Analysis of Hydro-fracturing Technique Using Ultra-deep Boreholes for Coal Mining with Hard Roofs: a Case Study
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Analysis of Hydro-fracturing Technique Using Ultra-deep Boreholes for Coal Mining with Hard Roofs: a Case Study Jianwei Zheng 1,2,3 & Wenjun Ju 1,2,3 & Xiaodong Sun 1,2,3,4 & Pengfei Jiang 1,2,3 & Yangfa Zheng 1,2,3 & Zhaorui Ma 1,2,3 & Lingfu Zhu 1,2,3,5 & Bingding Yi 1,2,3,5 Received: 29 May 2020 / Accepted: 6 October 2020 # Society for Mining, Metallurgy & Exploration Inc. 2020
Abstract The presence of hard roof poses a significant threat to the safety of underground coal mining. In this study, a mechanical model is established for underground stopes to analyze the overburden structure with the advancing of the mining face. It is indicated that the load-bearing arch structure (LBAS) is formed above the stope for roofs with regular hardness, whereas the reversed-basin bearing structure (RBBS) is formed for hard roofs. Compared with the LBAS, the RBBS can induce an additional pressure at the foot of the bearing structure, and this effect becomes less as the distance between the hard roof and stope increases. The ultra-deep borehole hydro-fracturing technique (UHT) is proposed to weaken the hard roof for pressure release, and the associated equipment and procedures are also presented. The UHT is based on horizontal drilling along the axial direction of the roadway in the roof, and then the receding segmented hydraulic fracturing technique is used to achieve the purpose of fracturing (weakening) of the surrounding rocks. Field tests are carried out in 3022 roadway of Daliangwan coal mine in Yulin to assess the developed technique, equipment, and fracturing procedures. To evaluate the fracturing effect, deep borehole stress-meters are installed at different depths of the fractured and un-fractured zones of the roadway, along with hydraulic support pressure sensors placed at the mining face. The results show that compared with the un-fractured zone, the pressure on the wall and pillar sides is lower than that in the fractured zone, and the associated weighting duration and weighting area ratio of the fractured are reduced by 53.23% and 33.59%, respectively. This indicates that the presented UHT can provide a new solution for the prevention and control of mining disasters induced by hard roof failures in underground coal mining. Keywords Ultra-deep borehole hydro-fracturing technique . Hard roof . Strata spatial structure . Stress arch . Fracturing-before-injecting
1 Introduction Coal is the most important raw material and strategic reserve resource in China, with approximately 80% of the total coal production coming from underground coal mining. In general,
* Jianwei Zheng [email protected] 1
Beijing Mining Research Institute, China Coal Research Institute, Beijing 100013, China
2
CCTEG Coal Mining Research Institute, Beijing 100013, China
3
Coal Mining & Designing Department, Tiandi Science & Technology Co., Ltd., Beijing 100013, China
4
Institute of Geology and Geophysics Chinese Academy of Sciences, Beijing 100029, China
5
Daliangwan coal mine, Yulin 719000, Shaanxi, China
one third of the total coal
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