To investigate the mechanical properties of frozen saline soil, the deep calcareous clay in the Huanghuai mining area was chosen as the research object, and an orthogonal test was carried out to study the true triaxial mechanical properties of frozen saline calcareous clay under the influence of multiple factors. The stress–strain characteristics, strength, and influence trend of salted frozen calcareous clay with different salt content, stress paths, and water content, and the relationships among the above-mentioned factors, were investigated. The analysis of the test results by an orthogonal test revealed the order of importance of the factors that influenced strength. The primary and secondary order of influence σ₁ is as follows: confining pressure σ₃, water content ω, temperature T, medium principal stress coefficient b, and salt content φ. Under the influence of multiple factors, the strength of frozen soil in the real state is not the result of single factors with independent influences that are then simply superimposed. Instead, the complex interactions of various factors affect strength. The stress path significantly influences the stress–strain relationship of frozen calcareous clay. As the coefficient of the intermediate principal stress b increases, its influence on the strength of salted frozen calcareous clay diminishes, and the optimal principal stress coefficient b = 0.33 maximizes the strength of the specimen. The influence of the moisture content on the strength of the sample is negatively correlated. The effect of different moisture contents on the deformation and failure characteristics of unsaturated saline calcareous clay is not significantly different, and this difference does not exceed 5%.

Taking the Qingdong Mine as the research object, combined with field measurement data, numerical simulation and theoretical analysis are used to examine the temperature field and stability of the frozen wall in the mine, respectively. The results show that during the active freezing period, under the same freezing time, the average temperature of the effective frozen wall of the fine sand layer is 0.2–1.0 and 0.5–2.5 °C lower than that of the sandy clay layer and clay layer, respectively. The effective frozen wall thickness of the fine sand layer is 0.04–0.17 and 0.17–0.33 m larger than that of the sandy clay layer and clay layer, respectively. The soil cooling between the two circles of freezing holes is the fastest. Due to the deflection of the freezing holes, the interface temperature field is asymmetrical. For deep clay with a depth of 200–250 m, it is most economical and reasonable for the brine temperature in the active freezing period to be −25 and −30 °C. At the designed brine temperature for cooling, during the excavation of the control layer of the topsoil layer (−216 m sandy clay), the side-wall temperature, average temperature, and thickness of the frozen wall meet the design requirements. The ultimate bearing capacity of the frozen wall is 3.20 MPa. When the well is empty for 30 h after excavation, the maximum radial displacement is 26.85 mm, so the frozen wall strength and stability are in a safe state. Overall, the findings of this study can serve as a useful reference for similar freezing projects.

In the Huainan and Huaibei mining areas, a layer of calcareous clay is buried deep in the surface soil layer (at approximately 400 m). This layer is in a high-stress state and is prone to freezing pipe fractures in the freezing method. To obtain the true triaxial mechanical properties of this clay in its frozen state, this study conducted a cross test (L₁₆(4⁵)) to explore the change law of the strength of frozen calcareous clay under the influence of multiple factors. The results showed that the true triaxial stress–strain curve of frozen calcareous clay was divided into three stages: the strain within 0.5% showed linear elasticity. Under compressive stress, ice crystals and their cements were damaged or melted and shrank. At approximately 5%, they showed plastic hardening. The soil particles and ice crystals in the frozen soil recombined and became denser, resulting in irreversible deformation. As the compression progressed, cracks bred and swelled. The failure stage was manifested as strain hardening due to the test loading conditions. As the deformation increased, the stress also slightly increased. The consistent strength-influencing factors could be obtained through range and hierarchy analyses. The primary and secondary order of influence of σ₁ was the confining pressure σ₃, water content ω, temperature T, Bishop parameter b, and salt content ψ. The influence weight of each factor was quantitatively calculated. In the significance analysis, when the interaction was not considered, the effects of the pressure and moisture content on the strength were always significant. The effect of temperature was significant only when the significance level Ω > 0.05. The salt content and b value had no significant influence on the strength, and the significance of each factor followed the order of the results of the range analysis method and analytic hierarchy process; when considering the interaction, the interaction factors had different effects on the strength. When Ω > 0.01, the influence of factor A (temperature T) × B (water content ω) on the strength showed significance, even exceeding that of temperature. This demonstrated that when studying the strength characteristics of frozen soil, it is necessary to comprehensively consider the various factors and their interaction to more accurately characterize the mechanical behavior of frozen solids.

We aimed to assess the temporal and spatial evolution law of the freezing temperature field of water-rich sandy soil in underground freezing engineering, taking the newly built west ventilating shaft freezing engineering in the Yuandian No. 2 Mine of Huaibei Coalfield as the engineering background. The influence of groundwater seepage on the freezing temperature field was qualitatively analyzed using field measured data. Based on the mixture medium theory, a hydrothermal coupling numerical calculation model of the freezing temperature field was established. The temporal and spatial evolution law of the freezing temperature field of water-rich sandy soil was obtained via the analysis of field measured data and numerical calculation results. It was found that the proportion of water that froze into ice in the soil mass within the freezing pipe circle is more than that outside of the freezing pipe circle; thus, the phase change in the soil mass within the freezing pipe circle is highly obvious. Groundwater seepage has an “erosion” effect on the upstream and side frozen walls and a “cooling superposition” effect on the downstream frozen wall. Under the effect of groundwater seepage of 2.81 m/d, the average temperature of the effective frozen wall during excavation is below −15 °C, while the thickness is above 5 m for the selected sandy layer at the site, meeting the construction and design requirements. When the groundwater flow rate increases from 0 to 10 m/d, the closure time of the frozen wall increases from 27 to 49 days, an 81.48% increase; the upstream thickness of the effective frozen wall decreases from 5.635 to 4.65 m, which represents a 17.48% decrease, while the downstream thickness increases from 5.664 to 7.393 m, an increase of 30.60%. The numerical calculation model in this paper can be used to predict the development law of the freezing temperature field of the water-rich sandy layers in the Yuandian No. 2 mine and to adjust the on-site cooling plan in real time according to the construction progress. This study provides some theoretical basis and reference for the construction and designs of the freezing temperature fields of water-rich sandy soil layers.