Geopolymer is characterized by high strength

denseness

low thermal conductivity

and resource conservation

and it meets the needs of coarse-grained fill improvement for high-speed railway roadbed engineering in terms of seismic safety and feasibility of resource acquisition. The unconfined compression strength tests of geopolymer-stabilized fine-grained fillings with different mixing ratios of metakaolin and alkali-activator and the dynamic triaxial tests of geopolymer-stabilized coarse-grained fillings with different rock block contents and confining pressures were carried out. The mixing ratio of raw material and alkali activator for composing metakaolin-based geopolymer and their optimum mixing ratio in fine-grained fillings were analyzed. The impacts of rock block content and confining pressure on the dynamic characteristics of the geopolymer-stabilized coarse-grained fillings were discussed. The results indicated that the optimum ratio of metakaolin and alkali activator for composing geopolymer was 2:1

and their optimum content in fine-grained fillings was 15%; the maximum dynamic shear modulus of geopolymer-stabilized coarse-grained fillings had an approximately linear relationship with the rock block content and a non-linear relationship with the confining pressure; when the shear strain was normalized

the dynamic shear modulus ratios of the geopolymer-stabilized coarse-grained fillings were distributed in a narrow band

while the damping ratio showed a relatively high dispersion in values. The results of this study can provide the design parameter basis for the application and popularization of geopolymer-stabilized coarse-grained fillings.