Research On New Grouting Material For Water-rich Sandy Gravel Stratum

In recent years,water inrush,sand gushing,and collapse accidents caused by defects of grouting materials have occurred frequently when grouting in water-rich sandy gravel stratum.Therefore,considering the hydrogeological characteristics of water-rich sandy gravel stratum and the defects of traditional grouts,developing special grouting materials is essential to prevent geological disasters in this type of stratum.Take the water-rich sandy gravel stratum in Beijing as an example,the methods such as model tests,thermodynamic simulations,and laboratory experiments were used to study the law of grouting diffusion and the anti-dynamic water washing performance of grouts and to simulate the hydration process of bentonite-cement-based grout.New grouting materials were developed successfully,which have low bleeding,strong resistance to dynamic water,low price and are environment-friendly.The main content and results are as follows:（1）Based on the similarity theory,the grouting model test about sandy gravel stratum in dynamic water conditions was carried out.The spatial distribution of the grouting bodies were obtained,the quantitative relationship between grouting parameters（water flow velocity,grouting pressure,permeability and water-cement ratio）and diffusion distance was analyzed.And the grouting effect of cement grouts was evaluated.The experimental results showed that the grouting bodies were distributed in an ellipsoid or column shape;and the groundwater hindered the spread of the grouts in the reverse and vertical water flow directions,which reduced the grouting water blocking effect.Based on the anti-dynamic water washing test,the evaluation index of anti-dynamic water washing was proposed,and the influences of dynamic water flow and grouts’performance（viscosity,bleeding and setting time）on grout retention rate were studied.The defects of cement-sodium silicate grout were pointed out,such as high bleeding,low retention rate,and flowing around easily.On this basis,the requirements for grouting materials and design principles for water-rich sandy gravel stratum were clarified.（2）Based on the thermodynamic method and PHREEQC programming,the effects of bentonite,temperature and admixtures on the hydration products,p H value and saturation index of bentonite-cement-based grouts were simulated and studied.The simulation results showed that bentonite promoted the formation of aluminum phase products（C₃AH₆）and improved the thermal stability of grouts.Under the condition of temperature change,compared with cement grout and cement-water glass grout,bentonite-cement-based grout was slightly less alkaline and had better thermal stability.Admixtures could further expand the application range of bentonite-cement-based grout to temperature and reduce the alkalinity of grouts.Na Cl,Na₂SO₄,Li₂CO₃,Li₂SO₄,etc.improved the thermal stability of grouts.Al Cl₃ reduced the alkalinity of grouts,and the p H value of grouts was 6.4～8.1.（3）Sodium-based bentonite/lithium-based bentonite-cement-based grouting materials were developed.The influence of composition,water-solid ratio,admixtures on the viscosity,bleeding,setting time,retention rate,permeability,and compressive strength of grouts were studied.In addition,the performance of the grouts can be controlled flexibly by adding admixtures.The experimental results of the heat of hydration analysis showed that the hydration rate of the lithium-based bentonite-cement-based grout was much greater than that of the sodium-based bentonite-cement-based grout,and its maximum hydration rate was 146 times that of the sodium-based bentonite-cement-based grout.XRD,SEM,and BET analysis results showed that the hydration products of lithium-based bentonite-cement-based stone bodies and sodium-based bentonite-cement-based stone bodies were the same（CSH,AFt,AFm,etc.）,and no CH that can easily cause structural cracking was found.The pore structure of the former was denser and the cumulative pore volume was 21%smaller than that of the latter.Finally,field applications were carried out on the water-rich sand and pebble formations of Beijing Metro Line 8 and Fangshan Line,which solved the problems of water seepage and water gushing of the project.