Frost Heave Research Articles

Freeze-necking and volumetric change of clay during freezing by 3D X-ray Computed Tomography

Abstract In artificial freezing engineering, the freezing temperature is an important factor affecting soil frost heave deformation, and studying its impact is of great significance. The frost heave ratio of soil is a crucial factor for designing and predicting soil frost heave. However, it only considers vertical deformation while neglecting radial deformation. This paper introduces a simple unidirectional freezing apparatus specifically designed for three-dimensional X-ray computed tomography (CT) scanning, which allows for the investigation of internal structural changes in clay during freezing at four different freezing temperatures (i.e., -3 ºC, -5 ºC, -7 ºC, and -9 ºC). Freeze-necking of the soil was observed during freezing. An image processing method was proposed to segment the soil samples, and parameters such as length, equivalent diameter, and volume were measured to assess changes during freezing. The observed variations in necking depth and equivalent diameter indicate that freeze-necking is uniform. As the freezing temperature decreased, the necking depth reduced from 72.4 mm to 38.1 mm, and within this necking depth, the equivalent diameter decreased progressively from the bottom to the top. Moisture content increased near the cold end of the soil and decreased near the warm end, suggesting that freeze-necking is due to moisture migration within the soil. Considering freeze-necking, the volumetric frost heave ratio was defined to characterize soil frost heave deformation. This ratio also decreases as the freezing temperature decreases, and the values are smaller than those of the traditional frost heave ratio. The discrepancies become more pronounced at higher freezing temperatures, reaching up to 1.8% at -3 °C. The results indicate that lower freezing temperatures can reduce frost heave deformation, and freeze-necking requires greater attention in engineering at higher freezing temperature.

Enhanced Short-Term Temperature Prediction of Seasonally Frozen Soil Subgrades Using the NARX Neural Network

Accurate prediction of subgrade temperatures in seasonally frozen regions is crucial for understanding thermal states, frost heave phenomena, stability, and other critical characteristics. This study employs a nonlinear autoregressive with exogenous input (NARX) network to predict short-term subgrade temperatures in the Golmud-Nagqu section of China’s National Highway 109. The methodology involves preprocessing subgrade monitoring data, including temperature, water content, and frost heave, followed by developing a temperature prediction model. This tailored NARX neural network, compared to the traditional BP neural network, integrates feedback and delay mechanisms for monitoring data, offering superior memory and dynamic response capabilities. The precision of the NARX model is assessed with the backpropagation (BP) network, indicating that the NARX neural network significantly outperforms the BP model in both precision and stability for temperature prediction in seasonally frozen subgrades. These findings suggest that the NARX model is a valuable tool for accurately predicting subgrade temperatures in seasonally frozen regions, offering significant insights for practical engineering applications.

Investigation of coupled thermo-hydro-mechanical processes on soil slopes in seasonally frozen regions

Freeze-thaw cycles significantly affect slope stability in seasonally frozen regions, posing serious threats to the functionality and safety of infrastructure. This study developed a coupled thermo-hydro-mechanical (THM) model of frozen soils that accounts for water migration, water-ice phase change, groundwater recharge, frost heave and thaw settlement deformation. The accuracy and reliability of the model was verified based on soil column test results. The change of temperature, water content, and displacement of a soil slope during freeze-thaw process was investigated. The results show that the water-heat transfer and deformation mainly occur in the shallow soils of the slope with changes in air temperature. The temperature fluctuations at the shoulder and face of the slope are more pronounced than those at the toe and crest of the slope. Water migration from the unfrozen zone to the freezing front due to the temperature gradient results in an increase in water content in the frozen zone. The slope shoulder exhibits the largest temperature fluctuations, leading to increased water migration and greater deformation. The rising groundwater table increases the total water content at the slope toe and base, exacerbating the frost heave and thaw settlement deformation, and reasonable groundwater table control intervals are provided. This study elucidates the thermo-hydro-mechanical coupling process and deformation mechanism of seasonally frozen soil slopes, and summarizes the failure modes, which provides a reference for the stability assessment and disaster prevention of soil slopes in cold regions.

Atomistic origin of montmorillonite clay subjected to freeze-thaw hysteresis

The freeze-thaw cycles of frozen soil could significantly affect its thermo-hydro-mechanical-chemical (THMC) properties, causing the frost heaving and thawing settlement. The microscale essence is the water-ice phase transition, but the microscale details are still poorly understood, especially at ultra-low temperatures. Nuclear magnetic resonance (NMR) technology and molecular dynamics (MD) simulation methods were performed to explore the freeze-thaw behaviors of montmorillonite clay under temperature of 210 - 293 K. Then, the water-ice phase transition, freeze-thaw hysteresis, ice nucleation mechanism, and surface effect of clay at an atomistic level were discussed. A classification method of different types of unfrozen water through NMR experiment was proposed, including bulk, capillary, and bound water. Here, it is found that: (1) the freeze-thaw process of frozen soil at the macroscale was essentially the occurrence of ice-water phase transition at the microscale. (2) The freeze-thaw hysteresis was caused by different growth and melting rates of ice crystals, where the ice growth/nucleation on clay surface was more difficult to develop. (3) The surface effect of clay was essential for the ice nucleation and the existence of bound water. For example, little unfrozen water still existed in unfrozen soil even at 213 K. (4) For unsaturated frozen soil, the quasi-liquid water was an essential component of unfrozen water that cannot be ignored. This work could provide an atomistic insight to unravel the atomistic origin of the freeze-thaw mechanism of montmorillonite clay and complement relevant experimental evidence.

Study on Frost Heave and Thaw Settlement Characteristics of Sanya Estuary Channel Soil Layer

In order to explore the frost heave and thaw settlement characteristics of soil layers in the Sanya Estuary Channel Project, the frost heave rate and thaw settlement coefficient of gravel sand, fine sand, silty clay, and clay are obtained. The most unfavorable soil layers are then compared and analyzed. The variation law of frost heave and thaw settlement performance of the most unfavorable soil layer under different water content is studied. The results are as follows: (1) The freezing stage of the passage through the typical soil layer is divided into four stages: frost shrinkage, rapid frost heave, slow frost heave, and frost heave stability. The melting stage is divided into three stages: slow thaw settlement, rapid thaw settlement, and thaw settlement stability. (2) The most unfavorable soil layer in the typical soil layer of the Sanya Estuary Channel Project is silty clay, with a frost heave rate and thaw settlement coefficient of 4.51% and 5.88% at −28 °C. (3) The frost heave and thaw settlement performance of the most unfavorable soil layer is linearly related to water content. The larger the water content, the greater the frost heave rate and thaw settlement coefficient, and the more prone to damage.

Моделирование теплового режима дорожной одежды и земляного полотна лесовозных дорог

Soil freezing is observed throughout almost the entire forested area of the Russian Federarion in winter. The effect of negative temperatures on dusty-clay soils causes a number of adverse processes that change the properties of the soils themselves. One of the most unfavorable of these processes is the accumulation of moisture in soils under the influence of the movement of the freezing front. When freezing, water-saturated clay soils increase dramatically in volume. This leads to the appearance of frost heaving in the active zone of the forest roadbed, which has an extremely adverse effect on the structure of the entire pavement and can lead to damage to the pavement with a sharp deterioration in the transport and operational qualities of forest roads. To combat frost heaving, it is necessary to study the patterns of changes in the water-thermal regime of road structures. The depth of freezing of the pavement and the roadbed is of the greatest importance for predicting frost heaving and developing measures to combat this phenomenon. The article describes the developed system for monitoring the temperature of the road structure to a depth of 3 m and the measurement results which allow us to evaluate the temperature change at different depths from the road surface and determine the freezing depth. A total of 32 sensors have been installed with a step of 10 cm. A numerical simulation of the freezing process of the pavement and the upper part of the roadbed of a forest road has been performed, with the results compared with the indicators of field observations. Good data convergence has been revealed. According to the results of experimental studies, the freezing value has been 173 cm, and according to the results of numerical simulation – 190 cm. The average error in the results of numerical simulation of the freezing process of the pavement and the upper zone of the forest roadbed has been 8–10 % compared to the experimental data.

Investigation on moisture-heat-deformation behaviors of the ordinary railway subgrade in seasonally frozen regions

The stability and service performance of ordinary railway subgrade are often challenged by frost heave distresses in seasonally frozen regions. This paper analysis the moisture-heat process and frost heave characteristics of the subgrade of Qinghai-Tibet Railway (QTR) using on-site monitoring data. The development mechanism of deep frost heave in ordinary railway is discussed, and combined with numerical simulation, the mechanism of significant lateral differential frost heave of ordinary railway subgrade is also revealed. The monitoring results show that the maximum freezing depth of the subgrade is 1.88 m, and the maximum frost heave is 32 mm. The freezing cycle can be divided into four stages by freezing rate and thawing rate: repeated freezing-thawing cycles, rapid freezing stage, slow freezing stage, and bidirectional thawing stage. The freezing rate of 0.53 cm/d and high moisture content of subgrade in the slow freezing stage are the main reasons for the development of deep frost heave in ordinary railway subgrade. The existence of ballast layer is the primary factor that causes the difference of initial freezing time, moisture-heat change and distribution at different positions of ordinary railway subgrade, which ultimately results in the lateral differential frost heave exceeding the allowable value of 15 mm.

A systematic investigation of the freezing process of silty clay through unidirectional stepwise freezing method combined with digital imaging processing technology

Soil freezing represents a complex thermo-hydro-mechanical coupling process that encompasses a range of physical and mechanical phenomena, such as heat transfer, moisture migration, cryostructure development, ice lens segregation, frost heave, and consolidation, all of which interact and influence one another throughout the freezing process. This study conducted a unidirectional stepwise freezing test, comprising three distinct freezing stages, to investigate the freezing behavior of Qinghai-Tibet silty clay using digital imaging processing technology (DIPT), which includes an image acquisition system and a digital image processing system. The results demonstrate that the stepwise freezing test provides a more comprehensive insight into the physical and mechanical processes occurring during unidirectional soil freezing. At various stages of freezing, the temperature distribution within the sample achieves a linear stabilization, with the frozen zone exhibiting a slightly larger extent compared to the unfrozen zone. The longitudinal section of the sample developed layered cryogenic cracks, whereas the horizontal section revealed interconnected cryogenic polygonal cracks of varying sizes, which facilitated moisture migration and ice segregation. Furthermore, ice lenses can segregate within a broad temperature range below the soil freezing point in the frozen zone, resulting in frost heave within the frozen zone and consolidation of the unfrozen zone. This study proposes an experimental method to clarify the complex phenomenon and mechanisms of frost heave during soil freezing.

Frost-resistant embankments with a novel ground source heat pump system

This study introduces a novel artificial heating technique aimed at addressing frost heave issues in embankments on frozen ground, offering a sustainable solution. Initial evaluations assessed various heating systems, including boilers, heat pumps, solar heaters, and electric heaters, focusing on their thermal performance and applicability. The study subsequently designed and implemented a direct-expansion ground source heat pump (DX-GSHP) system as the primary heat source for embankment warming. Rigorous testing confirmed the DX-GSHP system's ability to maintain a heat-supply temperature above 40 °C and a heat-absorption temperature below −3.5 °C, effectively extracting geothermal energy for transfer to the topsoil layers. With a demonstrated coefficient of performance (COP) of 3.49, the DX-GSHP system not only proves its energy efficiency but also suggests a potential role in reducing the strain on electricity supply systems. Installation of DX-GSHPs, with heating capacities ranging from 1.0–2.0 kW and spaced at intervals of 2.0–4.0 m, provides a rapid thermal response to frost heave in single-track railway embankments, thereby potentially mitigating frost-induced damage in cold climate regions.

Strength degradation characteristics and damage constitutive model of sandstone under freeze-thaw cycles.

Thorough investigation into the laws governing frozen rock damage in high-altitude and cold regions can offer valuable insights for advancing infrastructure construction, ecological environment protection, and sustainable development on the Qinghai-Xizang Plateau. This study combined with the seasonal variation patterns of frozen rocks in the Qinghai-Xizang Plateau, and processed the rock samples using a freeze-thaw interval of -20 °C~20 °C. Uniaxial compression test was conducted based on the MTS816 rock mechanics testing system. The porosity changes of rock samples with different freeze-thaw cycles were analyzed using the MesoMR12-060H-I nuclear magnetic response analysis system. A rock freeze-thaw load coupled damage constitutive model was derived using the Lemaitre equivalent strain theory. Research has shown that during the freezing process, the pore water inside the rock sample is affected by the phase change of water-ice, resulting in frost heave force, which further promotes the expansion of the pore walls and the initiation of new cracks. When melted, pore water migrates towards newly formed micropores, thereby affecting the changes in the pores of rock samples. The increase in porosity at the micro level weakens the mechanical parameters of rocks at the macro level. The segmented freeze-thaw damage constitutive model based on Lemaitre equivalent strain theory can well fit the experimental results involved in this study, as well as the experimental results obtained by other researchers. The compaction stage can partially reflect the changes in sandstone pore structure under freeze-thaw cycles.

Experimental investigations of the shear strength and deformation behavior of a frozen unsaturated silt

There are limited studies in literature with respect to the deformation and shear strength behavior of frozen unsaturated soils that consider sensitive changes in temperatures below 0 °C. For this reason, the focus of the present study is directed towards investigating the shear strength and deformation behavior of a frozen unsaturated silt. As a part of the study, one-dimensional freezing tests were performed on compacted silt samples with various initial water contents and dry densities. The pulsed nuclear magnetic resonance (P-NMR) method was used to obtain distribution of unfrozen water content of silt samples; this information was used to explain the deformation behavior during freezing. The volume change behavior in unsaturated soils due to freezing can be associated to three primary factors: expansion caused by the ice-water phase transition and shrinkage induced by ice-cementation and dehydration. A critical water saturation was also observed at which the frost heave is minimum, or no volume change occurs. In addition, conventional direct shear tests were performed on compacted unsaturated silt samples both in frozen and unfrozen conditions to determine and quantify the shear strength contribution arising from the different cohesion components. The investigations in this study provide valuable information that can be used in rational explanation of the strength and deformation behavior of unsaturated frozen soils.

Changes in the standard freezing depth of seasonally frozen ground in China over the last 50 years

ABSTRACT In recent years, under the influence of global warming, the freezing depth of seasonally frozen ground (SFG) has decreased at an accelerating rate. This has affected engineering and construction insofar as accurate determinations are needed of SFG areas and the amount of frost heaving. In this study, a method of deriving the E-factor using the improved Stefan formula was used to study changes in the standard freezing depth (SFD) of SFG in China. The method was used to reveal the trends and patterns of changes in the SFD of SFG over the past fifty years. The study relied on ERA5L and reanalysis data and empirical formulas for standard sites in China’s SFG regions. Raster data of the interdecadal SFD in SFG areas of China from 1971 to 2020 were generated to analyze changes in the SFD. Our results show that in the past fifty years, the SFD in China’s SFG areas has shown a downward trend, with the SFD changing at an average rate of −6.749 cm/10a years. The average SFD in the 1970s, 1980s, 1990s, 2000s, and 2010s was 111.31, 107.13, 95.69, 89.84, and 86.21 cm, respectively. From the overall performance of the SFD in different decadal periods, the SFD in central and northeast China changed sharply within the range of 35° N to 50° N in SFG regions. The boundary lines of low-value SFDs expanded sharply to the north as the latitude increased, and the boundary lines of high-value SFDs contracted sharply.

Study of freeze-thaw deterioration of saturated and unsaturated hydraulic concrete based on measured strain

In actual concrete water projects, areas such as the back surface, above-water surface, and even areas where the water level fluctuates are in the unsaturated freeze-thaw state. The complexity of freeze-thaw tests of unsaturated hydraulic concrete has thus far prevented a sound understanding of the mechanisms at work in freeze-thaw deterioration of unsaturated hydraulic concrete. Given this situation, this study first compares three different unsaturated hydraulic concrete freeze-thaw test processes (polyurea seal, paraffin seal, and vacuum-bag seal) and then uses the vacuum-bag seal method to implement freeze-thaw tests of unsaturated hydraulic concrete. Afterward, three test schemes (unsaturated sealed freeze-thaw, water-freeze-thaw without air-entraining agent, and water-freeze-thaw with air-entraining agents) are conducted and the mechanisms of freeze-thaw deterioration of saturated and unsaturated hydraulic concrete are evaluated based on the measured temperature and strain of the concrete specimens. The results reveal a continuous and irreversible deterioration leading to the freeze-thaw damage of unsaturated sealed freeze-thaw specimens and water-freeze-thaw specimens with and without an air-entraining agent. After 200 freeze-thaw cycles, the cumulative residual strain of the aforementioned three test schemes reach 47 με, 616 με, and 273 με, respectively. The thermal expansion coefficient of concrete remains relatively constant with increasing freeze-thaw cycles. Water-freeze-thaw specimens without air-entraining agents have a greater thermal expansion coefficient than those with air-entraining agents, and unsaturated sealed freeze-thaw specimens have the smallest thermal expansion coefficient. The frost heave coefficient increases with increasing freeze-thaw cycles, and water-freeze-thaw specimens without air-entraining agents have greater frost heave coefficients than those with air-entraining agents.

Initiation mechanism of landslides in cold regions: Role of freeze-thaw cycles

Freeze-thaw cycles are recognized as one of the key triggers for some major landslides in cold regions around the world. Though the effects of freeze-thaw cycles on the rock strength degradation have been studied extensively, little effort has been made to qualitatively evaluate how it contributes to the evolution from a stable rock slope to a large-scale mass movement. In this study, we use a discrete element-based numerical model to simulate the entire process of the initiation of landslide under the action of freeze-thaw cycles in a slope with randomly distributed initial cracks. The main goal of this work is to quantitatively describe the landslide evolution process regarding the slope displacement, crack propagation, stress chain and load-bearing structure. Our results show the essence of the displacement evolution of a landslide subjected to freeze-thaw cycles; namely frost heave pressure induces the generation of new cracks, leading to the failure and reconstruction of the load-bearing structure of the slope. Deep-seated landslides can occur when the slope is crossed by a fault; otherwise, the slope is prone to surface erosion or shallow landslides.

Freeze-thaw impacts on geocell-stabilized bases considering effects of water supply and compaction

Although Novel Polymeric Alloy (NPA) geocells have been applied to stabilize road bases against the freeze-thaw (F-T) damage in practice, the relevant research lags the application. A scarcity of research has been reported to comprehensively evaluate the benefits of geocell stabilization in enhancing the F-T performance of bases. This study aims to investigate quantitatively the F-T performance of geocell-stabilized bases, focusing on two influencing factors-i.e., water supply and degree of compaction in the bases. A series of model-scale experimental tests (19 tests) was conducted using an upgraded customized apparatus. The results showed that the inclusion of geocells was beneficial for reducing frost heave and thaw settlement as well as mechanical properties (i.e., stiffness and ultimate bearing capacity) of road bases. The benefit of geocells was more remarkable for the well compacted bases than for the poorly compacted bases. The benefit was more pronounced in the open system than in the closed system.

A Quasi-Steady Model for Estimating the Rate of Frost Heave When Subjected to Overburden Pressure

The soil beneath buildings constructed in cold regions is affected by frost heave, causing the walls to crack and even the buildings to incline and collapse. Therefore, predicting the frost heave when subjected to overburden pressure is crucial for engineering buildings in cold areas. Utilizing the conservation equation of mass, Darcy’s equation, and the assumption that the pore water pressure at the top of a frozen fringe, denoted as uw, during the quasi-steady state can be approximately estimated using the Clapeyron equation, a quasi-steady frost heave rate model considering the overburden pressure was proposed. This study considered the difference in pore water pressure within the frozen fringe, which causes water to move from the unfrozen zone to the ice lens, where it subsequently accumulates and freezes into ice. The pore water pressure at the bottom of the frozen fringe, denoted as uu, can be estimated using the soil water characteristic curve (SWCC). The thickness of the frozen fringe was determined using the freezing temperature, segregation temperature, and temperature gradient. The segregation temperature was determined using the two-point method. Additionally, the model suggested that, when uw = uu, the movement of water stopped, leading to the end of frost heave. To validate the proposed model, three existing frost-heaving experiments were analyzed. The findings demonstrated that the estimated rates of frost heave of the samples closely matched the experimental data. Additionally, external pressure delayed water migration. This study can offer theoretical support for building engineering in cold regions.

Study on the Dispersion Characteristics of Coal Complex Resistivity under the Effect of Liquid Nitrogen Cyclic Freeze-Thaw and Evaluation of Permeability Enhancement.

The effect of liquid nitrogen freeze-thaw fracturing on coal seams can be potentially evaluated by the complex resistivity method. The real part (Reρ) and the imaginary part (Imρ) of the complex resistivity and permeability of coal were determined under different cycle times and in different bedding directions. The reason for permeability enhancement was discussed, and the dispersion mechanism of complex resistivity during cyclic freeze-thaw fracturing was analyzed. The results indicated that (1) the complex resistivity parameters have a good response to the cycle times; Reρ, |Imρ|, and the dispersion degree (α) are positively correlated with cycle time; the fully polarized frequency (f p) of Reρ, the characteristic frequency (f c) of Imρ, and variation are negatively correlated with cycle time. (2) The difference in complex resistivity parameters between the vertical bedding direction and the parallel bedding direction is significant, and the difference in electrical properties of the bedding structure continuously decreases with the increase in cycle time. (3) Under the effect of liquid nitrogen cyclic freeze-thaw, a complex network of fractures in coal is formed, the anisotropic characteristics of coal are weakened, and effective conductive channels are damaged. The peak frost heave force decreases exponentially with the increase in cycle time, and the difference in bedding electrical properties gradually disappears. (4) Comparing the inversion degree of measured data with three conductive models, ρ0 and τ are selected as the optimum parameters for evaluating the effect of liquid nitrogen cyclic freeze-thaw. A logarithmic permeability evaluation model is constructed based on ρ0 and τ. This work provides a new perspective based on electrical detection for evaluating the permeability enhancement of coal during liquid nitrogen cyclic freeze-thaw.

Advances in InSAR Analysis of Permafrost Terrain

ABSTRACTDifferential interferometric synthetic aperture radar (InSAR) is a remote sensing technique for measuring surface displacements with precision down to millimeters, most commonly from satellites. In permafrost landscapes, InSAR measurements can provide valuable information on geomorphic processes and hazards, including thaw subsidence and frost heave, thermokarst, and permafrost creep. We first review recent progress in InSAR data availability, InSAR processing and uncertainty analysis methods relevant to permafrost studies. These technical advances have contributed to our understanding of surface deformation in flat and sloping terrain in polar and mountainous regions. We emphasize two emerging trends. First, InSAR increasingly enables insight into the mechanisms, controls, and drivers of permafrost landscape dynamics on subseasonal to decadal time scales. Second, InSAR observations in conjunction with models enable novel ways to infer subsurface parameters, such as near‐surface ground ice content and active layer thickness. We anticipate that in the coming decade, InSAR will mature into a widely used operational tool for monitoring, modeling, and planning across rapidly changing permafrost landscapes.

Mechanical, freeze-thaw resistance and heavy metals leaching properties of alkali-activated recycled concrete powder solidified sludge

Solidified sludge was an efficient method to consume the large amount of sludge, which can be used as the subgrade filler in road engineering. However, the traditional solidified materials, such as cement and lime, consumed a large amount of natural resources and increased carbon emissions. This study used the alkali-activated recycled concrete powder (ARCP) to solidify sludge, which could be used as a potential subgrade stabilization filler. The optimal factors of ARCP were firstly determined by orthogonal test according to the compressive strength. Then the influences of different ARCP dosage, sludge moisture content and curing method on the mechanical properties, freeze-thaw resistance and heavy metals immobilization of the ARCP solidified sludge (ARCPS) were investigated. At last, microstructures of ARCPS were analyzed by SEM, XRD and TG-DTG tests. The experimental results demonstrated that the optimal mixture for ARCP: the silicate modulus of 1, liquid-solid ratio of 0.48 and calcium hydroxide content of 3 %. The solidified process by ARCP improved the mechanical properties and freeze-thaw resistance of ARCPS greatly. The 7 d unconfined compressive strength of ARCPS could reach 1305–2033 kPa when the sludge moisture content was 15 %, which meet the requirement of 500 kPa from the Chinese standard. The frost heaving rates of ARCPS were between non-frost heaving and mild frost heaving. The sludge moisture content was the most important factor affecting the freeze-thaw resistance of ARCPS. The properties of ARCPS were further improved after carbonation curing. The leaching mass concentration of heavy metals decreased significantly after the solidification of sludge. After 5 freeze-thaw cycles, the heavy metal leaching concentration increased but was still met the requirement of standards. SEM results showed that the surface of carbonated ARCPS was covered by dense scale-like carbonation products, which further enhanced the strength and freeze-thaw resistance of ARCPS. The results can be used to guide the application of sludge and ARCP in construction.

Physical properties and anisotropy of sandstone during freeze-thaw cycle under unidirectional constraint

To investigate the evolution of physical properties of sandstone under unidirectional constraint during freeze-thaw cycles, an experimental device was specifically designed. Unidirectional constraint freeze-thaw tests were performed on sandstone specimens. The study analyzed variations in the dry mass, saturated mass, and longitudinal wave velocity of the sandstone both before and after undergoing freeze-thaw cycles, as well as examining the evolution of resistivity throughout the process. Results revealed that an increase in the number of freeze-thaw cycles leads to a gradual increase in the saturated mass of sandstone, while its dry mass consistently decreases, irrespective of whether it is subjected to constraint or not. The change rates of both dry mass and saturated mass were found to be significantly lower under unidirectional constraint compared to that without constraint. With more freeze-thaw cycles, a decline in longitudinal wave velocity was noted. Under unconstrained conditions, no significant direction dependence in longitudinal wave velocity was detected. However, under unidirectional constraint, there was a smaller decrease in the longitudinal wave velocity along the direction of constraint compared to other directions. This indicates that constraint mitigates frost heave damage. In the temperature rise and maintenance stages, resistivity initially dropped, then increased prior to stabilizing at a constant value. Conversely, in temperature decrease and maintenance stages, resistivity first rose, then dipped before ultimately rising again. Temperature primarily influenced resistivity by affecting the ion movement velocity within pore water and the connectivity of the conductive network.