316 RESEARCH AND APPLICATION OF HARD ROOF HYDRAULIC FRACTURING FOR STRONG STRATA PRESSURE CONTROL IN THE WORLD’S FIRST 10METER ULTRA-LARGE MINING HEIGHT FULLY MECHANIZED FACE *Yan-jun FENG1,2,3, Hongpu KANG 1, 2, 3, Kaikai ZHAO 1, 2, 3 1. Coal Mining Research Institute, China Coal Technology and Engineering Group Co., Ltd., Beijing 100013, China;,(Yan-jun FENG :cristiarno@163.com) 2. State Key Laboratory of Intelligent Coal Mining and Strata Control, Beijing 100013, China 3. Coal 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 ultralarge 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 in-situ 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 largearea 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
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