Simulation Of Modified Silica Sol For Grouting In Sand Considering Phase Transformation Of Slurry

Grouting is an important means to improve unfavorable geological conditions.Ordinary cement in sand layer can be poorly irrigated.Chemical grouting materials which has certain toxicity to the envronment have low viscosity,and condensation time can be controlled.Silica sol is especially suitable for sand and soil layers with low porosity.But the strength of silica sol is slightly lower after reinforcement.The modified silica sol can avoid the above defects and is a superior grouting material developed in recent years.An important issue that needs special attention in grouting in rock and soil is the secondary hazard during the grouting process.Due to the fast setting time of the modified silica sol slurry,the material changes from liquid to solid in a short time,which significantly changes properties of the composite stratum after grouting.Therefore,the changes of grouting pressure and foundation response have to be paid attention to.Based on the indoor material performance tests,grouting tests and the phase transition theory,the change of phase state of the modified silica sol slurry during the grouting process and the results in foundation response,including deformation and plastic damage,were studied by numerical simulation to optimize the grouting prcess.The main research contents are as follows:(1)Based on the mechanism of gel chemical reaction,the influencing factors of modified silica sol gel time were studied.Through the indoor mix ratio experiments,the mix ratio of modified silica sol meeting the requirements of the index was selected.The reinforcement performance and phase transformation rule of modified silica sol were studied through laboratory performance tests.(2)The indoor two-dimensional sand grouting simulation test device was developed to study the diffusion law and phase transformation range of modified silica sol in sand media with or without groundwater.The forming mechanism and phase transition characteristics of silica sol sand body were studied.(3)A two-dimensional numerical model for modified silica sol grouting in sand was established.Based on phase transition theory and fluid-solid coupling,the dynamic law of slurry diffusion in sand,space-time law of stress field,seepage field and displacement field were studied.And the property change of the composite formation after phase transformation were studied,thereby causing redistribution of subsequent grouting displacement and deformation.(4)The application of modified silica sol in diversion tunnel of water conveying project in Xinjiang shows that the modified silica sol has good potability in highly-weathered rock strata with properties similar to sand,reliable condensation time under abnormal conditions.The properties(like permeability)of the composite formation after phase change of slurry conform to engineering requirements,which has broad application prospects.The theoretical analysis and engineering practice results show that the modified silica sol slurry has good diffusibility and reliable setting time.The phase transformation occurs in the 25 min period after the slurry material is poured under ground water condition.The formation characteristics changes obviously after the phase transformation of slurry,which significantly affects the base deformation and displacement distribution during the subsequent grouting.