cycle, only needs one advanced gateway excavation; while the other one is automatically formed during the last mining cycle without coal pillars left in the mining area by using this mining technology. The core idea of the 110 mining method is that, first, the natural ground pressure is used to make part of the roof fall down, instead of fully reinforcing it by artificial supporting system and coal pillar; second, the gob roof rock is used to form one side wall of the gob-side gateway; and third, the expansion characteristic of broken gob roof rock is used to reduce the surface subsidence. This mining method will reduce 50% of gateway excavation workload in the stope and fulfill 100% coal pillar recovery, which achieves a significant reduction in mining costs and more importantly, will reduce the accidents in the stope. It may be used to fulfill the “N00 mining method” in the future, which is the optimization and innovation of the 110 mining method. The symbol “N00” means no matter how many mining cycles and working faces are in the district, all the gateways would be formed automatically with CCBT, suggesting no need for gateways to be excavated when using traditional methods. In this paper, China’s three innovations in longwall mining will be reviewed and discussed, including the related theories and the 121 mining method, the CCBT and the 110 mining method, and the key technologies involved. The CCBT and 110 mining method will be considered to be the basis for China’s next-generation mining industry development, from mining giants to mining powers.

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