Study on the Influence of Mineral Compositions of Weathered Rock Mucks on the Performance of Backfill Grouting in Shield Tunnelling
The mineral compositions of rock mucks generated in shield tunnelling in weathered rocks are complex,and its impact on grout performance is not well understood.Based on the Nanjing Heyan Road River Crossing Project,different mineral powders were used to replace fine particles(＜75 μm)in the rock mucks.The basic performance of rock muck-hard grout,prepared by replacing commercial sand with weathered rock muck,was tested.Microscopic tests such as XRD and SEM were conducted to explore the mechanism by which the mineral compositions of fine particles in rock muck affects grout performance.The results show that the quartz has almost no impact on grout fluidi-ty and consistency.The addition of kaolinite significantly reduces grout fluidity and consistency.When commercial sand is completely replaced by kaolinite-rock muck,the initial fluidity loss of the grout is about 31%,and the con-sistency decreases by 48%.The kaolinite content is the main factor affecting grout fluidity.Kaolinite can promote the formation of C-S-H gel and ettringite,shorten the grout setting time by an average of 23.6%.The produced C-S-H gel intertwines and bonds,fills into pores and increases grout strength.However,excessive kaolinite content will re-sult in the formation of excess ettringite,which will cover the cement surface and prevent further hydration,thereby reducing grout compressive strength.
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