Thermo Hydro Research Articles

The effect of thermal–hydro–mechanical coupling on grouting in a single fracture under coal mine flowing water conditions

AbstractGroundwater inrush is a hazard that always occurs during underground mining. Grouting is one of the most effective processes to seal underground water inflow for hazard prevention. In this study, grouting experiments are conducted by using a visualized transparent single‐fracture replica with plane roughness. Image processing and analysis are performed to investigate the thermo–hydro–mechanical coupling effect on the grouting diffusion under coal mine flowing water conditions. The results show that higher ambient temperature leads to shorter initial gel time of chemical grout and leads to a better relative sealing efficiency in the case of a lower flow rate. However, with a higher water flow rate, the relative sealing efficiency is gradually reduced under higher temperature conditions. The grouting pressure, the seepage pressure, and the temperature are measured. The results reveal that the seepage pressure shows a positive correlation with the grouting pressure, while the temperature change shows a negative correlation with the seepage pressure and the grouting pressure. The “equivalent grouting point offset” effect of grouting shows an eccentric elliptical diffusion with larger grouting distance and width under lower temperature conditions.

Analysis of Long-Term Thermo–Hydro–Mechanical Behavior in the Near-Field of a Deep Geological Repository System

The deep geological repository (DGR) system has been selected by most of the world’s nuclear waste management organizations for the long-term disposal of radioactive wastes. The DGR mainly consists of a multi-barrier system—comprising the natural host rock and an engineered barrier system—to contain and isolate high-level radioactive waste, including used fuel containers (UFCs), to protect humans and the environment. Bentonite materials and host rock are the main components of the DGR’s engineered and natural barrier system, respectively. It is crucial to understand the coupled behavior of bentonite and rock materials under various in situ conditions over long-term durations, as it supports safety assessments and enhances the overall safety level of DGR systems. This study presents a methodology for the numerical modeling of a hypothetical DGR using developed coupled models. The developed model was used to investigate the hydromechanical (HM) and thermomechanical (TM) response within the near-field (the area within a radius of 50 m near the UFC and multiple-barrier system) of a simplified hypothetical DGR, based on the proposed design concept of the Nuclear Waste Management Organization (NWMO) of Canada. The analysis results included the evolution of temperature, thermal stresses, saturation, and swelling pressure at different stages of the DGR system’s lifetime. The results indicated that it could take up to 10,000 years to fully saturate the bentonite materials with a corresponding swelling pressure of 2.7 MPa associated with a decrease in the rock’s strength/stress ratio near the placement room; however, the ratio did not indicate a significant system failure. Sensitivity analysis was also conducted to assess the impact of various parameters on the saturation time and the strength/stress ratio in a DGR. The results highlighted that saturation time was highly influenced by the permeability of both the rock formation and the bentonite, resulting in saturation times ranging from 500 to 20,000 years. Moreover, the strength/stress ratio was found to be sensitive to the model’s parameters, particularly the maximum swelling pressure. The results of the TM analysis show that temperature development around the placement of rooms in a DGR is highly influenced by room spacing, with a lower factor of safety (FOS) as time and temperature progressed due to elevated temperature, while the rock remained stable over the 150-year analysis period. The inclusion of temperature-dependent mechanical properties produced negligible changes to the overall stability of the rock around the placement rooms of the DGR.

A numerical analysis of Thermo–Hydro–Mechanical behavior in the FE experiment at Mont Terri URL: Investigating capillary effects in bentonite on the disposal system

We investigated thermo–hydro–mechanical (T-H–M) coupled behavior observed during the full-scale heater emplacement experiment at the Mont-Terri underground research laboratory conducted in the Opalinus clay as part of the DECOVALEX-2023 Task C project. Utilizing the OGS-FLAC simulator, we created a three-dimensional model to simulate multiphase flow in the experiment, applying extended Philip and de Vries’ model and incorporating the anisotropic T–H–M properties of the Opalinus clay. The simulation, which included a ventilation process, spanned five years of heating experiments and successfully replicated the measured temperature, pore pressure, displacement, and relative humidity results in bentonite and host rock during the experiment. The analysis revealed that capillary pressure significantly influenced the pore pressure change in the host rock near the tunnel, while thermal pressurization became dominant with increasing distance. Consequently, we conducted a sensitivity analysis on a simplified model to evaluate the effect of capillary pressure on the disposal system. Capillarity is a dominant factor for the multiphase flow depending on the distance from the heat. Variations in capillary pressure were observed depending on the gas entry pressure and water retention model, indicating that the capillarity of unsaturated bentonite could inherently affect the T–H–M results within the disposal system.

Disaster effects of climate change in High Mountain Asia: State of art and scientific challenges

High Mountain Asia (HMA) shows a remarkable warming tendency and divergent trend of regional precipitation with enhanced meteorological extremes. The rapid thawing of the HMA cryosphere may alter the magnitude and frequency of nature hazards. We reviewed the influence of climate change on various types of nature hazards in HMA region, including their phenomena, mechanisms and impacts. It reveals that: 1) the occurrences of extreme rainfall, heavy snowfall, and drifting snow hazards are escalating; accelerated ice and snow melting have advanced the onset and increased the magnitude of snowmelt floods; 2) due to elevating trigger factors, such as glacier debuttressing and the rapid shift of thermal and hydrological regime of bedrock/snow/ice interface or subsurface, the mass flow hazards including bedrock landslide, snow avalanche, ice-rock avalanches or glacier detachment, and debris flow will become more severe; 3) increased active-layer detachment and retrogressive thaw slumps slope failures, thaw settlement and thermokarst lake will damage many important engineering structures and infrastructure in permafrost region; 4) multi-hazards cascading hazard in HMA, such as the glacial lake outburst flood (GLOF) and avalanche-induced mass flow may greatly enlarge the destructive power of the primary hazard by amplifying its volume, mobility, and impact force; and 5) enhanced slope instability and sediment supply in the highland areas could impose remote catastrophic impacts upon lowland regions, and threat hydropower security and future water shortage. In future, ongoing thawing of HMA will profoundly weaken the multiple-phase material of bedrock, ice, water, and soil, and enhance activities of nature hazards. Compounding and cascading hazards of high magnitude will prevail in HMA. As the glacier runoff overpasses the peak water, low flow or droughts in lowland areas downstream of glacierized mountain regions will became more frequent and severe. Addressing escalating hazards in the HMA region requires tackling scientific challenges, including understanding multiscale evolution and formation mechanism of HMA hazard-prone systems, coupling thermo‒hydro‒mechanical processes in multi-phase flows, predicting catastrophes arising from extreme weather and climate events, and comprehending how highland hazards propagate to lowlands due to climate change.

Shear Banding and Cracking in Unsaturated Porous Media through a Nonlocal THM Meshfree Paradigm

The mechanical behavior of unsaturated porous media under non-isothermal conditions plays a vital role in geo-hazards and geo-energy engineering (e.g., landslides triggered by fire and geothermal energy harvest and foundations). Temperature increase can trigger localized failure and cracking in unsaturated porous media. This article investigates the shear banding and cracking in unsaturated porous media under non-isothermal conditions through a thermo–hydro–mechanical (THM) periporomechanics (PPM) paradigm. PPM is a nonlocal formulation of classical poromechanics using integral equations, which is robust in simulating continuous and discontinuous deformation in porous media. As a new contribution, we formulate a nonlocal THM constitutive model for unsaturated porous media in the PPM paradigm in this study. The THM meshfree paradigm is implemented through an explicit Lagrangian meshfree algorithm. The return mapping algorithm is used to implement the nonlocal THM constitutive model numerically. Numerical examples are presented to assess the capability of the proposed THM mesh-free paradigm for modeling shear banding and cracking in unsaturated porous media under non-isothermal conditions. The numerical results are examined to study the effect of temperature variations on the formation of shear banding and cracking in unsaturated porous media.

Dynamic Response of Gas Recovery Enhancement Efficiency in Coalbed Methane Displacement by Hot Flue Gas: From the Perspective of Thermo–Hydro–Mechanical–Chemical Coupling

Dynamic Response of Gas Recovery Enhancement Efficiency in Coalbed Methane Displacement by Hot Flue Gas: From the Perspective of Thermo–Hydro–Mechanical–Chemical Coupling

Constitutive Model for Thermo–Hydro–Mechanical Behaviors of Saturated Partially Frozen Cohesionless Soils: A Theoretical Pore-Scale Study

Constitutive Model for Thermo–Hydro–Mechanical Behaviors of Saturated Partially Frozen Cohesionless Soils: A Theoretical Pore-Scale Study

THM model of rock tunnels in cold regions and numerical simulation

The freezing damage of rock tunnels in cold region involves ice-water phase change and complicated interaction of Thermo–Hydro–Mechanical (THM) field. Taking the fractured rock mass of cold region tunnels as research subject, the THM coupling model of cold region tunnels was established, which is based on the seepage mechanics, heat transfer theory, damage mechanics and equivalent continuum theory. This model could reflect the anisotropic properties of deformation, water migration and heat transfer caused by the initial fracture of rock mass. The construction and operation processes of a rock tunnel in cold region were simulated, and results were compared with the measured value and predecessor’s achievements. It shows that proposed model could reflect the anisotropic property of surrounding rock and the simulated deformation and stress are not symmetrical. Compared with the literature, the calculated results in this paper are closer to the measured values. The insulating layer has a significant effect on the stress of the supporting structures. The maximum tension stress of the lining is 4.5 times as that without insulating layer, and the lining will be destroyed for the overlarge tension stress.

Evolution of the mixed mode FPZ and fracture roughness of Beishan granite after coupled thermo-hydro-mechanical treatment

Deep surrounding rocks contain a network of longitudinally intersecting fissures. Exploration of their fracture process zone (FPZ) size evolution during mixed loading and fracture surface roughness after failure has always been a hot topic, especially for coupled thermo–hydro–mechanical (THM) treatment. This study takes Beishan granite as the research object. The fracture surface roughness and FPZ length were obtained using Grasselli statistical and mixed strain–displacement methods. Finally, an electron microscope was employed to observe the fracture surface after failure at different temperatures and loading angles. Results reveal a notable temperature and load dependence of the fracture surface roughness and FPZ length evolution. In the low-temperature stage (25°C–300°C), the mineral primarily exhibited transgranular fractures and the average fracture surface roughness showed a slightly decrease with increasing temperature. In the high-temperature stage (500℃–650℃), the degree of internal damage to the prepared specimens substantially increased, with intergranular fractures being the dominant fracture mode, and rapid roughness growth occurred. Under the same temperature condition, the roughness value was in the order of mode I > mixed mode > mode II. The FPZ length increased, stabilized, and decreased as the load increased. In the low-temperature stage, the FPZ length reached its maximum value at the maximum load, whereas in the high-temperature stage, the FPZ length was fully developed before the peak load. Under the same loading angle condition, the FPZ lengths corresponding to the three loading modes followed the order of mode I < mixed mode < mode II.

Numerical Research of Thermo–Hydro–Mechanical Response and Heat Transfer in a Multiwell EGS with Rough-Walled Fractures after Shear Deformation

Numerical Research of Thermo–Hydro–Mechanical Response and Heat Transfer in a Multiwell EGS with Rough-Walled Fractures after Shear Deformation

Influence of anionic polyacrylamide on the freeze–thaw resistance of silty clay

Freeze–thaw (FT) alternation can severely affect the properties of fine–grained soils, often leading to the failure of foundation backfill projects, such as open canals and roads in cold regions. To address these problems, a water–soluble anionic polyacrylamide (APAM) was used to improve the properties of fine–grained soils, particularly silty clay. This study aims to analyze the effects of the APAM polymer on the physico–mechanical and microstructural properties of silty clay under both unfrozen and FT cycles. For this purpose, different addition dosages and FT cycle numbers were determined, and then a series of zeta potential, thermal conductivity, permeability, triaxial compression, and scanning electron microscopy (SEM) tests were conducted on the soil samples. Additionally, a unidirectional freezing test was constructed to investigate the coupled thermo–hydro–mechanical processes of APAM–treated soil samples under subzero temperature conditions. The results showed that the addition of the APAM polymer significantly enhanced the macroscopic engineering properties and microstructural characteristics of silty clay. This improvement was attributed to the charge neutralization, adsorption bridging effect, and hydrophobic interaction provided by the APAM polymer. However, all the soil samples showed a significant deterioration in their engineering properties during FT cycles, especially after the third FT cycle. It was notable that APAM–treated soil samples were superior to the untreated sample in terms of FT resistance. During the unidirectional freezing process, the pore water migrated from the unfrozen zone towards the freezing front due to the temperature gradient. The treated sample's pore water migration volume was considerably lower than that of the untreated sample, resulting in a 55.25% reduction in total frost heave when the APAM dosage was 0.30%. The findings of this paper may be utilized to mitigate the risk of frost damage to foundation backfill projects in cold regions, as well as to get a better understanding of the stabilization mechanism of the eco–friendly APAM polymer.

Prediction of Dynamic Temperature and Thermal Front in a Multi-Aquifer Thermal Energy Storage System with Reinjection

The accurate temperature and thermal front prediction in aquifer thermal energy storage systems during reinjection are crucial for optimal management and sustainable utilization. In this paper, a novel two-way fully coupled thermo–hydro model was developed to investigate the dynamic thermal performance and fronts for multiple aquifer thermal energy storage systems. The model was validated using a typical model, and the evolution characteristics of wellbore temperature before and after the breakthrough of the hydraulic front and thermal front were deeply studied. Sensitivity analysis was conducted to delineate the influence of various reservoir and reinjection factors on the thermal extraction temperature (TET). The results revealed that thermal conductivity significantly impacts the thermal extraction rate among the various reservoir factors. In contrast, volumetric heat capacity has the weakest influence and negatively correlates with the TET. Concerning the reinjection factors, the effect of the reinjection volume rate on the TET was significantly more significant than the reinjection temperature. Furthermore, the correlation between the TET and different properties was observed to be seriously affected by the exploitation period. The coupled model presented in this study offers insight into designing the exploitation scheme in deep reservoirs and geothermal resources.

Laboratory Tests and Numerical Simulation of the Thermal–Mechanical Response of a Fiber-Reinforced Phase Change Concrete Pile

The critical problem restricting the development and application of phase change energy piles is that adding phase change materials to concrete generally reduces its thermal conductivity. Therefore, exploring a scheme to improve the heat transfer performance of phase change energy piles is necessary. In this study, steel fibers were added to energy piles to enhance the heat exchange capacity between the pile and the surrounding soil. The model tests were conducted on two types of energy piles: a fiber-reinforced pile and a fiber-reinforced phase change pile. Based on laboratory tests, a three-dimensional thermo–hydro–mechanical coupled finite-element model was established to characterize the phase transformation process of FRPC piles accurately. Then, the thermal parameters of the phase change concrete pile were optimized and analyzed to explore the feasibility of improving the application of the phase change pile. The results reveal that the cooling condition where the initial ground temperature was higher than the phase change temperature was more suitable for the FRPC pile. When the flow rate was increased by 50%, the peak heat power of the FRPC pile increased by 25.7%. There is an optimal economic flow rate to balance the system’s energy consumption and heat power in different conditions. Increasing thermal conductivity and specific heat capacity are effective solutions to improve the heat transfer capacity of concrete piles. The energy pile that was enhanced with the high-thermal-conductivity PCM is a good choice to improve long-term operation performance.

Thermo–Hydro–Mechanical Behavior of Unsaturated Loess Considering the Effect of Porosity and Temperature on Water Retention Properties

Thermo–Hydro–Mechanical Behavior of Unsaturated Loess Considering the Effect of Porosity and Temperature on Water Retention Properties

Toward coupled fire‐structure simulations for forecasting smoke leakage in case of concrete structures under fire

AbstractComputational modeling of the fire‐structure interaction demands the coupling between several models typically implemented in independent simulation software describing distinct physical processes. For instance, in the event of a fire breakout or building on fire, the fire not only increases the temperature of the immediate area but also initiates structural damage, leading to the spalling of the concrete along with the propagation of the smoke, heat, and radiation originating from the fire. As a result of the progressive structural damage caused by the fire such as macro cracks or breakthroughs in the wall, smoke and other hazardous gases begin to disperse and spread into previously unaffected zones. Thus, it represents a coupled multi‐physics problem, which is not well addressed in the scientific community, yet. Therefore, the investigation of such fire‐structure interactions requires a comprehensive computational modeling and simulation framework that couples the consequences of various phenomena with minimal invasive solver modifications. In this work, the structural model treats concrete as a multi‐phase porous material exposed to high temperatures resulting from the fire. For this purpose, the structural solver is at the moment manually coupled with a computational fluid dynamics (CFD) solver to setup a computational framework for such fire‐structure simulations. Herein, the combustion process of the fire and the smoke propagation is carried out using the open‐source software denoted as Fire Dynamics Simulator (FDS) and the thermo–hydro–mechanical fracture is computed using a FEniCS‐based solver. The finite‐difference method based FDS solves the filtered Navier–Stokes equations using the large‐eddy simulation technique to describe the turbulent flow and heat transfer including radiation and combustion inside the fluid domain. The concrete damage such as cracks, holes, or spalling is computed using a phase‐field method in a separate solver based on the thermal boundary conditions from the fire simulation. Subsequently, both solvers are coupled using the open‐source coupling framework preCICE. Based on the rate at which the crack or spalling is developing, the computational domain of the fluid solver has to be adapted taking the generated holes in the wall structure into account for the ongoing CFD simulation. It allows for the leakage of smoke gases through the concrete wall structure and thus the spreading of the fire scenario. The proposed model is illustrated by an exemplary case that forecasts the leakage of smoke and hazardous gases from the successive damage caused by the thermal spalling induced on a concrete wall structure.

A Peridynamic-enhanced finite element method for Thermo–Hydro–Mechanical coupled problems in saturated porous media involving cracks

In this paper, a peridynamic-enhanced finite element formulation is introduced for the numerical simulation of thermo–hydro–mechanical coupled problems in saturated porous media with cracks. The proposed approach combines the Finite Element (FE) method for governing heat conduction–advection and fluid flow in the fractured porous domain, and the Peridynamic (PD) method for describing solid phase deformation and capturing crack propagation. Firstly, the consolidation problem of a porous column is simulated by using the proposed approach. The m- and δ-convergence studies are carried out with the isothermal condition to determine suitable discretization parameters for the PD model. Subsequently, non-isothermal conditions are considered, and the accuracy and reliability of the proposed approach are validated by comparing the numerical solutions with those obtained from a FE-only model. Furthermore, several numerical examples focusing on scenarios involving cracks are solved and presented to further highlight the capabilities of the proposed approach in addressing heat conduction–advection problems in fractured saturated porous media, as well as hydraulic fracture propagation problems with considerations of thermo–hydro–mechanical coupled effects.

Methods for the quantification of uncertainties in thermo–hydro–mechanical simulations for safety analyses and influence of modelling decisions

Abstract. The simulation of thermal, hydraulic, and mechanical coupled processes can be a decisive factor in the integrity assessment of geotechnical and geological barriers. Modelling decisions, such as the representation of heterogeneity and the constitutive models used, significantly impact the simulation outcome (Wagener and Pianosi, 2019). Furthermore, numerical inputs to the simulation, i.e. material parameters and boundary conditions, are subject to uncertainty. This results in a lower confidence level of the outcome, even if the overall simulation framework is well validated. To derive robust conclusions from such analyses, it is important to quantify the relative impact of modelling decisions and inputs on certain quantities of interest. Parameter uncertainties can be quantified by their forward propagation through the discretized problem (Helton, 1994), providing a natural frame of reference for quantifying structural uncertainty (Bond et al., 2007), such as the representation of heterogeneity, and for model validation. This contribution will focus on the latter aspects. We present research on workflows for the unification of evaluating uncertainty in experimental data and certain modelling decisions. We first focus on parameter uncertainty quantification and the resulting conclusions concerning the chosen modelling approach. Hereafter, scale questions are addressed in the context of heterogeneity and anisotropy, based on selected case studies. We close by discussing two example applications, namely one at the Underground Research Laboratory (URL) scale (Mount Terri Full-Scale Emplacement (FE) experiment) and one at the repository scale (ANSICHT Ton Nord model). This work is done as part of the Bundesministerium für Umwelt, Naturschutz, nukleare Sicherheit und Verbraucherschutz (BGE URS) research cluster.

Study on the Periodic Collapse of Suspended Sandstone Interlayer under Coupled Thermo–Hydro–Mechanical Environment

In the process of in situ heat injection mining of coal seams, a circular combustion chamber will gradually be formed. However, for the interlayer coal seam, the interlayer will gradually suspend in the combustion chamber. When the critical distance is reached, the initial collapse and periodic collapse will occur, which will affect the flow field distribution and extraction efficiency of combustion gas. In order to study the initial and periodic collapse steps of interlayer in real-time high temperature and high-pressure thermo–hydro–mechanical (THM) coupling environments, sandstone specimens were collected from the field, and the macroscopic mechanical parameters of sandstone interlayer were tested using a self-developed thermo–hydro–mechanical coupling tester. The mechanical parameters (e.g., triaxial compressive strength, elastic modulus, Poisson’s ratio) of sandstone under different stress conditions were obtained. Then, based on the elastic thin plate theory, the mechanical modeling of the annular sandstone interlayer is carried out and the preceding mechanical parameters are brought into the generated analysis equation. Thus, the periodic collapse step of the suspended circular sandstone interlayer is obtained. The study results show that: (1) the macroscopic physicomechanical parameters of the sandstone interlayer do not vary monotonically with temperature—a slight increase in macroscopic parameters occurs at 400°C; and (2) the periodic caving pace of the sandstone interlayer decreases with the increase in the number of collapses. With the increase of temperature, the periodic caving pace of the sandstone interlayer decreases first, then increases, and then decreases. It gradually decreases with the increase of surrounding pressure. The research results of this paper can provide theoretical guidance and technical support for in situ heat injection mining technology.

Numerical analysis of the impacts of rainfall on permafrost-related slope stability on the Qinghai–Tibet Plateau

Study regionThis study interrogates a landslide in ice-rich permafrost region in the Eastern Qinghai–Tibet Plateau, China. Study focusClimate warming has increased the frequency and intensity of rainfall events, changing hydrothermal processes and the soil mechanical properties, thus affecting slope stability in permafrost region. The purpose of this paper is to elucidate the variations in soil volumetric water content (VWC) which may influence the mechanical properties of unstable slopes in ice-rich permafrost region under different rainfall conditions. New hydrological insights for the regionThis paper integrates the rainfall infiltration boundary conditions and Mohr–Coulomb criterion into a thermo–hydro–mechanical (THM) model and analyzes a landslide case in the permafrost regions. The results show that the THM model can effectively account for the impacts of VWC variation under different rainfall conditions. The influence of rainfall on the VWC diminishes as depth increases, with a more pronounced effect observed at depths less than 1 m. At depths exceeding 1 m, the impact is relatively minor. Under the condition of low-intensity, long-duration rainfall, with accumulated precipitation exceeding 60 mm, the cohesion and internal friction angle decrease to 4.2kPa and 8.1°, respectively, with a deep-layer integral slippage. In contrast, under the condition of high-intensity, short-term rainfall, the accumulated rainfall exceeds 75 mm and the internal friction angle decreases from 39° to 26°, with shallow-layer slippage. The results add on to our understanding engineering problems and periglacial geomorphic processes under the influence of climate warming.

Model and experiment of shrinkage effect during hypobaric storage of Agaricus bisporus

AbstractThis study presents a comprehensive multiphase porous media model with thermo‐hydro‐mechanical (THM) bi‐directional coupling for hypobaric storage of porous food. Agaricus bisporus is used as a case study, and the proposed model is compared to the thermo‐hydro (TH) coupling model, which does not consider product shrinkage. The results indicate that the THM model is more sensitive to pressure changes, accurately simulates the development of the evaporation front, and considers the edge gradient effect. The model is validated through experiments and provides a deeper understanding of the mechanism of heat and mass transfer of porous food under low pressure. Increasing humidity reduces product shrinkage. The model's average relative errors for pressure, temperature, weight loss, and shrinkage are 3.64%, 0.06%, 6.07%, and 4.76%, respectively. This model can be used to optimize the hypobaric storage process and improve product quality.Practical applicationsIn this manuscript, a multiphase porous media model with THM bi‐directional coupling for the process of hypobaric storage was developed. Taking A. bisporus as an example, pressure, temperature, weight loss, and shrinkage were predicted. In addition, the effect of humidity on shrinkage of porous food during hypobaric storage has also been studied. In engineering practice, the model can be used to optimize the hypobaric storage process and evaluate product quality.