Abstract: The planned high-speed railway in the Belt and Road area will frequently shuttle through salt desert areas, and it is difficult to find high-quality subgrade filler without salt along high-speed railway. To solve the technical problems faced by filling high-speed railway subgrade with coarse-grained saline soil, combined with the construction of Tehran-Isfahan high-speed railway in Iran, taking the coarse-grained saline soil subgrade filler obtained from on-site as the object, the test on water and salt migration and deformation response of compacted coarse-grained saline soil under temperature cycle was carried out. The results show that after each temperature cycle, the temperature wave amplitude is attenuated from superficial soil layer to deep soil layer. The temperature wave amplitude on closer to the surface of soil layers increases with the longer constant temperature time. The compacted coarse-grained saline soil with uniform distribution of water and salt gradually evolves into a non-uniform distribution after repeated temperature cycles. Water and salt migrate to the surface of soil layers, and the closer the position to the soil surface, the greater the increment of water and salt. In the first five temperature cycles, the plastic salt swelling or plastic thawing subsidence appears on the compacted coarse-grained saline soil. With the increase in number of temperature cycles, the plastic salt swelling or plastic thawing subsidence of saline soil decreases significantly or even disappears. The non-salted soil layer resting on coarse-grained saline soil layer has the functions of delaying salt migration up to the surface of soil layers, energy dissipation and expansion reduction. The structural layering technology should be adopted for the construction of high-speed railway subgrade with coarse-grained saline soil. The thickness of non-salted soil layer should not be less than the depth that significantly affected by the local temperature radiation. In the design of coarse-grained saline soil subgrade, the heterogeneous distribution of water and salt formed after repeated temperature cycles and the possible increase effect of salt swelling and thawing subsidence should be considered, and the degree of compaction of coarse-grained saline soil subgrade should not be too large. The research results will play a demonstration and reference role for the construction of high-speed railway subgrade engineering in saline soil areas.

Key words: compacted coarse-grained saline soil, temperature cycle, water and salt migration, salt swelling and thawing subsidence, high-speed railway, subgrade engineering