1555 RESEARCH AND APPLICATION OF HARD ROOF HYDRAULIC FRACTURING FOR STRONG STRATA PRESSURE CONTROL IN THE WORLD’S FIRST 10-METER ULTRALARGE MINING HEIGHT FULLY MECHANIZED FACE *Yan-jun FENG1,2,3, Hongpu KANG 1, 2, 3, Kaikai ZHAO 1, 2, 3 1Coal Mining Research Institute, China Coal Technology and Engineering Group Co., Ltd., Beijing 100013, China;,(Yan-jun FENG :cristiarno@163.com) 2State Key Laboratory of Intelligent Coal Mining and Strata Control, Beijing 100013, China 3Coal Mining and Design Department, Tiandi Science and Technology Co., Ltd., Beijing 100013, China ABSTRACT In China, coal seams associated with hard roof strata account for over 30% of the total. Hard roofs are prone to inducing dynamic load impacts, large-area roof weighting, air blasts, and support damage. Addressing the challenges of controlling strong strata pressure in 10m ultra-large mining height faces with thick-hard roofs, this research developed China's first set of underground regional fracturing technology and equipment with a capacity of 5 m³/min, underground abrasive jet technology, and a comprehensive evaluation method for pressure relief effectiveness. Field trials were conducted at Caojiatan Coal Mine. Based on insitu roof testing, key strata for fracturing were identified. Directional horizontal boreholes of 400–800 m were drilled using underground directional drilling rigs. Large-displacement fracturing pump sets and isolation tools were employed to perform large-displacement segmented retreat fracturing for roof modification. The results show that the issues of large-area roof hanging and minor air blasts during the initial mining stage were resolved. The first weighting span was 49.35 m, with the proportion of support leg safety valves opening being 24.81%. Periodic weighting spans were controlled below 25 m, and rib spalling was concentrated within 0.2–0.5 m. This ensured the safe and efficient extraction of the world's first 10m ultra-large mining height face. KEYWORDS Ultra-large mining height; Thick hard roof; Hydraulic fracturing; Strong strata pressure; Strata control; Directional drilling 1. INTRODUCTION Fracturing technology involves injecting high-pressure fluid into target rock strata to create fractures or reopen natural fractures. By modifying the rock structure and forming a fracture network system, it aims to increase resource recovery or weaken strata. Hydraulic fracturing technology is widely used in unconventional oil and gas development, geothermal resource exploitation, in-situ stress measurement, and strata control. The United States first applied hydraulic fracturing to address challenges in shale gas development. The first 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
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