| Silica sol slurry is an excellent green grouting material for micro-porous media.It has the advantages of low viscosity,good pourability,controllable gel time,non-toxic and environmentally friendly.However,the solidification mechanism of silica sol slurry has not yet been concluded,and its durability has also been questioned due to the lack of strong evidence.This research uses silica sol slurry as the research object,and aims to explore the coagulation performance and durability of silica sol slurry through indoor tests.Further,based on microscopic tests to study the solidification mechanism and degradation characteristics of silica sol.Then,we use independently developed test device to study the diffusion law of silica sol in the sandy soil layer.Finally,using numerical simulation and considering the time-varying characteristics of silica sol and the characteristics of composite solidification materials,the deformation and stress characteristics caused by the grouting pressure during the staged grouting process are studied,which can provide a basis for the engineering application of the material.The main research contents and conclusions are as follows:(1)Study on solidification mechanism of silica sol slurry.Based on scanning electron microscope,X-ray diffraction and nuclear magnetic resonance technology,this paper explains and evaluates the properties of silica sol from the microscopic level,and then explores its solidification mechanism.The results show that the solidification mechanism of silica sol is related to the presence of silanol on the surface of the particles.Because the silanol has a high activity and condensation reaction between silanol can occur,so that new bonds between silica sol particles are continuously produced.It will form a net-like scaffold structure in the entire volume and lose fluidity,eventually forming a silicone gel.(2)Study on durability and micro-mechanism of silica sol slurry.Relying on indoor tests,the changes in the mass,volume,strength,and silica dissolution rate of silica sol with time under acid-base environment,dry-wet cycle,and freeze-thaw cycle were studied.Then,we further explored the durability of silica sol in various complex environments,and finally studied the reasons for the degradation of its material properties using microscopic tests.The results show that the silica sol gel has good stability in acidic environment,slightly poorer stability in alkaline environment,and has good anti-dry and wet performance,but its anti-freezing and thawing performance is poor.(3)Silica sol slurry sand grouting test.Based on the development of an indoor three-dimensional sand grouting simulation test device that can visualize the final grouting range,this paper studies the diffusion law and range of silica sol slurry in sand under different grouting pressures,and explores the phase transition characteristics of silica sol solid sand body.The results show that the injection of silica sol slurry into sandy soil is effective.(4)Numerical simulation of the staged grouting of silica sol with time-varying characteristics.Using numerical simulation as the main method and considering the time-varying characteristics of silica sol,the slurry diffusion process of staged grouting is studied.At the same time,the characteristics of silica sol solid sand body are considered to study the deformation and stress characteristics caused by the grouting pressure.The results show that the critical value of pressure for plastic failure is 0.54 MPa.When the second-stage grouting pressure is 0.40MPa～0.53 MPa,there will be no plastic zone,and the slurry diffusion range can also meet the requirements,so it is a more appropriate second-stage grouting pressure. |
