Yongning Sun’s research while affiliated with China Railway and other places

The embankment–bridge transition section (EBTS) is one of the zones where railway diseases occur frequently in permafrost regions. Disease risk assessment of EBTSs can provide guidance for maintenance. In this study, considering the engineering geological conditions, climate characteristics, and embankment structure types along the Qinghai–Tibet Railway (QTR) as well as based on the disease inventory of the QTR from 2010 to 2019, the logistic regression (LR), support vector machine (SVM), and combination-weight-based gay relation analysis (GRA) were used for disease risk assessment of the EBTSs along the QTR in permafrost regions. The results indicate that the LR and SVM models have a better capability for EBTS disease prediction than the GRA model, and the SVM model can select more disease samples in relatively larger regions than the LR model. Based on the SVM and LR models, the risk level of EBTSs is divided into four classes: low- (29.9%), moderate- (39.6%), high- (22.1%), and very high (8.4%) risk. Finally, we selected 272 EBTSs in high- and very-high-risk classes for key observation during the maintenance of the QTR in permafrost regions. This study provides a reference for the risk assessment of railways built in permafrost regions using data-driven methods.

Large landslides are one of the most menacing geological hazards in mountainous regions around the world due to their high-speed, large-scale characteristics. Up to now, the thermo-poro-mechanical coupling mechanism of catastrophic landslides under initial water-saturated conditions has been recognized by many scholars. Nevertheless, most slip zones of landslides are located in both the unsaturated and saturated zones and the unsaturated zone can account for a much larger portion when the groundwater level is relatively low. Typical examples of this situation include many loess landslides which have occurred in northwestern China. In this study, a unified quasi two-dimensional thermo-poro-mechanical model was proposed taking into account both the unsaturated and saturated zones in the slip band of landslides and an attempt was made to describe the complete movement process. Moreover, the Dongfeng loess landslide was chosen as a case study with an assumed triggering condition, and the model was validated by comparison between the simulation results and previous published work. A sensitivity analysis demonstrated that the frictional heating mechanism and the presence of a dry air phase in the slip band have clear impacts on the characteristics of the landslide. In particular, it was found that the soil-water characteristic curve and the initial degree of saturation are of significance.

A key issue in ensuring the stability of transportation infrastructure in permafrost regions of the Qinghai–Tibet Plateau (QTP) is to prevent the degradation of the underlying permafrost. Therefore, several cooling methods (such as sun sheds, duct-ventilated embankment, thermosyphon, crushed-rock embankment, and dry bridge) have been developed to stabilize the underlying permafrost and mitigate thaw settlement. In this study, considering climate warming and engineering geologic conditions, a necessity model of cooling methods for transportation infrastructure was proposed. The application features of cooling methods along the Qinghai–Tibet Railway (QTR) in permafrost regions were systematically and comprehensively summarized to validate the model accuracy. The results indicated that the model has satisfactory performance and can determine the necessity index (NI) of cooling methods in a certain area. Based on the NI values, convenient application criteria for cooling methods were proposed. Specifically, the transportation infrastructure can be constructed without cooling methods in regions where the NI is less than 1.088. The results indicated that approximately 97% of the regions (NI < 1.088) in the study area are located in talik and low-temperature and ice-poor permafrost regions. Therefore, NI = 1.088 was determined to be a reasonable boundary value for deciding whether to apply cooling methods. Finally, the reliability of the criteria was validated by analyzing the settlement data of six typical embankment sections. This model can improve the reasonableness of the decision-making process of cooling method selection during the design and construction of transportation infrastructure, not only in the Qinghai–Tibet engineering corridor but also in a wide region of the QTP.