Abstract
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 the Design 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.
Highlights
As an important way to alleviate the imbalance between the supply and demand of oil and gas and the safe production of coal resources [1,2,3], coalbed methane (CBM) development and utilization can facilitate the optimization of national energy structure and the reduction of greenhouse gas emissions [4]
By taking the Shengli East No 2 open-pit coal mine as a case study, the 3D modeling of fracture geometry caused by the CBM well fracturing was achieved by the Fracpro PT software, and the impact of CBM well fracturing on slope instability before and after open-pit coal mining was simulated by the FLAC3D software. e evaluations of physical and mechanical property changes of the strata after CBM well fracturing and their influence on slope stability of coal mine provide guidance for the collaborative development and utilization of CBM and coal resources in the study area as well as engineering experience for similar projects
According to the stratigraphic conditions of study area, a numerical simulation model was established about the southern slope of the mine pit, in order to evaluate the impact of the nearly horizontal deep fractures induced by CBM exploration well fracturing on slope stability [19, 20]
Summary
As an important way to alleviate the imbalance between the supply and demand of oil and gas and the safe production of coal resources [1,2,3], CBM development and utilization can facilitate the optimization of national energy structure and the reduction of greenhouse gas emissions [4]. Some previous studies on slope stability of open-pit coal mines proposed that the alterant or influential factors for stress state and strength property of slope rock mass mainly include lithology, rock mass structure, hydrological effect, weathering, earthquake, natural stress, topographic features, and human activities. E impact of CBM development on the stability of open-pit coal mines is mainly due to the large number of cracks generated during the fracturing process. Researches about the effect of CBM development on slope stability of open-pit coal mines are less, and there is no practical engineering experience for reference. E evaluations of physical and mechanical property changes of the strata after CBM well fracturing and their influence on slope stability of coal mine provide guidance for the collaborative development and utilization of CBM and coal resources in the study area as well as engineering experience for similar projects By taking the Shengli East No 2 open-pit coal mine as a case study, the 3D modeling of fracture geometry caused by the CBM well fracturing was achieved by the Fracpro PT software, and the impact of CBM well fracturing on slope instability before and after open-pit coal mining was simulated by the FLAC3D software. e evaluations of physical and mechanical property changes of the strata after CBM well fracturing and their influence on slope stability of coal mine provide guidance for the collaborative development and utilization of CBM and coal resources in the study area as well as engineering experience for similar projects
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