Experimental Research On Law And Prediction-control Of Slurry Diffusion Using Cement-based Grouting Material

Grouting technology is widely used in slope,subgrade,embankment,dam,tunnel and underground engineerings,for its special functions of waterproof,reinforcement and rectification.The commonly used grouting forms are permeation,compaction and fracture,but there's still no thorough recognition on the slurry diffusion and prediction-control,and the grouting theory lags behind engineering practice,which is due to its fuzzy,hidden,random and complex properties.Therefore,it's necessary to study the law and prediction-control of slurry diffusion in grouting process,thus providing reference for design and construction of grouting engineering,and promoting grouting technology to become scientifical,controllable and refined.Based on theoretical analyses of slurry property and equivalent calculation of permeation coefficient,three modelling tests were made using cement-based slurry by developing three different test devices,the research contents include: 1)Law of slurry diffusion under permeation grouting and its effective diffusion distance;2)Attenuation law of soil pressure and evaluation of grouting effect under compaction grouting;3)Slurry diffusion modes and vein shapes under fracture grouting;4)The variation characteristics and phenomenon representations of grouting parameters under fracture grouting,especially the prediction and control methods.The main works and conclusions are as follows.(1)Permeation mechanism of clay was analysed considering influence factor and spatial process.Based on equivalent permeation in terms of soil structure and permeation mechanism,the equivalent calculation method of permeation coefficient for clay was established by introducing parameter "equivalent void ratio" into the empirical calculation method of coarse-grained soil,which unifies the calculation of permeation coefficient for coarse-grained and fine soils.The results show: equivalent methods of Terzaghi and Curson-carmen can be used to calculate permeation coefficient of coarse-grained and fine soils compared with Equation Mesri.It provides reference for evaluating permeability and calculating permeation coefficient of grouting slurry.(2)"Test device of one-dimensional permeation grouting" was developed first,the orthogonal test was designed and done considering porosity,water-to-cement ratio,grouting pressure and time.The time-space laws of percolation diffusion and formula ofeffective diffusion distances were obtained.The results show: percolation effect has the apparent time-space effect,slurry flow and density reduce linearly with time,the actual water-to-cement ratio increases linearly along the diffusion direction,"permeation coefficient" is the function of grouting time and diffusion distance.Relationship between effective diffusion distance and four influence factors is one power function model,which improves the calculation accuracy.It provides reference for designing water-to-cement ratio and space of grouting hole.(3)"Test device for compaction grouting" was developed first,tests under different grouting pressures were designed and done,the attenuation laws of soil pressure with time and position were obtained,variation formula of soil pressure with position was given,and the relationship of influence radius and grouting pressure as well.Parameter "filling rate" was suggested to evaluate the grouting effect,method calculating effective reinforcement region based on compression model of soil was established.The results show: attenuation of soil pressure has the time-space effect,it varies nonlinearly and phasely with time,and in power function with position,the attenuation degree can be represented by "attenuation parameters".Attenuation process includes the increase phase,slowly-decrease phase,fast-decrease phase and stable phase,the critical points are "difficulty in grouting" and "grouting stop" for the former three phases.Relationship of influence radius and grouting pressure is logarithmic,the effective reinforcement region can be solved by combining formulas of residual porosity,soil pressure-position,permeation coefficient and critical criterion.It provides reference for designing grouting process and space of grouting hole.(4)"Test device of plane strain model for fracture grouting" was developed first,tests considering soil compactness and grouting depth were designed and done.The vein shape,geometrical characteristics and diffusion process under different tests were obtained,then analysing the slurry diffusion mode,property and forming mechanism of vein.The results show: slurry diffusion modes are non-uniform or uniform compaction in loose soil,compaction-inrush in slight-dense soil,compaction-fracture in middle-dense soil and compaction-uplift in dense soil.The diffusion mode,direction and grouting effect can be adjusted through change of grouting method.Vein shapes include compaction type,inrush type,fracture type and filling type.Especially,fracture and filling veins are asymmetrical generally.Meanwhile,shape of fracture crack is asymmetrical,but the uplift crack is symmetrical,their shapes are "concave" and "convex" respectively.It provides reference for designing grouting process,evaluating grouting effect and studying grouting mechanism.(5)Based on variation analysis of grouting parameter during the process of fracture grouting,the variation characteristics and phenomenon representation were summarized.Then illustrating the correspondence between diffusion form and variation of grouting parameter,establishing the prediction-control method of slurry diffusion for compaction-fracture form.The results show: diffusion form can be defined preliminarily by variation of grouting parameter,and defined ultimately by "move of maximum increment position of surface displacement".Diffusion direction and position can be defined respectively by "zero increment position of displacement" and "maximum increment position of displacement"."Displacement increment method" can be used to predict the slurry diffusion,the prediction deviations of angle and horizontal diffusion distance are respectively-17.3%?33.7% and-16.7%?5.7%.It provides reference for promoting grouting technology to become scientifical,controllable and refined.