Analysis Of Deep Soft Coal And Rock Loose Deformation With Time Evolution

With the increasing intensity of coal mining,the shallow resources have gradually depleted and the depth of the tunnel excavation is increasing,a large number of coal mines has entered the stage of deep mining,China’s coal industry has to face for problems and difficulties what caused by deep mining,such as high ground temperature,gas volume,large underground pressure,supporting difficulties.As a weak organic rock,coal is more sensitive to temperature and stress,in deep conditions showed strong creep deformation characteristics.Studies have shown that:Deep Rock has sustained strong rheological properties,the performance of large deformation,long duration,which has a significant time effect.Therefore,the use of scientific research methods on the creep characteristics and variation of deep soft rock of coal to carry out studies to determine the scope of loose circle evolution over time,and has a theoretical and practical engineering to solve practical engineering problems associated with creep.Based on a comprehensive analysis of domestic and foreign rock creep testing machine and creep numerical simulation,carried out the following studies and draw some conclusions:(1)Using the SD-20 instrument for rock creep grade coal and rock uniaxial loading and unloading creep compression test,and obtain creep parameters of coal by nonlinear fitting.Through the analysis of coal and rock uniaxial compression creep test curve,you can see: at lower stress levels,coal and rock specimens transition from the initial stage and quickly into stable creep stage,when the stress level exceeds its yield the limit,the rock comes into the constant creep stage,the strain increases with time going by,if the strain value exceeds its limit strain value,the specimen will damage;sectional shape of the roadway has the greater inpact on roadway displacement,the displacement of rectangular roadway largest,followed by a curved wall and circular roadway minimum.(2)Using the finite difference software FLAC3 D select strain softening /hardening model combines Burger creep model and simulation deep soft coal and rock roadway surface stress and displacement changes with time under different conditions(different stresses,different cross-sectional shape).The simulation results show that with the increase of the stress level,the displacement of the roof,floor and floor of the roadway is gradually increased,but the increase is gradually reduced;roadway surface displacement amount under the same stress level overall exhibit "with the side of displacement greater than the top floor displacement and greater than the amount of displacement" feature;depth deeper roadway surface vertical stress increases within a certain time,the growth rate transitioned from increases into decreases,and appeared slightly reduced vertical stress phenomena,which produce a stress relaxation phenomenon;(3)Monitoring points are arranged on the periphery of the roadway around 10 directions,taking displacement attenuation coefficient as a standard to determine the changing trend of loosening range of the rock under different stress.The simulation results show that at lower stress levels,the initial tunnel excavation,the corners loose circle of development lags behind the tunnel with the side and the top floor on tunnel excavation initial stage,with the increase of the creep time,the shape of loose circle fuller,the greater the stress,the shape of loose circle more close to the circle shape.