Ground Freezing Research Articles

Artificial ground freezing for underground construction – a brief review of the theory, practice and challenge

Since Artificial ground Freezing (AGF) appeared in the 1880s in the mining sector in Europe, it has been used for various construction applications worldwide. In recent years, it has been increasingly popular in urban projects due to its versatility and applicability to complicated site conditions. So far, it has been used to stabilize substrata to nearly 1,000 m below the ground surface, which is considered not possible for many other ground improvement technologies. Due to the growth in field applications, the practice and theories related to AGF have become more mature in the most recent two decades. The improvement in understanding of this topic is a result of lessons that have been learned through numerous projects, as well as a variety of comprehensive studies that have been completed. This paper reviews the existing practice, the recent development on AGF and the challenges of AGF.

Water budgets in an arid and alpine permafrost basin: Observations from the High Mountain Asia

Ground freeze‒thaw processes have significant impacts on infiltration, runoff and evapotranspiration. However, there are still critical knowledge gaps in understanding of hydrological processes in permafrost regions, especially of the interactions among permafrost, ecology, and hydrology. In this study, an alpine permafrost basin on the northeastern Qinghai‒Tibet Plateau was selected to conduct hydrological and meteorological observations. We analyzed the annual variations in runoff, precipitation, evapotranspiration, and changes in water storage, as well as the mechanisms for runoff generation in the basin from May 2014 to December 2015. The annual flow curve in the basin exhibited peaks both in spring and autumn floods. The high ratio of evapotranspiration to annual precipitation (>1.0) in the investigated wetland is mainly due to the considerably underestimated ‘observed’ precipitation caused by the wind-induced instrumental error and the neglect of snow sublimation. The stream flow from early May to late October probably came from the lateral discharge of subsurface flow in alpine wetlands. This study can provide data support and validation for hydrological model simulation and prediction, as well as water resource assessment, in the upper Yellow River Basin, especially for the headwater area. The results also provide case support for permafrost hydrology modeling in ungauged or poorly gauged watersheds in the High Mountain Asia.

Artificial Ground Freezing—On the Soil Deformations during Freeze–Thaw Cycles

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.

Fluid-Solid-Thermal Coupled Freezing Modeling Test of Soil under the Low-Temperature Condition of LNG Storage Tank

Due to the extensive utilization of liquid nature gas (abbreviated as LNG) resources and a multitude of considerations, LNG storage tanks are gradually transitioning towards smaller footprints and heightened safety standards. Consequently, underground LNG storage tanks are being designed and constructed. However, underground LNG storage tanks release a considerable quantity of cold into the ground under both accidental and normal conditions. The influence of cold results in the ground freezing, which further compromises the safety of the structure. Existing research has neglected to consider the effects of this. This oversight could potentially lead to serious safety accidents. In this work, a complete set of experiments using a novel LNG underground storage tank fluid-solid-thermal coupled cryogenic leakage scale model were conducted for the first time to simulate the effect of the tank on the soil temperature field, stress field, and displacement field and to analyze the development of the three fields and the results of the effect. This research helps the related personnel to better design, construct, and evaluate the LNG underground storage tanks to avoid the catastrophic engineering risks associated with cryogenic leakage and helps to improve the design process of LNG underground storage tanks.

Monitoring of the Icing Process and Simulation of Its Formation Mechanism in the Cut Slope of Beihei Highway

Icing in cut slopes is a serious risk to transportation safety in cold regions. Research on the occurrence process and mechanism of icing is a prerequisite for proposing effective management measures. We took the cut slopes of the K162 section of the Beihei Highway as the research object. We used a combination of field investigation, geological exploration, monitoring, and simulation to study and analyze the power source, occurrence process, and triggering mechanism of icing in cut slopes. The results show that the geologic type of this cut slope is a mudstone–sandstone interaction stratum. Abundant shallow groundwater is the source of water for icing. The excavation of cut slopes extends the effect of negative temperatures on groundwater flow during the winter period. The process of ice formation in cut slopes can be described as follows: As the environmental temperature drops, the surface soil begins to freeze, resulting in a gradual narrowing of the water channel; then, the groundwater flow is blocked, so that the internal pressure begins to rise. When the internal pressure of the pressurized groundwater exceeds the strength of the frozen soil, groundwater overflows from the sandstone layer to the surface, forming icing. The high pore water pressure inside the cut slope is the precursor for the occurrence of icing. The dynamic pressure of the pore water pressure is the main driving force for the formation of icing in cut slopes. The obstruction of the water channel due to ground freezing is the triggering condition for ice formation in cut slopes.

Investigation on evolution law of frozen wall thickness in artificial ground freezing under seepage conditions

Frozen wall thickness (E) is an important index that reflects the freezing performance of artificial ground freezing (AGF). In previous design and numerical studies, the inherent spatial variability of soil properties is often neglected. Moreover, groundwater seepage can remarkably affect the freezing performance in the AGF system, while the specific relations between seepage and E remain unclear. Accordingly, this study aims to explore the evolution of frozen wall thickness under seepage conditions via a numerical model that considers the coupled thermo-hydraulic process and variations in hydrothermal properties. As two vital soil properties, spatial variability of thermal conductivity and intrinsic permeability is simulated by random field combined with Monte Carlo simulations (MCs). Based on the coupled model, the effects of seepage velocity, direction, and pipe spacing are examined by sensitivity analysis. Two indicators are introduced to quantify the influences of uncertainty in hydrothermal properties and seepage. The unfavourable scenarios (i.e., lower bound) of E from random models are tabulated and formulated via evolutionary polynomial regression for practical references. These findings contribute to an enhanced understanding of the freezing behaviours of AGF and provide a rule of thumb for predicting frozen wall thickness under complex seepage conditions and design parameters.

Numerical investigation of artificial ground freezing–thawing processes in tunnel construction

Artificial ground freezing is a frequently used method for temporary support of the soil in geotechnical interventions, such as tunneling. Besides the time required to form a supporting frozen soil structure during freezing, the prediction of temperature evolution during the thawing process and the final thawing time are also relevant, since settlements induced by thawing of the frozen soil can pose a risk to sensitive structures in urban tunneling. The freezing and thawing process of soils depends strongly on the unfrozen liquid content. The unfrozen liquid content during the freezing and thawing cycles is known to have a pronounced hysteresis response, whose effect on the temperature distribution and groundwater flow, especially at the structural level has not been extensively studied. In this work, we present a thermo-hydraulic finite element model for freezing soils and incorporate the hysteresis behavior of soil. We aim to investigate the suitability of the presented numerical model for tunnel construction on the one hand, and quantify the extent of the influence of the hysteresis response of the unfrozen liquid content at the structural level on the other. To this end, the model is first validated with the help of experimental data from a soil test subjected to a freezing–thawing cycle and subsequently used to analyze three problems of artificial ground freezing in tunnel construction during the freezing phase or freezing–thawing phases. The results show a good agreement with the experimental measurements. We show that the computational model is capable of providing accurate prognosis of the temperature profile as well as broader metrics such as the thickness and shape of the frozen body for tunneling applications under hydrostatic and seepage flow conditions. The hysteresis response is shown to have a significant influence on the coupled thermo-hydraulic process, with thawing times differing depending on whether hysteresis is considered. It is concluded, that the inclusion of the hysteresis response is crucial for obtaining an accurate representation of the freezing process.

Effects of Salt Content and Freeze-Thaw Conditions on Dynamic characteristics and its microscopic mechanism of Chloride Silty Clay

Generally, artificial ground freezing (AGF) technology is utilized to guarantee tunnel safety during construction. However, the soil structure changes significantly after freeze-thaw, resulting in uneven deformation of the tunnel under traffic loading from subway vibration. To solve this problem effectively, it is necessary to consider the combined impact of freeze-thaw, salt, and traffic loading damage that marine soft soil must withstand simultaneously. For this reason, cyclic triaxial test and NMR test were performed on the silty clay saturated with NaCl solution in this study. The influence of three main factors on dynamic properties has been thoroughly investigated, namely freeze-thaw, salt content, and confining pressure. According to cyclic triaxial test, the shape of the hysteresis loop of the specimens after freeze-thaw changed more significantly with increasing loading cycles. The dynamic elastic modulus was weakened by freeze-thaw, while improved by the addition of NaCl. Damping ratio was consistent with the dynamic elastic modulus law. It was worth noting that the different freezing temperatures (−10 °C, −20 °C and − 30 °C) had only a slight impact on dynamic elastic modulus, as well as damping ratio. Mathematical models were proposed to forecast the dynamic elastic modulus and damping ratio regarding marine soft clay. NMR test indicated that the addition of salt made the internal pore environment of the specimens tend to be consistent and enhanced the water-solid interaction. The increase in porosity resulted in the decrease in dynamic elastic modulus. The results have provided valuable insights into the mechanical characteristics of marine soft clay when AGF technology is applied.

Numerical Analyses of the Effect of the Freezing Wall on Ground Movement in the Artificial Ground Freezing Method

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.

Simulation-based approach for the optimization of ground freezing in tunneling

Artificial ground freezing is used in tunnelling for temporary ground improvement primarily to control groundwater flow and provide excavation support. The principle of ground freezing is based on freeze pipes bored into the ground where a coolant flows through the freeze pipes. Eventually, the ground freezing process converts pore water into ice by withdrawing the heat from the soil. In tunneling, artificial ground freezing is applied to form a closed arch frozen ground around the tunnel. Under the presence of high seepage flow, the formation time of the frozen arch is delayed. In some cases, it cannot be formed, leading to high construction costs or unsafe temporary frozen ground support. This study proposes a strategy for systematically reducing the freezing time through an optimal design arrangement of the freeze pipes. The strategy is based on the combination of the numerical modeling of the ground freezing process using a multifield finite element model in conjunction with a surrogate model to enable real-time prediction.

Study on the shear characteristics of the cemented soil-concrete interface after artificial freeze-thaw under vibration loading

Underground construction has reduced underground space. Consequently, engineering construction is being done near existing structures. The artificial ground freezing (AGF) method is effective in such projects, and cement is often used to reduce frost heave and thaw settlement. A cemented soil-concrete interface is formed around underground structures. The interface serves as the primary medium for interaction between the two materials. Therefore, the shear characteristics of the cemented soil–concrete interface after artificial freeze–thaw cycles under the influence of the surrounding vibration load in underground engineering must be understood. This study conducted large-scale interface shear tests of a cemented soil–concrete interface with vibration loading. The effects of curing time and artificial freeze–thaw cycles on interface shear characteristics were studied. Furthermore, unconfined compressive tests of the cemented soil under artificial freeze–thaw conditions were conducted. The shear strength of the interface increased with curing time. The shear strength of the interface and the unconfined compressive strength of the cemented soil increased rapidly in the early stage of curing and gradually slowed after seven days. Artificial freeze–thaw reduced the shear strength of the interface with vibration loading. The results enrich ongoing research on the shear characteristics of cemented soil-concrete interfaces.

Investigation of creep characteristics and microscopic mechanism of cemented-soil subjected to freeze-thaw

With the development of underground construction, higher safety demands have been placed on construction methods. The improved freezing method, which combines artificial ground freezing and cemented soil stabilization techniques, is more suitable for studying the typical creep characteristics of muddy clay in Shanghai. However, research on the creep behavior of freeze-thaw cemented-soil is limited. In this study, the creep characteristics of freeze-thawed cemented soil were investigated through triaxial creep tests, and the micromechanism was explored using scanning electron microscopy (SEM). The results indicate that the creep deformation of freeze-thawed cemented soil is higher than that of non-freeze-thawed cemented soil. The freezing temperature decreased with an increase in deformation. By analyzing SEM images, the porosities of non-freeze-thawed cemented-soil and soil freeze-thawed at -5°C, -15°C, and -25°C, were extracted, which were 28.5%, 28.7%, 30.1%, and 39.1% respectively. During the freeze-thaw cycle, both the soil and cemented soil particles undergo movement and reordering. Freeze-thaw exacerbates creep degradation because frost heave weakens particle adhesion and affects structural stability. These results provide a scientific reference for the development of underground spaces in soft areas.

Influence of frost heave with confining pressure under seepage on compressive strength of frozen silt in artificial ground freezing

Artificial ground freezing (AGF) is used for constructing subway cross passages in coastal areas. The continuous construction of complex projects (cross-sea or cross-river tunnels) has resulted in freezing environments with high groundwater seepage velocities. Seepage cannot provide an open system in soil freezing for moisture migration, resulting in large amount of frost heave owing to segregated ice compared to close freezing system. The influence of frost heave under seepage on the compressive strength of frozen silt during artificial ground freezing must be studied to ensure AGF construction safety. Thus, a unidirectional freezing device that can control seepage and confining pressure conditions during freezing was designed to prepare frozen silt samples under different seepage velocities with confining pressures and to measure the relevant segregation frost heave. Subsequently, uniaxial compression tests were performed. The compressive strength of frozen silt under the influence of frost heave and seepage conditions was analyzed. The frost heave rate, uniaxial compressive strength, and elastic modulus of frozen silt in an open freezing system were measured. The seepage velocity during freezing increased the frost heave rate of the silt; the uniaxial compressive strength and elastic modulus of the frozen silt increased subsequently. The effective confining pressure suppressed frost heave of silt and reduced the uniaxial compressive strength and elastic modulus of the frozen silt. The test results were analyzed considering the segregation frost heave formation mechanism, and a theoretical improvement model of the uniaxial compressive strength and elastic modulus of frozen silt related to the content of segregated ice was proposed. This research is significant for ensuring the AGF construction safety in cross-river or ocean tunnel engineering under seepage conditions.

Seasonal ground cold energy storage potential for data center cooling using thermosyphon: A comparative study of five cities in Canada for carbon footprint reduction

Artificial Ground Freezing (AGF), using two-phase-closed-thermosyphon (TPCT) device, is an emerging technique for storing the cold energy of the winter season in the ground. The stored energy can later be used in the summer season for data center cooling, building comfort, etc. However, this energy storage potential has not been quantified so far. This study is conducted using an experimentally validated numerical model that simulates the ground freezing phenomenon in five Canadian cities over a 2-years period for 1%, 5%, 10% and 20% soil porosity. Each city offers a different energy storage potential based on ambient conditions and soil porosity — ranging from 3.31 – 23.19 MWh per TPCT, annually. In addition, up to 4,851 kg of carbon footprint can be reduced per TPCT in each city. This study examines and ranks the cities based on the potential for cold energy storage and associated carbon footprint for new and commissioned (already operating) cooling-intensive facilities. Yellowknife is ranked number one for commissioned cooling-intensive facilities and Montreal is ranked number one for new cooling-intensive facilities. It also provides a pre-feasibility guideline for selecting the geographic location to implement the novel idea in cities with similar weather conditions. A new parameter, carbon emission efficiency, is also introduced and used for ranking.

Thermal performance of cast-in-place piles with artificial ground freezing in permafrost regions

Thermal performance of cast-in-place piles with artificial ground freezing in permafrost regions

Electrical Resistivity Behavior of Saline Soil under Low-Temperature Conditions

Freeze-thaw cycling of frozen soils is known to be the cause of various engineering failures of infrastructure in cold regions. Researchers found that electrical resistivity methods outperform traditional ground surveying methods in frozen soils for their greater convenience and cost-effectiveness. However, detailed investigation into the relationship between the electrical resistivity of soil and a variety of soil properties is still needed. In this study, a series of laboratory experiments using the Wenner method were conducted to determine the relationship between soil electrical resistivity and soil geotechnical properties such as initial water content and pore fluid concentration under freeze-thaw conditions. Cylindrical soil samples undergo artificial freeze-thaw cycles to a temperature as low as −70°C, and electrical resistivity and temperature values are recorded simultaneously. Measurement results are summarized for curve fitting, and a statistical model showing relationship between electrical resistivity and temperature during freezing and thawing was given. Above freezing point, the log of electrical resistivity had a linear relationship with temperature. Below freezing point and above −15°C, the log of electrical resistivity had a square root relationship with temperature. Different trends in electrical resistivity change in extremely low-temperature regions (from −15°C to −70°C) are also discussed. In extremely low-temperature regions, the electrical resistivity of frozen soils did not monotonously increase with lower temperature, which may be because of increasing salt concentration in the unfrozen water phase. The findings of this study are expected to bring more insights to frozen soil structure, and assist in geophysical surveying in cold regions and construction methods utilizing ground freezing.

Advancing Permafrost Monitoring With Autonomous Electrical Resistivity Tomography (A‐ERT): Low‐Cost Instrumentation and Open‐Source Data Processing Tool

AbstractPermafrost is a widespread phenomenon in the cold regions of the globe and is under‐represented in global monitoring networks. This study presents a novel low‐cost, low‐power, and robust Autonomous Electrical Resistivity Tomography (A‐ERT) monitoring system and open‐source processing tools for permafrost monitoring. The processing workflow incorporates diagnostic and filtering tools and utilizes open‐source software, ResIPy, for data inversion. The workflow facilitates quick and efficient extraction of key information from large data sets. Field experiments conducted in Antarctica demonstrated the system's capability to operate in harsh and remote environments and provided high‐temporal‐resolution imaging of ground freezing and thawing dynamics. This data set and processing workflow allow for a detailed investigation of how meteorological conditions impact subsurface processes. The A‐ERT setup can complement existing monitoring networks on permafrost and is suitable for continuous monitoring in polar and mountainous regions, contributing to cryosphere research and gaining deeper insights into permafrost and active layer dynamics.

Uncoupled thermo-hydro-mechanical modeling of a pykrete diaphragm wall for an alternative artificial ground freezing application

El Harrach Center metro station is an actual project constructed with conventional diaphragm walls in Algiers. This article primarily consists of a parametric study that makes use of the station's geometry for comparative analysis. In this way, three gaps are investigated using an alternative artificial ground freezing (AGF) application. The impact of thermal conductivity, specific heat capacity, and thermal expansion on the diaphragm wall’s stability were examined; an innovative pykrete wall was investigated; and a new procedure was developed after modeling 216 cases of diaphragm walls with uncoupled thermo-hydro-mechanical modeling via the Plaxis program. In terms of total displacement, ground settlement, horizontal displacement, and excavation uplift, the diaphragm walls were different with and without thermal modeling by 96.20, 100.50, 4.20, and 2.50 mm, respectively. The effectiveness and stability of the innovative pykrete wall have been demonstrated to accurately represent on-site behaviour due to its perfect comportment against internal forces compared to other types of walls. The new procedure was developed regarding the optimum case that facilitates understanding the factors affecting the AGF method (distance between pipes, pipe diameter, freezing temperature, and freezing duration) according to its importance, cost, and the novel potential of thermal modeling for deep excavation projects.

Experimental research on optimum freezing temperature of sandy gravels in artificial ground freezing

Experimental research on optimum freezing temperature of sandy gravels in artificial ground freezing

Experimental research on the cooling effect of a novel two-phase closed thermosyphon with semiconductor refrigeration in permafrost regions

Hybrid two-phase closed thermosyphon (TPCT) artificial ground freezing technique is an effective cooling strategy adaptable to different geological and meteorological conditions in permafrost regions. Previous studies have focused on the feasibility of hybrid TPCT with little attention given to the cooling characteristics and long-term effects of this technique under actual environmental conditions. In this study, a novel structured semiconductor refrigeration device, with simple structure, small size, and wide operating temperature range, was designed and manufactured to act as the active condenser of a hybrid TPCT, and the cooling effect of this device was investigated during a two-year field test under stable power supply. This study showed that: 1) The minimum (maximum) average temperature of the semiconductor refrigeration two-phase closed thermosyphon (SRTPCT) evaporator was 0.5 (2.1) °C lower than the TPCT evaporator. The average ground temperature decreased by 0.3 °C, and the permafrost table rose to 0.2 m at 1 m from the evaporators around SRTPCT. The semiconductor refrigeration device added more than 9.75 MJ of cold storage to the soil around the TPCT evaporator during an operating cycle. 2) The optimal working period for the semiconductor refrigeration device was from June to October, and the cooling effect was better when the ambient temperature was low in the warm season. 3) As active condenser of hybrid TPCT in permafrost regions, semiconductor refrigeration device has a larger heat transfer power enhancement for TPCTs than vapor compression refrigeration device in the warm season, and vice versa in the cold season, as well as a higher heat transfer power enhancement for TPCTs than adsorption refrigeration device. The results of this study provide relevant parameters and references for the design and engineering application of future SRTPCT.