Study on mechanical properties and microscopic mechanism of fibre-modified subgrade soil under freeze–thaw cycles

In order to solve the problem of low freeze-thaw deformation strength of railway road genes in cold regions, railway subgrade soil was improved with polypropylene fibres. The failure mechanism of fibres improved foundation soil is revealed by experiments. The test results showed the following: (1) The strength decreased with the increase in the water content in the melting state and reached its maximum when the water content was 12% in the freezing state. The strength reached the maximum when fibre incorporation was 0.3% and fibre length was 15 mm. (2) The shear strength of the improved subgrade soil gradually decreased and tended to be stable with the increase in the number of freeze–thaw cycles in the frozen state. There was no significant change with the increasing number of freeze–thaw cycles in the thawing state. (3) Before and after the cyclic loading of the fibre-modified subgrade soil, the strength after cyclic loading was greater than that before. (4) Through scanning electron microscopy, the optimal fibre content was determined to be 0.3%. The research results can provide a strong reference for the improvement of railway subgrades, and they have broad application prospects.