| With the continuous acceleration of urbanization in China,the development of urban underground space and subway construction are developing vigorously.The geological conditions in the construction of engineering are more complex.Water-rich the fault fracture zone is an adverse geological condition frequently encountered in urban construction,which is very likely to induce a large amount of gushing water,sudden mud,collapse and other geological disasters,seriously threatening engineering construction and safety of life and property,and causing adverse social risks.Grouting is one of the most effective and quickest engineering measures to manage poor geology,and the grouting material is the key factor to determine the effect of grouting management.However,traditional cement grouting materials are difficult to effectively treat water-rich fracture zones because of the long setting time,serious water precipitation,low stone formation rate,low early strength and volume shrinkage.In addition,the raw materials for cement are non-renewable,while the production process requires huge energy consumption and emits large amounts of carbon dioxide.Therefore,the development of a low-carbon,green,high-performance grouting material is essential for the treatment of water-rich fracture zones.This paper addresses the key scientific issues of grouting treatment in water-rich fracture zones and investigates the modified grouting materials using graphene oxide(GO)-fly ash(FA)synergistic effect,and carried out study the modified grouting material.The performance of GO-FA slurry is comprehensively analyzed through systematic performance tests of grouting materials,the optimal ratio is determined,and the mechanism of GO-FA synergistic effect to improve the performance of cement grouting materials is clarified.The macro-mechanical properties and coupling strengthening mechanism of slurry-rock interface are studied.The superiority of GO-FA grouting material was analyzed by grouting model test,and the cementation mode of slurry and rock interface was determined using microscopic testing technology then revealing the grouting reinforcement mechanism of water-rich fracture zone.The field application was carried out,and the grouting effect was excellent.The main research results are as follows.(1)The influence rules of GO and FA on slurry performance was analyzed by systematic slurry properties test.The test results show that GO can improve the stability of the slurry,shorten the setting time of the slurry,and have a certain deteriorating effect on the liquidity of the slurry.Mixed FA can effectively compensate the loss of slurry fluidity while keeping other properties basically unchanged.It is found that the initial setting time of GO-FA grouting material can be effectively regulated from several minutes to several hours by adding quick-setting agent,which can meet the grouting requirements of different projects.The addition of GO to cement-based slurry increases the yield stress and plastic viscosity of the slurry,and the flow pattern of the grout does not change.The flow pattern of the grout is mainly affected by the water-binder ratio.GO-FA synergistic effect cement-based composite slurry exhibits the phenomenon of shear thinning.The time-varying model of GO-FA grout is established,and the relationship between rheological parameters and macroscopic fluidity is given.(2)GO can effectively improve the early flexural strength,compressive strength and impermeability of the stone body by adding GO into the slurry,while FA can reduce the strength performance of the stone body.It was found that the early strength of GO-FA slurry nodules was slightly lower than that of GO alone,but the later strength was enhanced,and the flexural and compressive strengths at 28 d age were enhanced by 4.4% and 8.3% respectively compared with that of GO alone.When GO dosing is 0.03% and FA dosing is 20%,the impermeability of the stone body is increased by 5.66% compared with GO dosing alone.GO-FA slurry stone body has favorable resistance to chloride ion erosion,and its erosion resistance coefficient is1.007.(3)The slurry fluidity,stability,setting time,rheological parameters,stone body strength,erosion resistance,seepage resistance and economic benefits is comprehensive considered,it is determined that the cement-based slurry is compounded with 0.03% GO and 20% FA.To ensure the good performance of the slurry injection and reduce the amount of cement,for the comprehensive utilization of industrial waste fly ash,which meets the demand of low-carbon green development.The mechanism of the synergistic effect of GO-FA to improve the properties of cement-based grout was revealed using microscopic testing technology combined with hydration reaction.GO gave full play to the effect of promoting coagulation and thickening,nano-filling effect and chemical bond cooperation.FA showed the lubricant tumbling effect and later activated the volcanic ash effect of FA to promote the secondary hydration reaction.(4)A series of straight shear tests were conducted using a shear box designed and manufactured independently.The relationship between the shear strength of different grouting material nodules and the shear strength of grouting-rock was studied,and the effect rule of GO and FA on the shear mechanical behavior and shear strength characteristics of the slurry-rock interface was analyzed.The mechanism of coupled shear strength enhancement at the slurry-rock interface was revealed,and the relationship between the shear strength of slurry-rock and the physical parameters of grouting material nodules was established.(5)Conducted grouting model tests of water-rich fracture zone using independently designed visualized large-scale grouting simulation system.The grouting effects of conventional cement slurry,GO-FA composite cement slurry and fractured strata under different grouting pressures were compared to determine the factors influencing the grouting reinforcement effect.The water-rich fractured rock body grouting reinforcement grout-rock cementation surface accords with the Xie song shan mode by the analysis of microstructure.The slurry penetrates into the fractured rock body internal chemical reaction,calcium hydroxide has obvious orientation.The obvious physical and chemical reactions occurred on the cementation surface,and new hydration products were generated,which enhanced the effect of grouting reinforcement and revealed the mechanism of grouting rock consolidation in water-rich fracture zone.(6)The field grouting application test of water-rich broken zone was carried out in the Guangzhou Metro Line 11 Wufeng Station.The pumping test and core drilling showed that the grouting effect was excellent and verified the superiority of GO-FA slurry,which can be promoted and used in similar engineering. |
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