Due to the threat of global warming and the accelerated melting of glaciers and permafrost, the stability of slopes in permafrost regions has received an increasing amount of attention from scholars. However, research on the stability of soil-rock road cutting slopes in high-latitude and low-altitude permafrost regions of the Greater Khingan Mountains in the Inner Mongolia Autonomous Region has not been reported. For this reason, a study of the stability of a slope with a high ice content in section K105 + 600 to K105 + 700 of National Highway 332 is conducted. The slope is 20 m high and the slope angle is 45°, and the risk of landslides on this slope under the action of freeze-thaw erosion is very high. Because of this, field in situ monitoring, indoor freeze-thaw tests, thermal parameter tests, and ABAQUS numerical simulation models are used to study the stability of the slope. After collecting the continuous temperature, moisture, settlement, and slope deformation data, it was found that the slope was undergoing dynamic changes. The creep of shallow slopes increased with the number of freeze-thaw cycles. After approximately 150 freeze-thaw cycles, the slope safety factor was less than 1, which means that the slope had reached the limit equilibrium state. Therefore, freeze-thaw erosion greatly reduced the stability of the slope. Hence, the stability of the slope must be protected during its entire life cycle. This study provides a reference for the design and construction of road cutting slopes in the high-latitude and low-altitude permafrost regions of the Greater Khingan Mountains.

Under the action of freeze-thaw erosion, slopes in permafrost regions frequently suffer from geological disasters. The unique properties of soil-rock-mixture slopes further complicate this freeze-thaw stability problem. To study the effects of freeze-thaw erosion on the stability of soil-rock-mixture slopes, several indoor tests were first carried out on the specimens collected from the target bare slope at the K105+750~K105+850 section of the Ali River to the Kubuchun Forest Farm along National Highway 332 in permafrost regions of Greater Khingan Mountains, and then, according to the test results, damage theory, strength reduction method, Python script, and ABAQUS numerical analysis software, the slippage and safety factor of the bare slope under freeze-thaw cycles were obtained, and finally, the damage degree of freeze-thaw erosion to the bare slope was quantified. To improve the stability of bare slope in the freeze-thaw environment, the composite ecological slope protection measures of arched skeleton + three-dimensional net + grass planting were finally selected, and its feasibility is verified with the help of on-site monitoring and numerical simulation; then, the long-term freeze-thaw stability of the slope after revetment was studied. Key findings indicated that (1) the threshold between soil and rock in the target slope was 5 mm, the soil-to-rock mass and volume ratios of the slope were 55.04% : 44.96% and 69.38% : 30.62%, respectively. (2) After the 150 freeze-thaw cycles, the peak strength and elastic modulus of the specimens decreased 59.7% and 79.50%, respectively. (3) Meanwhile, the freeze-thaw damage was 0.79. (4) The slope safety factor was inversely proportional to the number of freeze-thaw cycles. The target bare slope was unstable after 150 freeze-thaw cycles, and the safety stability reduction rate was 41%. (5) Compared with the bare slope, the shallow horizontal slip of the slope after revetment decreased from 1.528 m to 4.971 cm, and the slope safety factor increased from 0.997 to 4.501, which shows that the slope protection measures are initially feasible. In addition, the numerical analysis results are consistent with the field monitoring data, and the error between the two is ≤2.01%, which proves the rationality of the numerical model established in this paper and provides data support for subsequent research.

In order to study the influence of freeze–thaw cycles on the stability of cutting slopes in high-latitude and low-altitude permafrost regions, we selected a cutting slope (the K105+700–800 section of National Highway 332) in the Elunchun Autonomous Banner in Inner Mongolia as the research object. Located in the Greater Xing’an Mountains, the permafrost in the Elunchun Autonomous Banner is a high-latitude and low-altitude permafrost. The area is also dominated by island-shaped permafrost, which increases the difficulty of dealing with cutting slopes, due to its morphological complexity. Surface collapse, caused by freeze–thaw erosion in this area, is the main reason for the instability of the cutting slope. Indoor freeze–thaw tests, field monitoring, and an ABAQUS numerical simulation model were conducted so as to quantify the decrease in rock strength and slope stability under freeze–thaw conditions. The following conclusions were drawn. (1) As the number of freeze–thaw cycles increased, the compressive strength of the rock specimens obtained from this slope gradually decreased. After 50 freeze–thaw cycles, the uniaxial compressive strength measured by the test decreased from 40 MPa to 12 MPa, a decrease of 37%. The elastic modulus value was reduced by 47%. (2) The safety factor of the slope—calculated by the strength reduction method under the dynamic analysis of coupled heat, moisture, and stress—gradually decreased. After 50 freeze–thaw cycles, the safety factor of the slope was only 0.74. (3) Reasonably reducing the number of freeze–thaw cycles, reducing the water content of the slope, slowing down the slope, and increasing the number of grading steps can effectively improve the stability of the slope. The results of this study can provide a reference for the design and stability analysis of slopes in permafrost regions of the Greater Xing’an Mountains.

National Highway 332 (referred to as line 332) is the most convenient way for the forest areas (Oroqen Autonomous Banner, etc.) in northern China. This area is located in the high-latitude permafrost regions of the Daxing’anling Mountains. The section of line 332 from Ali River to Kubuchun Forest Farm is 116 km long, and the permafrost section is 7.45 km. Part of the section, K105+700-K105+800, is a road cutting slope with high ice content, and it is also our research object. The slope to be studied is difficult to construct and has high landslide risk, so we arranged thirty-five temperature sensors, four moisture sensors, and eighteen landmarks on the slope to grasp the dynamic changes of the slope under freeze-thaw conditions. After collecting the continuous data of temperature, moisture, settlement, and deformation of the slope, we found that the slope was undergoing freeze-thaw cycles, and the shallow slippage of the slope reached 6.811 cm in 2019. Besides, the drilled core samples were tested in the laboratory and relevant parameters were obtained. Then, the slope stability was numerically simulated in ABAQUS numerical simulation software. After two hundred freeze-thaw cycles, the slope safety factor reached 0.997, indicating that the slope was in a state of extreme equilibrium, so the potential freeze-thaw disasters must be considered during road operation, and higher requirements for the permanent protection of slopes should also be put forward. The study can provide guidance for the design and construction of road cutting slope in the permafrost regions of the Daxing’anling Mountains.