Study On Fracture Mechanism And Fractional Order Model Of Seepage-creep For Coal Measures Sandstone

With the deep mining stage of coal mine,the rheological characteristics of coal and rock mass under the complex geological environment are significant,and the stability control of roadway surrounding rock is more difficult.In that case,the safety production of coal mine is facing severe challenges.For some coal mine in the water rich area,the influence of groundwater seepage to accelerate the deformation of roadway surrounding rock.The groundwater influx tunnel water inrush happened at the same time.Study on the characteristics of seepage creep damage and creep model of coal and rock medium is the theoretical basis for controlling the stability of roadway surrounding rock.In this paper,the typical coal seam roof sandstone was taken as the object of study,the scanning electron microscope(SEM)test was built,and the damage mechanism of sandstone under the seepage stress was studied systematically from two aspects of macroscopic and mesoscopic level.Based on the fractional calculus theory,the corresponding creep model was established.The main research have got the following results:(1)The creep characteristics curves of sandstone under four conditions are obtained.As the effects of osmotic pressure and confining pressure on the seepage creep characteristics of sandstone were studied,we obtained the variation law of creep parameters,such as the maximum creep,the creep deformation rate and the seepage parameters in different stages.(2)The macroscopic characteristics of seepage creep failure of sandstone,such as the macroscopic failure mode and the fracture surface roughness,were studied by the built system.Based on the scanning electron microscope(SEM),the microscopic characteristics of the seepage creep failure of sandstone under different conditions were obtained.The evolution law of sandstone damage fracture model with confining pressure and seepage pressure was analyzed.The relationship between local mesoscopic fracture and macroscopic failure of sandstone was established.The mechanisms of creep fracture of sandstone under seepage were brought to light.(3)Based on the theory of rock creep and the theory of fractional calculus and the basic mechanical elements,the integral and fractional nonlinear viscoelastic plastic creep model was built in this paper.Based on the principle of Taisha stress,the integral order and fractional seepage-creep model of coal sandstone were established.The least squares method is used to determine the model parameters.Through the verification and comparison of the model,the accuracy of the model and the superiority of the fractional model were verified.(4)Based on the theory of fractional calculus,apply the thought of element networks,establish the fractional three-parameter solid model based on the distributed order dashpot,and verify its rheological response through a specific example.Based on a single fractional order dashpot with a damaged fraction,propose a damaged distributed order dashpot.Based on the integer Nishihara model,establish a damaged distributed order Nishihara model.At last,verify its creep characteristic response through a specific example.The conclusion can provide the theoretical basis for the stability control of the surrounding rock in deep rich waters and the prevention and control of water inrush.