Influences of freeze-thaw and fines content on mechanical properties of coarse-grained soil

For the promotion and application of coarse-grained soil fillings in the railway subgrade in frozen regions, the shear strength properties of coarse-grained soil with fines content under freeze-thaw cycles are directly related to the subgrade stability. The influencing rules of freeze-thaw cycles, fines content and confining pressure on the shear strength properties of coarse-grained soil are therefore thoroughly studied and analyzed in laboratory tests. The results show that with the increasing increment of fines content, the stress-strain curve of coarse-grained soil changes from strain-softening before freeze-thaw cycles to strain-hardening after freeze-thaw cycles. With the increasing of fines content, the cohesion function of fines effectively enhances the shear strength of coarse-grained soil before freeze-thaw cycles, but the frost heave properties of fines decrease the shear strength of coarse-grained soil after freeze-thaw cycles. The shear strength indexes of coarse-grained soil decrease and then are steady after 6 freeze-thaw cycles. The confining pressure effectively enhances the shear strength of coarse-grained soil. Finally, the reasonable fines content of 5% is recommended for the railway subgrade coarse-grained soil fillings in frozen regions, and the mechanical indexes of the 6^th freeze-thaw cycle are suggested for the engineering design values.