Engineering Application Research Based On Diffusion Law Of Low Viscosity Slurry In Fine Sand Formation

Silty fine sand stratum is one of the most common soft strata in underground construction.Its particles are loose,its mechanical properties are poor,and it has self flowing property under water or dynamic disturbance.If it is not effectively controlled,it is easy to cause sand gushing,land subsidence and other disasters,which brings great difficulties to the construction of underground engineering.At present,grouting is one of the most effective and economical methods to control the silty sand stratum.The grouting method has the advantages of strong adaptability,simple operation,low cost and no environmental pollution.Due to the small size and dense structure of fine sand,the diffusion effect of cement and other large particle slurry in fine sand layer is not good.In order to solve this problem,the research group has developed a new type of chemical slurry for fine sand layer,which has the advantages of low viscosity,high strength of consolidation body,adjustable setting time and so on.In this paper,based on the newly developed low viscosity slurry,the basic performance of the slurry is mastered through laboratory tests.Through numerical simulation,model test and engineering application,the diffusion characteristics of the slurry in the silty sand formation are studied and analyzed.Finally,the diffusion law of the slurry in the silty sand formation is obtained,and the practical application of the slurry in the engineering is guided.The main research contents and achievements of this paper are as follows:(1)This paper analyzes the basic properties and engineering properties of the fine sand layer and the basic physical properties of the slurry.The porosity,permeability coefficient,water content and internal friction angle of the fine sand used in the test are determined through laboratory test,and its injectability is analyzed.By testing the viscosity and setting time of the slurry,the whole process characteristics of the slurry curing reaction are mastered.The influence of water content,slurry sand ratio and curing time on the consolidation of silty fine sand by slurry was analyzed by orthogonal test.The following conclusions are drawn: the silty sand used in the test is suitable for grouting with low viscosity slurry;the viscosity of the two components of the slurry is relatively low,and the viscosity in the early stage after mixing basically remains unchanged,but the viscosity increases sharply in the late stage of reaction,which has the conditions for injecting a large amount of water into the silty sand layer;the orthogonal test results show that the factors affecting the consolidation of silty sand by slurry from large to small are: water content Slurry sand ratio and curing time.(2)Based on the properties of fine sand and slurry,the slurry diffusion test was carried out.Firstly,the influence of grouting pressure on slurry diffusion is analyzed,and five grouting pressure gradients are set.The results show that the shape of consolidated body formed under each grouting pressure is cylinder,but its size is different.The larger the grouting pressure is,the larger the diffusion radius is,and the increasing speed of the diffusion radius first increases and then decreases The pressure at the same position tends to be stable under the grouting pressure,and the greater the grouting pressure is,the greater the stable value is.Then,the relationship between grouting time and diffusion radius is simulated,and a total of six grouting time gradients are set.The results show that the shape of the consolidated body under different grouting time is cylinder.The influence rule on diffusion radius is that the longer the grouting time is,the larger the diffusion radius is,but the increasing speed of diffusion radius gradually decreases.Finally,the pressure measurement is carried out at different positions from the grouting outlet The results show that the farther the distance is,the smaller the final stable value is.(3)The model test is designed by numerical simulation model and tested by the self-developed test device.The model box is a 1.5m square with side length,which can avoid the influence of boundary on the slurry diffusion as much as possible.The model test of different strata,different compactness and grouting conditions can be simulated.This model test mainly studies the relationship between grouting pressure and diffusion radius,and sets three grouting pressure gradients which are the same as those of numerical simulation test to carry out the test,and compares the results with numerical simulation.The results show that the diffusion law of the slurry obtained by the two is basically the same,but there are some differences in numerical value.The reasons for the difference between the experimental value and the simulation value are analyzed.(4)According to the research results,the design scheme is applied to the reinforcement of underground excavation channel of Taiyuan metro station in silt stratum with large water content,and the field effect is good.When cement,water glass and other grout are used in the early stage,which has no effect and causes surface uplift,this low viscosity grout is used for grouting,and the grout diffusion distance is 40-50 cm,which achieves the expected effect,ensures the safety of excavation and does not cause new surface uplift,and effectively solves the problems encountered in the project.The research results have a certain guidance and reference for the application of low viscosity slurry in fine sand layer,and also provide a certain reference for the improvement of low viscosity slurry.