Research On The Overlying Strata Rupture Law And Control Technology Of Narrow Coal Pillar Roadway With Shallow-buried And Thin Bedrock

Under the action of dynamic pressure,coal pillar wall of shallow buried thin bedrock narrow coal pillar tunnel is easy to creep buckling,the entity coal is under high concentrated stress,and surrounding rock control is difficult.The overlying rock layers rupture rules and stability control techniques of shallow buried thin bedrock narrow coal pillar tunnel was studied systematically by adopting integrated methods of theoretical analysis,numerical simulation and field test.The main works accomplished in the dissertation are as follow:(1)Based on the half infinite Winkler cantilever beam theory on elastic foundation,the calculation formula of bedrock breaking location in the lateral coal pillar and the relation between bedrock lateral breaking location,suspension girder length and periodic weighting length were proposed.Because of basic roof thickness is big,periodic weighting length is long,and lateral breaking location is deeper inside the coal pillar,a larger range of pressure reducing area is formed in the coal pillar,which provide powerful position for supporting tunnel with narrow coal pillar.(2)The rectangular hole surrounding rock mechanics analysis model was built,the calculation formula of rectangular roadway surrounding rock stress and vertical stress in coal pillar were given,the i MPact of overburden pressure,section size and side pressure coefficient on them was analyzed,and the instability mechanism of shallow buried thin bedrock narrow coal pillar tunnel was revealed.When driving with narrow coal pillar,affected by the stress superposition,the stress concentration factor in shoulder angle is greater than the single lane driving.The surrounding rock in shoulder angle under high bearing pressure is easy to shear instability.When the narrow coal pillar width is small,narrow coal pillar stress concentration factor increases,is easy to buckle in compression.(3)Based on elastic foundation theory,the calculation formula of bedrock broken lateral plastic zone width was given.When the bedrock thickness is big and is the only main key stratum,bedrock fracture is not affected by overburden pressure and mining space.the rational width range of coal pillar was determined as B≤11.2m.The roadway surrounding rock stress distribution,deformation and destruction law were studied under the condition of different coal pillar width using numerical simulation method.The rational width of coal pillar is 10 m.There is stable bearing area under shear failure,two side coal-walls bearing uniform,Entity coal-walls have relatively large bearing capacity;the stress concentration coefficient is relatively high.For better stress distribution state,only appeared destruction in central of coal-walls,the control difficulty is relatively low.(4)The two zone(Large deformation zone of narrow coal pillar and high stress concentration zone in entity coal)of shallow thin bedrock narrow coal pillar tunnel are the weak area of surrounding rock control,the control techniques of high pre-stressed let pressure bolt support and secondary support in coal side were developed.On the basis of the control techniques of shallow buried thin bedrock narrow coal pillar tunnel,the industrial test was carried out in the 42113 assisted transport tunnel of Liangshuijing coal mine.Field application shows that the control techniques effectively control the deformation of surrounding rock,and ensure the stability of surrounding rock and supporting structure.