The stability of loess subgrade is affected by many factors. Freeze-thaw cycles are a common factor that causes the strength of loess subgrades to be damaged. In order to study the influence of freezethaw cycles on the stability of loess subgrades, reveal the mechanism of freeze-thaw cycles on the strength of loess subgrades. It is necessary to sample the loess soil samples in this area, and perform compaction test, freeze-thaw cycle test, unconfined compression test and electron microscope scanning test on the soil sample to analyze the influence of freeze-thaw cycle on the strength and microstructure of loess soil. . In this way, the potential relationship between the microstructure and the strength of the soil can be obtained. The results found that the freeze-thaw cycle of loess led to a trend of first increase and then decrease in soil strength. The microstructure showed a trend of smaller soil particles and increased soil voids. The potential relationship between the microstructure and the strength of the soil was analyzed. It explains the conclusion that the strength of the soil first increases and then decreases.

Taking loess as the research object, the effect of lime content on mechanical properties of loess was studied. Firstly, the basic physical parameters of loess were obtained by laboratory physical index test and improved by lime. Secondly, the mechanical parameters of lime-modified loess were obtained by heavy compaction test and liquid-plastic limit test under different incorporation ratios (3%, 5%, 7%, 9%). Finally, the shear strength parameters and compressive strength of improved soil samples were obtained by unconsolidated and undrained triaxial shear test and unconfined compressive strength test respectively. The results showed that the liquid limit, plastic limit and plastic index of the loess improved by adding lime increased compared with the original soil sample, indicating that the binding force between soil particles was improved and the plasticity was enhanced. The variation range of dry density and water content had no obvious relationship with the dosage of lime. At the same time, the compressibility of soil is reduced and the collapsibility of soil is eliminated. With the increase of age, the strength of lime-modified soil also increases. Through unconsolidated and undrained triaxial shear tests and unconfined compressive strength tests, the strength of the loess improved by adding lime is significantly improved, and the strength of soil-cement increases with the increase of the dosage, and the water stability is obviously improved.

The stability of loess subgrade is affected by many factors. Dry-wet cycle is a common factor that causes damage to the strength of loess subgrade. In order to study the influence of dry-wet cycle on the stability of loess subgrade, reveal the mechanism of dry-wet cycle damage to the strength of loess subgrade It is necessary to sample the loess soil samples in this area, and perform compaction test, dry-wet cycle test, unconfined compression test and scanning electron microscope test on the soil sample to analyze the influence of dry-wet cycle on the strength and microstructure of loess soil. . In this way, the potential relationship between the microstructure and the strength of the soil can be obtained. The results show that the loess drywet cycle causes the loess's tensile strength and compressive strength to decrease with the increase of the number of dry-wet cycles. The dry-wet cycle effect gradually reduces the shear structural strength of the undisturbed loess and eventually disappears. Scanning electron microscope tests found that the humidification process caused slight movement of the particles, while the drying process resulted in permanent deformation of small pores.