Study On Modification Of Cement Grout With Low Sodium Bentonite Content

With the development of economy,underground space utilization becomes more and more important.Water disaster is one of the main disasters in underground engineering construction.Grouting is a common method to prevent and control this kind of disaster.Common cement slurry is a solid-liquid two-phase fluid with particle suspension.There are two effects of seepage and sedimentation during slurry grouting.Based on this,the basic properties of sodium bentonite modified ordinary cement slurry with a dosage of ≤ 5% were studied by laboratory test and model test.The main research work and results are as follows:(1)Based on the analysis of the hydration mechanism of cement and the action mechanism of bentonite and cement,the mechanism of bentonite improving the suspensibility of cement slurry is divided into two types:firstly,the particles of bentonite adsorb each other,which causes the cement slurry to transform into a "gel" state,and this "gel" state may hinder the subsidence of cement particles;secondly,the static attraction between bentonite particles and cement particles forms a bridged structure,reduces the free water in the cement slurry,and improves the suspensibility of the cement slurry.(2)The modification results of the properties of ordinary cement slurry with low content of sodium bentonite were obtained through the tests of the properties of the cement slurry with multiple water-cement ratios(0.8 ～ 2.0)and different content(1% ～ 5%),such as water evolution rate,stone formation rate,viscosity and compressive strength of the stone body.The optimum dosage of sodium bentonite was determined to be 3% of the solid mass of the slurry.(3)Based on the study of basic properties of bentonite modified ordinary cement grout,the visualization test of single channel and 3D printing single fracture model grouting was carried out.The results show that low sodium bentonite content can increase the pore filling ratio of common cement grout,which indicates that low sodium bentonite content can improve the grouting permeability.(4)Based on the seepage control engineering of foundation pit in the State Key Laboratory of Deep Geotechnical Mechanics and Underground Engineering of China University of Mining and Engineering and in combination with the relevant parameters of indoor test,the layout of grouting hole,grouting pressure,grouting technology and grouting materials are designed.The application effect of low content sodium bentonite modified ordinary cement slurry was verified by field test.The thesis has 54 figures,16 tables and 91 references.