The Qinghai–Tibet Plateau is the highest and largest permafrost area in the middle and low latitudes of China. In this region, permafrost thaw settlement is the main form of expressway subgrade disaster. Therefore, the quantitative analysis and regionalization study of permafrost thaw settlement deformation are of great significance for expressway construction and maintenance in the Qinghai–Tibet region. This paper establishes a thaw settlement prediction model using the thaw settlement coefficient and thaw depth. The thaw depth was predicted by the mean annual ground temperatures and active-layer thicknesses using the Radial Basis Function (RBF) neural network model, and the thaw settlement coefficient was determined according to the type of ice content. Further, the distribution characteristics of thaw settlement risk of the permafrost subgrade in the study region were mapped and analyzed. The results showed that the thaw settlement risk was able to be divided into four risk levels, namely significant risk, high risk, medium risk and low risk levels, with the areas of these four risk levels covering 3868.67 km², 1594.21 km², 2456.10 km² and 558.78 km², respectively, of the total study region. The significant risk level had the highest proportion among all the risk levels and was mainly distributed across the Chumar River Basin, Beiluhe River Basin and Gaerqu River Basin regions. Moreover, ice content was found to be the main factor affecting thaw settlement, with thaw settlement found to increase as the ice content increased.

As a result of global warming, the thawing settlement disasters of permafrost in the Qinghai–Tibet Engineering Corridor (QTEC) have intensified, which has serious effects on the safe operation of permafrost highway engineering. In this work, a prediction model for the thawing depth of permafrost subgrade in the QTEC under the climate warming scenario was established. Based on the survey results of permafrost ice content along the QTEC and the classification of thawing settlement risks, the zoning characteristics of thawing settlement of permafrost subgrade in the QTEC were obtained and analyzed. The results showed that the thawing depth of permafrost underlying the 26 m width subgrade in the QTEC will mainly remain below 9 m, and the area with a thawing depth of 6~9 m will have the widest spread within the next 20 years. The thawing settlement will be between 0.02 m and 5.45 m, with an average value of about 0.93 m after 20 years. Furthermore, after 50 years, the thawing depth of permafrost underlying the 26 m width subgrade will almost always be greater than 9 m, and the average thawing settlement will be about 1.12 m. Within the next 20 to 50 years, the risk of permafrost subgrade thawing settlement in the QTEC will be the most significant risk type, and this effect will mainly be distributed in the Kunlun Mountains, Chumar River Plain, Kekexili Mountains, Beiluhe Basin, Tanggula Mountains and intermountain Basins.

Due to climate change and seasonal precipitation, water conditions in the Qinghai–Tibet region are a significant factor affecting the stability of subgrades. The accumulation of large amounts of surface water leads to subgrade diseases along the Qinghai–Tibet Highway. Based on remote sensing photos obtained from Google Earth Engine and processing the photos using ENVI 5.6.3 and CAD 2019 software, this paper analyzed the distribution characteristics of surface water and studied the impact of roadside ponding on subgrade diseases. The results showed that the total area of surface water was more than 3.7 million m², and the surface water was most widely distributed in large river areas such as the Tuotuo River and Buqu River. The subgrade diseases of the Qinghai–Tibet Highway could be categorized into three types: settlement, longitudinal crack, and frost boiling, which accounted for 71.09%, 17.13%, and 11.78% of the total number of subgrade diseases, respectively. Additionally, the ground mean annual temperature was an important factor affecting the distribution of surface water, with the surface water area showing an increasing trend with the increase in ground mean annual temperature, and roadside ponding was most likely to form in the high-temperature extremely unstable permafrost area.