The higher strength of a hard roof leads to higher coal pressure during coal mining, especially under extra-thick coal seam conditions. This study addresses the hard roof control problem for extra-thick coal seams using the air return roadway 4106 (AR 4106) of the Wenjiapo Coal Mine as a case study. A new surrounding rock control strategy is proposed, which mainly includes 44 m deep-hole pre-splitting blasting for stress releasing and flexible 4-m-long bolt for roof supporting. Based on the new support scheme, field tests were performed. The results show that roadway support failure in traditional scenarios is caused by insufficient bolt length and extensive rotary subsidence of the long cantilever beam of the hard roof. In the new proposed scheme, flexible 4-m-long bolts are shown to effectively restrain the initial expansion deformation of the top coal. The deflection of the rock beam anchored by the roof foundation are improved. Deep-hole pre-splitting blasting effectively reduces the cantilever distance of the “block B” of the voussoir beam structure. The stress environment of the roadway surrounding rock is optimized and anchorage structure damage is inhibited. The results provide insights regarding the safe control of roadway roofs under extra-thick coal seam conditions.

The safety of coal mine is an important link in coal mine production,gas disaster is the most harmful for the safety of coal mine production. During the process of mine development, it is very important to measure the gas concentration in mines. For the present of situation of gas concentration monitoring system, this paper proposes a Bluetooth-based coal mine gas concentration monitoring system design, describes the ideas and specific methods software and hardware design. As a standard of unified global short-range wireless communication, Bluetooth technology is to establish a common low-power, low-cost wireless air interface and controlling software opening system. This paper describes the development background, technical features and the structure of the protocol stack of Bluetooth technology, and proposed the solutions of the Bluetooth host controller interface (HCI) wireless communication for the complexity of its development. At the same time, the system uses CAN bus technology maturely, has realized the combination of wired and wireless data transmission system. This paper presents the complete block diagram of the system and the various parts of the circuit diagram, describes how to use micro controllers and Bluetooth module to build system, introduced the principle used in the device. Analyzed the solution of the theoretical basis of the Bluetooth HCI protocol and the HCI UART transport layer of instruction in detail. Parsing a process of using the HCI protocol in Bluetooth device initialization, querying other equipment, establishing the link, data transmission and disconnect the link, and describe the flow chart of software development in Bluetooth main transceiver unit. Meanwhile, this paper describes the hardware and software design of CAN nodes. This article presents some debugging information to prove that the Bluetooth technology can convenient replacement cable interface in this system, provide a new way of data transmission for security and monitoring of coal mine.

A fault is a common geological structure in coal mining. Large deformation or even instability and collapse often occur in roadways in fault areas, which restricts the safe and efficient production of mines. With the track roadway of the 5206 working face of Xin’an Coal Mine as the engineering background, this study aims to explore the failure mechanism of surrounding rock under the influence of fault structures. Field investigation and numerical simulation were used comprehensively to analyze the failure characteristics of the surrounding rock under the influence of a unidirectional fault structure. Based on the principle of thick-layer transboundary anchorage, the hierarchical continuous support technology of transboundary anchoring in the fault structure area was proposed. The results show that the stress near the fault area is relatively concentrated, and the rock mass strength is low, which may easily cause the deformation and failure of the surrounding rock under the dynamic stress response. Using the new technology to reconstruct the bearing structure of the broken surrounding rock mass, the deformation of the surrounding rock can be effectively restrained. According to the monitoring feedback, the roadway deformation in the roof and two sides is reduced by 68.5% and 35.4%, respectively; and the maximum evolutionary depth of the roof crack is reduced to 3.5 m from 7.5 m in the original support scheme. Moreover, this study also explored the necessity of wedge anchorage for corner anchor cables and the deformation characteristics of surrounding rock at different fault dip angles. These results provide an important reference for the maintenance and control of coal roadways under the influence of unidirectional fault structures.

In Sichuan Province, China, most coal seams that are mined are steeply inclined; their roadways’ surrounding rocks are asymmetric, with non-equilibrium deformations and unstable anchorage structures, thus making major safety hazards highly likely. Using field observations and a universal distinct element code (UDEC) numerical simulation method, this paper analyzed the time-dependent failure of the ventilation roadway of Working Face 1961 of the Zhaojiaba Mine, revealing the preconditions for such damage and a bidirectional deterioration mechanism for the deformation as well as stress of surrounding rocks. Moreover, this paper built an anchorage mechanical model for the thick layer of the roadway roof and proposed a cross-boundary anchor-grouting (CBAG) differential support technique. Calculations proved that the new support was particularly effective in restraining the expansion of tension cracks, thus preventing the slipping and dislocation deformations of rock masses on the curved roof side. The feedback of engineering applications showed that the maximum development depths of cracks in the arc roof and straight inclined roof of the roadway 150 m behind the working face are only 1.5 m and 1.10 m, decreasing by 61.3% and 47.6%, respectively, compared with the primary support. The proposed technology offers an overall thick-layer bearing structure for the surrounding rocks of roadways, effectively restraining the non-equilibrium large deformations of roadways in steeply inclined coal seams.

One of the important factors affecting the anchoring force of the end encapsulated bolt is the mechanical properties of the rock formation at the anchoring end. For the fully encapsulated bolt, its bearing performance is closely related to the mechanical properties of the bolt passing through the rock stratum and its permutation mode. In this study, a series of laboratory pull-out tests of multi-strata anchorage systems was carried out based on an actual engineering background. The bearing performances and failure mechanisms of the multi-strata anchorage system under different anchoring methods and combinations of rock stratum were studied. The evolution law of the axial force and shear stress of the Agent-Rock interface was also analyzed. The test results showed that, for end encapsulation, changes in the mechanical properties of the rock strata at the anchoring end caused differences in bearing capacity, while full-length encapsulation markedly reduced the disparities. The position of the stratum with the highest general interface shear strength affected the mechanical response of the anchoring interface. The progressive failure process of multi-strata anchorage systems was discussed, and suggestions for rock bolt support in coal mine roadways were also proposed.