317 hydraulic fracturing test was conducted in an oil field in Kansas in 1947. By the late 1990s, breakthroughs in hydraulic fracturing technology significantly improved shale gas extraction efficiency, leading to large-scale commercial application after 2000. Hydraulic fracturing has been extensively applied in China's unconventional oil and gas development, becoming a core technology for increasing reserves and production. In the coal industry, hydraulic fracturing is primarily applied in two areas: firstly, coal seam permeability enhancement to facilitate gas drainage; secondly, strata control, including hard roof weakening and high-stress surrounding rock destressing. China's coal mines are predominantly underground, making strata control a core technology for ensuring safe and efficient mining. With increasing mining depth and intensity, along with more complex geological conditions, coal mine strata control faces a series of challenges. Regarding mining depth, Chinese coal mines are extending deeper at a rate of 10–25 m per year. There are 47 mines with depths exceeding 1000 m, and the maximum mining depth has reached 1510 m. Deep mining introduces high stress, high ground temperature, high seepage pressure, and intense mining disturbance, leading to disasters such as large surrounding rock deformation, roof collapse, and rockburst. Regarding mining intensity, a number of ten-million-tonnage mines and faces have emerged, with some mines exceeding 30 million t/a and face production exceeding 15 million t/a. Mining faces are developing towards super-height and super-length: the mining height of ultra-large fully mechanized faces reaches 10 m, and the total mining-cutting height of fully mechanized top-coal caving faces reaches 20 m; the length of super-long faces in medium-thick seams reaches 450 m. High-intensity mining creates ultra-large excavated spaces, resulting in extensive overburden movement and more intense strata pressure behavior, imposing higher requirements on face strata control. Strata control is divided into face strata control and roadway surrounding rock control. Under conditions of hard or fractured roofs, hydraulic supports alone cannot fully resolve face strata control issues; measures such as destressing and reinforcement are required. In China, coal seams with hard roofs account for over 30%, covering more than 50% of mining areas. Hard roofs are characterized by great thickness, underdeveloped fractures, good integrity, high strength, and strong self-stability. After face extraction, hard roofs do not cave timely, easily causing large-area roof hanging. Sudden collapse of such roofs releases elastic energy instantaneously, forming intense impact loads leading to disasters like large-area weighting, rockburst, and air blasts. For roadway surrounding rock control, the synergistic control technology of "support-modification-destressing" has been proposed, where destressing employs techniques like hydraulic fracturing and blasting to reduce or transfer high stress in the surrounding rock, mitigating mining disturbance effects , thereby controlling deformation and failure. Hydraulic fracturing has become an effective means for controlling strong strata pressure in coal faces, managing large deformations in high-stress and strongly disturbed roadways, and preventing rockburst. This paper takes the hard roof hydraulic fracturing project in a 10m ultra-large mining height face as an example to introduce the research and application of underground coal mine hydraulic fracturing technology for strong strata pressure control.
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