Search Results (38)

Accurate prediction of the temperature field around shallow-buried freezing pipes is important for the design and assessment of artificial ground freezing systems in shallow tunnel and underground structure construction. This study develops a semi-analytical series solution for the steady-state temperature field around a twin-pipe freezing unit in a semi-infinite domain under Dirichlet boundary conditions. The model assumes steady-state heat conduction in homogeneous and isotropic soil with prescribed pipe wall and ground surface temperatures; transient phase change, groundwater seepage, and thermo-hydro-mechanical coupling are not considered. Conformal mappings are used to transform the original semi-infinite and eccentric domains into bounded circular domains. The temperature field is decomposed into two subproblems by superposition, and the corresponding general solutions are expressed using Fourier series. The unknown coefficients are determined through boundary discretization and the solution of a finite linear algebraic system. The proposed method is compared with ANSYS Fluent results in the transformed domain at six selected points, yielding a pointwise NRMSE of 0.758% at a truncation order of 20. Parametric analyses further illustrate the qualitative sensitivity of the calculated temperature field to different ground surface temperatures, pipe radii, burial depths, and pipe spacings. The proposed method provides a preliminary semi-analytical framework for rapid quasi-steady temperature field estimation and qualitative parameter sensitivity analysis of shallow-buried twin-pipe artificial ground freezing systems. Full article

Background: Artificial intelligence (AI)-driven gait analysis using plantar pressure and ground reaction force (GRF) signals may provide objective digital biomarkers for rehabilitation, but clinical translation remains uncertain. This scoping review and evidence map aimed to summarize clinical applications, compare evidence maturity, and identify methodological and translational gaps. Methods: PubMed, Web of Science, Embase, and Scopus were searched from the earliest available indexed records in each database to May 2026. Original clinical studies using plantar pressure- or GRF-derived signals with AI methods for disease recognition, severity assessment, risk prediction, rehabilitation monitoring, or decision support were included. Results: Fifteen studies met the eligibility criteria. Evidence was concentrated in Parkinson’s disease (PD), particularly PD recognition and freezing of gait prediction, where relatively more mature evidence was supported by multiple studies and participant-level or cross-dataset validation. Evidence for PD severity assessment, knee osteoarthritis monitoring, chronic ankle instability rehabilitation, fall-risk stratification, sarcopenia screening, peripheral artery disease recognition, and functional gait disorder classification remained less mature. Translation was limited by small or single-center samples, unclear participant-level data splitting, limited external validation, absent calibration, sparse explainable AI reporting, and insufficient real-world workflow testing. Conclusions: Future studies should prioritize prospective, externally validated, interpretable, calibrated, and clinically embedded models before routine rehabilitation implementation. Full article

Soil thermal conductivity is a key parameter in modeling heat transfer, temperature-driven moisture migration, artificial ground freezing, and geothermal systems. However, most existing thermal-conductivity models do not account for temperature effects. This study aims to determine the temperature-dependent thermal conductivity of silty and fine sandy soils at elevated temperatures using a steady-state heat cell method, addressing the limitations of transient probe techniques, which are affected by air voids and heat loss at the needle–soil interface. The experiment employs a heat cell under one-dimensional steady-state heat-transfer conditions, with sufficiently small temperature gradients to prevent temperature-induced moisture migration, and measures the soil’s thermal properties at steady state by indirect temperature and heat-flux measurements using various sensors. The test observations showed well-correlated thermal conductivity readings from steady state and transient probe methods at room temperature. Furthermore, the measured thermal conductivity of the sandy soil demonstrated a near-linear increase with temperature, with the highest dependence at 15.1% and 22.5% saturation for Benbrook (SM) and fine-grained Ottawa (SP) sands, respectively. Several commonly used existing thermal conductivity models were used to fit the measured thermal conductivity. A new thermal conductivity model was developed, incorporating a temperature-dependent correction based on the best-fit model. The proposed model could more accurately capture the increased thermal conductivity of soils with temperature. The findings will significantly improve the modeling of soil-temperature-dependent multi-physics behavior. Full article

The construction industry faces urgent challenges in reducing its carbon footprint, particularly in geotechnical engineering where conventional methods often involve high-emission materials. Artificial Ground Freezing (AGF) presents a sustainable, material-saving alternative for stabilizing water-rich strata, but its efficiency relies on accurate characterization of frozen soil behavior under in situ conditions. This study advances the understanding of AGF’s sustainability by investigating the directional shear behavior of pressurized frozen saturated medium sand (Fujian ISO standard sand) at −10 °C using a novel hollow cylinder apparatus. Through systematic testing under varying mean principal stresses (p = 0.5–6 MPa) with fixed intermediate principal stress coefficient (b = 0.5) and principal stress direction (α = 30°), we demonstrate that pressurized freezing creates a fundamentally different soil–ice composite compared to conventional unpressurized freezing. Key findings reveal (1) a linear strength increase described by the failure criterion q_f = 1.17p + 3.77 (R² = 0.98) without pressure melting effects within the tested range; (2) a distinct brittle-to-ductile transition at p ≈ 4 MPa, with associated failure mode changes from localized shear bands to homogeneous plastic flow; (3) a stable peak stress ratio (q/p ≈ 1.8) for p ≥ 4 MPa. These findings enable more reliable and potentially less conservative frozen wall design, directly contributing to reduced energy consumption in AGF operations. The research provides mechanical insights and practical parameters that enhance AGF’s viability as a low-carbon ground stabilization technology, supporting the construction industry’s transition toward sustainable underground development. Full article

Shaft sinking in soft, water-rich strata frequently suffers from low cutting efficiency, cycle-time mismatches between excavation and muck removal, and weak system-level coordination. To elucidate the synergistic mechanisms governing excavation–muck removal interactions and to realize end-to-end performance gains, we investigate the East Ventilation Shaft of the Xinjie Taigemiao mining district as a representative artificial ground freezing (AGF) project. First, drawing on the mechanics of frozen ground and field monitoring, we establish a relationship model linking advance rate, drum rotational speed, cutting depth, and muck production, thereby clarifying why lower rotational speeds, moderate cutting depths, and rational traction reduce energy consumption and mitigate disturbances to the frozen wall. Next, for muck handling, we build a full-process discrete element method (DEM) model, integrate design-of-experiments with response-surface optimization to identify key factors, calibrate contact models, and select collection geometries. The results show that a graded-angle collecting structure improves pile concentration and discharge compliance; combined with a tiered chain-bucket–vertical belt–twin-skip configuration, it delivers matched cycle times and stable “gather–convey–hoist” operation. Finally, two-stage full-scale tests jointly validate excavation and muck removal, demonstrating that the proposed synergy model and optimized parameters sustain continuous, efficient performance across operating conditions. The study provides a reusable mechanistic framework and parameterization blueprint for AGF shaft design and construction. Full article

The complex condition of an adjacent tunnel in urban city includes high water content, limited construction space, and the presence of an adjacent tunnel. To address these challenges, the artificial ground freezing method is employed to ensure construction safety and stability. Considering the complex problem of temperature field interaction in the freezing construction process of adjacent tunnels, for the first time, this paper proposes a generalized analytical solution for two-dimensional steady-state temperature fields suitable for the annular double-loop freezing system of adjacent tunnels. Based on the polar coordinate heat conduction control equation and the conformal transformation method, the complex geometric arrangement is mapped into a linear system that can be solved, and the analytical solution expression is constructed by combining the heat source superposition principle. In this paper, a numerical model of the adjacent tunnel annular double-loop freezing pipe is established through COMSOL Multiphysics 6.2 software. At the same time, the formula of the analytical method is programmed and solved using Python 3.12, and finally the temperature fields obtained by the two methods are compared. The results show that the analytical solution has good consistency in isotherm distribution, temperature field trend and characterization of frozen core area, which verifies the theoretical rationality and practicability of the constructed model. Full article

With the continuous expansion of urban rail transit networks, construction safety of connecting passages—as critical weak links in underground structural systems—has become pivotal for project success. Although artificial ground freezing technology effectively addresses adverse geological conditions (e.g., high permeability and weak self-stability), it is influenced by multi-field coupling effects (temperature, stress, and seepage fields), which may trigger chain risks such as freezing pipe fractures and frozen curtain leakage during construction. This study deconstructed the freezing method workflow (‘drilling pipe-laying → active freezing → channel excavation → structural support’) and established a hierarchical evaluation index system incorporating geological characteristics, technological parameters, and environmental impacts by considering sandy soil phase-change features and hydro-thermal coupling effects. For weight calculation, the Analytic Hierarchy Process (AHP) was innovatively applied to balance subjective-objective assignment deviations, revealing that the excavation support stage (weight: 52.94%) and thawing-grouting stage (31.48%) most significantly influenced overall risk. Subsequently, a Bayesian network-based risk assessment model was constructed, with prior probabilities updated in real-time using construction monitoring data. Results indicated an overall construction risk probability of 46.3%, with the excavation stage exhibiting the highest sensitivity index (3.97%), identifying it as the core risk control link. These findings provide a quantitative basis for dynamically identifying construction risks and optimizing mitigation measures, offering substantial practical value for enhancing safety in subway connecting passage construction within water-rich sandy strata. Full article

Artificial ground freezing (AGF), recognized for its environmental sustainability and safety, is commonly used in underground construction projects within water-saturated soils. This study presents the design scheme and monitoring results of an AGF reinforcement project for a cross passage located in strata with low seepage velocity on Hohhot Metro Line 2. A transient heat transfer model, based on the assumption of no seepage, was developed, incorporating phase transitions and nonlinear changes in thermal parameters. In the model, soil thermal parameters are treated as variables dependent on unfrozen water content, which is represented by the soil freezing characteristic curve (SFCC). To derive the SFCC expressions, a semi-empirical approach was employed. This approach avoids the complexity of obtaining SFCCs experimentally and mitigates the arbitrariness inherent in the commonly used traditional apparent heat capacity method. The model was subsequently validated using experimental data from the literature and field monitoring results. The development and key indicators, including the thickness and average temperature of the frozen curtain in a single stratum without seepage, were investigated. The results show that the central and slightly right areas of the cross-passage axis exhibit a thinner frozen curtain and higher average temperature, especially in the pump room area, where the effective thickness of the curtain is at its minimum. Therefore, it is recommended to closely monitor the development of the frozen curtain in these areas and optimize the layout of freezing pipes. This study may serve as a reference for similar projects. Full article

The artificial ground freezing method (AGF) is widely used in underground construction to reinforce the ground and ensure construction safety. This study systematically evaluates the implementation of the artificial ground freezing method in the construction of a metro tunnel cross-passage, with a focus on analyzing the soil’s thermo-mechanical behavior and assessing safety performance throughout the construction process. A combined approach integrating field monitoring and refined three-dimensional numerical simulation using FLAC3D is adopted, considering critical factors, such as freezing pipe inclination, thermo-mechanical coupling, and ice–water phase transitions. Both field data and simulation results demonstrate that increasing the density of freezing pipes accelerates temperature reduction and intensifies frost heave-induced displacements near the pipes. After 45 days of active freezing, the freezing curtain reaches a thickness of 3.7 m with an average temperature below −10 °C. Extending the freezing duration beyond this period yields negligible improvement in curtain performance. Frost heave deformation develops rapidly during the initial phase and stabilizes after approximately 25 days, with maximum vertical displacements reaching 12 cm. Significant stress concentrations occur in the soil adjacent to the freezing pipes, with shield tunnel segments experiencing up to 5 MPa of stress. Thaw settlement is primarily concentrated in areas previously affected by frost heave, with a maximum settlement of 3 cm. Even after 45 days of natural thawing, a frozen curtain approximately 3.3 m thick remains intact, maintaining sufficient structural strength. The refined numerical model accurately captures the mechanical response of soil during the freezing and thawing processes under realistic engineering conditions, with field monitoring data validating its effectiveness. This research provides valuable guidance for managing construction risks and ensuring safety in similar cross-passage and cross-river tunnel projects, with broader implications for underground engineering requiring precise control of frost heave and thaw settlement. Full article

This study explored the feasibility of applying transcritical CO₂ in an artificial ground freezing method. By carrying out indoor modeling tests, the temperature field evolution law and the development characteristics of the freezing front during the freezing process of transcritical CO₂ in a sand layer were analyzed, and the freezing effect of transcritical CO₂ was compared with that of traditional alcohol. The theoretical solution of the freezing temperature field was derived, and the accuracy of the theoretical analytical solution was verified by test results. The results showed that the freezing efficiency of transcritical CO₂ was significantly higher than that of alcohol. After 6 h of freezing, the temperature range of the measuring point (C1–C7/C10–C16) can reach −28 °C–3.5 °C, and the freezing front radius exceeded 60 mm. The temperature range of the alcohol measuring point (J1–J7/J10–J16) was only −12.6 °C–8.8 °C, and it took 24 h to achieve the same radius. The test data were in good agreement with the theoretically predicted values, verifying the rationality of the theoretical formula. Freezing temperature T_d had a significant influence on the calculation results of freezing front radius. After transcritical CO₂ freezing for 24 h, the difference in the freezing front radius R(T_d = −2) reached 8.02 mm when the freezing temperature T_d was −2 °C and 0 °C. The difference in the freezing front radius caused by the freezing temperature T_d was concentrated in the range of 1.5–8.1 mm, and the difference in the effect on different types of refrigerants was small. The research results not only confirm the feasibility of the application of transcritical CO₂ in the freezing method but also provide test data and experience for engineering applications, which promotes the innovation and development of freezing method technology. Full article

Artificial ground freezing technology is the most important construction method of complex water-bearing soft clay rock. The thermodynamic properties of soft clay rock are important evidence for the design and construction of space resources development, and the variable hydrothermal parameter can directly affect the uncertain thermodynamic properties of soft clay rock. In this work, an array of field experiments on the soft clay rock are carried out, and the anisotropic spatial variations of hydrothermal parameters of soft clay rock are obtained. The statistical variability characteristics of variable hydrothermal parameters are estimated. A stochastic coupling model of soft clay rock with heat conduction and porous flow is proposed, and the uncertain thermodynamic properties of soft clay rock are computed by the self-compiled program. Model validation with the experimental and numerical temperatures is also presented. According to the relationship between anisotropic spatial variations and statistical variability characteristics for the different random field correlation models, the effects of the autocorrelation function, coefficient of variation, and autocorrelation distance of variable hydrothermal parameters on the uncertain thermodynamic properties of soft clay rock are analyzed. The results show that the proposed stochastic analysis model for the thermal characteristics of soft clay rock, considering the spatial variability of frozen soil layers, is scientifically reasonable. The maximum standard deviation of average thickness is 2.33 m, and the maximum average temperature is 2.25 °C. For the autocorrelation function, the most significant impact comes from DBIN. For the coefficient of variation, the most significant impact comes from thermal conductivity. Different variations of hydrothermal parameters have different effects on the standard deviation of soft clay rock temperature. The biggest influence is the thermal conductivity, while the lowest influence is the specific heat capacity. Full article

In this paper, the freezing and strengthening project of the Sanya estuary tunnel is analyzed, which is facilitated by the use of the partial differential equation (PDE) module in COMSOL Multiphysics software. The solid–liquid ratio is utilized as the water–heat coupling term, and the solid mechanics module is introduced to achieve three-field coupling. Numerical simulations are conducted to study changes in the temperature field, moisture field, and vertical displacement due to freezing and expansion in the most unfavorable soil layer during the freezing process. The results indicate that a complete freezing curtain forms around the 30th day. The distribution of freezing pipes significantly influences the freezing effect. The strong freezing zone is characterized by a high cooling rate and rapid water content reduction with the opposite trends being observed in the weak freezing zone. Upon completion of the freezing process, a large uplift of the ground surface is observed with more pronounced vertical displacement changes in areas affected by temperature and phase changes. The maximum vertical displacement of the ground surface deviates from the center position. While the frozen soil curtain meets the design requirements for freezing, the effects of freezing and expansion should be taken into account. These findings could be instrumental in elaborating the most effective freezing and expansion control measures for areas with powdery clay-based layers in AGF-based projects. Full article

Artificial ground freezing (AGF) has emerged as a prominent treatment method due to its ability to mechanically strengthen the soil while reducing its permeability. However, its implementation has raised concerns about its impact, particularly with respect to frost heave and subsequent thaw-induced displacements. These soil movements can cause subsidence and pose a significant threat to the integrity of surface structures. Overburden pressure plays a crucial role in AGF and determines the amount of heave generated. This paper presents an analysis of the existing literature about soil freezing and thawing. The aim is to offer an understanding of these processes, specifically with regard to their application in AGF. This paper explains the behavior of soil during freezing, with particular emphasis on the influence of overburden pressure. It also investigates frozen soils’ thawing and freeze–thaw (FT) cycles’ long-term effects on soil properties. AGF offers improved soil strength and reduced water permeability, enhancing construction project stability. However, the interplay between the temperature, soil composition, and initial ground conditions during freezing is complex. This thermo-hydro-chemo-mechanical process strengthens the soil and reduces its permeability, but it can also induce frost heave due to water expansion and ice lens formation. Overburden pressure from the overlying soil limits ice lens growth. FT cycles significantly impact soil properties. In fine-grained soils, FT cycles can lead to over-consolidation, while rapid thawing can generate high pore pressures and compromise stability. Importantly, FT acts as a weathering mechanism, influencing soil properties at both the microscopic and macroscopic scales. These cycles can loosen over-consolidated soil, densify normally consolidated soil, and increase overall hydraulic conductivity due to structural changes. They can also weaken the soil’s structure and deteriorate its mechanical performance. Full article

The advancement of massive construction in urban subway projects contributes to the increased use of the artificial ground freezing (AGF) method in the construction of cross passages due to its reliability and environmental friendliness. However, the uplift or subsidence of the ground surface induced by the frost heave and thawing settlement of the soil can be a problem for existing buildings, and the current design method places way too much emphasis on the strength requirement of the freezing wall. In this study, FLAC3D was employed to develop a series of state-of-the-art numerical models of the construction of a typical subway cross passage by the AGF method, utilizing freezing walls with different thicknesses. The results of this study can be used to examine the ground deformation arising from the AGF method and the influence of the thickness of the freezing wall on the AGF method. Full article

The artificial freezing method can effectively improve the stability of strata and provide favorable conditions for the construction safety of shield tunnel in water-rich strata. Based on the frozen shield tunneling project of a metro station, which is close to important buildings, a reasonable freezing method and parameters are proposed in this paper. The simulation model was established by using Plaxis 3D finite element software (Version 2017). The numerical model was verified based on a large amount of field data. The characteristics of segment deformation, ground surface settlement and vertical displacement of buildings were compared between frozen layer and nonfrozen layer during shield tunnel excavation. It was found that segment deformation in the nonfrozen layer is three times that in the frozen layer. The surface settlement above the frozen layer is less than 2 mm. Expansion excavation of shield tunnel was carried out to meet the space function of subway station using artificial freezing method. The deformation of frozen layer was compared between full section excavation and partial excavation. It was found that the deformation of the former is 4.5 times that of the latter, so the partial excavation was chosen as the main research object. Subsequently, the characteristics of vertical displacement and surface settlement of buildings under partial excavation were studied. It was found that the vertical settlement of buildings away from the frozen layer is greater than that of buildings near the frozen layer. All settlement values meet the requirements, thus ensuring the feasibility of partial excavation and ensuring the safety of construction. Full article