Research On Diffusion Mechanism Andreinforcement Effect Of Groutingreinforcement For Slope Gravel Soil

Slope instability and treatment is a common problem in engineering field.Grouting reinforcement method is one of the effective technical means of slope reinforcement.At present,the grouting reinforcement method is mostly used in the field of sand and clay,and the research on gravel soil is relatively less.Because of the engineering characteristics of gravel soil,such as high stone content,large particle size,loose structure,large porosity and permeability,the diffusion law of slurry in gravel soil during grouting is quite different from that in sand and clay.At the same time,due to the strong concealment and complexity of slurry diffusion in grouting reinforcement,it is difficult to grasp the law of slurry diffusion in grouting process.through numerical simulation and model test,combined with the engineering practice,the widely exists in the central and western regions of China,especially in Tibet,xinjiang and other regions of the gravel soil grouting strengthening grout diffusion regularity and reinforcement effect is studied.The main research contents and results of this paper are as follows:(1)Based on the existing formula of Newtonian fluid,Bingham fluid and power-law fluid slurry laminar diffusion theory,aiming at the engineering characteristics of slope gravel soil,such as high stone content,loose structure,large porosity and permeability,the limitations of existing seepage grouting theory and the slurry flow law in the process of slope gravel soil grouting are discussed,and the influence of slurry diffusion law is analyzed theoretically The theoretical formula of turbulent diffusion radius of Newtonian fluid slurry is derived.(2)Through numerical simulation,aiming at the influence factors such as water cement ratio of cement slurry,grouting pressure and slope gradient,the empirical values of permeability coefficient,porosity and other parameters of slope gravel soil are adopted,and different working conditions are set to study the diffusion law of slurry in slope gravel soil during grouting.The results show that the diffusion radius of the slurry is proportional to the water cement ratio of the cement slurry and the grouting pressure.The diffusion direction of the slurry is mainly perpendicular to the grouting steel pipe.Taking the grouting steel pipe as the center,the slurry diffuses outwards in a cylindrical shape.The insertion angle of the grouting steel pipe is different in different slopes,and the diffusion direction of the slurry is also different.The value is bigger,and there is a significant gap.The results show that the diffusion radius of slurry is larger than that of turbulent diffusion theory and smaller than that of laminar diffusion theory.The pressure along the pipeline decreases with the increase of the distance from the grouting pipe.The attenuation rate of the pressure along the pipeline is related to the water-cement ratio of the cement grout.When the water-cement ratio is 0.5,the attenuation rate is the fastest,then when the water cement ratio is 0.8,and the attenuation rate is the slowest when the water cement ratio is 1.Compared with the empirical attenuation rate of pressure in sand.the attenuation rate of pressure in slope gravel soil is significantly less than that in sand and clay.(3)Through the indoor grouting test,the model in the numerical simulation is reduced to the same scale,and the diffusion law of cement slurry with different water cement ratio in the slope gravel soil layer in the grouting process is studied.The indoor grouting test shows that the diffusion range of cement slurry is directly proportional to the water cement ratio of the slurry,and the slurry diffuses outward in a cylindrical shape with the grouting steel pipe.The range and velocity of slurry diffusion are much larger than empirical values in sand and clay.The diffusion radius of cement slurry with water cement ratio of 1 in the test is compared with that calculated by the theoretical formula of slurry laminar and turbulent diffusion.The diffusion radius of cement slurry in the test is larger than that calculated by the theoretical formula of slurry turbulent diffusion and smaller than that calculated by the formula of laminar diffusion.The results show that the diffusion law of slurry in soil layer is the same in laboratory test and numerical simulation.After grouting,the porosity of soil layer decreases.(4)In engineering application,Through the numerical simulation analysis,it shows that the displacement of the tunnel vault is significantly reduced after the surface grouting reinforcement,the stress state of the tunnel surrounding rock is better,and the plastic zone of the tunnel surrounding rock is reduced,which proves that the surface grouting reinforcement can effectively improve the stability of the tunnel surrounding rock.