## 1 Introduction  
Land resources are fundamental to human survival. Soil contamination represents a critical global environmental challenge. The 2014 National Soil Condition Survey Bulletin indicates that the overall soil environmental situation in China is concerning, with approximately 16.1% of soil classified as contaminated. Of this, heavy metal contamination accounts for about 3%, and the levels of heavy metal contamination have significantly exceeded acceptable standards [1]. According to a 2020 United Nations Food and Agriculture Organization (FAO) report, over 33% of the world's soils are degraded by pollution, with heavy metals implicated in nearly 10% of agricultural land degradation [2]. In Europe, the European Environment Agency (EEA) highlights heavy metal contamination as a pressing concern, affecting 24% of industrial zones--particularly in post-mining regions of Poland and the Czech Republic [3]. Similarly, the U.S. Environmental Protection Agency (EPA) identifies heavy metals in 30% of Superfund sites, demanding durable containment strategies [4]. Heavy metal contaminated sites are defined as locations where the concentration of trace metal elements in the soil exceeds background levels due to human activities. These heavy metals, which include mercury, lead, cadmium, and arsenic [5], pose a risk of leaching into groundwater and farmland, thereby jeopardizing public health [6]. Given the challenges associated with the short-term elimination of contamination through direct treatment, cut-off and obstruction have become the most commonly employed remedial strategies [7]. The vertical cut-off wall, depicted in Figure 1[8], is an effective anti-seepage and blockage technology widely utilized in developed countries, particularly in Europe and the United States, for the cut-off and containment of polluted sites. This technology is employed to block the diffusion of contaminated groundwater and to enclose leachate from landfills and mine tailings [9]. Among various technologies, vertical soil bentonite (SB) cut-off walls are often preferred for pollution prevention and control. They have low permeability, good chemical compatibility, and cost-effectiveness. Table 1 presents the relative advantages or limitations of SB cut-off walls compared to other similar containment technologies like cement-bentonite walls and slurry trenches. Pollutant cut-off walls must function effectively over the long term to block contaminants, making the study of their service performance essential for ensuring environmental safety and effective pollution control. Typically, breakdown time serves as a reference index for measuring the service life of cut-off walls [12]. The long-term service performance evaluation model, or seepage cut-off wall evaluation model, primarily considers key processes such as convection, diffusion, dispersion, and adsorption, as illustrated in Figure 1[8]. The long-term performance of soil-bentonite cut-off walls hinges on parameters like permeability, microstructure, and chemical stability. To optimize impermeability, it is crucial to balance bentonite content, particle packing, and compaction. Challenges such as cations, pH changes, and contaminants can impact performance. Ensuring durability demands a combination of material engineering, sound construction practices, and site-specific assessments. The researchers employed \"soil-bentonite vertical cut-off walls\" and \"heavy metal contaminated sites\" as key search terms, resulting in the identification of 154 relevant