Study On Seepage-stress Coupling Rheological Characteristics Of Cracked Conglomerate Under Unloading Confining Pressure

With the continuous development of underground coal resources,a large number of constructions of hydropower tunnels and deep traffic,these disaster problems become more prominent which problems such as rheological deformation due to support failure,water-rich and crack growth in the process of tunnel excavation unloading.The rapid excavation and safe operation of the tunnel are seriously affected,so it is urgent to research the evolution law of the seepage-stress coupling rheological characteristics of cracked rock mass under the action of confining pressure unloading disturbance.This paper,taking the main shaft conglomerate section in the construction of Hong Qing Liang coal mine as the research object,and analyzing the seepage-stress coupling rheological characteristics of cracked conglomerate under confining pressure unloading disturbance,and adopting the methods which field investigation,laboratory test,similar material model test,theoretical analysis,numerical calculation and field monitoring.The main results are obtained as following:?1?Through the conventional triaxial compression test of conglomerate,the relationship between the deviatoric stress and the strain of conglomerate are obtained,and the relationship among the volumetric strain,the crack volume strain and the axial strain are also obtained.Based on the M-C principle,the peak stress is most sensitive to the confining pressure,and the closed stress is the least sensitive to the confining pressure.There is a positive correlation between the internal friction angle and the deviatoric stress.If the deviatoric stress is not greater than the peak stress,the cohesion is positively correlated with the deviatoric stress,and vice versa.When the confining pressure is less than 12MPa,the deformation parameters and confining pressure is positively related,whereas is negative correlation,and then the nonlinear function relationship between the deformation parameters and confining pressure is established.?2?The curve of the stress-strain-permeability coefficient of conglomerate is obtained by the conventional triaxial compression test under seepage-stress coupling,and the function relationship between the permeability coefficient and axial deformation of conglomerate under seepage-stress coupling is presented.The relationship between the characteristic strength,elastic modulus and seepage water pressure is negative,and it satisfies the development rule of the attenuation index model,and then the coupling function of seepage pressure and confining pressure is established.Poisson's ratio has positive correlation with seepage pressure,and the relationship between poisson's ratio and seepage pressure is presented under different confining pressures,and then the coupling function of seepage pressure and confining pressure of conglomerate poisson's ratio is established.?3?Base on analyzing seepage-stress coupling theory of continuous homogeneous medium,the similarity parameters and similarity ratio of quasi-conglomerate are determined.By using orthogonal design method,the quasi-conglomerate similar material ratio of main shaft conglomerate section is obtained,cement:Sand:water:water reducing agent=1:2:0.4:0.6%,and sand grain size is 1.0mm².0mm.?4?By considering the crack angle,crack length and crack space relative position sensitivity factors,the uniform experimental design scheme for quasi-conglomerate similar material of single and double cracked is obtained based on the theory of uniform design,and an experimental device of single and double cracked conglomerate specimens is designed and developed.?5?Through seepage-rheology coupling test of single cracked conglomerate under unloading confining pressure,the complete rheological curve of single cracked conglomerate is obtained,respectively.Based on sensitivity analysis of five indexes including confining pressure,seepage pressure,crack angle,crack length and single crack relative to rock specimen top position,the instantaneous strain and creep strain of single cracked conglomerate have the same sensitive for these index,which is seepage pressure>crack length>crack angle>confining pressure>single crack relative to rock specimen top position.The complete rheological rate curve of single cracked conglomerate is obtained under unloading confining pressure,respectively.?6?Through seepage-rheology coupling test of double cracked conglomerate under unloading confining pressure,the complete rheological curve of double cracked conglomerate is obtained.The sensitivity analysis of seven indexes such as different unloading confining pressure,seepage pressure,first crack angle,first crack length,second crack angle,second crack length and rock bridge length,the axial and radial instantaneous strain have the same sensitive for these index,which is seepage pressure>unloading confining pressure>second crack length>first crack length>rock bridge length>second crack angle>first crack angle,and axial creep strain is sensitivity to the these index which is seepage pressure>unloading confining pressure>second crack length>first crack length>first crack angle>rock bridge length>second crack angle,and radial creep strain is sensitivity to the these index which is seepage pressure>unloading confining pressure>second crack length>first crack length>rock bridge length>first crack angle>second crack angle.The complete rheological rate curve of double cracked conglomerate is obtained under unloading confining pressure,respectively.?7?Through the analysis of rheological characteristic and rheological model,which a nonlinear viscoplastic body is introduced to improve the model of accelerated rheological failure stage,the HKN model is obtained which describes the characteristics of seepage-rheology coupling of cracked conglomerate under unloading confining pressure.The constitutive model parameters of seepage-rheology coupling are obtained by using the algorithm of BFGS and general global optimization.?8?Base on the constitutive model and parameters of seepage-rheology coupling of cracked conglomerate under unloading confining pressure,the secondary development of FLAC^3D is adopted to analyze the surrounding rock deformation of the conglomerate test section,and the field monitoring is also introduced,it shows that the combined support system,which is bolt+steel mesh+closed shotcrete+grouting+U-shaped steel bracket,control effectively deformation of main shaft conglomerate section with water-rich and crack growth,and ensure the stability of the surrounding rock of the conglomerate and the rapid excavation safety.