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ABSTRACT N2105 mining face of Yuwu coal mine, in Shanxi Provence of China, are in conditions of low bursting of coal stratum, roof and floor. Combined action of static and dynamic load on coal and rock can induce the occurrence of rockburst. The prevention of rockburst needs to be consider on two aspects: (1) change the mechanical properties of coal and rock to weaken the capability to store elastic energy, (2) modify the stress state of coal and rock to decrease the degree of stress concentration. The prevention measures of pre-split blasting and destress drilling were put forward. A numerical model established by FLAC3D was investigates the stress evolution in surrounding rock and coal pillar during the implemen-tation of prevention measures. The pre-split measure reduces the disturbance of roof fractur-ing and destress drilling measure can bring down the degree of stress concentration. In field test, sandstone strata with height from 23 m to 32 m was target region for pre-split blasting and the drilling borehole in pillar range from 20 m to 30 m in length. The implementation of comprehensive measures guaranteed N2105 working face was in normal production and advanced 1200 m securely.
1 INTRODUCTION Rockburst hazard have been a major safety concern in underground coal mining for recent decades (Jiang, 2012; Wang, 2017). Rockburst occurs with a sudden and violent failure of coal mass and rock to releases elastic energy. A large amount of coal and rock are expelled into roadway or working tace where men and machinery are present (Jiang, 2012). With the depletion of mineral resources in near surface ground, mining exploitation at great depth become an inevitable trend and the occurrences of rockburst significantly increase and seri-ously threaten safety production (Li, 2013).
Application of Longwall mining method in underground results in generation of gob area, millions of cube meter in space. Longwall mining is characterized by variation of mining-induced stress, frequent disturbances to surrounding rock and macroscopic failure region. Cai suggests that the kernel function of the measure is to reduce rock stress concentration and disturbance energy accumulation in rock mass (Cai, 2016). Geomechanical methods, comprising destress drill, distress blasting and seams watering, are used in Ostrava-Karviná Coalfield. Multiple measures were adopted to prevent rockburst by Wang et al., including the prediction and early warning measures, stress relief by blasting in advance, optimized blasting design and optimized tunnel support (Wang, 2012). A technology of directional hydraulic fracturing was used to cut groove in hard roof for rockburst prevention by He and Dou et al. (He, 2012). In the Polish part of the USCB, torpedo blasting are performed to decrease local stress concentrations and to fracture roof rocks to minimize the impact of high-energy tremors on excavations (Wojtecki, 2017). Zhu and Lu et el. studied prevention of rock burst by Guide holes based on numerical simulation (Zhu, 2009). He et al. developed the constant-resistance and large-deformation bolt to control and prevent rockburst (He, 2015).
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