Uneven displacement of permafrost has become a major concern in cold regions, particularly under repeated freezing-thawing cycles. This issue poses a significant geohazard, jeopardizing the safety of transportation infrastructure. Statistical analyses of thermal penetration suggest that the problem is likely to intensify as water erosion expands, with increasing occurrences of uneven displacement. To tackle the challenges related to mechanical behavior under cyclic loading, the New Geocell Soil System has been implemented to mitigate hydrothermal effects. Assessment results indicate that the New Geocell Soil System is stable and effective, offering advantages in controlling weak zones on connecting slopes and reducing uneven solar radiation. Consequently, the New Geocell Soil System provides valuable insights into the quality of embankments and ensures operational safety by maintaining displacement at an even level below 1.0 mm. The thermal gradient is positive, with displacement below 6 degrees C/m, serving as a framework for understanding the stability of the subgrade. This system also enhances stress and release the sealing phenomenon.

In order to investigate the frost-heaving characteristics of wintering foundation pits in the seasonal frozen ground area, an outdoor in-situ test of wintering foundation pits was carried out to study the changing rules of horizontal frost heave forces, vertical frost heave forces, vertical displacement, and horizontal displacement of the tops of the supporting piles under the effect of groundwater and natural winterization. Based on the monitoring condition data of the in-situ test and the data, a coupled numerical model integrating hydrothermal and mechanical interactions of the foundation pit, considering the groundwater level and phase change, was established and verified by numerical simulation. The research results show that in the silty clay-sandy soil strata with water replenishment conditions and the all-silty clay strata without water replenishment conditions, the horizontal frost heave force presents a distribution feature of being larger in the middle and smaller on both sides in the early stage of overwintering. With the extension of freezing time, the horizontal frost heave force distribution of silty clay-sand strata gradually changes from the initial form to the Z shape, while the all-silty clay strata maintain the original distribution characteristics unchanged. Meanwhile, the peak point of the horizontal frost heave force in the all-silty clay stratum will gradually shift downward during the overwintering process. This phenomenon corresponds to the stage when the horizontal displacement of the pile top enters a stable and fluctuating phase. Based on the monitoring conditions of the in-situ test, a numerical model of the hydro-thermo-mechanical coupling in the overwintering foundation pit was established, considering the effects of the groundwater level and ice-water phase change. The accuracy and reliability of the model were verified by comparison with the monitoring data of the in-situ test using FLAC3D finite element analysis software. The evolution of the horizontal frost heaving force of the overwintering foundation pit and the change rule of its distribution pattern under different groundwater level conditions are revealed. This research can provide a reference for the prevention of frost heave damage and safety design of foundation pit engineering in seasonal frozen soil areas.

This computational study focuses on the thermo-hydro-mechanical simulations of the behaviors of freezing soils used for artificial ground freezing (AGF) in a metro project. Leveraging the experimental and field data available in the literature, we simulate the sequential freezing and excavation of a twin tunneling that occurred in months during the actual construction of the tunnel. A thermo-hydro-mechanical model is developed to capture the multi-physical rate-dependent behaviors triggered by phase transitions, as well as the creeping and secondary consolidation of the soil skeleton and the ice crystals. We then calibrate the material models and establish the THM finite element model coupled with the rate-dependent multi-physical models, which may accurately predict the surface heave induced by ground freezing throughout the project. To showcase the potential of using simulations to guide the AGF, we simulate the scenario where a simultaneous freezing scheme is employed as an alternative to the actual sequential scheme design. We then compared the simulated performance with the recorded results obtained from the sequential scheme. Finally, parametric studies on the effect of ground temperature, the porosity of the frozen soil, and the intrinsic elastic modulus of the solid skeleton are conducted. The maximum surface heave is inferred from finite element simulations to quantify the sensitivity and the impact on the safety of AGF operations.

The fundamental cause of frost heave and salt expansion of saline soil is the water condensation and salt crystallization during the freezing process. Therefore, controlling the water and salt content is crucial to inhibit the expansion behaviors of saline soil. Recently, electroosmosis has been demonstrated to accelerate soil dewatering by driving hydrated cations. However, its efficiency in mitigating the salt-induced freezing damages of saline soil requires further improvement. In this study, a series of comparative experiments were conducted to investigate the synergistic effects of electroosmosis and calcium chloride (CaCl2) on inhibiting the deformation of sodium sulfate saline soil. The results demonstrated that electroosmosis combined with CaCl2 dramatically increased the cumulative drainage volume by improving soil conductivity. Under the external electric field, excess Na+ and SO42- ions migrated towards the cathode and anode, respectively, with a portion being removed from the soil via electroosmotic flow. These processes collectively contributed to a significant reduction in the crystallization-induced deformation of saline soil. Additionally, abundant Ca2+ ions migrated to cathode under the electric force and reacted with OH- ions or soluble silicate to form cementing substances, significantly improving the mechanical strength and freeze-thaw resistance of the soil. Among all electrochemical treatment groups, the soil sample treated with 10 % CaCl2 exhibited optimal performance, with a 71 % increase in drainage volume, a 180 similar to 443 % enhancement in shear strength, and a 65.1 % reduction in freezing deformation. However, excessive addition of CaCl2 resulted in the degradation of soil strength, microstructure, and freeze-thaw resistance.

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.

Freeze-thaw cycles significantly affect soil behavior, leading to pavement failures and infrastructure damage, especially in seasonally freezing regions. The application of road salt for deicing operations introduces high salt concentrations into soils, which can alter their physical properties. Salt in soils affects their freezing point, moisture migration, and overall freeze-thaw behavior. This study investigates the effects of varying sodium chloride (NaCl) concentrations on sandy soil using both the ASTM and low-temperature-gradient methods to simulate different freezing protocols. The methodology involved subjecting soil specimens with 0%, 0.2%, 1%, and 5% salt concentrations to freeze-thaw cycles and measuring parameters such as heave rate, maximum heave, water intake, moisture content, and salt migration. The results revealed that increasing salt concentration leads to a reduction in the freezing point, with the 5% NaCl concentration showing the most significant depression at 2.96 degrees C. The heave rate and maximum heave decreased with higher salt concentrations: the 5% NaCl concentration reduced the heave rate to 11.3 mm/day (ASTM method) and 1.5 mm/day (low-temperature-gradient method) from 22.5 mm/day (ASTM method) and 17.2 mm/day (low-temperature-gradient method) in control. Salt migration analysis indicated more variability in salt distribution within the soil profile under the low-temperature-gradient method, especially at higher salt concentrations. This variability is linked to osmotic suction effects, which retain more water within the soil matrix during freeze-thaw cycles. The study highlights the importance of considering both salinity and freezing protocols in understanding soil behavior under freeze-thaw conditions.

Engineering geological investigations indicate that confined water exists in the stratum during the warm season in permafrost regions and in underground engineering employing artificial ground freezing (AGF) to isolate groundwater, causing significant upward deformation of the stratum and frost damage to engineering structures. However, limited studies have explored the effect and mechanism of hydraulic pressure on ice growth during soil freezing upwards. Therefore, this study designs and conducts four groups of bottom-up freezing tests under various hydraulic pressures, and develops a model to investigate the mechanism of hydraulic pressure on ice growth, based on the theory that liquid water migrates towards the ice lens through an unfrozen water film. The experimental results, including thermal regime, frost heave, cryo-structure, and water redistribution are analyzed systematically, which show the frozen depth, frost heave increment, ice lens thickness, and the layered water content in the samples all increase with hydraulic pressure. The model is validated with experimental data, and the calculation results demonstrate that the ice growth rate increases with hydraulic pressure due to a higher pore water pressure (PWP) gradient in the unfrozen water film. Thus, the characteristics and mechanisms of ice growth in the stratum, accelerated by hydraulic pressure, are clarified. Finally, the applications and implications of this study to engineering geology are discussed, which contribute to a better understanding of ground ice formation in permafrost regions and frost damage prevention in underground engineering performing AGF.

Coarse-grained soil is generally used in cold-regions infrastructure to mitigate the frost damage to engineering because of its non-frost heave susceptibility; however, in certain cases, coarse-grained fill has been observed to experience frost heave under hydraulic pressure. To reveal the mechanism of hydraulic pressure on coarsegrained soil frost heave, a model was developed to describe the frost heave in coarse-grained soil, incorporating the migration of external water to ice lenses through an unfrozen water film under hydraulic pressure, then the model was validated using published results. Subsequently, based on the validated model, the influence mechanism of hydraulic pressure and fine content on coarse-grained soil frost heave were analyzed. The calculation results demonstrate that the hydraulic pressure aggravates frost heave by increasing the pore water pressure gradient in the unfrozen water film. Additionally, frost heave rate increases with fine content because of the thickening of the film, which facilitates water flow and ice segregation. Furthermore, gray correlation analysis demonstrated that the impact of hydraulic pressure on frost heave in coarse-grained soil is more significant than that of fine content. Finally, the study discusses frost damage that occurred in high-speed railway subgrade and proposes the preventive measures.

Grouting below the tunnel invert is commonly used to remediate the settlement. Case histories demonstrate that the tunnel settlement still develops after the grouting is completed, especially in structured clay. The principal mechanism behind this is the grouting-induced soil disturbance, including the generation of excess-pore-water pressure (EPWP), degradation in soil structure, and changes in compressibility. To date, the mechanism behind the grouting-induced soil disturbance and responses of the ground heave is not yet fully understood. Toward this end, laboratory tests on grouting in mud with different sand content are carried out. Earth pressure, pore water pressure, shear stiffness, undrained shear strength, and ground heave are measured and analyzed. The results indicate that grouting causes increases in the lateral earth pressure and significant EPWP in the surrounding soil. Changes in undrained shear strength and shear stiffness are closely related to the comprehensive effects of increases in stress level and shear disturbance. The increased stress level leads to the growth in stiffness and strength, while shear disturbance causes degradation. The soils right nearby the grouting zone are subjected to significant shear disturbance and also increases in stress level. As a result, the soil stiffness and strength exhibit negligible change. In comparison, the soils above and below the grouting zone mainly experience an increase in stiffness and strength, because shear disturbance is comparatively smaller than the influence of the increases in stress level. Furthermore, the development of the vertical displacement of the ground surface demonstrates two stages of initial uplift during grouting and then settlement after the grouting is completed. In addition, stronger soil structure corresponds to larger settlement after the grouting is completed.

Problematic soils like expansive soils cause significant damages to civil infrastructure. The use of calcium-based stabilizers in the treatment of sulfate-rich expansive soils is not suggested due to the formation of ettringite. Infrastructure such as pavements and embankments built on expansive soil are often exposed to the damaging impacts of freeze-thaw cycles in areas prone to seasonal freezing, making them vulnerable to cracking and spalling. A native expansive soil from South Dakota with a sulfate content of more than 10,000 ppm was stabilized using biopolymer (BP) and cement in this study. A comparison of the geotechnical properties of the untreated and treated soil such as Atterberg limits, one-dimensional (1D) swell, linear shrinkage, unconfined compressive strength (UCS), and resilient modulus (MR) for curing periods of 7 and 28 days were presented in the study. The swelling in cement-stabilized soil specimens was observed to increase after a long period due to the formation of ettringite. The study investigated the effectiveness of cement and biopolymers as co-additives to treat the sulfate-rich expansive soil. The experimental study investigated the strength and stiffness properties of the control and treated soil after the various freeze-thaw (F-T) cycles. The reduction of strength and stiffness properties of soil for 6% cement and the co-addition of 3% cement and 1.5% biopolymer after the F-T cycles were found to be comparatively less. Soil morphology provided insights into the configuration of biopolymer networks and the development of ettringite within treated soils. Biopolymers were used as an environmentally friendly substitute for traditional energy-intensive stabilizers in expansive soil stabilization, and potentially reducing carbon footprints. The study found that the incorporation of biopolymer as a co-additive with cement can be a viable alternative for stabilizing sulfate-rich expansive soil subgrade.