Abstract
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.
Highlights
The geological conditions of coal seams in China are complex and highly variable, among which coal seams with hard roofs account for approximately 1/3 [1]
This paper focuses on the problem of surrounding rock control under hard-roof and extra-thick coal seam conditions in the Wenjiapo Coal Mine (Shaanxi Province, China)
This study investigates the surrounding rock instability mechanism of a roadway induced by strong mining in an extra-thick coal seam and the synergistic control mechanism
Summary
The geological conditions of coal seams in China are complex and highly variable, among which coal seams with hard roofs account for approximately 1/3 [1]. The suspension of long-distance roofs significantly influences the periodic pressure of the working face and affects the lateral support stress distribution characteristics [2,3]. Concentrated stress of the protective coal pillar deforms the roadway, deteriorates the surrounding rock stress field, and aggravates damage to the roof anchorage structure [4]. This problem is pressing because roofing accidents alone have been reported to account for 70–80% of all working face accidents [5]. Extensive research attention has been paid to understand the ore pressure behavior and damage mechanism of roadway rock mass mined under hard-roof conditions
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