| For top-coal caving working face, gob-side entrydriving is the important supporting technologies for mining and development replacement, continuous production, raising the recovery rate of coal resources. It is widely used in coal mine in our country. The gob-side entrydriving is on the verge of mined-out area. In this area the surrounding rock stress conditions is deteriorated and the stability of the surrounding rock is broken down due to the influence of the breakage structure of lateral upper roof and the mining of working face during service. There are great threats to the stability of surrounding rock of gob-side roadway, and it has became the most important technology of gob-side entrydriving in field application.Combined methods of theoretical analysis, numerical simulation and physical simulation were employed in this study. Based on the breakthrough point of the lateral upper roof breaking the many times structure, the structure character of surrounding rock of the gob-side roadway in different conditions was studied, the deformation mechanism of surrounding rock of the gob-side roadway was revealed. On these basis, the surrounding rock strengthening technology which is used to control the deformation of small coal pillar and floor was proposed. The main results were concluded as follows:(1) The structure of lateral upper roof produces an immense horizontal thrust by the fully mechanized caving faces results severe stress disturbance on the lateral coal mass. The influential distance and stress concentration factor of the advanced support pressure have discrepancy in the working face top coal pillar, the lateral structure of main roof breakage and the working face. The stress distribution on top coal pillar is influenced by the lateral structure of main roof breakage structure, and the leading role is different under different pillar condition.(2) The relationship between main roof breakage form and pillar size is revealed: When the pillar is in small size, the "three hinged arch" structure of last face make the breakage structure of main roof transferring from clamped cantilever beam structure to the hinge beam structure. Rock fracture length is long and the secondary fracture occurs in some certain conditions. The clamped breakage also occurs in the next face and the movement range of the roof gradually near the coal pillar.(3)The instability mechanism was analyzed based on the study of the mechanics characteristic and deformation law of the small pillar. The deformation neutral surface is proposed and it can serve as the anchor rod anchor points. The anchor bolt support can increase the wide and load capacity of the ultimate bearing area, realizing the stabilization of the small pillar. Thus the full-plasticity small pillar strengthen control technology is developed.(4) The gob-side entry mechanism of floor heave under dissymmetrical vertical stress is carried out, the discrimination formula of the bottom plate bending rupture and longitudinal shear fault uplift in thin hard stratum is obtained. Under the vertical stress, the breakage of the upper hard stratum is the cut-off point: The hard stratum bending dominant the bottom up and limit the deformation of the weak layer in preliminary stage. Then in later stage the hard stratum was broken, the weak layer slippage became the main part of bottom deformation without restriction.(5) Based on the bottom deformation character of the gob-side entry, by making the bolt pre-tightening force and bottom layers into one unit, it can increase the flexural strength and improve the ability of resisting interlayer sliding to limit the sliding space of the central soft rock.These research results has been successfully applied to the field test in typical geological conditions of Pangpangta coal mine.The essay has 137 pictures, 14 tables and 153 references. |
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