| Integrated pillarless coal production and methane extraction is the scientific mining mode for coal muti-seams with high gas content and low permeability, which is safe and highly efficient. However, the gas extraction borehole arranged in lateral roof above the roadway retaining is easy to deformation and failure by mining-induced influence and the borehole cann’t reach its full extraction potential. How to guarantee the stability of borehole during the dynamic process of coal face advancing has become one of the key problems of implementing the integrated pillarless coal production and methane extraction.The comprehensive research methods, such as physical simulation, theoretic analysis and numerical simulation, are used in this dissertation. Firstly, taking the small environment of borehole as the research object, the compression and shear fracture mechanism of borehole are analyzed intensively and the corresponding instability criterions are proposed. Secondly, taking the big environment of mining-induced surrounding strata as the research object, the interfacial shear slip laws and mining-induced stress distribution characteristics of lateral roof above the roadway retaining are researched. Then, the space-time evolution regularities of borehole fracture are obtained based on the instability criterions of borehole built earlier. Ultimately, three implementation patterns and security technologies for the integrated pillarless coal production and methane extraction are put forword. The main conclusions in this dissertation are as follows:(1) The self-stabilized evaluation model of borehole under in-situ stress is built. It points out that there exists a self-stabilized critical depth of borehole. When mining depth is less than the critical depth the borehole can maintain its stability. Whereas the casing should be installed to prevent the occurrence of borehole collapse. Then, the compression and shear fracture mechanical model of casing are built and the corresponding instability criterions of casing is presented. Furthermore, the deformation fracture law and influence factors of casing under compression and shear effects are investigated to validate the proposed theoretical model based on FLAC3 D.(2) The similar material experiment is adopted to analyze the displacement distribution characteristic of lateral roof above the roadway retaining. Given the reduced-span effect of roadway retaining, the interfacial shear slip formula of lateral roof is derivated based on the surface subsidence probability integral method, and the effect of mining height, mining depth and roof subsidence in backfilling wall side is studied.(3) The multidimensional coupling numerical simulation method is proposed and the dynamic simulate of the gob area is realized based on the double-yield model. The dynamic variation rule of mining-induced stress, displacement and permeability are obtained. Combination with the instability criterions of borehole built earlier, the space-time distribution characteristics of borehole fracture are revealed and control principles for borehole stability are proposed.(4) On the basis of effective space in retained entry, three measures to conduct the integrated pillarless coal production and methane extraction are presented. They are combination of roadway retaining and face-lagging inclined borehole, combination of roadway retaining & face-advancing inclined borehole, and combination of roadway retaining & high return airway inclined borehole. Moreover, several essential techniques to guarantee the integrated pillarless coal production and methane extraction are also put forward.(5) Combination with two engineering cases of the integrated pillarless coal production and methane extraction which contains roadway retaining & face-advancing inclined borehole of working face 1111(1) and roadway retaining & high return airway inclined borehole of working face 1112(1) in Zhuji coalmine, Huainan area, these above technologies are tested and verified in this dissertation. |
PDF Full Text Request