Study On Diffusion Characteristic Of Grout In Soil-Rock Mixture By Damage Theory

Natural soil has the characteristic of structure irreversible changes during the loading process.During the process of grouting reinforcement,the slurry continuously enters the soil from the grouting hole wall under pressure,occupying the pore space in the soil,the exteral pressure is also transmitted from the grout itself to the soil skeleton,the mechanical properties of the soil gradually change from the Original state to the damaged state.The damage theory is based on the basic principles of irreversible thermodynamics,and it introduces mechanical variables to simulate the damage state of the soil.It can be used as a supplement to classical solid mechanics to study the diffusion law of slurry in soil.In grouting lifting and rectification engineering,soil-rock mixture formation is a common geological body which must be properly treated.The particle size composition of internal materials and the distribution of physical parameters have a significant impact on the overall mechanical properties and deformation characteristics.In order to study the problem of slurry diffusion in soil-rock mixture formation,the non-uniformity of its composition materials and mechanical properties should be considered first.This thesis takes the grouting diffusion problem in the soil-rock mixture formation as the research background,mainly considering the structural damage characteristics of the material and the heterogeneity of the soil-rock mixture formation.It comprehensively studies the damage development and the dynamic change process of its physical or mechanical parameters,which is caused by the slurry diffusion under the action of the grouting pressure.Based on the elastic damage theory of soil and the finite element analysis method,the numerical model of grouting diffusion for soil-rock mixtures was established.It considers the seepage characteristics of grout in homogeneous soil and soil-rock mixture under different grouting pressures,including diffusion range,stable diffusion form,dynamic changes of physical parameters,seepage field and stress field changes,and compared with the situation when the damage is not considered.The focus of the discussion is the influence of continuous damage to the diffusion behavior of the soil structure during the grouting process.The main research contents and results are as follows.(1)This thesis presents an improved construction method of soil-rock mixture numerical model.The Monte-Carlo simulation method is used to generate geometric information such as increment of random radius and length,and the block-rock model library considering angularity is constructed.When considering the random placement of stones,Aligned Axis Bounding Box method is used to preliminarily judge the position of stones,and the improved boundary interference algorithm is used to quickly exclude the stones with unreasonable spatial position.Combining fractal theory with particle size distribution of laboratory test,the complete particle size distribution of soil-rock mixture stratum in the study area is inversed.Based on this,the generation program of random geometric model of soil-rock mixture is written.Finally,assuming that the mechanical properties of the meso-element accord with Weibull distribution function,different material parameters are given to the soil and stone in the area by the method of dividing the regional grid,and the mechanical model of soil-stone mixture is constructed,the simulated loding test is carried out also.The results show that the larger strain occurs at the soil-rock interface where the rock is relatively sparsely distributed.And the rock in the middle of the model is closely arranged,its angularity enhances the overall self-locking effect,which cause strain reduction in the middle of the model.It also proves that the model constructed by considering the geometric shape and random distribution of the block stone can better reflect the real material properties.(2)Aiming at the problem of soil damage-stress caused by hole wall pressure in grouting engineering,the relationship between hole wall pressure and radius of damage zone is studied by using the theory of column hole expansion under undrained condition.Taking the elastic coefficient of soil as the damage variable,a set of soil damage model suitable for grouting diffusion problem is established.With the help of Realistic Failure Process Analysis method,based on the failure criterion and damage law of soil,the linear elastic finite element method is used as the solver,and the numerical solution of soil damage during column expansion is realized by programming.(3)The saturated seepage equation and stress equation in porous media are introduced.Combined with the elastic damage theory of soil,the relationship between damage variable and soil seepage parameters is derived.Based on the elastic damage analysis program established in Chapter 3 and the coupling theory of seepage field and stress field in porous media,the realization process of seepage-stress coupling numerical calculation considering slurry diffusion under damage is expounded.Taking the damage variable as the basic condition,combined with the relationship between permeability parameters and mechanical parameters in the process of slurry diffusion,a three-dimensional single-hole grouting numerical model under homogeneous conditions was established,and the simulation results were compared with the calculation results of the classical grouting theory.The results show that the model can effectively reflect the soil damage response and material mechanical properties degradation caused by the slurry diffusion process.The development speed of the damage interval in the homogeneous layer decreases with the increase of depth.(4)Based on the survey data of a project in the Three Gorges Reservoir area,the Weibull distribution function combined with the fractal interpolation algorithm is used to show the spatial distribution characteristics of formation parameters,and the two-dimensional prediction profile model of porosity and related parameters is established.Based on the theory of damage-seepage-stress field,the grouting diffusion behavior of heterogeneous soil-rock mixture stratum considering soil structural damage is simulated.This thesis studied the influence of different grouting pressure,different initial conditions of stratum,considering soil damage and not considering damage on the diffusion range,spatial distribution form,dynamic change of formation parameters and seepage-stress field.The results show that the grouting diffusion effect is affected by multiple factors such as the distribution of rocks in the formation,the structural damage of the soil and the initial formation parameters.Based on the grouting diffusion model considering the damage process,it can reflect and predict the diffusion of grouting and uplifting effect.