Research On Loose Zone Of Fractured Rock Roadway Based On H-B Strength Criterion

China is the largest energy consumer in the world.The resource endowment of "rich coal,little oil and poor gas" determines that for quite a long time in the future,coal is still the main body and basic energy in China.At present,in the process of underground coal mining,the serious deformation of the roadway hinders the normal production of coal,resulting in the improvement of the repair rate of the roadways that have been excavated,increasing the support cost of the roadway,and seriously affecting the safety and efficiency of coal production.The loose zone of surrounding rock means that the surrounding rock is disturbed by the excavation process,which will form a ring-shaped area of severe fracture inside the surrounding rock of the roadway,and there is a ringshaped plastic softening area outside the area of severe fracture,The severe rupture zone and plastic softening zone are collectively known as loose zones.In order to accurately determine the size of the loosening circle,this paper,relying on the project of "detection of the loosening circle of the Berlin coal mine" signed by DaZhou company of Sichuan coal group,carried out the detection research on the size of the loosening circle of the surrounding rock of the tunnel.The conclusions are as followings:(1)This paper systematically expounds and analyzes the characteristics and classification of surrounding rock loose zone,discusses the application conditions of HB strength criterion,studies the application of H-B strength criterion in the theory of surrounding rock loose zone and the selection method of relevant parameters.(2)Taking Berlin coal mine as the background,the in-situ stress test was carried out to get the maximum principal stress close to the horizontal direction,and the minimum principal stress is vertical direction.Through the field measurement of the surrounding rock of the coal mine roadway by GPR,it is found that the range of roadway loose zone is 1.91m-3.11 m,which belongs to the large loose zone,and the surrounding rock type is V type unstable surrounding rock(soft surrounding rock).(3)The FLAC numerical software is used to simulate the dynamic evolution process from occurrence to stability of the loose zone after the tunnel excavation.It is found that the development speed of the loose zone of the surrounding rock is first steep then slow with time.At the same time,the section of the mine roadway is modeled with equal proportion,and the scope of the loose circle of the surrounding rock of the roadway under the existing support is simulated.(4)In view of the deficiency of existing support,the process of deformation of surrounding rock of roadway under two different support conditions is simulated.It is found that the optimized support method can effectively limit the expansion of the loose area of surrounding rock,reduce the deformation of surrounding rock,and control the subsidence and spalling of the roof of roadway.