Effect of Coalbed Methane Well Fracturing on Slope Stability of Open-Pit Coal Mine: A Case Study of Shengli East No. 2 Open-Pit Coal Mine

The impact of hydraulic fracture from CBM well fracturing on slope stability of the Shengli East No. 2 open-pit coal mine is analyzed by numerical simulation and limit equilibrium methods. The interference effect of coalbed methane (CBM) well fracturing on slope stability of the open-pit coal mine promotes the coordinated development of CBM, and open-pit coal is discussed before and after coal mining. It shows that nearly horizontal fractures are formed in the coal seam due to CBM well fracturing, of which the dynamic facture length and propping fracture length are 137.2 m and 105.2 m, respectively. Moreover, the dynamic fracture height is 137.2 m and propping fracture height is 130.6 m. At the location of perforation, the dynamic fracture width is 0.873 cm and average propping fracture width is 0.111 cm. The CBM well fracturing barely imposed any effect on slope stability before open-pit coal mining. The maximum vertical displacement at the toe of slope induced by fracturing is 0.293 mm. In situations with and without CBM well fracturing, vertical stress distributions in the toe, top, and interior of slope have no obvious difference. There is some extent of vertical stress increase within the interior of slope, which is merely 0.2 MPa higher than that in the condition of initial in situ stress equilibrium. The presence of hydraulic fractures has little effect on the overall displacement of slope during coal mining; and there is no obvious difference between the slope stability during coal mining and the slope stability impacted by fracturing. According to the results of limit equilibrium method and numerical simulation, the overall slope stability coefficient is 1.5–1.97, which accords with the requirements of theDesign Code for Open-Pit Mine of Coal Industry (GB50197-2015). Therefore, more attentions should be paid to the ways of excavation and sloping during coal mining, avoiding slope instability caused by excavation.

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