More than 80% of open-pit coal mines in China are located in northern regions, and the mechanical properties and stability of loose soil–rock mixtures in waste disposal sites are significantly affected by freeze–thaw effects. This article takes the external dumping site of the Baorixile open-pit coal mine in the northern high-altitude region of the Inner Mongolia Autonomous Region as the research object. Through on-site investigation and sampling, indoor triaxial tests (confining pressures of 100 KPa, 200 KPa, and 300 Kpa; moisture contents of 18%, 21%, and 24%), numerical simulation, and other methods, the mechanical properties of soil–rock mixtures in the dumping site under different freeze–thaw cycle conditions were tested to reveal the specific influence of the number of freeze–thaw cycles on the mechanical properties of soil–rock mixtures. Using the discrete element software PFC, the microstructural changes in soil–rock mixtures formed by freeze–thaw cycles were studied, and the deformation mechanism and slip mode of loose slopes in waste disposal sites under different freeze–thaw cycle conditions were explored. The relationship between the number of freeze–thaw cycles and slope stability was clarified. The following conclusions can be drawn: the compressive strength of soil–rock mixtures decreases as a quadratic function with increasing freeze–thaw cycles; as the number of freeze–thaw cycles increases, the internal cracks of the soil–rock mixture model increase exponentially; and as the number of freeze–thaw cycles increases, the stability of the slope in the dumping site decreases significantly, and this stability also decreases with an increase in dumping height.

Damage deterioration of rocks in cold regions under seasonal changes and daily cycles of freezing and thawing generate a series of engineering geological problems. These problems will seriously affect the safe and efficient production of open-pit mines. In this paper, a freeze–thaw cycle test and uniaxial compression test considering the natural conditions of the slope were carried out. Mechanical properties and damage mechanisms of open-pit mine mudstone under freeze–thaw conditions were investigated based on nuclear magnetic resonance (NMR) technology. The test results show that the microscopic internal pore structure of mudstone was changed under the superimposed effect of freeze–thaw damage and hydration damage. The internal pore size of mudstone increased with the number of freeze–thaw cycles, while the average pore size of the natural mudstone test increased more. Macroscopically, the compressive strength and modulus of elasticity of mudstone varied linearly with the number of freezing cycles, and the compressive strength and modulus of elasticity showed a decreasing trend. The strain-softening characteristics of mudstone samples were significant for more freeze–thaw cycles. The study explains the microscopic causes of mudstone deterioration in open-pit mines in cold regions and offers guidance for solving engineering disasters caused by mudstone deterioration.

The stability of open-pit mine slopes is crucial for safety, especially for spoil dump slopes, which are prone to cracks leading to landslides. This study investigates the use of xanthan gum (XG) to enhance the stability of mudstone in spoil dumps. Various concentrations of xanthan gum were mixed with mudstone and subjected to dry–wet cycle tests to assess the impact on crack development. Pore and crack analysis system (PCAS) was utilized for image recognition and crack analysis, comparing the efficiency of crack rate and length modification. The study found that xanthan gum addition significantly improved mudstone’s resistance to crack development post-drying shrinkage. A 2% xanthan gum content reduced the mudstone crack rate by 45% on average, while 1.5% xanthan gum reduced crack length by 46.2% and crack width by 26.3%. Xanthan gum also influenced the fractal dimension and water retention of mudstone cracks. The optimal xanthan gum content for mudstone modification was identified as between 1.5% and 2%. Scanning electron microscopy imaging and X-ray diffraction tests supported the findings, indicating that xanthan gum modifies mudstone by encapsulation and penetration in wet conditions and matrix concentration and connection in dry conditions. These results are expected to aid in the development of crack prevention methods and engineering applications for open-pit mine spoil dump slopes.

Open-pit mining often exposes weak rock layers, the strength of which significantly affects the stability of slopes. If these rock layers are also prone to disintegration and expansion, cyclic rainfall can exacerbate instability. Rainfall-induced changes in the seepage field also indirectly threaten the stability of slopes. Therefore, investigating the characteristics of mudstone limestone and the impact of the seepage field on slope instability under different wet–dry cycles is of great significance for the safe mining of open-pit mines. This paper takes the mudstone limestone slope of a certain open-pit mine in the southwest as the starting point and conducts experiments on saturated density, water absorption rate, permeability coefficient, compressive strength, and variable angle shear strength. Combined with scanning electron microscopy and phase analysis of X-ray diffraction analysis, the macroscopic and microscopic characteristics of the samples are comprehensively analyzed. FLAC3D software is used to explore the changes in the seepage field and the mechanism of instability. Our research found that for the preparation of mudstone limestone samples, a particle size of less than 1 mm and a drying temperature of 50 °C are optimal, with specific values for initial natural and saturated density, and natural water content. As the number of wet–dry cycles increases, the saturated density of mudstone limestone increases; the water absorption rate first rises sharply and then rises slowly; the permeability coefficient first rises sharply and then stabilizes, finally dropping sharply; the compressive and shear strength decreases slowly, and the internal friction angle changes little; frequent cycles also lead to mudification and seepage filtration. At the microscopic level, pores become larger and more regular, and the distribution is more concentrated; changes in mineral content weaken the strength. Combined with numerical simulation, the changes in the seepage field at the bottom of the slope exceed those at the slope surface and top, the transient saturated area expands, and the overall and local slope stability coefficients gradually decrease. During the third cycle, the local stability is lower than the overall stability, and the landslide trend shifts. In conclusion, wet–dry cycles change the pores and mineral content, affecting the physical and mechanical properties, leading to the deterioration of the transient saturated area, a decrease in matrix suction, and an increase in surface gravity, eventually causing slope instability.