Study on the mechanism of subgrade deformation of the Qinghai-Tibet railway in permafrost regions based on multisource data

Climate change and engineering activities have accelerated the degradation of permafrost, leading to significant settlement and deformation damage of subgrades in permafrost regions. Environmental conditions significantly influence the stability of subgrades in permafrost regions. However, previous research on subgrade deformation mechanisms primarily concentrated on analyzing the ground temperature, ice content, and thermo-hydro-mechanical processes within individual sections, ignoring the impact of permafrost environment. Based on multisource data sets combined with long-term field deformation monitoring data, this study utilized methods including normality test and correlation analysis to establish an evaluation index system for subgrade deformation. With this procedure, the mechanisms of subgrade deformation of the Qinghai-Tibet railway in the permafrost regions were investigated using a genetic algorithm-random forest regression method (GA-RFR). The results indicated that the environmental system played a crucial role in determining the susceptibility and severity of subgrade deformation. The primary disaster-inducing factors controlling subgrade deformation comprised solar radiation (SR), stream power index (SPI), subgrade trend (ST), and annual average ground temperature. This study found that the underlying permafrost and engineering accounted for less than 50% of total subgrade deformations, which indicated that previous research overestimated the contribution of these two factors. Furthermore, previous research underestimated the role of permafrost environment, including SR and SPI, particularly thermal erosion by surface and groundwater. Our findings also revealed that the environment is the dominant factor for the change of weight results across different periods within the same region or across different regions during the same period. This study provided important basic data and overall references for the safe operation and maintenance of existing railways, the prevention and control of deformation damages, and the rational design of future railways in permafrost regions.