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.

There is a huge reservation of loess in the Shanxi mining area in China, which has great potential for preparing supplementary cementitious materials. Loess was modified via mechanical and thermal activation, and the pozzolanic activity was evaluated using an Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES). Moreover, the workability of grouting materials prepared using modified loess was assessed. The experimental results revealed that the number of ultrafine particles gradually increased with the grinding time, enhancing the grouting performance. The coordination number of Al decreased upon the breakage of the Al-O-Si bond post-calcination at 400 degrees C, 550 degrees C, 700 degrees C, and 850 degrees C. Moreover, the breaking of the Si-O covalent bond produced Si-phases, and the pozzolanic activity of loess increased. Furthermore, the modified loess was hydrated with different cement proportions. With increasing grinding time, the overall setting time increased until the longest time of 14.5 h and the fluidity of the slurry decreased until the lowest fluidity of 9.7 cm. However, the fluidity and setting time decreased with increasing calcination temperature. The lowest values were 12.03 cm and 10.05 h. With the increase in pozzolanic activity, more ettringite was produced via hydration, which enhanced the mechanical properties. The maximum strength of the hydrated loess after grinding for 20 min reached 16.5 MPa. The strength of the hydrated loess calcined at 850 degrees C reached 21 MPa. These experimental findings provide theoretical support for the practical application of loess in grouting.