Study On Particles Flocculation Effect Of Cement Slurry And Injectability Of Porous Media

China's underground engineering construction mostly crosses the Quaternary sand layer.The characteristics of this stratum is larger internal porosity,low bonding strength,and poor self-stabilizing ability,so major disasters such as landslide instability and sand collapse often occur under the disturbance of external forces.Grouting method is the most commonly used method for controlling sand-land layer disasters.Affected by the flocculation effect of cement particles,although the pore size of the sand layer is much larger than the particle size of the cement powder,the cement cannot be effectively infiltrated into the sand layer.In this paper,the flocculation effect of cement particles is studied by focusing beam reflectivity measurement system,viscometer and hydration heat analyzer.The particle size characteristics of flocculated particles in the slurry are analyzed.The relationship between slurry rheology,flocculation structure and hydration heat release is discussed.Finally,the influence of cement flocculating particle size and sand layer pore size on the injectability of sand layer was studied through indoor grouting test.The main work and innovations of this paper are as follows:(1)The particle size distribution characteristics of the flocculated particles in the slurry under the in-situ state were obtained by the focused beam reflectance measurement system.Significant flocculation effect occurs when cement particles are mixed with water,and the size of cement particles was about 3 times that of cement powders.(2)Combined with sand grouting engineering,the influences of water-cement ratio,cement fineness and water reducing agent commonly used in underground engineering on the flocculation structure of cement slurry were studied.The particle size of cement powder and the particle size of slurry flocculation are compared.It indicates that Water-cement ratio,cement fineness and water reducing agent significantly change the particle size distribution characteristics of flocculated particles in the slurry,and ccement fineness has the greatest influence on the particle size of slurry flocculation particles,followed by the ratio of water reducing agent and water-cement ratio.The larger the flocculated particles in the slurry,the more unstable the structure.In addition to the action of the water reducing agent,the smaller the initial flocculated particles,the faster the growth rate.On this basis,the quantitative relationship between water-cement ratio,cement particle specific surface area,hydration time and cement flocculation average particle size is established by numerical fitting.(3)The change of the viscosity of the slurry is the change of the flocculated particles in the slurry.The water-cement ratio is increased,the water reducing agent is increased,the particle size is reduced,the flocculation structure is broken,the free water content is increased,the particle spacing is increased,and the viscosity of the slurry is lowered.The fineness of the cement is reduced,the flocculated particles in the cement slurry are significantly increased,the adsorbed water of the particles is significantly increased,the free water is reduced,the particle spacing is decreased,and the viscosity is increased.The hydration time promotes particle growth,consumes free water,reduces particle spacing,and increases slurry viscosity.The relationship between the macroscopic viscosity of the slurry and the hydration time and the average particle size of the flocculated particles of the slurry was established by numerical fitting with the water-cement ratio,cement fineness and water reducing agent.(4)The effect of flocculation on cement hydration was obtained by studying the hydration properties of grouting material,the law reveals the root cause of the flocculation of the slurry and the viscosity at the time of viscosity.In addition to the water reducing agent,the smaller the particle size of the flocculated granular material,the faster the hydration of the cement and the higher the heat release.The hydration of the cement consumes water,and the C-S-H gel is formed,which promotes the increase of the particle size and macroscopic viscosity of the flocculated particles.(5)The injectability test of indoor sand layer was carried out,and the influence of the pore size of the sand layer and the particle size of the cement flocculated particles on the injectability of the sand layer was studied.The results show that large particles and pore diameters in the flocculation slurry seriously affect the injectability of the sand layer.The injectability criterion was established based on the particle size of the mud flocculating particles and the pore size of the sand layer.