The Deformation Mechanics Of Surrounding Rock And Supportive Technology Of Secondary Gob-Side Entry Retaining

This thesis was done with the aimed of researching the secondary gob-side entry retaining under the mining situation of inclined close range thin coal seams. Based on above conditions, the distribution and evolution of mining induced stress and fracture in surrounding rock during the whole process of mining were analyzed. According to the charactertics of damage and structure of overlying rock stratum, the stability of roof in stope and mechanical behavior of surrounding rock in different mining stages were discussed. The internal force, stress, fragmentation and damage characteristics of roof were analyzed. Furthermore, the stability analysis model for key block in secondary gob-side entry retaining was established. Accordingly, the stability of the key block was calculated under series of supportive situation. In addition, the experiments and research on the mechanical properities of gangue were conducted. Through the above work in this thesis, the main research results and progresses were as follows:(1) During the whole process of secondary gob-side entry retaining, the dynamic distribution and evolution of the distressed zone, abutment stress, stress in gob-side support and fracture in stope were measured and studyed. The new defination of damage factor was proposed in this thesis. It was based on the ratio between the numbers of interparticle breaking bond and the initial bond. Then it was used to analyze the damage evolution of surrounding rock in different mining processes.(2) According to the deformation and fracture criterions, the key stratum above stope was determind. The mechanical model for calculating the hight of fracture zone was also established. This model was based on energy conservation theory. Based on the mining and geological situation of Weijiagou coal mine, the hight of fracture zone was calculated. Through the use of fractal theory, the varation of fractal box dimention in surrounding rock during different mining strages was analyzed. Such stages included the whole process of secondary gob-side entry retaining.(3) Based on the particle flow theory, the elastic modulus, stiffness ratio of particle and bond and the interparticle friction coefficient were selected as variables. The relationship betwee these paramaters and peak strength, peak strain, elastic modulus was calculated. The macroscopic mechanical response with the changes of microscopic parameters of particle and bond was acquired. According to the results of sensitivity analysis and calibration, the development and evolution of fracture field in stope were analyzed.(4) The simplified plate model with the boundary condation of four edges clamped was establish in this thesis. By applying gradient and uniform load to simulat the stress boundary condation of inclined and horizontal coal seam. The weighted residual method was used to deduce the formular of the deflection function and the distribution function of internal force and stress in roof. According to the result of numerical simulation, the breakage of roof under uniform and gradient load were studied. Moreover, the plain truss structure model of rock block(result from roof breaking) was established. According to the motor method, the calculating function of rock block size was deduced. The sensitivity analisis of the influence factors was also conducted. It suggested that the thickness of strata had the greastest impact on the size of key block, load of overburden strata followed, the influence of roof tensile strength was relative distinct in smaller range of value, the length of working face had the least influence amoung all paramaters.(5) Based on the deformation and breakage of roof during secondary gob-side entry retaining, the stability mechanical model of key-block was constructed. This model could be used to describe the equilibrium state of key block behind mining face in the first and second mining and in frount of mining face in secondary mining. The stability decision functions and were proposed. The stability of key block was analyzed in different mining stages with the changing of support paramaters. Additionally, the deformation, load-bearing capacity and breakage of gob-side support was simulated.(6) In order to test the bearing capacity of gangue under free compaction, the particle flow simulation and physical experiments were carried out. The results indicated that when the particle size of the gangue was small, the load-increasing rate was less than larger particle at first, but it increased faster larger ones. If the gradation of gangue was conformed to Talbot’s gradation, the early compressing displacement of gangue was much smaller than single gradation ones and the loading-increasing rate repaidly rised. Moreover, the anchored gangue had better mechanical properity. The compaction of gangue could be divided into three stages in times: rearranging stage(stage I); breaking stage(stage II) and consolidating stage(stage III). According to the force state in stage II and III, the spoils can be divided into three zones: rearranging zone(zone I); interlocking zone(zone II) and consolidating zone(zone III) from outside 1K2 Kto inside. Among them, the consolidating zone was the main part to bear the weight of overlying strata which had greatest impact on the compaction properity.(7) According to the deformation of roof during the secondary gob-side entry retaining, supporting polices are proposed as follow: adopt mechanical reasonable supportive material; utilize the sef-bearing properity of surround rock sufficently; couple the mechanical behavior of system; design the technology reasonablly; regard the project as an extremely complex system engineering. This thesis also explored adopting the scheme of “anchored gangue bags” to conduct secondary gob-side entry retaining. Accordingly, the complete supportive technology was formed based on the industrial situation. Finially, by using the supportive design in this thesis, a better supporting effect was acquired through industry test.