| Grouts are a typical Non-Newtonian fluid,the flow and diffusion behavior of which is governed by its own properties,the Reynolds number,and geometrical characteristics of rock fractures such as surface roughness,aperture and contact areas.To study the flow behavior of non-Newtonian fluids in rock fractures,a compression test was conducted on a granite fracture and its deformation and asperity damage behavior was numerically calculated based on an elastic-plastic contact model.After validation through comparison between the experimental and numerical results,the calculated high-resolution aperture fields under four different normal stresses were selected to establish numerical models,explained in detail its basic principles and simulation methods,upon which the Non-Newtonian fluid flow behavior was studied by numerically solving the Navier-Stokes equations.At the same time,combined with 3D scanning technology,3D printing technology and CT scanning technology,a set of fracture seepage visualization test system has been established,which can observe and study the seepage phenomenon of fracture surface more intuitively.Through the visual experiment,the seepage of non-Newtonian fluid inside the fracture was described,and the reliability of the numerical simulation program was verified.Numerical simulations of non-Newtonian fluid seepage were carried out based on the models under four different stress conditions.The flow characteristics of grout in rock fractures were studied,and the effects of normal stress,fracture roughness,fracture opening,and Re number on the grout flow process were revealed.The main results of this research are as follows:(1)Using 3D scanning technology,3D printing technology and CT scanning technology,using the preparation method of natural rock fracture three-dimensional experimental model,a set of visual test system of fracture seepage flow is established,which can not only change fluid type,but also control fluid pressure and flow.(2)The internal cavity of the rough rock mass crack is gradually compressed during the compression process,causing the contact area to increase and the contact stress concentration is damaged,forming a complex cavity geometry,which significantly affects the nonlinear flow behavior of non-Newtonian fluids,Resulting in a complex distribution of seepage field,and causing phenomena such as channeling and eddy currents.(3)Unlike Newtonian fluids,the flow of non-Newtonian fluids is non-linear,and its permeability coefficient increases first and then slowly decreases with the increase of Re number.The critical Re number appears in the interval of 5-25.It is an important parameter that characterizes the inertial effect,but it is not the only parameter.It always needs to be combined with the specific geometric characteristics and boundary conditions of the fracture to jointly determine the nonlinear flow characteristics of the slurry.Therefore,it is necessary to determine the critical Re number according to the characteristics of the engineering rock mass,so as to design a more scientific grouting scheme according to the actual flow state.(4)Forchheimer's law is suitable for describing the nonlinear relationship between the pressure difference and flow rate of Bingham fluid.The coefficients A and B are linearly and positively related to the normal stress,and there is a hyperbolic function relationship with the RSD of the crack opening.(5)Based on the COMSOL numerical simulation program,the Herschel-Bulkley-Papanastasiou fluid's seepage characteristics in natural rock fractures are numerically simulated.The results show that its permeability in rock fractures is directly proportional to the normal stress and fluid flow velocity,fracture roughness,fluid concentrations,Fissure opening is inversely proportional. |
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