Research On Experiment And Numerical Simulation Of Grouting Reinforcement In Silty Sand Stratum Of Shijiazhuang Metro

Silty fine sand stratum is soft and weak,which is usually founded in the construction of geotechnical underground engineering.The silty fine sand stratum has no cohesive force and poor self-stability.When the subway tunnel and other underground projects pass through this kind of stratum,it is very easy to cause large surface settlement,even water gushing,collapse and other engineering disasters.In order to ensure the safety of underground engineering construction in silty sand stratum,it is necessary to carry out advance grouting reinforcement for silty sand stratum.Advance grouting reinforcement is a concealed project,which mostly relies on experience and field grouting test,so the grouting effect is difficult to achieve expectations.For this reason,the in-depth study of the grout diffusion mechanism,the water-cement ratio of the grout,and the formation characteristics in the advance grouting reinforcement project of the silt formation has important theoretical and engineering significance.Using the self-developed grouting model test system,combined with the three-dimensional meso grouting numerical model of silty fine sand stratum,this paper systematically studies the influence of water-cement ratio,grouting pressure,soil moisture content,void ratio and confining pressure on the diffusion rule of ultra-fine cement slurry in silty fine sand formation.The main research contents and achievements are as follows:（1）Based on the different flow forms of the grout,the analysis and summary of the permeation grouting theory,compaction grouting theory and fracture grouting theory of grout in silt fine sand stratum provide theoretical support for the smooth progress of laboratory tests and numerical simulations.（2）Based on the self-developed three-dimensional grouting model test system,an indoor grouting model test for silt fine sand formations was carried out.The influence of grouting pressure,water-cement ratio,soil moisture content and void ratio on the diffusion law of the grout is studied,the geometric characteristics of the grouting stone body are obtained,and the diffusion mechanism of the ultrafine cement slurry is revealed.（3）Using discrete element software PFC^3D,a three-dimensional grouting micro-model based on the micro-mechanism of the interaction between soil particles and grout particles was established.On the basis of verifying the rationality of the model,the influence of factors such as grouting pressure,grouting volume and confining pressure on the grout diffusion are numerically studied,and the law of grout diffusion and the change of soil stress and porosity in the whole process of grouting are obtained.