Three-Dimensional Numerical Investigation on the Seepage Field and Stability of Soil Slope Subjected to Snowmelt Infiltration

Cutting slope failures occur frequently along the high-speed railways in Northeast China during the construction due to snowmelt infiltration. This study addresses this issue by applying a three-dimensional numerical model. The influence of the depth of accumulated snow (ds), daily temperature variation (ΔT), and freeze-thaw (F-T) cycles on the seepage field and stability of cutting slopes is discussed. The results demonstrate that water seepage due to snowmelt infiltration primarily extends through the ground surface by about 10 m. The deep-seated instability is likely to occur under a prolonged and highly accumulated infiltration, while shallow failure is associated with intense, short-duration snowmelt infiltration. The maximum degree of saturation (Sr) and pore-water pressure (PWP) values are observed at the slope toe. Increasing ds and ΔT increase the Sr and PWP due to snowmelt infiltration and thereby decreases cutting slope stability. Compared to the ds and ΔT, the F-T cycle is more likely to cause slope failure. In addition, the F-T cycle also induces the reduction of soil strength and the crack propagation. Overall, the conducted study provided useful help toward the process of safer design for cutting slope along the high-speed railway in seasonally cold regions.

Freeze-Thaw Stability Analysis of the High-Ice Content Soil-Rock Cutting Slope: A Case Study in Oroqen Autonomous Banner, North China

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.

Effect of Freeze-Thaw on the Stability of a Cutting Slope in a High-Latitude and Low-Altitude Permafrost Region

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.