To investigate the freeze-thaw resistance of hydroxypropyl methylcellulose (HPMC)-modified loess, the study analyzed the effects of HPMC dosage and the number of freeze-thaw cycles on the shear strength of modified loess through triaxial shear tests. The results indicated that the peak stress of modified loess exhibited a tendency to increase and then decrease with the increase of the dosage. The optimal dosage of HPMC was 0.5 %. When the confining pressure were 100kPa and 200kPa, the stress-strain relationship curves of modified loess with optimal dosage after freeze-thaw cycles exhibited a weak hardening behavior; at confining pressures of 300kPa and 400kPa, the stress-strain curves exhibited weak softening behavior. As the number of freeze-thaw cycles increased, the peak stress and shear strength indices of the optimal dosage of modified loess exhibited fluctuations. with the lowest values observed after five freeze-thaw cycles. Based on the peak stress, an anti-freezethaw modification effect parameter was proposed, which exhibited a positive correlation with the number of freeze-thaw cycles. The anti-freeze-thaw modification effect parameters for modified loess with optimal dosage were all greater than 1, indicating that the addition of HPMC significantly enhances the freeze-thaw resistance of seasonally frozen soil. HPMC functions both within the soil and at the air-water interface, forming hydrogen bonds, three-dimensional network structures, and flocculated agglomerates, thereby enhancing the strength and freeze-thaw resistance of the soil.

The effects of moisture and drying shrinkage can lead to uneven settlement, cracking, and other diseases in loess subgrade. The objective of this study was to investigate the effects of amide polymer (AP) on the permeability, mechanical properties and crack resistance of loess by orthogonal experiments. The basic properties of AP and the permeability, mechanical properties, and dry-wet variation properties of polymer-modified loess were tested, and a scale model verification and simulation analysis were conducted. In this paper, water migration in subgrade is regulated by improving the water sensitivity of loess. By reducing the variation range of subgrade water content, the stress accumulation in subgrade caused by water is weakened. The results show that the curing time and mechanical properties of AP are directly affected by the oxidant and reducing agent, and the mechanical properties of AP are compatible with the characteristics of loess. AP filled the grain gap and reduced the permeability of loess by 34.05-280.83%. The ductility of polymer-modified loess is significantly increased, and the strain of peak strength is increased by 17.21-126.36%. AP can regulate moisture change, reduce the surface tension between particles, and reduce stress concentration. The strength loss rate was reduced by 19.98-51.21% by enhancing the cracking resistance and weakening the strength loss caused by dry and wet cycling. The increase of upper layer moisture content in the scale model of polymer-modified loess subgrade is reduced by 31.38-36.11%.