Jinchang Wang’s research while affiliated with China Railway Eryuan Engineering Group and other places

A retrogressive thaw slump (RTS) is a slope failure formed by slope thaw settlement and retrogressive slump following the thawing of ice‐rich permafrost or the melting of massive ice. Here, we review recent literature on RTSs, one of the main geomorphological landscapes developed in the process of permafrost degradation. The main topics are as follows: development and temporal evolution, mechanisms and processes, influencing factors, evaluation susceptibility and calculation, and assessment of engineering and environmental impacts. There has been a rapid increase in the number and distribution area of RTSs over permafrost in recent years. Climate warming events, extreme rainfall, forest fires, bank and coast erosion, and anthropogenic activity are the primary factors leading to RTSs in permafrost regions, disrupting the initial hydrothermal equilibrium of permafrost slopes. This causes a rise in ground temperature and the thaw of ice‐rich permafrost. Meltwater seeps down and collects on the ice surface, weakening freeze–thaw interface shear resistance and resulting in soil collapse. The development of RTSs may last several decades or longer. RTSs destabilize infrastructure, destroy vegetation, boost soil erosion and land desertification, alter the environment of nearby waters, and increase emissions of some major greenhouse gases. Numerous methods have been developed and adopted to explore RTSs, including geographic information systems (GIS) and equilibrium, numerical, and reliability analysis methods. However, research on formation mechanisms and processes, quantitative prediction, engineering and environmental influences, and mitigative measures of RTSs under a warming climate are still inadequate. Existing research methods, such as numerical simulations, remote sensing, airborne ground‐based geophysical surveys, investigations and mapping, and hydrothermal and deformation field monitoring, should be systematically integrated. Additionally, equipment for laboratory testing and numerical models for simulating RTSs may need to be timely introduced and better developed.

Different from other geotechnical materials, the strength characteristics of saturated frozen soil have nonlinear characteristics that first increase and then reduce with the increasing confining pressure, and are sensitive to varying temperature due to the existence of ice inclusions. Based on analysis on the breakage of frozen soil, it is believed that the proportion of each material component and ice-soil cementation breakage are the internal mechanisms to control the macroscopic strength. On the basis of this analysis, a multiscale strength criterion is proposed to account for this coupling mechanism. Firstly, the linear strength criterion of soil skeleton and ice inclusions in broken/unbroken states are defined, based on which the strength criterion of the bonded elements (unbroken material aggregate) and frictional elements (broken material aggregate) are deduced through the yield design theory and linear comparison composite. Secondly, the failure of ice-soil cementation is reflected by the transformation of the bonded elements to frictional elements, thus the multi-scale nonlinear strength criterion of representative volume element is derived by combining the binary medium model and strength homogenization method. These results have been verified by the test results of different types of saturated frozen soils.

Two-phase closed thermosyphon (TPCT) is widely used to cool foundation soil and improve the stability of structures in cold regions. However, along with the cooling of soil surrounding a TPCT, frost heaving of soil can occur, which might pull the structures out, but this phenomenon has rarely been reported. In this paper, based on field observations along the Qinghai–Tibet power transmission line, we present a case study on the frost jacking of piles, with the largest jacking amount being up to 65 mm from December 2011 to November 2018, because of the application of TPCTs. Owing to a greatly enlarged frozen section around the piles due to the cooling of TPCTs, moisture migration toward and frost heaving around the pile were greatly intensified. This resulted in an obvious increase in the tangential frost heaving force and a decrease in the anti-frost jacking force. Thus, the pile might be jacked out from the ground. In areas with shallow developed artesian ground water, the frost jacking of the pile with TPCTs was determined to be more probable because the tangential frost heaving force will be greatly increased. The influence of the decreasing efficiency, or even the failure of TPCTs applied in engineering structures, might give rise to the development of differential deformation, threatening the stability of the tower on the piles. The results indicate that the application of TPCTs for engineering in talik or seasonally frozen areas should be more careful and increasing concern should be given for the engineering influence of TPCT failure.

Frost heave is a crucial issue of concern in seasonally frozen regions, which directly causes many engineering freezing damage problems, especially affecting the stability of embankments. To treat the frost heave diseases that occur on the embankment in seasonally frozen regions, we propose a new solar circulating heated embankment system (SCHES) based on the idea of using solar energy to provide a heat source. A field experiment of heating a full-scale simulated embankment was first time carried out based on the SCHES. The heating performance and applicability of the SCHES were analyzed. Experimental results show that the SCHES has a good heating effect for a full-scale simulated embankment, which changes the temperature state of the surrounding soil of the heat accumulation pipe (HAP, is the heating embankment part of the SCHES) in the cold season. The surrounding soil mean temperature of the HAP exceeds 2 °C, and the effective heat storage is 404 MJ / 391 MJ, while the soil temperature without the heating action of the SCHES is below −1 °C and the effective heat storage is −68 MJ. The HAP mean daily temperature ranged from 10 °C to 35 °C, and solar radiation is the determining factor of the HAP temperature. The SCHES has a good heat collection performance with an effective daily heat collection of 8 MJ ∼ 26 MJ and a heat collection efficiency of 0.32–0.62. Comparing the seasonally frozen regions and the solar-rich regions of China, it is found that the SCHES has good applicability.

Frost heave has a significant influence on the stability of embankment in seasonally frozen regions, where the active heating embankment has become a new method for preventing and controlling frost heave. In this study, a field experiment was conducted based on a solar circulating heating embankment system (SCHES), and the heat collection performance of the SCHES and the heating effect of the soil were analyzed. Additionally, the numerical simulation of the coupled moisture-heat of the embankment under heating conditions was performed, and the heating effects of different buried forms and buried depths of the heat accumulation pipe (HAP) were discussed. The experimental results showed that the SCHES can provide a heating temperature of up to 70 °C and a mean heating flux of 87 W m⁻² during the cold season. The heating action of the SCHES makes the temperature of the surrounding soil of HAP above 0 °C in cold season, which significantly reduces the freezing depth. The numerical results also show that the maximum freezing depth of the embankment can be reduced by 70%, the volumetric ice content can be reduced by more than 60%, and the heating embankment can reduce the frost heave deformation by more than 60% compared with the normal embankment. The buried form of the HAP is recommended to be the horizontal insertion on both sides and the horizontal insertion on sunny sides. The optimal buried depth is between 0.5 m ~ 1.0 m when the HAP burial form is the horizontal insertion on both sides. As a preliminary study, the concept of the active heating embankment utilizing solar energy can provide a reference for the prevention and control of frost heave in seasonally frozen regions.

Two-phase closed thermosyphons (TPCTs) are widely used in enhancing mechanical strength of foundation soils in permafrost regions. However, engineering problems develop in embankments containing TPCTs. Based on numerical simulations, we herein discuss the influence of four important parameters, namely model size, daily variations in air and ground surface temperatures (AGST), decreasing cooling power of a TPCT, and adiabatic section, on the simulation accuracy or the application results of a TPCT. Results show that the simulated thermal influence of the TPCT can be severely impacted by the model size. It is also found that neglecting daily AGST variations results in 0.3–0.4 °C temperature increase in soil 2 m away from the TPCT. The decreasing cooling power of a TPCT can increase the ground temperature. When the cooling power decreases by 30% and 50%, the ground temperature 2 m away from the TPCT increases by 0.2–0.3 °C and 0.4–0.6 °C in cold seasons, respectively. Although adiabatic section was applied in many TPCTs, but it has limited effect on the cooling performance of a TPCT. The results may help improving the accuracy of a simulation model and help optimize field applications of TPCTs 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.