Research On Coalseam Instability Beside Roadway Based On The Unified Strength Theory

In the process of coal mining,the stability of coalseam beside roadway is always an important subject in coal engineering.The coalseam instability beside roadway can be divided into three aspects: the translatory coalseam burst and instability and the translatory coalseam bumps beside roadway before mining;and the strip coal pillar instability in protection roadway after mining.At present,most of the theoretical researches take the Mohr-Coulomb strength criterion and Hoek-Brown strength criterion as the yield criterion of the coalseam plastic zone,without considering the beneficial effect of intermediate principal stress on the coalseam strength.It can't calculate the coalseam stress or stability correctly and give full play to the strength potential of coalseam.The unified strength theory reasonably considers the intermediate principal stress effect and includes the existing main strength criterion,which can be applied to various engineering materials with different characteristics.Therefore,based on the unified strength theory,this paper makes an in-depth and systematic study of the coalseam instability beside roadway from these three aspects.The main research contents and conclusions are as follows:(1)Aiming at the problem of the translatory coalseam burst and instability beside roadway,based on Lippmann theory,the unified stress expressions in plastic zone and elastic zone of coalseam before instability are derived.According to the vertical stress disturbance increment equilibrium and the horizontal stress boundary condition,the analytical formula of the disturbance depth and the unified solution of the plastic zone width are obtained.Then the correctness of the solution is verified by comparing relevant literatures.The results show that deep buried coalseam has a high tendency of instability and a large failure range,while thin coalseam is more prone to burst and instability in a small range.(2)Aiming at the problem of the translatory coalseam bumps beside roadway,the bump model of coalseam containing gas is established.Combined with linear,sinusoidal and exponential gas distribution forms,the unified solution of stress,disturbance depth and the plastic zone width under the different gas distribution were derived,and the correctness was verified by the relevant literature.The research shows that when the lateral pressure coefficient is higher,the tendency of coalseam bumps decreases.The gas pressure and its distribution form have a great influence on the coalseam bumps,and the adverse effects of gas should be considered to protect the safety of the roadway in the actual project.(3)Aiming at the problem of the strip coal pillar instability in protection roadway,by classifying inclined coalseam into horizontal coalseam,the ultimate strength formula of the inclined strip coal pillar with reasonable consideration of the intermediate principal stress is proposed.Then,combining with Wilson theory,the unified solution of inclined strip coal pillar width considering the effect of gangue support and coalseam dip angle is established.The results were verified by comparing the empirical formula based on Mohr-Coulomb strength criterion.It can be concluded that the caving gangue has more obvious supporting effect on the overlying strata for the coal seam with shallow burial or large mining width.In addition,the specificity of the inclined coalseam should be considered when the coalseam dip angle is greater than 10°.(4)Based on the above study,it can be concluded that the intermediate principal stress has obvious influence on the coalseam stability.Reasonable consideration of the beneficial effect of intermediate principal stress is conducive to the correct analysis of coal seam stress and give full play to the bearing potential of coalseam.(5)Cohesion and internal friction angle are important strength parameters of coalseam,and their variability should be fully considered,especially internal friction angle.The interface strength parameters reflect the sliding effect of coal-rock interface and have a significant influence on the coalseam stability,which should be taken seriously in the research.