Horizontal frost heave disasters frequently occur in cold-region engineering projects, making it essential to understand water migration mechanisms along horizontal directions during freezing processes. Using a selfdeveloped one-dimensional visualization horizontal freezing apparatus, unidirectional horizontal freezing tests were conducted on soft clay under varying temperature gradients, and the development process of the cryostructures was continuously observed. The results indicate that the thermal-hydraulic processes, including temperature evolution, water content variation, pore-water pressure dynamics, and soil pressure changes, demonstrate similarities to vertical freezing patterns, with temperature gradients primarily influencing the magnitude of parameter variations. Under the influence of gravity, the freezing front forms an angle with the freezing direction, attributed to differential freezing rates within soil strata. Post-freezing analysis showed dualdirectional water redistribution (horizontal and vertical), with horizontal migration dominating. Maximum water content was observed 1-3 cm from the freezing front. Distinct cryostructures formed in frozen zones were identified as products of tensile stresses generated by low-temperature suction and crystallization forces. The study highlights the coupling of water transfer, thermal changes, mechanical stresses, and structural evolution during freezing and suggests that water migration and cryostructure formation are interrelated processes. This research provides robust experimental evidence for advancing the theoretical framework of horizontal water migration mechanisms in frozen soil systems.

With the Bulk Jupiter accident, the dynamic separation behavior of solid bulk cargoes in sea transportation, which is different from the usual liquefaction of cargoes, has gradually come to people's attention and is an almost empty field that urgently needs to be researched. In this work, we first conducted vibration table tests for bauxite, replaced bauxite with transparent soil with the same particle size distribution and moisture content, and combined image processing and analysis techniques to complete the detailed visualization of the dynamic separation process. Through the above research, this article reveals the essential characteristics of dynamic separation, including the changing rules of layer-wise water content, pore water pressure, particle motion, and pore water migration. It is concluded that the most apparent feature of the dynamic separation process is the generation of a free liquid surface containing fine particles in the upper layer. The article concludes with a systematic study of the dynamic separation of typical mineral soil. The novel experimental system developed in this study contributes to elucidating the mechanism of dynamic separation of minerals and soil from a precise perspective. [GRAPHICS] .

Using steel slag concrete (SSC) as a pile material not only promotes industrial waste recycling but also improves ground conditions through its distinct hydrological and chemical properties. This study investigated the hydrological processes of SSC piles under no-load conditions, offering new insights into pile-soil interactions. A novel visualization test device was developed to continuously monitor water migration, pore water pressure fluctuations, and soil disturbance over six months. Macro-scale observations and micro-scale analyses were conducted to elucidate physical and chemical reactions at the pile-soil interface. Compared to ordinary concrete piles, SSC piles demonstrated superior expansion and drainage capabilities, characterized by enhanced radial and vertical water flow, increased surface porosity, and the formation of a distinct interface layer enriched with calcium carbonate and cementitious hydration products. These improvements facilitate effective water distribution and drainage while reinforcing the pile-soil bond, thereby contributing to a more robust composite system for ground improvement. This integrated approach and its findings offer valuable contributions to the broader field of soil-pile interactions by detailing the multi-scale mechanisms governing the hydrological behavior and interface evolution of composite foundation systems.

The moisture accumulation and freezing damage of coarse-grained fill (CGF) in high-speed railway (HSR) subgrades have been widely concerned. Based on the newly developed water-vapor-heat-mechanical coupling test apparatus, a series of soil column tests were carried out to investigate the frost heave mechanism of CGF. The results indicate that the liquid water in CGF is discontinuous and difficult to migrate to the freezing front. The primary mechanism of moisture accumulation and frost heave in CGF is vapor migration and phase transition. With increasing freeze-thaw cycles, both vapor migration and frost heave reduce. The thaw settlement of the CGF is less than the frost heave, so there is a net upward deformation in each cycle. Furthermore, the fine particle content has a prominent effect on the heat transfer and frost heave of the CGF compared to the fine particle type. Even under the condition of vapor replenishment, controlling the content of fine particles is still an important way to inhibit frost heave. Moreover, after reducing the maximum particle size of CGF, the frost heave of the sample increases. Nuclear magnetic resonance (NMR) test results show that CGF is dominated by large pores, and the freeze-thaw cycle further promote the development of large pores, providing a good channel for the migration of vapor. In conclusion, the frost heave development caused by vapor migration is slow and continuous, posing a non-negligible risk to HSR subgrades during long-term service.

The shear strength index of seasonally frozen soil is significantly affected by the freezing-thawing and water replenishment methods. To simulate the actual freeze-thaw and water replenishment process in seasonally frozen soil, a new method called the unidirectional freeze-thaw and natural water replenishment method was proposed. A test device was developed to facilitate this method. By using soil as the medium for water migration, the temperature change and water migration characteristics during the freeze-thaw process were investigated. The study also considered the influence of the samples' water content and the gradient between the water content of the test samples and the water replenishment soil layer. The changes in the soil stress-strain curve, static strength, and shear strength index under freeze-thaw were analyzed based on triaxial tests. The results revealed that the temperature change during the test process can be divided into six stages: rapid cooling, slow cooling, temperature stability, slow heating, continuous phase change around 0 degrees C, and positive temperature stability. After freeze-thaw, the sample water content without gradient increased by approximately 0.6%, while the sample water content with a gradient increased by about 1.5%. However, the distribution characteristics of the water content were different. The static strength, cohesive force, and internal friction angles were all lower after freeze-thaw under different water content conditions. The maximum static strength and cohesion decreased by approximately 50% and 60%, respectively, under freeze-thaw, while the internal friction angle showed a slight decrease. The new freeze-thaw and natural water supplement method can serve as a basis for selecting the shear strength index of seasonally frozen soil.

In the process of expanding ballasted railway capacity, there is a significant increase in train axle load and speed, which leads to significant mud pumping disease under multi-stage/multi-frequency train load-wetting coupling, and its mechanism is still unclear. Mud pumping model tests from ballasted track subgrades under multi-stage/ multi-frequency train load-wetting (MSC-W test/MFC-W test) coupling were conducted. The test results show that in the unsaturated state, the accumulated deformation of MSC-W test is more significant than that of MFC-W test, and the compactness of the subgrade filler is greater without significant particle migration. Under saturated or near saturated conditions, the MSC-W and MFC-W tests produces significant mud pumping by the driving force of dynamic pore water pressure. The amounts of mud pumping, fine particle layer displacement and void contaminant index (VCI) of the MFC-W test are significantly higher than those of the MSC-W test.

Expansive soils are susceptible to cracking due to significant moisture fluctuations, which can potentially lead to structural instability. Although geogrid reinforcement is widely used to control soil swelling and shrinkage, its effects on cracking behavior are not fully understood. This study investigates the influence of geogrid reinforcement on the cracking behavior of expansive soils by comparing soil samples reinforced with two layers of geogrid to unreinforced samples under evaporation conditions. Crack development was monitored using high- resolution imaging and fluorescence tracing to measure crack depth and calculate surface crack ratio. Additionally, moisture content distribution and evaporation rates were assessed. The results show that geogrid reinforcement reduced the total crack ratio by 1.34% and decreased average crack depth by 43.5%, leading to a more uniform crack distribution with smaller openings. Both internal and external cracks facilitated moisture exchange between the soil and atmosphere. The frictional and interlocking effects at the soil-geogrid interface effectively inhibited cracking and reduced moisture migration. The uniaxial geogrid also induced anisotropy crack restraint, with environmental exposure and geogrid orientation playing critical roles in crack control. Overall, these findings demonstrate the effectiveness of geogrids in enhancing the stability of expansive soils and limiting atmospheric influence through crack suppression.

Liquefaction behaviors of sand deposits with impervious stratum are quite different from that of homogeneous geological conditions. However, the micro- liquefaction behaviors of the interlayered deposits have been infrequently documented. This study introduces a novel experimental methodology aimed at examining the influence of silt interlayer on the liquefaction mechanisms of sand deposits from both macro and micro perspectives. In the experiments, the Excess Pore Water Pressure (EPWP) was analyzed in conjunction with recorded micro liquefaction images. The migration mechanism of fine sand particles beneath the silt interlayer was revealed. The existence of low permeability interlayer leads to prolonged retention of EPWP beneath the silt interlayer. Substantially, the water film on the base of the interlayer is demonstrated to be the mixture of pore water and silt particles flowing with high velocity under seismic motions, thereby resulting in significant strain localization. An agminated zone of loose fine sand particles is usually generated beneath the silt interlayer after the dissipation of EPWP.

In order to address the issue of surface deformation in wintering foundation pits in seasonal frozen soil areas due to excavation and freeze-thaw, an indoor scale model test was conducted to examine the displacement relationship between pit wall soil and supporting structures under freeze-thaw conditions, as well as the temperature change and water migration of soil surrounding the foundation pit. The distribution mode of surface settlement under excavation and freeze-thaw conditions was examined and a surface settlement calculation model was established based on the maximum value of surface settlement. The water will move from the frozen to the unfrozen region as a result of the freeze-thaw cycle. About 1.1 m is the freezing depth. An increase in surface settlement will result from the coordination of deformation between the soil and the supporting structure during freezing and thawing. The greatest surface settlement value following the initial freeze-thaw cycle is 1.082 mm, which is around 215% greater than that of excavation. The skewed distribution is comparable to the surface settlement curves produced by excavation and freeze-thaw cycles. The calculated model's results and the measured settlement values agree rather well.

The underestimated risk of contact erosion failure in railway substructures poses a significant threat to railway safety, particularly at the interface between the ballast/subballast and subgrade. The larger constriction size at this interface exacerbates the potential for long-term erosion, necessitating attention to safeguard railway integrity. This study introduces a novel laboratory erosion testing apparatus to evaluate contact erosion at the subballast-subgrade interface under cyclic loading. Subgrade soils with varying fines contents are tested, and the effect of pressure head on erosion is investigated in detail. The results indicate that sandy soil with higher internal stability exhibits a higher critical pressure head for contact erosion. Cyclic loading induces oscillations in pore water pressure within the subballast layer, with higher pressure heads leading to larger amplitudes. Excess pore water pressure is generated in the sandy soil layer during cyclic loading and gradually dissipates over time. Fine eroded particles migrate into the subballast layer, forming mud, while coarse eroded particles accumulate at the base, creating low-permeability interlayers. Notably, the geometric conditions alone may not guarantee effective prevention of contact erosion in railway substructures. The hydraulic conditions for contact erosion are more easily achieved under cyclic loading compared to static loading. These distinctive features of contact erosion in railway substructures, different from those observed in hydraulic structures, provide some insights for the development of remediation strategies and improvements in railway substructure design.