Abstract: To investigate the effects of cement content on the compaction characteristics and microstructural evolution of granite residual soil,this study used granite residual soil from Yiyang,Hunan Province,and conducted compaction tests,scanning electron microscopy (SEM) image analysis,and energy dispersive spectrometer (EDS) spectroscopy with cement contents of 0%,3%,5%,7%,and 9%.The experiments revealed that the modifying effect of cement does not continue to increase as the cement content rises.Microscopic tests further revealed the underlying mechanisms within the soil.SEM observations showed that as the hydration reaction progressed,the microscopic porosity decreased significantly from 14.16% in its natural state to 6.00%;EDS spectroscopy results showed that the mass fraction of Ca in the soil increased significantly from 0% to 10.02%,indicating enhanced cement hydration.The formation of hydration products promoted pore filling and led to a redistribution of the elemental composition in the specimens.In engineering practice,it is recommended that the admixture dosage for conventional subgrade projects be controlled at around 5%;if higher compaction requirements are needed for specific sections,a dosage of 7% may be selected,but this must be accompanied by strict crack-prevention and curing measures.

Key words: granite residual soil, cement-improved soil, compaction characteristics, three-stage model