Abstract
Sudden falls of large-area hard roofs in a mined area release a large amount of elastic energy, generate dynamic loads, and cause disasters such as impact ground pressure and gas outbursts. To address these problems, in this study, the sleeve fracturing method (SFM) was applied to weaken a hard roof. The numerical simulation software FLAC3D was used to develop three models based on an analysis of the SFM working mechanism. These models were applied to an analysis of the fracturing effects of various factors such as the borehole diameter, hole spacing, and sleeve pressure. Finally, the results of a simulation were validated using experiments with similar models. Our research indicated the following: (1) The crack propagation directions in the models were affected by the maximum principal stress and hole spacing. When the borehole diameter was fixed, the fracturing pressure increased with increasing hole spacing. In contrast, when the fracturing pressure was fixed, the fracturing range increased with increasing borehole diameter; (2) The most ideal fracturing effect was found at a fracturing pressure of 17.6 MPa in the model with a borehole diameter of 40 mm and hole spacing of 400 mm. The results showed that it is possible to regulate the falls of hard roofs using the SFM. This research may provide a theoretical basis for controlling hard roofs in mining.
Highlights
Hard roofs in mining areas may generate very strong pressures
A high pressure load on the roof control area of a fully mechanized mining face (FMMF) can seriously damage the FMMF support structures if no timely and effective measures are taken to regulate the fall of the hard roof
A few of the drawbacks of other methods could be overcome by applying the sleeve fracturing method (SFM) to hard-roof weakening at the FMMF of a deep mine
Summary
Hard roofs in mining areas may generate very strong pressures Their dynamic load coefficient may reach 3.5, with maximum pressure spacing as large as 160 m. A high pressure load on the roof control area of a fully mechanized mining face (FMMF) can seriously damage the FMMF support structures if no timely and effective measures are taken to regulate the fall of the hard roof. This high pressure load may cause a hurricane or impact ground pressure, which leads to accidents, including serious damage to equipment, heavy mining staff casualties, and instantaneous outbursts of accumulated gas in the mined areas [5,6,7,8,9]
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