Research On Mechanical Behavior Of Grout In Gravelly Soil Foundations

Grout expels the water and air by filling, permeability and compaction ways in soil or rock fissure to occupy its position, and size of the original loose soil material or fracture cemented to form "stone body." Loose foundation soil parameters distribution has the obvious characteristics of the random and irregular, strongly influences slurry infiltration process, which causing grouting concretion shape randomly and mechanical parameters of the spatial distribution uncertainty. This makes the foundation strength and bearing capacity of the natural foundation improved after grouting, but overall still showed heterogeneity and anisotropy. Even though grouting technique has been widely used as foundation treatment and soil reinforcement, there is still a considerable gap between the theory and practice, bearing capacity of foundation deformation calculation theory study is also not mature enough. The inhomogeneity and uncertainty of the injection medium, slurry material variability, the theory and mechanism of slurry infiltration and so on still has many difficultiesBased on the gravelly soil foundation of the Three Gorges Reservoir Area, using soil test data of gravel soil foundation and indoor grouting test results, from the aspect of grout material properties, soil parameters, grouting pressure and grouting mode, considering the dynamic effect of grouting process parameter correlation, the spatial distribution of the structural and random, the key parameters of the time-varying characteristics, based on grouting process in seepage field and stress field coupling to analysis of the diffusion stone shapes and mechanical parameters of randomness, and the change of stress and displacement under soil grouting reinforcement loads, studied the mechanical behavior of heterogeneous loose rock and soil reinforcementThe main work are as follows:(1)Starting from the grouting technology and grouting material, based on previous research, systemically analysis of the slurry flow model, from the perspective of the slurry viscosity variability and slurry considering the influence of diffusion effect factors on slurry properties of grouting slurry.The test analyzed the relationship between the viscosity of the cement slurry and time under different water conditions. The experimental data shows cement slurry viscosity changes exponentially with time under a certain slurry concentration. The viscosity and shear strength of cement slurry is relatively stable in the early stage, but with the setting time of arrival, the viscosity and shear strength of rapid growth. According to this characteristic, cement slurry at the right time to complete the permeation grouting, otherwise it will affect the cement grouting property.The test results also shows, viscosity changes with time, and the same to slurry concentration. The slurry concentration will significantly change the viscosity, and especially in the water cement ratio is less than1. Grouting cement slurry concentration and duration have different influences to the viscosity changes. If the slurry by unsaturated soil adsorbed or groundwater mixing effect and make the particle precipitation, and change the flow of the slurry concentration, it will change the water cement ratio and significantly affect viscosity and diffusion process. Construction process and geological conditions on soil grouting slurry concentration and time also can’t be neglected.Underground grout diffusion process may have different flow patterns of the conversion process, diffusion characteristics has a close relationship with mechanical parameters and grouting technology. Real grouting process has obvious non-stability characteristics and grouting theory formula in the practical grouting process is also quite complex.(2)Soil testing and indoor grouting experiment were conducted on the gravel soil sample from governance and strengthening works of Three Gorges Reservoir Area to obtain the soil compression modulus, effective particle size, permeability coefficient, permeability coefficient, grouting pressure and other data. At the same time, this article based on the artificial intelligence method of support vector machine to establish the relationship between the measured test data and the compressive strength of the test grouting stone body, elastic modulus and other mechanical parameters, be associated with be associated multiple factors related joint action grouting stone body mechanics parameter prediction, which analyze the impact of stones body mechanical characteristics of the main factors and their variation.Because of the strength of stone body and elastic modulus affected by many factors, any of these factors change can have a profound effect on grouting results. However, based on the method of support vector machine, we can be very good to analyze and predict the complex relationship and nonlinear multidimensional variable parameters and physical parameters of grouting stone, which provide a reference for the research note pulp stones body shape distribution and strength distribution of space randomness, analysis stones body random distribution on reinforcement Foundation of hosted force effects and deformation inhibition, and evaluation foundation reinforcement before and after of strength and the deformation characteristics.(3)The random spatial distribution prediction model based on random fractal interpolation formation parameters was established. The loose structure of gravel soil, uneven space distribution of physical parameters, and concentration of particles in the soil are also likely to form a high porosity overhead structure. Therefore, gravel soil grouting reinforcement mechanism and grouting reinforcement process research focus on soil inhomogeneity loose bring the problem of gravel soil local subtle change. Researched based on the use of diamond-square method of in random fractal theory and analyzes the spatial distribution characteristics of soil. Simultaneously, the spatial random distribution forecast about the formation of unknown data density, permeability, porosity, soil compression modulus were build based on soil already known data model.As we all know, properties of soil in the conventional soil profiles, thickness and engineering were expressed by single values, which ignored the parameters fluctuation. But, in random distribution of grouting the soil profile during the study, we consider the distribution of porosity and surface characteristics of random fractal characteristics, and taking the impact parameter profile characteristics as the coordinates of the random function. Based on the fractal characteristics of distribution of geotechnical parameters, the improved count box method was used to obtain the fractal dimension of the porosity distribution curve, reflecting the porosity parameters unearthed in the space distribution heterogeneity and complexity.The coordinates of points were taken as control points were known and the porosity of corresponding points as physical parameters of variable data source, and taking advantage of fractal interpolation method associated with the fractional Brown motion, and finally the formation porosity distribution characteristics as stochastic processes to describe the random grouting formation porosity parametersConsidering the mutual relativity between physical and mechanical parameters in geotechnical engineering, taking the porosity known quantity from geological survey as the basic amount of the variable parameters, and the multi-dimensional variable correlation coefficient of permeability, compressive modulus, soil bulk density, bulk modulus, and other basic physical parameters in the finite element nodes were discussed.Based on the above ideas, this paper simulates the formation of porous medium porosity, permeability coefficient, soil bulk density, compressive modulus, bulk modulus of the spatial random distribution, and generate suitable for grouting porous formation of two-dimensional numerical parameters randomly distributed geological sections and three-dimensional figures formations.(4)The grouting diffusion model of parameters changes in coupled seepage and stress fields in porous media were established. On the one hand, the porous media equations of motion, continuity equation and biot equation based on generalized were introduced. Meanwhile, the macro-level and micro-level comprehensive analysis methods were used to establish deformation and stress equation under saturated porous media flow to research the time-varying of the slurry viscosity as a special flow diffusion process. On the other hand, we considered the porous medium multi-field coupling effects based on the physical field and diffuse seepage physical field theory, and at the same time, the dynamic mathematical model was exported according to the concept of volumetric strain, which considered porosity, permeability, porosity and other physical parameters. The establishment of grouting diffusion model provides an effective way for the achievement of heterogeneous formations flowing solid coupling numerical simulation of grouting.(5)This paper conducted a multi-field coupling of homogeneous and heterogeneous soil grouting process simulation.Based on the physical flow field and diffuse-physics coupling theory and considered the effects of time-varying grout spread, the dynamic changes of soil parameters, simulation of homogeneous soil grouting point source in the column under the conditions of slurry grout hole diffusion range. At the same time, the magg theoretical calculation methods and laboratory test results were compared and analyzed to verify the effect of fluid-structure interaction based slurry diffusion process parameters correctness and soil dynamics is reasonable.The non-homogeneous soil layers mutual relativity parameters and random distribution were considered, combined with the results of the test program, Simultaneously, combined with the finite element software grouting process simulation and discussed the uneven distribution of soil, grouting pressure, slurry water cement ratio and viscosity time-varying on grouting diffusion, diffusion paths, diffusion pattern effects, and the random distribution of grouting stone body. Numerical simulation results show that the gravel soil grouting holes around the fluid-structure interaction effect is strong and the physical parameters dynamically changed obvious.(6)The distribution of the stress field and the displacement field of grouting the soil under the effect of the load were studied.Observed the effect of fluid-solid coupling interaction simulation of grouting spread and Matlab software were used to extract calculated field region before grouting unit apparent density, osmotic pressure, porosity, compressive modulus, compression coefficient distribution status and value, further extraction of non-homogeneous soil grouting simulation finite element model of the grid node after the elastic modulus, Poisson’s ratio and the density of the physical and mechanical parameters; based on the laboratory test results of grouting diffusion and method of support vector machine to extract the known physical parameters of finite element unit body, the Matlab software were used to predict the mechanical parameters such as modulus of elasticity of grouting stone body, and assignment the finite element unit in distribution space.The grouting process of heterogeneous soil must be accompanied by the random distribution of grouting stone body skeleton. Grouting depends on the mechanical properties of composite stone body skeleton with the joint action of the surrounding soil. The no grouting and grouting after soil reinforcement complex numerical model was established based on the above assignment before and after strengthening of soil physical and the calculation results of the physical and mechanical dynamic parameter,. Through the computer simulation, comparative analysis of the stress field and the displacement field of non-homogeneous soil grouting, the mechanical behavior of grouting gravel soil characteristics were studied.The main innovation points are as follows:(1)Combined indoor simulation test results and based on the theory of support vector machine, studied the relevant law of stone body compressive strength, elastic modulus E and grouting medium structure (coefficient of permeability, porosity, effective particle size, compression modulus), grouting pressure, grout water cement ratio, which has a practical significance for guiding the design of grouting engineering and prediction of grouting effect. Experiment and studies show that water cement ratio, grouting pressure and medium structure (porosity, coefficient of permeability) are as the key factors of impacting grouting that all effect on grouting process, thus affect the bearing mechanical properties of gravelly soil foundation after the grouting. Studying the process of seepage of Grout in the loose soil, analyzing viscosity time-varying characteristics of cement slurry in different water cement ratio introduced slurry diffusion process, derived and simulated penetration and diffusion regularity of time-varying slurry in heterogeneous soil.(2)Based on the method of diamond-square in random fractal theory, considered the interdependence effect of multiple random variables, and established the space random distribution prediction model of the soil physical parameters. The finite element unit assignment of heterogeneous soil includes two aspects:the one is the known control points as representative unit body, which the parameter value of porosity as the basic amount of regional variables assigned to the unit nodes of finite element unit body, according to discuss and analyze mutual relativity of physical property parameters variable in loose soil unit, obtained the relationship of other parameters of the unit body and porosity, and achieved the association assignment of apparent density, permeability coefficient, modulus of compression and compression coefficient of finite element. The second is the porosity parameter values of the known control points as the data source of regional variables, considered the fractal characteristics of soil features parameter distribution, made formation characteristics as random process, and predicted the space distribution of the parameter of porosity, permeability and compression modulus to the unknown data area of the formation, generated the digital formation profile that is suitable for pore formation grouting numerical simulation.(3)Integrated using of time-varying equation of Grout and dynamic change process equation of physical parameters, doing the numerical simulation of heterogeneous soil in Grout diffusion and coupling effect of soil stress field. Researched and simulated the relationship and law of pressure head distribution, pressure gradient distribution, velocity distribution, and grouting amount, grout diffusion distance and grouting time of cement grout in the process of diffusion in the gravel soil, revealed slurry movement process within the formation, which has important theoretical significance to the quantitative calculation of slurry movement in loose heterogeneous soil. Based on the coupling simulation results of grout diffusion and the stress field of soil, discussed the distribution form, diffusion model and diffusion mechanism of grouting stone body in heterogeneous soil. Stone rate is affected by the parameters of soil and construction technology, the random distribution of stone body of shape and size is regular. Based on the study of grouting stone body skeleton and time-space law of random distribution of physical parameters, doing quantitative calculation and analysis of grouting effect. The calculation results show that the physical and mechanical properties of soil improved under the common action of the stone body skeleton and soil, and the effect of foundation reinforcement is obvious, bearing capacity of the foundation improved significantly.Considering the effect of soil physical association parameters, the fractal characteristics of soil parameter distribution, random geological profile, the influence of many factors such as slurry time-varying characteristic, heterogeneous soil parameters of random fractal model of geological profile are established and slurry diffusion process and grouting reinforcement mechanical behavior and the numerical simulation of grouting process are developed, which providing a theoretical basis for grouting calculation analysis, quantitative evaluation of the grouting effect, quality traceability of grouting engineering problems and engineering safety evaluation of grouting reinforcement. It provided scientific basis for structure grouting reinforcement and correcting mechanism research and technology applications, and provided the effective way of strengthening effect for grouting of loose rock and soil under complex environmental conditions. But at present the study of some theories and methods need to be enriched and perfected. This paper only does the preliminary exploration, the following several aspects still need to be further researched in the future.(l)Study on grouting mechanism, focusing on the slurry diffusion process of permeation grouting, and considering the compaction effect of soil by injection. The grouting mechanism and diffusion mechanism of grouting medium are different at different process conditions and grouting pressure. Introducing the digital stratigraphic profile, fractal random theory and variation equation dynamic of porous medium physical parameters into grouting simulation under the splitting grouting effect still need to be further studied.(2)The effect of underground water has not been considered in the test of slurry diffusion and numerical simulation. Further research on the motion of fluid with different manifolds in the mixed time should be considered in the simulation and test of water dynamic effect, soil stress field distribution and the coupling effect of slurry diffusion process.(3)The interaction of foundation with solid and the surrounding soil, how to consider the reinforcement effect under the complex geological condition and stratigraphic structure boundary conditions and load distribution, grouting composite foundation under additional stress and it’s optimization design need to be further explored and studied.(4)The effect of different water content on the grouting process has not been considered in the research results. Cement is a typical suspension, slurry in soil sedimentation, water filtration, coagulation and unsaturated soil body capillarity will change the water cement ratio along the path of the grouting, then change the viscosity variation. The effects of these factors on the grouting process and how to introduce the effect of the unsaturated soil adsorption of slurry concentration changes into the grouting simulation process in a better way still need a more in-depth study. The influence of matric suction of unsaturated soil of fluid infiltration and soil seepage is a complex problem of soil mechanics, the relationship between unsaturated permeability coefficient and saturation in the soil still needs a lot of research and study.(5)Slurry in soil sedimentation, water filtration, coagulation and unsaturated soil body capillarity will also change the effective porosity of soil. Due to the conditions of the test, this paper mainly based on the existing literatures, only from the macroscopic angle to discuss the process of serous granule soil water cement slurry chemical slurry flocculation. Through experiments in the two respects of microcosmic and macroscopic on particle migration, deposition characteristics were studied, analyzed the flocculation process of slurry, to provide a more reliable basis for quantitative description of slurry penetration termination criteria, this is the work what needs to be done in the future.