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The measurement of the saturated internal friction angle of landslide sliding zone soils during the geological investigation could assist in engineering design, as it is a crucial parameter for landslide control. This research developed a comprehensive method to predict the saturated internal friction angle based on the support vector machine (SVM), after investigating the relationship between the saturated internal friction angle and the factors that affect the saturated internal friction angle. The procedure mainly consists of exploratory data analysis, influencing factors analysis, and prediction model set-up. Among the 18 factors, the evolution stage, gravel content, plasticity index, and dry unit weight were the most relevant factors predicting the saturated internal friction angle. The proposed method was illustrated and verified by a model accuracy test with the mean absolute error of the radial basis functions (RBF) kernel function was 0.90°, and the mean relative error was 8.77%. Therefore, this method could provide a reliable saturated internal friction angle in assisting engineers during landslide control.

Thermal conductivity of soils is a key parameter in determining the heat transfer and temperature field in thermal engineering. This paper developed a thermal conductivity model of soils with a consideration of the thermo-hydro-deformation interaction during a freezing process. The model was proposed based on the concept of normalized thermal conductivity, and integrated the temperature, volumetric unfrozen water content, porosity, mineralogy, solid particle type and frost heave. Then, the steps to calculate thermal conductivity of soils during a freezing process were illustrated. Additionally, compared with the other two widely used empirical models, i.e., model based on the apparent heat capacity method and model based on the Heaviside function, the proposed model was more effective and reasonable, while the other two models had some limitations in calculating thermal conductivity of soils during a freezing process. Moreover, the proposed model was comprehensively verified by the 32 soil samples, and the good agreements between the measured and model-calculated thermal conductivities of soils confirmed that the proposed model can be used to calculate the thermal conductivity of soils in the numerical simulations, and could also well reflect the effect of phase transition of water-ice on thermal conductivity of soils during a freezing process.

Strong salt expansion and frost heave are induced to make the infrastructure in the salted region damaged with water or salt phase change at low temperature. Laboratory test based on differential scanning calorimetry is used to investigate salt and water phase transformation and their crystallization mechanism in sodium sulfate soils and solutions. During the experimental process, crystallization heat release, crystallization period and supercooling are measured. According to the conservation principle of mass and heat, salt and ice crystallization are separated, and unfrozen water content is calculated at different temperatures. Moreover, variations of unfrozen water content, as well as the supercooling degree of sodium sulfate soils with different size are compared and analyzed based on heterogeneous nucleation theory. The results demonstarte occurance of the ice crystallization before salt crystallization in minor soil samples; however, salt crystallization appears first in pure solution at high concentration. The interval at which the ice and salt crystallization begin decreases as the salt content increases, and the supercooling decreases as the salt content or sample size increases. Additionally, water freezing in small soil samples is more difficult than that in larger soil samples, and the unfrozen water content increases as the salt content or sample size decreases.

Ganluo County is located in the southwestern part of Sichuan Province in China. It has strong geological tectonic movement, strong earthquake affected area and frequent debris flow disasters. There are two huge debris flows occurred in Zile Valley of Ganluo County in 1987 and 2019, a large amount of debris flow deposits went down the valley, destroyed the buildings at the mouth of the valley, causing huge property damage to local residents. In this regard, based on data of field survey and UAV aerial photography, the Arcgis and Massflow software were used to invert and analyze the movement characteristics of the debris flows occurred in 1987 and 2019, and the future activity characteristics of the valley are predicted. The results show that if the debris flow breaks out in the valley again based on the existing sources, the maximum mud depth will reach to 11.9m, the flow intensity will reach to 123.37m2/s, the total volume of material flushed out is 11.18×104m3 and the accumulation fan area is 6.925×104m2. However, after adopting reasonable engineering measures, the maximum mud depth is reduced to 8.5m, the flow intensity is reduced by 52.7% to 58.32m2/s, the accumulation fan area is reduced by 80% to 1.406×104m2 and the total volume of material flushed out is reduced by 75% to 2.75×104m3. This shows that the use of retaining measures to control the debris flow in Zile Valley can achieve good results.

This paper presents a computational model of the freezing point of soil and the nucleation rate of ice based on the soil volume for saline soils. Physicochemical methods and crystallization theory are used to explore the macroscopic mechanism of water freezing induced by ice crystallization, and the influence of water undercooling is discussed with regard to different soil volumes and salt contents. Growth sites, shapes, and sizes of ice crystals are determined by an assumption of heterogeneous nucleation, and the contact angle is introduced to represent a wide range of soils. The relationship between the initial contact angle and the salt content is analyzed quantitatively through an indoor cooling test and thermal difference analysis. Moreover, the van Genuchten model is applied to provide an equation for the unfrozen water content in salty soils, and the probability of ice formation is introduced to investigate the variation of contact angle during the soil freezing process. This study shows that the initial radius of an ice crystal decreases as the salt concentration decreases. The temperature of ice nucleation is determined mainly by the contact angle of ice crystals, which decreases as the soil volume increases and results in decreased supercooling.

Saline soils is porous medium whose thermal conductivity is affected by components and particle shape. However, the particle shapes in geomaterials are various, and the component and its content ar...

Thermal conductivity of soils is significant on the thermal simulations in cold region engineering. Based on the generalized thermal conductivity for geotechnical materials, a thermal conductivity model for saline soil was proposed in this paper. At the micro level, the microstructure composition of sodium sulfate soils in the proposed model was redefined. Macroscopically, the variation of salt crystals and ice crystals with temperature and the relationship between the arrangements of components (i.e., liquid water, ice, soil particles) of saline soil were studied. Shape parameters α, β, τ were adopted to define the volume proportion of needle shape soil particles, spherical shape soil particles and disk shape soil particles, respectively. Besides, the proposed thermal conductivity model considered the heat loss due to the heat radiation in the measurement process. Furthermore, the accuracy of the proposed model was verified by the experimental data. The results showed that the soil particles can be defined as SWCA (i.e., soil particles, water, crystals mixture of salt and ice, air) four-layer concentric structure in the calculation of the thermal conductivity model of saline soil. Shape parameters have significant influence on simulation results. By comparing test data with calculated values, it can be found that at positive temperature, silty clay soil particles are mainly spherical (β = 0.5) and disc-shaped (τ = 0.5), while the sandy soil and soil-rock particles are more similar to the needle shape (α = 1.0). With the decrease of temperature, the particle parameters of silty clay soil change, β decreases to 0, τ increases to 0.75, and α increases to 0.25. However, at negative temperature, the soil particles of sandy soil and loess are still mainly needle-shaped (α = 1.0).

The unfrozen water content is a result of soil freezing, and its variation is closely related to temperature. To study the change in unfrozen water content, a relationship between water pr...

Salt migration and accumulation are the main sources of salt expansion. To study the role of salt transport in soil, laboratory tests were conducted to simulate salt transfer under real conditions. Temperature, water content, salt content and soil displacement of a sodium sulfate soil were measured during the freezing process/freeze-thaw cycles. Meanwhile, Salt concentration was regressed bases on test data to investigate the movement of salt diffusion, in the process, the Pitzer ion model was employed to calculate the freezing point of saline soils to determine the frozen depth. Moreover, the amount of crystallization was estimated by the saturation curve of a sodium sulfate solution and the detected salt content. The results show that salt transfer in soil occurs as a result of numerous physicochemical processes and that the maximum salt transport occurred in the frozen fringe zone in the soil. Salt crystallization increases the effect of salt transfer in the soil unidirectional freezing process. In addition, salt expansion had an accumulative effect, and it increases as the number of freeze-thaw cycles increases. The quantity of salt that is transported increases as the salt content increases.

The occurrence of different ice and salt phases in saline soils may result in severe failure in engineering practice. Therefore, studying the phase changes of these two components may improve the understanding of saline soils. Through a series of cooling experiments on sulfate saline soils, the internal temperature variation of soils is obtained to study the rule of salt crystallization and the effect of salt on liquid water content. Based on the thermodynamic principle, the heat transfer equation is expressed considering the phase changes of ice and salt, and the control volume approach is applied to discretize the differential equation of heat transfer. Combined with the internal temperature curve of the soils, the discrete equations allow the calculation of ice porosity variation, salt crystal porosity, and unfrozen water content in saline soils. Additionally, the equations provide a useful general criterion for salt crystallization at different temperatures. Experimental and theoretical results confirm that unfrozen water content in saline soils decreases as the salt content increases, and that liquid water content is lower in salt-free soils. In addition, the concentration of salt solution in soils with low salt content increases owing to the phase change between water and ice; salt crystallization can only occur if the concentration reaches 20% at a negative temperature.