Xin Ju’s research while affiliated with Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences and other places

As a "magnifier" of climate change, the Qinghai-Tibet Plateau (QTP) is particularly sensitive to warming, leading to the widespread distribution of Retrogressive thaw slump (RTS). However, the spatiotemporal dynamics of RTS development remain inadequately studied. In this research, remote sensing and geophysical techniques- such as RTK, UAV-based LiDAR, and Ground Penetrating Radar (GPR)- were employed to systematically monitor and analyze the dynamic development characteristics and topographic changes of a typical RTS in the Gu Hill area of the Beiluhe basin on the QTP during the 2023 and 2024. By processing multi-temporal high-resolution point cloud data, this study reveals the spatiotemporal coupling between the retreating erosion at the headwall and the deposition of slope mudflows of RTS. The findings show that the degree of RTS erosion in the summer of 2023 was significantly higher than in 2024, with the increased precipitation in 2024 leading to an expansion in the area of mudflow deposition. GPR profile analysis further indicates that the heterogeneity of the subsurface structures significantly regulates RTS development, and the rapid melting of shallow ground ice exacerbates RTS erosion. Meteorological data additionally suggest that, in the context of long-term climate warming, precipitation changes played a critical role in driving mudflow deposition during the RTS process. This study deepens the understanding of RTS’s development in the permafrost regions of the QTP, offering a reliable scientific basis for the formulation of disaster prevention strategies and ecological restoration measures.

The reliable operation of railway embankments traversing degrading permafrost regions is challenged by climate warming. This study examines performances of four main types of railway embankments on the Qinghai-Tibet Plateau in thermally stabilizing permafrost foundation over warm permafrost using numerical modelling and 10-year monitoring data. Then, a reinforcement measure that combines a thermal conductivity variable system (TCVS) was designed to improve the cooling capacity of the crushed-rock sloped embankment (CRSE) by countering the heat absorption of slopes during summers. A coupled thermal-fluid-solid model was built to simulate and assess the cooling performance and reinforcing capacity of the new design. Results show that the crushed-rock embankments can produce convection cooling on the permafrost subgrade but the performances vary with different structures. The CRSE has insufficient cooling capacity to withstand the underlying permafrost degradation in warm permafrost regions. The optimized CRSE that combines the TCVS can effectively cool the underlying warm permafrost and decrease the shady-sunny slope effect under a warming climate, and can be used as an effective reinforcement measure. This study confirms the application of air-cooled embankments in protecting permafrost subgrade and provides guidance for structural design of embankment traversing degrading permafrost.

The degree of water saturation significantly affects the rate of rock deterioration caused by freeze–thaw weathering, which may trigger serious geological engineering hazards. This study aimed to explore the impacts of water saturation on freeze–thaw-induced deterioration of sandstone, and to improve our understanding of this damage mechanism. Sandstone specimens with varying degrees of moisture saturation were subjected to freeze–thaw tests, computed tomography scanning, and uniaxial compressive tests. The distribution of the areal porosity along the computed tomography slices, evolution of the pore volume, and changes in the pore network model parameters of the sandstone samples were visually and quantitatively characterised to assess the damage evolution. The results show that the parameters of the pore-fracture structure reflect the influence of saturation and cyclic freeze–thaw actions on rock deterioration. As the moisture saturation increased, the sandstone transformed from being dominated by pores with a radius ranging from 0 to 100 μm to being dominated by pores of 200–300 μm. The increase in the equivalent radii of pores caused the rock to be more susceptible to deformation and failure, whereas an increase in the number of throats represents a disruption of the cementation between the rock grains, making to rock more susceptible to freeze–thaw actions. Furthermore, the damage mechanisms of sandstone can be interpreted by volumetric expansion and hydrostatic pressure theory in a rapid freeze–thaw environment. The results of this study provide a comprehensive insight into the influence of water saturation on freeze–thaw-induced damage evolution of rocks in cold regions.

Bedded sandstone is classified as sedimentary rock, which is a typical bedded rock with obvious layered structure characteristics. Bedded rocks formed different bedding orientations in the long and complicated geological tectonic evolution and thus have anisotropic mechanical characteristics. Therefore, the strength anisotropy of bedded sandstone depends on the bedding dip angles. In this study, the fracture characteristics and strength criterion of bedded sandstone were studied by triaxial compression tests on rock specimens with different bedding dip angles under different confining pressure. The test results show that the failure mode and strength of the bedded sandstone are related to the bedding dip angles, showing obvious anisotropy. The experimental data are broadly in line with the Jaeger’s surface of weakness (JPW) model. However, considering the difference in the strength of sandstone specimens with horizontal bedding dip (β = 0°) and vertical bedding dip (β = 90°), an improved JPW model is proposed to distinguish the strength criteria for the aforementioned differences. On the basis of considering the nonlinear relationship between confining pressure and rock strength, the JPW model is improved accordingly to make it suitable for predicting the strength behavior of bedded rocks.

In order to analyze the mechanical behavior of cracked rock in cold region subjected to cyclic loading, step cyclic loading and unloading (SCLU) triaxial tests with different stress paths have been designed. The mechanical responses such as strength, deformation, and failure mode were analyzed. The test results show that limestone has obvious strengthening effect under cyclic loading due to local crushing and filling of internal structural plane. The strengthening effect and fatigue damage effect caused by cyclic loading and the impact damage effect caused by the upgraded of stress level have an effect on mechanical response of cracked rock, and the degree of influence is related to the stress path. Under the stress path of constant stress lower limit (CSLL), the strengthening effect of rock was more prominent and its strength was enhanced. It was mainly subjected to progressive fatigue damage and had a buffering effect in the failure process. However, under the stress path of increasing the stress lower limit (ISLL), the rock suffered significant impact damage and entered the fatigue damage stage in advance, which led to its strength reduction and sudden failure when entering the next stress level. In addition, during the loading process, larger initial stress amplitudes led to more obvious cyclic strengthening effects, while smaller initial stress amplitudes led to greater plastic deformation and energy dissipation, and the rock was more prone to progressive damage.

A crushed-rock revetment (CRR) with high permeability that can be paved on embankment slopes is widely used to cool and protect the subgrade permafrost. In this study, a traditional CRR over warm permafrost was selected to investigate its cooling characteristics based on the ground temperature observed from 2003 to 2014. A new mitigation structure (NMS) was designed to improve the cooling capacity of the CRR and to counter the pore-filling of the rock layer. Numerical simulations were conducted to evaluate the cooling performance and reinforcing capacity of the NMS based on a developed heat and mass transfer model. The results indicate that the traditional CRR can improve the symmetry of the permafrost subgrade and decrease the ground temperature of shallow permafrost. However, the CRR cannot generate strong enough cooling to influence the deep (below 10 m depth) and warm permafrost with a mean annual ground temperature above −1.0°C. The wind-blown sand can further weaken the cooling of the CRR and cause significant permafrost warming and thawing beneath the slopes, posing a severe threat to the long-term safe operation of the embankment. The proposed NMS can produce a significantly superior cooling performance to the CRR. If the CRR is reinforced by the new structure, it can not only effectively cool the underlying warm permafrost but also elevate the permafrost table. The new structure can also protect the rock layer on the slopes from sand-filling. The NMS can be used as an effective method for roadbed design or maintenance over warm permafrost.