Study On The Diffusion Mechanisms Of Grouting Within Fractured Rock Mass Under Deep Ground

Grouting technology,as a common mean of tunnel excavation,roadway excavation,dam surrounding rock water plugging,underground oil storage,nuclear waste disposal and other underground engineering,has been widely used all over the world.Studying the seepage mechanism of grout in fractured rock mass under deep ground has important theoretical significance and engineering application value for perfecting grouting theory and improving grouting effect in fractured rock mass under deep ground.Based on the grouting of surrounding rock in deep roadway engineering,this paper comprehensively applies laboratory test,theoretical analysis,numerical simulation and on-site monitoring to deeply and systematically study the mechanism of seepage of slurry in fractured rock mass under deep ground.And the following innovative research results and main conclusions have been made:（1）Based on the concept of critical fracture aperture proposed by Eriksson and Stille,a test system for visualization grouting within a single fracture was developed,compared with traditional grouting seepage test system,this system has the following advantages:（1）Both sides of the fracture model are composed of transparent tempered glass,therefore,the flow mode of slurry in the fracture can be visually observed,which solved the problem of concealment of slurry diffusion from the level of laboratory experiment;（2）The microscope observation system consists of a long distance microscope and a high speed camera,which can real-time observe and record the movement law of slurry in fracture from microscopic level,for example,the mechanism of percolation threshold effect studied from the microscopic level;（3）The aperture of the fracture model is controlled by high-precision stainless steel gasket,which can adjust the fracture aperture more precisely,thus the more accurate critical fracture aperture b_critical and minimum fracture aperture b_min can be obtained.It provides an effective means of testing groutability in fractured rock mass under deep ground.（2）Based on the fractal Brown motion and Hurst indexes calculated by 10 typical rock contour curve of rock fracture surfaces,then the contour curves of joint surfaces with different fractal dimensions were reconstructed,and a single fracture grouting model with different fractal dimensions is developed by using the reconstructed contour curves.Combined with the single fracture visual grouting test system,a coarse fracture grouting test system based on fractal dimension is developed,and the seepage test of slurry in rough fracture under different pressure,different fracture apertures and different roughness was carried out,the seepage law of slurry in rough crack under different conditions was studied and the influence of parameters such as grouting pressure,roughness and fracture apertures on the seepage law of slurry in the crack is revealed.（3）Using the constitutive equation and motion equation of Bingham fluid,the expression of the average flow velocity of Bingham fluid in a one-dimensional flat fracture is derived,combined with the Forchheimer equation for Newtonian fluid under ideal conditions,the Forchheimer seepage equation of Bingham fluid flowing in a smooth fracture is obtained.Based on the comparison between the experimental results and theoretical results of Newtonian fluid and Bingham fluid seepage in the fracture,the effect of roughness on the seepage law of slurry was revealed.By introducing dimensionless coefficients a_D and b_D（a_D and b_D are functions of fractal dimension D）,the frictional resistance of fluid flow in the real fracture is reflected,and the Forchheimer seepage equation based on fractal dimension is established.The dimensionless coefficients a_D and b_D were determined according to the fitting formula of grouting seepage test data of smooth fracture model,then the expression of Forchheimer seepage equation based on fractal dimension is determined.By using the numerical calculation software COMSOL,the numerical calculation fracture models with different fractal dimensions were established and the influence of parameters such as grouting pressure,roughness and fracture aperture on the seepage law of slurry in the rough fracture was studied.（4）Based on the grouting of fractured rock mass in deep roadway engineering,using the Forchheimer seepage equation which based on fractal dimension,combining with the analysis of the fracture characteristics of the surrounding rock and the statistical law of fracture apertures obtained from the drillhole optical pictures of the fractured rock mass,the seepage model of borehole grouting in fractured rock mass is established.Then,the influence of surrounding rock fracture degree and grouting pressure on slurry diffusion distance was studied systematically,and the diffusion mechanism of grouting in fractured rock mass under deep ground is revealed.It provides a reference for the selection of reasonable supporting parameters for grouting in fractured rock mass under deep ground.The dissertation incudes 129 figures,36 tables and cites 183 references.