Analysis of subgrade deformation driving factors and climate resilience for highway in the Qinghai-Xizang Plateau permafrost region

To identify the main driving factors of deformation for inservice highway subgrades in the permafrost region of the Qinghai-Xizang Plateau and their adaptability to climate change, three inservice highways crossing the two major engineering corridors — Golmud to Nagqu and Gonghe to Yushu in the permafrost region of the Qinghai-Xizang Plateau were selected. The spatial correlations between indicators of subgrade deformation and a range of factors, including climate environment parameters, traffic loading differences, inherent parameters of subgrade engineering, and parameters of the site where the subgrade engineering was located were examined. The concept of climate resilience for highway subgrades in the permafrost region of the Qinghai-Xizang Plateau was proposed. Analysis results show that elevation and maximum frozen depth, as well as vegetation coverage and annual cumulative precipitation, are the predominant driving factors influencing the variation of the international roughness index and bumpiness index, with absolute correlation coefficients exceeding 0.4, significantly distinguishing them from other factors. In the seasonal frozen zone, regardless of the annual cumulative precipitation, the road quality index (RQI) remains above good level. In the permafrost zone, when the annual cumulative precipitation is in the range of 220-370 mm, the RQI is mostly poor. However, when the annual cumulative precipitation exceeds 370 mm, the main driving factors of subgrade deformation are the ice content of permafrost, groundwater, soil type, and the jump-like distribution of roadside accumulated water erosion along the route. Furthermore, the heat accumulation effect caused by annual precipitation exceeding 370 mm and roadside water accumulation leads to the alternating development of thaw zones and permafrost islands, which is the main reason for the lack of clear strong correlation with the driving factors in this region. The subgrade overall follows the long-cycle subsidence and seasonal frost heave-thaw collapse of the natural terrain, and the use of subgrades with special structures can slow down the subsidence rate, while pile-raft foundation can effectively terminate the subsidence trend. It is recommended to enhance the structural resilience of the pavement-subgrade-foundation system and reduce the adverse impact of climate environment on site parameters to improve the climate resilience of highway subgrades in permafrost regions. This study provides theoretical guidance and practical reference for the maintenance and renovation of highway engineering in this region.