Stability control mechanism of support-surrounding rocks at fully mechanized mining face with great cutting height

Abstract：Fully mechanized mining technology with great cutting height is an important development trend with safety,high efficiency and high recovery rate,but it is hard to control the difficulties of rib spalling,roof falling,high support pressurizing and failure rate with the cutting height development to 6.0~7.0 m which have become the prominent problems for the application of this technology.In order to face these challenges and consider the strong crossfeed connection of rib spalling,roof falling,support pressurizing and failure,this paper focused on 6.0 m fully mechanized high seam mining stope,the theoretical analysis,numerical simulation,physical modeling,simulation experiments,simulation experiments and field measurement are used in this study and the mechanism of support-rock stability control in the high seam mining stope is systemically researched,the following results are obtained：（1） The overlying rock structure and the reasonable loading of support in high seam mining is researched.According to the important influence of direct overlying thick and hard roof rocks on the collapsing of under rock,the concept and determination method of key direct overlying layer are proposed,the overlying strata collapsing features and the distribution of advanced supporting pressure are analyzed.Based on whether the direct roof having the key direct overlying layer or not,the direct support resistance is calculated,typeⅠwith no key direct overlying layer condition the support resistance is calculated by 4 to 8 times weight of cutting rock while the type Ⅱ with key direct overlying condition the support resistance is calculated by considering the thickness,intensity and of layer horizon features of key direct overlying layer.（2） The stability control mechanism in high seam mining is researched.Based on the research of critical instability angle,the mechanical characteristics of the support declining,dumping and tail twisting are analyzed,the sensitivity analysis method is used to control the support stability in high seam mining stope,the pertinence and validity of stability control are enhanced,the coal leaving method in the bottom is proposed,the combination of bottom coal recovery and stability improvement of the bottom declining support group is achieved.（3） The mechanism and prevention techniques of rib spalling of high coal wall are researched.Rib spalling is the instable process from micro fractures developing to macro ＂wedge＂ sliding body,in order to reveal the microscopic mechanism of rib spalling,the damage mechanics theory is used and the connection of coal wall damage variability and the degree of fracture development is established;based on the measurement of rib spalling of high coal wall characteristics,the three-dimensional mechanical model of coal wall with ＂wedge＂ sliding stability analysis is set up,the main factors affecting its stability is analyzed,the rib spalling macro mechanism is revealed,high rib spalling control technique is proposed.（4） The coal wall stability control is put into the system of stope support-surrounding rock control system,the concepts and calculation methods of support equivalent resistance and equivalent protecting force are proposed,the interaction mechanism of high seam mining stope ＂Coal wall-Roof-Floor＂ space rock movement and the support working state is revealed.（5） The stope support-rock interaction relationship is researched using the system dynamics method,the SD model of high seam mining stope ＂Coal wall-Roof-Floor-Support＂（W-R-F-S） system is initially established,through the simulating by Vensim simulation software,quantitative description of ＂W-R-F-S＂ system stability under different control conditions is achieved.（6） The above results are applied and validated in the Xutuan 7219 working face of Huaibei Coal Mining Group and Sijiazhuang 15104 working face of Yangquan Coal Mining Group,the pressure regulation,coal wall spalling features and support-rock interaction relationship of the typical high seam mining stope are measured in in-situ situation.