浅埋煤层关键层初次破断特征及垮落机理研究

Study on the first failure and caving mechanism of key strata of shallow coal seam

针对神东浅埋煤层关键层垮落容易造成大面积来压和动力灾害的问题,文章系统分析了关键层在工作面推进过程中的破坏过程及垮落机理。数值模拟结果表明,随着工作面的推进,关键层首先在跨中下表面受拉区发生屈服破坏,工作面中部煤壁前方关键层上表面受拉区发生屈服,并进一步沿煤壁延伸形成"O"型破裂带,与关键层下表面不断向四角延伸的受拉破坏区所形成的"X"型破坏带组合成大的"O-X"型破坏带。与弹性薄板理论相比,两者的开裂顺序不同,但最终的破坏形式相同。覆岩与关键层间保持同步变形,且随关键层一同垮落,失稳前挠度明显增加。关键层的失稳形式主要为沿"X"型破裂带发生屈曲失稳和沿"O"型破裂带发生沿煤壁的切落失稳,后者来压更为剧烈。

Considering the problem of large area weighting and dynamic disaster due to the key strata caving in Shendong shallow coal seam, this paper studies the cracking process and the caving mecha- nism of the key strata during the advancement of the coal face. Numerical simulation results indicate that as the coal face advances, failure behavior of the key strata occurred firstly in the downward surface above the center of goal, and then failure behavior of the upper surface of key strata appeared above rib around the centre of face and further formed the ＂0＂ failure pattern along the rib, which combined with the ＂X＂ failure pattern formed in the downward surface tensile failed zone that gradually extended to the four corners shaped the final ＂O-X＂ failure pattern. Compared with the elastic thin plate failure mode, the cracking sequence is different, but they have the same final failure pattern. The overburden and the key strata kept simultaneous deformation, and caved with the key strata; the deflection increased sub- stantially before all strata caved. The main caving patterns of key strata are buckling collapse along the ＂X＂ yield zones and shear failure along ＂0＂ yield zones in front of the face, and the latter will cause more serious weighting.