Abstract: To improve the grouting effectiveness in fractured rock masses of ultra-deep shafts and address the perform ance deficiencies of conventional grouting materials in water sealing and surrounding rock reinforcement,superfine cement was selected as the base material.The orthogonal tests and range analysis were used to investigate the effects of silica fume,fly ash, ultrafine ground granulated blast-furnace slag,and superplasticizer dosages on the fluidity,bleeding rate,setting time,and com pressive strength of superfine cement grout.The results indicate that fly ash exhibits the most significant influence on fluidity, bleeding rate,and compressive strength,while silica fume predominantly improves the setting time.The effects of ultrafine slag and superplasticizer are relatively minor.The combined use of multiple admixtures demonstrates complementary effects on grout performance,enabling synergistic optimization of fluidity,stability,and mechanical properties.Considering the priority order of compressive strength,setting time,fluidity,and bleeding rate,the optimum mix proportion was determined as 12% silica fume, 30% fly ash,20% ultrafine slag,and 0.15% superplasticizer by mass of cement.Field application shows that the water inflow of a single borehole was reduced to below 2 m3 /h after grouting,with a water sealing rate of 90%,confirming the favorable ap plicability and engineering effectiveness of the modified superfine cement grouting material in fractured rock mass grouting.

Key words: superfine cement,grouting material,orthogonal test,modification,silica fume,fly ash,ultra-deep shaft,frac tured rock mass grouting