This study presents a fully coupled thermo-hydro-mechanical (THM) constitutive model for clay rocks. The model is formulated within the elastic-viscoplasticity framework, which considers nonlinearity and softening aft...This study presents a fully coupled thermo-hydro-mechanical (THM) constitutive model for clay rocks. The model is formulated within the elastic-viscoplasticity framework, which considers nonlinearity and softening after peak strength, anisotropy of stiffness and strength, as well as permeability variation due to damage. In addition, the mechanical properties are coupled with thermal phenomena and accumulated plastic strains. The adopted nonlocal and viscoplastic approaches enhance numerical efficiency and provide the possibility to simulate localization phenomena. The model is validated against experimental data from laboratory tests conducted on Callovo-Oxfordian (COx) claystone samples that are initially unsaturated and under suction. The tests include a thermal phase where the COx specimens are subjected to different temperature increases. A good agreement with experimental data is obtained. In addition, parametric analyses are carried out to investigate the influence of the hydraulic boundary conditions (B.C.) and post-failure behavior models on the THM behavior evolution. It is shown that different drainage conditions affect the thermally induced pore pressures that, in turn, influence the onset of softening. The constitutive model presented constitutes a promising approach for simulating the most important features of the THM behavior of clay rocks. It is a tool with a high potential for application to several relevant case studies, such as thermal fracturing analysis of nuclear waste disposal systems.展开更多
The utilization of coalbed methane(CBM)cannot only alleviate the energy crisis,but also reduce greenhouse gas emissions.Gas injection is an effective method to enhance CBM recovery.Compared to single-gas injection,the...The utilization of coalbed methane(CBM)cannot only alleviate the energy crisis,but also reduce greenhouse gas emissions.Gas injection is an effective method to enhance CBM recovery.Compared to single-gas injection,the injection of CO_(2)/N_(2) mixtures can balance the sharp decline in permeability caused by pure CO_(2) and the premature breakthrough by pure N_(2).In this study,a more comprehensive thermo-hydro-mechanical(THM)coupled mathematical model was developed,incorporating processes such as ternary gas non-isothermal adsorption,gas dissolution in water,gas-water two-phase flow,energy exchange,and coal deformation.After experimental validation,the model was applied to simulate the entire process of gas mixtures for enhanced CBM recovery(GM-ECBM).Results indicate that the permeability near the production well(Pw)initially decreases due to increased effective stress,then increases as a result of CH_(4) desorption.Near the injection well(Iw),the permeability first increases due to reduced effective stress and later stabilizes under the combined effects of effective stress and CO_(2)/N_(2) adsorption.The initial CH_(4) pressure and coal seam permeability have the most significant impact on CH_(4) production,while the coal seam permeability and temperature significantly affect CO_(2)/N_(2) injection.As the coal seam permeability increases,the optimal CO_(2)/N_(2) ratio also increases accordingly.These findings provide important theoretical guidance for improving GM-ECBM efficiency in coal seams with varying permeabilities.展开更多
Based on fluid mechanics, thermodynamics and damage mechanics, thermal-hydro-mechanical （THM） coupling damage model of brittle rock is established by analyzing THM coupling mechanism, where THM coupling damage varia...Based on fluid mechanics, thermodynamics and damage mechanics, thermal-hydro-mechanical （THM） coupling damage model of brittle rock is established by analyzing THM coupling mechanism, where THM coupling damage variable DTHM is dominated by TH coupling damage variable DTH, TM coupling damage variable DTM and HM coupling damage variable DHM, and DTH is firstly expressed in term of dimensionless total thermal conductivity of the water Nu. Permeability test, uni-axial compression test and THM coupling test are conducted to measure the permeability, elastic modulus and THM coupling stress-strain curves of brittle rock. The tested values of THM coupling elastic modulus E＇HM are in good agreement with the predicted values of THM coupling elastic modulus ETHM, which can verify the newly established THM coupling damage model.展开更多
The freeze-thaw(FT)behavior of porous materials(PMs)involves the coupling of the thermo-hydromechanical(THM)processes and is significantly influenced by the microstructure.However,modeling FT in unsaturated PMs remain...The freeze-thaw(FT)behavior of porous materials(PMs)involves the coupling of the thermo-hydromechanical(THM)processes and is significantly influenced by the microstructure.However,modeling FT in unsaturated PMs remains an open issue,and the influence of microstructure is not yet fully understood.To address these challenges,we propose a THM model for FT in PMs that considers microstructure and variable air content.In this work,a non-equilibrium thermodynamic approach is proposed to capture ice formation/melting,the microstructure is accounted for utilizing micromechanics,and the FT processes in air-entrained PMs are formulated within the proposed THM model.This model incorporates variable air void characteristics,e.g.air content,spacing factor,specific surface area,and supercooled water-filled regimes,and distinguishes the roles of air voids between freezing and thawing.The FT behaviors,including deformation,ice formation/melting,spacing factor,and pore water pressure evolutions,are focused.Comparisons with experimental results,confirm the capability of the present model.The results demonstrate the effects of variable air voids on the FT behavior of air-entrained PMs.The findings reveal that assuming fixed air void characteristics can lead to underestimation of pore pressure and deformation,particularly at low air content.Additionally,air voids act as cryo-pumps during freezing and when the cooling temperature stabilizes.During thawing,air voids supply gas to the melting sites(i.e.“gas escape”),preventing further significant deformation reduction.These results can provide novel insights for understanding the frost damage of PMs.展开更多
Understanding strain and fracture evolution in rock masses under climate change is crucial for slope stability.This study presents a fully coupled thermo-hydro-mechanical(THM)simulation of a rock slope at the Požá...Understanding strain and fracture evolution in rock masses under climate change is crucial for slope stability.This study presents a fully coupled thermo-hydro-mechanical(THM)simulation of a rock slope at the Požáry test site in the Czech Republic,integrating field tests and laboratory analyses.The simulations used the exactly measured slope geometry and incorporated a pre-existing upper slope fracture.Key constitutive models for fluid and vapor flow,heat conduction,and porosity-dependent permeability were coupled with a viscoplastic damage model to capture the THM behavior of the rock slope.Laboratory tests on three rock samples(A,B,and C)with varying elastic moduli and porosities informed the material properties for three corresponding models.Simulation results showed greater thermal changes in the upper sections of the slope due to increased exposure to thermal effects.Model A,with the highest elastic modulus,exhibited lower initial strain changes,while Model C showed significant early strain variations.After 30 d,Model A experienced a sudden strain decrease due to thermal contraction-induced damage.The critical fractured zone(CFZ)analysis revealed that rock contraction under cooling led to an increase in pore water pressure,exacerbating the damage.Model B highlighted the impact of geometrical asymmetry on the propagation of the damaged zone.Over time,the thermal effects increased plastic deformation in Model A,while Model C remained elastic and exhibited no damage.These findings have significant implications for assessing rock slope stability,particularly in predicting failure zones due to permeability reduction and pore water pressure generation.展开更多
In this study,a powerful thermo-hydro-mechanical(THM)coupling solution scheme for saturated poroelastic media involving brittle fracturing is developed.Under the local thermal non-equilibrium(LTNE)assumption,this sche...In this study,a powerful thermo-hydro-mechanical(THM)coupling solution scheme for saturated poroelastic media involving brittle fracturing is developed.Under the local thermal non-equilibrium(LTNE)assumption,this scheme seamlessly combines the material point method(MPM)for accurately tracking solid-phase deformation and heat transport,and the Eulerian finite element method(FEM)for effectively capturing fluid flow and heat advection-diffusion behavior.The proposed approach circumvents the substantial challenges posed by large nonlinear equation systems with the monolithic solution scheme.The staggered solution process strategically separates each physical field through explicit or implicit integration.The characteristic-based method is used to stabilize advection-dominated heat flows for efficient numerical implementation.Furthermore,a fractional step approach is employed to decompose fluid velocity and pressure,thereby suppressing pore pressure oscillation on the linear background grid.The fracturing initiation and propagation are simulated by a rate-dependent phase field model.Through a series of quasi-static and transient simulations,the exceptional performance and promising potential of the proposed model in addressing THM fracturing problems in poro-elastic media is demonstrated.展开更多
The main objective of this paper is to investigate and analyse the thermo-hydro-mechanical（THM） coupling phenomena and their influences on the repository safety.In this paper,the high-level waste（HLW） disposal con...The main objective of this paper is to investigate and analyse the thermo-hydro-mechanical（THM） coupling phenomena and their influences on the repository safety.In this paper,the high-level waste（HLW） disposal concept in drifts in clay formation with backfilled bentonite buffer is represented numerically using the CODE BRIGHT developed by the Technical University of Catalonia in Barcelona.The parameters of clay and bentonite used in the simulation are determined by laboratory and in situ experiments.The calculation results are presented to show the hydro-mechanical（HM） processes during the operation phase and the THM processes in the after-closure phase.According to the simulation results,the most probable critical processes for the disposal project have been represented and analyzed.The work also provides an input for additional development regarding the design,assessment and validation of the HLW disposal concept.展开更多
This paper presents the development of a coupled modeling approach to simulate cryogenic thermo-hydro-mechanical(THM)processes associated with a freezing medium,which is then implemented in the combined finite-discret...This paper presents the development of a coupled modeling approach to simulate cryogenic thermo-hydro-mechanical(THM)processes associated with a freezing medium,which is then implemented in the combined finite-discrete element method code(FDEM)for multi-physics simulation.The governing equations are deduced based on energy and mass conservation,and static equilibrium equations,considering water/ice phase change,where the strong couplings between multi-fields are supplemented by critical coupling parameters(e.g.unfrozen water content,permeability,and thermal conductivity).The proposed model is validated against laboratory and field experiments.Results show that the cryogenic THM model can well predict the evolution of strongly coupled processes observed in frozen media(e.g.heat transfer,water migration,and frost heave deformation),while also capturing,as emergent properties of the model,important phenomena(e.g.latent heat,cryogenic suction,ice expansion and distinct three-zone distribution)caused by water/ice phase change at laboratory and field scales,which are difficult to be all revealed by existing THM models.The novel modeling framework presents a gateway to further understanding and predicting the multi-physical coupling behavior of frozen media in cold regions.展开更多
In fractured geothermal reservoirs,the fracture networks and internal fluid flow behaviors can significantly impact the thermal performance.In this study,we proposed a non-Darcy rough discrete fracture network(NR-DFN)...In fractured geothermal reservoirs,the fracture networks and internal fluid flow behaviors can significantly impact the thermal performance.In this study,we proposed a non-Darcy rough discrete fracture network(NR-DFN)model that can simultaneously consider the fracture evolution and non-Darcy flow dynamics in studying the thermo-hydro-mechanical(THM)coupling processes for heat extraction in geothermal reservoir.We further employed the model on the Habanero enhanced geothermal systems(EGS)project located in Australia.First,our findings illustrate a clear spatial-temporal variation in the thermal stress and pressure perturbations,as well as uneven spatial distribution of shear failure in 3D fracture networks.Activated shear failure is mainly concentrated in the first fracture cluster.Secondly,channeling flow have also been observed in DFNs during heat extraction and are further intensified by the expansion of fractures driven by thermal stresses.Moreover,the combined effect of non-Darcy flow and fracture evolution triggers a rapid decline in the resulting heat rate and temperature.The NR-DFN model framework and the Habanero EGS's results illustrate the importance of both fracture evolution and non-Darcy flow on the efficiency of EGS production and have the potential to promote the development of more sustainable and efficient EGS operations for stakeholders.展开更多
In this study,a new numerical model of ring shear tester for shear band soil of landslide was established.The special feature of this model is that it considers the mechanism of friction-induced thermal pressurization...In this study,a new numerical model of ring shear tester for shear band soil of landslide was established.The special feature of this model is that it considers the mechanism of friction-induced thermal pressurization,which is potentially an important cause of high-speed catastrophic landslides.The key to the construction of this numerical ring shear model is to realize the THM(thermo-hydro-mechanical)dynamic coupling of soil particles,which includes the processes of frictional heating,thermal pressurization,and strength softening during shearing of solid particles.All of these are completed by using discrete element method.Based on this new model,the characteristics of shear stress change with shear displacement,as well as the variation of temperature and pore pressure in the specimen,are studied at shear rates of 0.055 m/s,0.06 m/s,0.109 m/s and 1.09 m/s,respectively.The results show that the peak strength and residual strength of specimen are significantly reduced when the mechanism of frictioninduced thermal pressurization is considered.The greater the shear rate is,the higher the temperature as well as the pore pressure is.The effect of shear rate on the shear strength is bidirectional.The simulation results demonstrate that this model can effectively simulate the mechanism of friction-induced thermal pressurization of shear band soil during ring shear process,and the shear strength softening in the process.The new numerical ring shear model established in this study is of great significance for studying the dynamic mechanism of high-speed catastrophic landslides.展开更多
In this work, a novel thermal–hydraulic–mechanical (THM) coupling model is developed, where the real geological parameters of the reservoir properties are embedded. Accordingly, nine schemes of CO_(2) injection well...In this work, a novel thermal–hydraulic–mechanical (THM) coupling model is developed, where the real geological parameters of the reservoir properties are embedded. Accordingly, nine schemes of CO_(2) injection well (IW) and CH_(4) production well (PW) are established, aiming to explore the behavior of free gases after CO_(2) is injected into the depleted Wufeng–Longmaxi shale. The results indicate the free CH4 or CO2 content in the shale fractures/matrix is invariably heterogeneous. The CO_(2) involvement facilitates the ratio of free CH_(4)/CO_(2) in the matrix to that in the fractures declines and tends to be stable with time. Different combinations of IW–PWs induce a difference in the ratio of the free CH4 to the free CO_(2), in the ratio of the free CH_(4)/CO_(2) in the matrix to that in the fractures, in the content of the recovered free CH_(4), and in the content of the trapped free CO_(2). Basically, when the IW locates at the bottom Wufeng–Longmaxi shale, a farther IW–PWs distance allows more CO2 in the free phase to be trapped;furthermore, no matter where the IW is, a shorter IW–PWs distance benefits by getting more CH_(4) in the free phase recovered from the depleted Wufeng–Longmaxi shale. Hopefully, this work is helpful in gaining knowledge about the shale-based CO_(2) injection technique.展开更多
Considering the thermal contact resistance and elastic wave impedance at the interface,in this paper we theoretically investigate the thermo-hydro-mechanical(THM)coupling dynamic response of bilayered saturated porous...Considering the thermal contact resistance and elastic wave impedance at the interface,in this paper we theoretically investigate the thermo-hydro-mechanical(THM)coupling dynamic response of bilayered saturated porous media.Fractional thermoelastic theory is applied to porous media with imperfect thermal and mechanical contact.The analytical solutions of the dynamic response of the bilayered saturated porous media are obtained in frequency domain.Furthermore,the effects of fractional derivative parameters and thermal contact resistance on the dynamic response of such media are systematically discussed.Results show that the effects of fractional derivative parameters on the dynamic response of bilayered saturated porous media are related to the thermal contact resistance at the interface.With increasing thermal contact resistance,the displacement,pore water pressure,and stress decrease gradually.展开更多
In examining potential host rocks for such purposes as the disposal of high-level radioactive wastes,it is important to understand the coupled thermo-hydro-mechanical（THM） behavior of a porous medium.A rigorous and ...In examining potential host rocks for such purposes as the disposal of high-level radioactive wastes,it is important to understand the coupled thermo-hydro-mechanical（THM） behavior of a porous medium.A rigorous and fully unified coupled thermo-hydro-mechanical model for unsaturated porous media is required to simulate the complex coupling mechanisms involved.Based on modified Darcy＇s and Fourier＇s laws,equations of mechanical equilibrium,mass conservation and energy conservation are derived by introducing void ratio and volumetric liquid water content into the model.The newly derived model takes into account the effects of temperature on the dynamic viscosity of liquid water and void ratio,the influence of liquid flow on temperature gradient（thermo-osmosis）,the influence on mass and heat conservation equations,and the influence of heat flow on water pressure gradient and thermal convection.The new coupled THM constitutive model is constructed by a finite element program and is used to simulate the coupled behavior of a tunnel during excavation,ventilation and concrete lining stages.Oil and gas engineering,underground disposal of nuclear waste and tunnel engineering may be benefited from the development of the new model.展开更多
As is known, high-level radioactive waste （HLW） is commonly heat-emitting. Heat output from HLWwilldissipate through the surrounding rocks and induce complex thermo-hydro-mechanical-chemical（THMC） processes. In hi...As is known, high-level radioactive waste （HLW） is commonly heat-emitting. Heat output from HLWwilldissipate through the surrounding rocks and induce complex thermo-hydro-mechanical-chemical（THMC） processes. In highly consolidated clayey rocks, thermal effects are particularly significantbecause of their very low permeability and water-saturated state. Thermal impact on the integrity of thegeological barriers is of most importance with regard to the long-term safety of repositories. This studyfocuses on numerical analysis of thermal effects on hydro-mechanical properties of clayey rock using acoupled thermo-mechanical multiphase flow （TH2M） model which is implemented in the finite elementprogramme OpenGeoSys （OGS）. The material properties of the numerical model are characterised by atransversal isotropic elastic model based on Hooke＇s law, a non-isothermal multiphase flow model basedon van Genuchten function and Darcy＇s law, and a transversal isotropic heat transport model based onFourier＇s law. In the numerical approaches, special attention has been paid to the thermal expansion ofthree different phases： gas, fluid and solid, which could induce changes in pore pressure and porosity.Furthermore, the strong swelling and shrinkage behaviours of clayey material are also considered in thepresent model. The model has been applied to simulate a laboratory heating experiment on claystone.The numerical model gives a satisfactory representation of the observed material behaviour in thelaboratory experiment. The comparison of the calculated results with the laboratory findings verifies thatthe simulation with the present numerical model could provide a deeper understanding of the observedeffects. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.展开更多
Geo-energy and geo-engineering applications,such as improved oil recovery(IOR),geologic carbon storage,and enhanced geothermal systems(EGSs),involve coupled thermo-hydro-mechanical(THM)processes that result from fluid...Geo-energy and geo-engineering applications,such as improved oil recovery(IOR),geologic carbon storage,and enhanced geothermal systems(EGSs),involve coupled thermo-hydro-mechanical(THM)processes that result from fluid injection and production.In some cases,reservoirs are highly fractured and the geomechanical response is controlled by fractures.Therefore,fractures should explicitly be included into numerical models to realistically simulate the THM responses of the subsurface.In this study,we perform coupled THM numerical simulations of water injection into naturally fractured reservoirs(NFRs)using CODE_BRIGHT and TOUGH-UDEC codes.CODE_BRIGHT is a finite element method(FEM)code that performs fully coupled THM analysis in geological media and TOUGH-UDEC sequentially solves coupled THM processes by combining a finite volume method(FVM)code that solves nonisothermal multiphase flow(TOUGH2)with a distinct element method(DEM)code that solves the mechanical problem(UDEC).First,we validate the two codes against a semi-analytical solution for water injection into a single deformable fracture considering variable permeability based on the cubic law.Then,we compare simulation results of the two codes in an idealized conceptual model that includes one horizontal fracture and in a more realistic model with multiple fractures.Each code models fractures differently.UDEC calculates fracture deformation from the fracture normal and shear stiffnesses,while CODE_BRIGHT treats fractures as equivalent porous media and uses the equivalent Young’s modulus and Poisson’s ratio of the fracture.Finally,we obtain comparable results of pressure,temperature,stress and displacement distributions and evolutions for the single horizontal fracture model.Despite some similarities,the two codes provide increasingly different results as model complexity increases.These differences highlight the challenging task of accurately modeling coupled THM processes in fractured media given their high nonlinearity.展开更多
As one of the most important ways to reduce the greenhouse gas emission,carbon dioxide（CO2）enhanced gas recovery（CO2-EGR） is attractive since the gas recovery can be enhanced simultaneously with CO2sequestration.B...As one of the most important ways to reduce the greenhouse gas emission,carbon dioxide（CO2）enhanced gas recovery（CO2-EGR） is attractive since the gas recovery can be enhanced simultaneously with CO2sequestration.Based on the existing equation of state（EOS） module of TOUGH2 MP,extEOS7C is developed to calculate the phase partition of H2O-CO2-CH4-NaCl mixtures accurately with consideration of dissolved NaCI and brine properties at high pressure and temperature conditions.Verifications show that it can be applied up to the pressure of 100 MPa and temperature of 150℃.The module was implemented in the linked simulator TOUGH2MP-FLAC3 D for the coupled hydro-mechanical simulations.A simplified three-dimensional（3D）1/4 model（2.2 km×1 km×1 km） which consists of the whole reservoir,caprock and baserock was generated based on the geological conditions of a gas field in the North German Basin.The simulation results show that,under an injection rate of 200,000 t/yr and production rate of 200,000 sm3/d,CO2breakthrough occurred in the case with the initial reservoir pressure of 5 MPa but did not occur in the case of 42 MPa.Under low pressure conditions,the pressure driven horizontal transport is the dominant process;while under high pressure conditions,the density driven vertical flow is dominant.Under the considered conditions,the CO2-EGR caused only small pressure changes.The largest pore pressure increase（2 MPa） and uplift（7 mm） occurred at the caprock bottom induced by only CO2injection.The caprock had still the primary stress state and its integrity was not affected.The formation water salinity and temperature variations of ±20℃ had small influences on the CO2-EGR process.In order to slow down the breakthrough,it is suggested that CO2-EGR should be carried out before the reservoir pressure drops below the critical pressure of CO2.展开更多
Snowfall in the Tianshan Mountains in China is frequent during winter;thus,avalanches have become a severe issue in snow-covered areas.Accumulation and metamorphosis,as well as hydrothermal exchanges with the environm...Snowfall in the Tianshan Mountains in China is frequent during winter;thus,avalanches have become a severe issue in snow-covered areas.Accumulation and metamorphosis,as well as hydrothermal exchanges with the environment,considerably affect the stability of snow on slopes.Therefore,a hydrothermal model of snow cover and its underlying surfaces must be developed on the basis of meteorological data to predict and help manage avalanches.This study adopted the conceptual model of snow as a porous medium and quantitatively analysed its internal physical processes on the basis of the thermal exchanges amongst its components.The effects of local meteorological factors on snow structure and the redistribution of energy and mass inside the snow cover in the Tianshan Mountains were simulated.Simulation results showed that deformation as a result of overlying snow and sublimation of snow cover at the bottom is the main cause of density variation in the vertical profile of snow cover.Temperature drives water movement in snow.The low-density area of the bottom snow is the result of temperature gradient.The simulation results of the long-term snow internal mass distribution obtained by the method established in this study are highly consistent with the actual observed trend of variation.Such consistency indicates an accurate simulation of the physical characteristics of snow cover in small and microscale metamorphism in the Tianshan Mountains during the stable period.展开更多
In this paper,the thermo-hydro-mechanical(THM)response of claystone is studied via a series of parametric studies,considering the evolution of mechanical properties and deformation behavior of corroded steel.The numer...In this paper,the thermo-hydro-mechanical(THM)response of claystone is studied via a series of parametric studies,considering the evolution of mechanical properties and deformation behavior of corroded steel.The numerical simulations are performed by using a coupled THM finite element code and two different constitutive models:a visco-elastoplastic model for geological formation and a von Mises type model for steel liner.The mechanical properties and deformation behavior of corroded steel are described in a conceptual model.Finally,a disposal tunnel supported by a steel liner is studied and a series of parametric studies is defined to demonstrate the corrosion effects of steel liner on the THM response of the claystone.The comparison of different numerical calculations exhibits that the volumetric expansion related to corrosion products has an important impact on the stress and displacement fields in the claystone surrounding the disposal tunnel.However,the evolutions of temperature and liquid pressure in the claystone are essentially controlled by its THM properties and independent of the steel corrosion.展开更多
Damage caused by frost heave leads to costly maintenance in cold regions, like Hokkaido, Japan. Therefore, thestudy of the frost mechanism with experimental and numerical methods has been of great interest. Numerousmo...Damage caused by frost heave leads to costly maintenance in cold regions, like Hokkaido, Japan. Therefore, thestudy of the frost mechanism with experimental and numerical methods has been of great interest. Numerousmodels have been developed to describe the freezing process of saturated soil, which differs from the partiallysaturated conditions in the field. In fact, most subsurface soils are unsaturated. The freezing process of partiallysaturated soils is more complex than saturated soils, as the governing equations show strongly nonlinear characteristics. This study proposes a thermo-hydro-mechanical coupled model considering the heat transfer, waterinfiltration, and deformation of partially saturated soil to reproduce the freezing process of partially saturatedfrost susceptible soils distributed in Hokkaido. This model better considers the water-ice phase change and soilfreezing characteristic curve (SFCC) during freezing under field conditions. The results from the multiphysicssimulations agree well with the frost heave and water migration data from frost heave tests of Touryo soil andFujinomori soil. In addition, this study discussed the influence of the various factors on frost heave amount,including temperature gradients, overburden pressures, water supply conditions, cooling rates, and initial saturation. The simulation results indicate that the frost heave ratio is proportional to the initial degree of saturationand is inversely proportional to the cooling rate and overburden pressure.Moreover, simulation under the open system generates much more frost heave than under the closed system.Finally, the main features of the proposed model are revealed by simulating a closed-system frost heave test. Thesimulation results indicate that the proposed model adequately captures the coupling characteristics of water andice redistribution, temperature development, hydraulic conductivity, and suction in the freezing process. Togetherwith the decreased hydraulic conductivity, the increased suction controls the water flow in the freezing zone. Theinflow water driven by cryogenic suction gradient feeds the ice formation, leads to a rapid increase in total watercontent, expanding the voids that exceed the initial porosity and contributing to the frost heave.展开更多
This study numerically investigates the thermo-poromechanical effects in a Canadian geothermal reservoir caused by long-term fluid production and injection.Using finite element modeling,it explores pore pressure diffu...This study numerically investigates the thermo-poromechanical effects in a Canadian geothermal reservoir caused by long-term fluid production and injection.Using finite element modeling,it explores pore pressure diffusion and thermal dynamics,incorporating both the geological structure of the rock mass and faults.The simulations utilize the IAPWS(International Association for the Properties of Water and Steam)equations to model fluid density and viscosity,ensuring realistic representations of heterogeneous pressure fields.The system replicates a doublet configuration within a faulted zone,featuring two hydraulically stimulated fractures.The primary aim is to assess the likelihood of fault reactivation under varying in-situ stress conditions over a 100-year geothermal operation.Results show that stress distribution is largely influenced by thermal stresses along the fluid circulation pathway,with fluid velocity and temperature gradients affecting reservoir stability.Minimal pore pressure changes highlight the dominant role of thermal stresses in controlling fault behavior.The analysis indicates no potential for fault reactivation,as slip tendency values remain below the critical threshold,even when accounting for reduced mechanical properties using the Hoek-Brown criterion.Thermal effects continue to influence the surrounding rock throughout the operational period,suggesting that the reservoir maintains mechanical stability conducive to sustained geothermal production and injection.These findings provide valuable insights into the long-term safety and behavior of geothermal reservoirs,offering important implications for future geothermal energy development and management strategies.展开更多
基金funded by the European Union's Horizon 2020 research and innovation programme under a grant agreement (Grant No.847593)partially supported by the Fundamental Research Funds for the Central Universities (Grant No.22120240029).
文摘This study presents a fully coupled thermo-hydro-mechanical (THM) constitutive model for clay rocks. The model is formulated within the elastic-viscoplasticity framework, which considers nonlinearity and softening after peak strength, anisotropy of stiffness and strength, as well as permeability variation due to damage. In addition, the mechanical properties are coupled with thermal phenomena and accumulated plastic strains. The adopted nonlocal and viscoplastic approaches enhance numerical efficiency and provide the possibility to simulate localization phenomena. The model is validated against experimental data from laboratory tests conducted on Callovo-Oxfordian (COx) claystone samples that are initially unsaturated and under suction. The tests include a thermal phase where the COx specimens are subjected to different temperature increases. A good agreement with experimental data is obtained. In addition, parametric analyses are carried out to investigate the influence of the hydraulic boundary conditions (B.C.) and post-failure behavior models on the THM behavior evolution. It is shown that different drainage conditions affect the thermally induced pore pressures that, in turn, influence the onset of softening. The constitutive model presented constitutes a promising approach for simulating the most important features of the THM behavior of clay rocks. It is a tool with a high potential for application to several relevant case studies, such as thermal fracturing analysis of nuclear waste disposal systems.
基金supported by the National Natural Science Foundation of China(Grant No.52174117)the Universitylocal Government Scientific and Technical Cooperation Cultivation Project of Ordos Institute-LNTU(Grant No.YJY-XD-2024-A-009)+2 种基金the Basic Scientific Research Project of Liaoning Provincial Department of Education(Grant No.JYTZD2023073)the Liaoning Revitalization Talents Program(XLYC2203139)the Liaoning Provincial Natural Science Foundation Program(Excellent Youth Fund)(Grant No.2024JH3/10200043).
文摘The utilization of coalbed methane(CBM)cannot only alleviate the energy crisis,but also reduce greenhouse gas emissions.Gas injection is an effective method to enhance CBM recovery.Compared to single-gas injection,the injection of CO_(2)/N_(2) mixtures can balance the sharp decline in permeability caused by pure CO_(2) and the premature breakthrough by pure N_(2).In this study,a more comprehensive thermo-hydro-mechanical(THM)coupled mathematical model was developed,incorporating processes such as ternary gas non-isothermal adsorption,gas dissolution in water,gas-water two-phase flow,energy exchange,and coal deformation.After experimental validation,the model was applied to simulate the entire process of gas mixtures for enhanced CBM recovery(GM-ECBM).Results indicate that the permeability near the production well(Pw)initially decreases due to increased effective stress,then increases as a result of CH_(4) desorption.Near the injection well(Iw),the permeability first increases due to reduced effective stress and later stabilizes under the combined effects of effective stress and CO_(2)/N_(2) adsorption.The initial CH_(4) pressure and coal seam permeability have the most significant impact on CH_(4) production,while the coal seam permeability and temperature significantly affect CO_(2)/N_(2) injection.As the coal seam permeability increases,the optimal CO_(2)/N_(2) ratio also increases accordingly.These findings provide important theoretical guidance for improving GM-ECBM efficiency in coal seams with varying permeabilities.
基金Project(11072269) supported by the National Natural Science Foundation of ChinaProject(20090162110066) supported by the Research Fund for the Doctoral Program of Higher Education of China
文摘Based on fluid mechanics, thermodynamics and damage mechanics, thermal-hydro-mechanical （THM） coupling damage model of brittle rock is established by analyzing THM coupling mechanism, where THM coupling damage variable DTHM is dominated by TH coupling damage variable DTH, TM coupling damage variable DTM and HM coupling damage variable DHM, and DTH is firstly expressed in term of dimensionless total thermal conductivity of the water Nu. Permeability test, uni-axial compression test and THM coupling test are conducted to measure the permeability, elastic modulus and THM coupling stress-strain curves of brittle rock. The tested values of THM coupling elastic modulus E＇HM are in good agreement with the predicted values of THM coupling elastic modulus ETHM, which can verify the newly established THM coupling damage model.
基金the funding support from the National Natural Science Foundation of China(Grant Nos.52350004 and 51925903).
文摘The freeze-thaw(FT)behavior of porous materials(PMs)involves the coupling of the thermo-hydromechanical(THM)processes and is significantly influenced by the microstructure.However,modeling FT in unsaturated PMs remains an open issue,and the influence of microstructure is not yet fully understood.To address these challenges,we propose a THM model for FT in PMs that considers microstructure and variable air content.In this work,a non-equilibrium thermodynamic approach is proposed to capture ice formation/melting,the microstructure is accounted for utilizing micromechanics,and the FT processes in air-entrained PMs are formulated within the proposed THM model.This model incorporates variable air void characteristics,e.g.air content,spacing factor,specific surface area,and supercooled water-filled regimes,and distinguishes the roles of air voids between freezing and thawing.The FT behaviors,including deformation,ice formation/melting,spacing factor,and pore water pressure evolutions,are focused.Comparisons with experimental results,confirm the capability of the present model.The results demonstrate the effects of variable air voids on the FT behavior of air-entrained PMs.The findings reveal that assuming fixed air void characteristics can lead to underestimation of pore pressure and deformation,particularly at low air content.Additionally,air voids act as cryo-pumps during freezing and when the cooling temperature stabilizes.During thawing,air voids supply gas to the melting sites(i.e.“gas escape”),preventing further significant deformation reduction.These results can provide novel insights for understanding the frost damage of PMs.
基金support from the European Commission via a Marie Curie Fellowship(Grant No.101033084)awarded to Dr.Saeed Tourchi(corresponding author)the Research Grant Office at Sharif University of Technology for grants G4010902 and QB020105funding from the TACR project SS02030023,Rock Environment and Resources,under the“Environment for Life”program and the Institutional Research Plan RVO67985891 of the Institute of Rock Structure and Mechanics of the Czech Academy of Sciences.
文摘Understanding strain and fracture evolution in rock masses under climate change is crucial for slope stability.This study presents a fully coupled thermo-hydro-mechanical(THM)simulation of a rock slope at the Požáry test site in the Czech Republic,integrating field tests and laboratory analyses.The simulations used the exactly measured slope geometry and incorporated a pre-existing upper slope fracture.Key constitutive models for fluid and vapor flow,heat conduction,and porosity-dependent permeability were coupled with a viscoplastic damage model to capture the THM behavior of the rock slope.Laboratory tests on three rock samples(A,B,and C)with varying elastic moduli and porosities informed the material properties for three corresponding models.Simulation results showed greater thermal changes in the upper sections of the slope due to increased exposure to thermal effects.Model A,with the highest elastic modulus,exhibited lower initial strain changes,while Model C showed significant early strain variations.After 30 d,Model A experienced a sudden strain decrease due to thermal contraction-induced damage.The critical fractured zone(CFZ)analysis revealed that rock contraction under cooling led to an increase in pore water pressure,exacerbating the damage.Model B highlighted the impact of geometrical asymmetry on the propagation of the damaged zone.Over time,the thermal effects increased plastic deformation in Model A,while Model C remained elastic and exhibited no damage.These findings have significant implications for assessing rock slope stability,particularly in predicting failure zones due to permeability reduction and pore water pressure generation.
基金supported by National Natural Science Foundation of China(Grant No.42377149)the Research Grants Council of Hong Kong(General Research Fund Project No.17202423).
文摘In this study,a powerful thermo-hydro-mechanical(THM)coupling solution scheme for saturated poroelastic media involving brittle fracturing is developed.Under the local thermal non-equilibrium(LTNE)assumption,this scheme seamlessly combines the material point method(MPM)for accurately tracking solid-phase deformation and heat transport,and the Eulerian finite element method(FEM)for effectively capturing fluid flow and heat advection-diffusion behavior.The proposed approach circumvents the substantial challenges posed by large nonlinear equation systems with the monolithic solution scheme.The staggered solution process strategically separates each physical field through explicit or implicit integration.The characteristic-based method is used to stabilize advection-dominated heat flows for efficient numerical implementation.Furthermore,a fractional step approach is employed to decompose fluid velocity and pressure,thereby suppressing pore pressure oscillation on the linear background grid.The fracturing initiation and propagation are simulated by a rate-dependent phase field model.Through a series of quasi-static and transient simulations,the exceptional performance and promising potential of the proposed model in addressing THM fracturing problems in poro-elastic media is demonstrated.
基金financed and supported by the German research institute "Gesellschaft für Anlagen-und Reaktorsicherheit (GRS) mbH"
文摘The main objective of this paper is to investigate and analyse the thermo-hydro-mechanical（THM） coupling phenomena and their influences on the repository safety.In this paper,the high-level waste（HLW） disposal concept in drifts in clay formation with backfilled bentonite buffer is represented numerically using the CODE BRIGHT developed by the Technical University of Catalonia in Barcelona.The parameters of clay and bentonite used in the simulation are determined by laboratory and in situ experiments.The calculation results are presented to show the hydro-mechanical（HM） processes during the operation phase and the THM processes in the after-closure phase.According to the simulation results,the most probable critical processes for the disposal project have been represented and analyzed.The work also provides an input for additional development regarding the design,assessment and validation of the HLW disposal concept.
基金supported by the Natural Sciences and Engineering Research Council of Canada (NSERC)Discovery Grants 341275,NSERC CRDPJ 543894-19,and NSERC/Energi Simulation Industrial Research Chair programfunding he received from Lassonde International Graduate Scholarship in Mining at the University of Toronto+1 种基金supported by the FCE Start-up Fund for New Recruits at the Hong Kong Polytechnic University (P0034042)the Early Career Scheme and the General Research Fund Scheme of the Research Grants Council of the Hong Kong SAR,China (Project Nos.PolyU 25220021 and PolyU 15227222).
文摘This paper presents the development of a coupled modeling approach to simulate cryogenic thermo-hydro-mechanical(THM)processes associated with a freezing medium,which is then implemented in the combined finite-discrete element method code(FDEM)for multi-physics simulation.The governing equations are deduced based on energy and mass conservation,and static equilibrium equations,considering water/ice phase change,where the strong couplings between multi-fields are supplemented by critical coupling parameters(e.g.unfrozen water content,permeability,and thermal conductivity).The proposed model is validated against laboratory and field experiments.Results show that the cryogenic THM model can well predict the evolution of strongly coupled processes observed in frozen media(e.g.heat transfer,water migration,and frost heave deformation),while also capturing,as emergent properties of the model,important phenomena(e.g.latent heat,cryogenic suction,ice expansion and distinct three-zone distribution)caused by water/ice phase change at laboratory and field scales,which are difficult to be all revealed by existing THM models.The novel modeling framework presents a gateway to further understanding and predicting the multi-physical coupling behavior of frozen media in cold regions.
基金funded by the National Natural Science Foundation of China (No.U22A20166)Science and Technology Foundation of Guizhou Province (No.QKHJC-ZK[2023]YB074)+2 种基金Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical EngineeringInstitute of Rock and Soil MechanicsChinese Academy of Sciences (No.SKLGME022009)。
文摘In fractured geothermal reservoirs,the fracture networks and internal fluid flow behaviors can significantly impact the thermal performance.In this study,we proposed a non-Darcy rough discrete fracture network(NR-DFN)model that can simultaneously consider the fracture evolution and non-Darcy flow dynamics in studying the thermo-hydro-mechanical(THM)coupling processes for heat extraction in geothermal reservoir.We further employed the model on the Habanero enhanced geothermal systems(EGS)project located in Australia.First,our findings illustrate a clear spatial-temporal variation in the thermal stress and pressure perturbations,as well as uneven spatial distribution of shear failure in 3D fracture networks.Activated shear failure is mainly concentrated in the first fracture cluster.Secondly,channeling flow have also been observed in DFNs during heat extraction and are further intensified by the expansion of fractures driven by thermal stresses.Moreover,the combined effect of non-Darcy flow and fracture evolution triggers a rapid decline in the resulting heat rate and temperature.The NR-DFN model framework and the Habanero EGS's results illustrate the importance of both fracture evolution and non-Darcy flow on the efficiency of EGS production and have the potential to promote the development of more sustainable and efficient EGS operations for stakeholders.
基金financed by the Research Foundation of Key Laboratory of Geological Hazards on Three Gorges Reservoir Area(China Three Gorges University),Ministry of Education(Grant No.2020KDZ05)the National Natural Science Foundation of China(Grant Nos.42077239,41702378)。
文摘In this study,a new numerical model of ring shear tester for shear band soil of landslide was established.The special feature of this model is that it considers the mechanism of friction-induced thermal pressurization,which is potentially an important cause of high-speed catastrophic landslides.The key to the construction of this numerical ring shear model is to realize the THM(thermo-hydro-mechanical)dynamic coupling of soil particles,which includes the processes of frictional heating,thermal pressurization,and strength softening during shearing of solid particles.All of these are completed by using discrete element method.Based on this new model,the characteristics of shear stress change with shear displacement,as well as the variation of temperature and pore pressure in the specimen,are studied at shear rates of 0.055 m/s,0.06 m/s,0.109 m/s and 1.09 m/s,respectively.The results show that the peak strength and residual strength of specimen are significantly reduced when the mechanism of frictioninduced thermal pressurization is considered.The greater the shear rate is,the higher the temperature as well as the pore pressure is.The effect of shear rate on the shear strength is bidirectional.The simulation results demonstrate that this model can effectively simulate the mechanism of friction-induced thermal pressurization of shear band soil during ring shear process,and the shear strength softening in the process.The new numerical ring shear model established in this study is of great significance for studying the dynamic mechanism of high-speed catastrophic landslides.
基金This study was financially supported by the National Natural Science Foundation of China(Grant Nos.51704197 and 11872258)。
文摘In this work, a novel thermal–hydraulic–mechanical (THM) coupling model is developed, where the real geological parameters of the reservoir properties are embedded. Accordingly, nine schemes of CO_(2) injection well (IW) and CH_(4) production well (PW) are established, aiming to explore the behavior of free gases after CO_(2) is injected into the depleted Wufeng–Longmaxi shale. The results indicate the free CH4 or CO2 content in the shale fractures/matrix is invariably heterogeneous. The CO_(2) involvement facilitates the ratio of free CH_(4)/CO_(2) in the matrix to that in the fractures declines and tends to be stable with time. Different combinations of IW–PWs induce a difference in the ratio of the free CH4 to the free CO_(2), in the ratio of the free CH_(4)/CO_(2) in the matrix to that in the fractures, in the content of the recovered free CH_(4), and in the content of the trapped free CO_(2). Basically, when the IW locates at the bottom Wufeng–Longmaxi shale, a farther IW–PWs distance allows more CO2 in the free phase to be trapped;furthermore, no matter where the IW is, a shorter IW–PWs distance benefits by getting more CH_(4) in the free phase recovered from the depleted Wufeng–Longmaxi shale. Hopefully, this work is helpful in gaining knowledge about the shale-based CO_(2) injection technique.
基金Project supported by the National Natural Science Foundation of China(Nos.52108347 and 51779217)the Primary Research and Development Plan of Zhejiang Province(Nos.2019C03120 and 2020C01147),China。
文摘Considering the thermal contact resistance and elastic wave impedance at the interface,in this paper we theoretically investigate the thermo-hydro-mechanical(THM)coupling dynamic response of bilayered saturated porous media.Fractional thermoelastic theory is applied to porous media with imperfect thermal and mechanical contact.The analytical solutions of the dynamic response of the bilayered saturated porous media are obtained in frequency domain.Furthermore,the effects of fractional derivative parameters and thermal contact resistance on the dynamic response of such media are systematically discussed.Results show that the effects of fractional derivative parameters on the dynamic response of bilayered saturated porous media are related to the thermal contact resistance at the interface.With increasing thermal contact resistance,the displacement,pore water pressure,and stress decrease gradually.
基金Supported by the National Natural Science Foundation of China (50579087,50720135906, 50539050)CAS/SAFEA International Partnership Program for Creative Research Teams
文摘In examining potential host rocks for such purposes as the disposal of high-level radioactive wastes,it is important to understand the coupled thermo-hydro-mechanical（THM） behavior of a porous medium.A rigorous and fully unified coupled thermo-hydro-mechanical model for unsaturated porous media is required to simulate the complex coupling mechanisms involved.Based on modified Darcy＇s and Fourier＇s laws,equations of mechanical equilibrium,mass conservation and energy conservation are derived by introducing void ratio and volumetric liquid water content into the model.The newly derived model takes into account the effects of temperature on the dynamic viscosity of liquid water and void ratio,the influence of liquid flow on temperature gradient（thermo-osmosis）,the influence on mass and heat conservation equations,and the influence of heat flow on water pressure gradient and thermal convection.The new coupled THM constitutive model is constructed by a finite element program and is used to simulate the coupled behavior of a tunnel during excavation,ventilation and concrete lining stages.Oil and gas engineering,underground disposal of nuclear waste and tunnel engineering may be benefited from the development of the new model.
基金supported by BMWi (Bundesministerium für Wirtschaft und Energie,Berlin)
文摘As is known, high-level radioactive waste （HLW） is commonly heat-emitting. Heat output from HLWwilldissipate through the surrounding rocks and induce complex thermo-hydro-mechanical-chemical（THMC） processes. In highly consolidated clayey rocks, thermal effects are particularly significantbecause of their very low permeability and water-saturated state. Thermal impact on the integrity of thegeological barriers is of most importance with regard to the long-term safety of repositories. This studyfocuses on numerical analysis of thermal effects on hydro-mechanical properties of clayey rock using acoupled thermo-mechanical multiphase flow （TH2M） model which is implemented in the finite elementprogramme OpenGeoSys （OGS）. The material properties of the numerical model are characterised by atransversal isotropic elastic model based on Hooke＇s law, a non-isothermal multiphase flow model basedon van Genuchten function and Darcy＇s law, and a transversal isotropic heat transport model based onFourier＇s law. In the numerical approaches, special attention has been paid to the thermal expansion ofthree different phases： gas, fluid and solid, which could induce changes in pore pressure and porosity.Furthermore, the strong swelling and shrinkage behaviours of clayey material are also considered in thepresent model. The model has been applied to simulate a laboratory heating experiment on claystone.The numerical model gives a satisfactory representation of the observed material behaviour in thelaboratory experiment. The comparison of the calculated results with the laboratory findings verifies thatthe simulation with the present numerical model could provide a deeper understanding of the observedeffects. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.
基金financial support received from the“Iran’s Ministry of Science Research and Technology”(PhD students’sabbatical grants)funding from the European Research Council under the European Union’s Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST(www.georest.eu)(Grant Agreement No.801809)+1 种基金support by the Korea-EU Joint Research Program of the National Research Foundation of Korea through Grant No.NRF2015K1A3A7A03074226funded by the Korean Government’s Ministry of Science and Information and Communication Technology(ICT)in the framework of the European Union’s Horizon 2020 Research and Innovation Program(Grant No.691728)。
文摘Geo-energy and geo-engineering applications,such as improved oil recovery(IOR),geologic carbon storage,and enhanced geothermal systems(EGSs),involve coupled thermo-hydro-mechanical(THM)processes that result from fluid injection and production.In some cases,reservoirs are highly fractured and the geomechanical response is controlled by fractures.Therefore,fractures should explicitly be included into numerical models to realistically simulate the THM responses of the subsurface.In this study,we perform coupled THM numerical simulations of water injection into naturally fractured reservoirs(NFRs)using CODE_BRIGHT and TOUGH-UDEC codes.CODE_BRIGHT is a finite element method(FEM)code that performs fully coupled THM analysis in geological media and TOUGH-UDEC sequentially solves coupled THM processes by combining a finite volume method(FVM)code that solves nonisothermal multiphase flow(TOUGH2)with a distinct element method(DEM)code that solves the mechanical problem(UDEC).First,we validate the two codes against a semi-analytical solution for water injection into a single deformable fracture considering variable permeability based on the cubic law.Then,we compare simulation results of the two codes in an idealized conceptual model that includes one horizontal fracture and in a more realistic model with multiple fractures.Each code models fractures differently.UDEC calculates fracture deformation from the fracture normal and shear stiffnesses,while CODE_BRIGHT treats fractures as equivalent porous media and uses the equivalent Young’s modulus and Poisson’s ratio of the fracture.Finally,we obtain comparable results of pressure,temperature,stress and displacement distributions and evolutions for the single horizontal fracture model.Despite some similarities,the two codes provide increasingly different results as model complexity increases.These differences highlight the challenging task of accurately modeling coupled THM processes in fractured media given their high nonlinearity.
基金funded by the National Natural Science Foundation of China(Grant No.NSFC51374147)the German Society for Petroleum and Coal Science and Technology(Grant No.DGMK680-4)
文摘As one of the most important ways to reduce the greenhouse gas emission,carbon dioxide（CO2）enhanced gas recovery（CO2-EGR） is attractive since the gas recovery can be enhanced simultaneously with CO2sequestration.Based on the existing equation of state（EOS） module of TOUGH2 MP,extEOS7C is developed to calculate the phase partition of H2O-CO2-CH4-NaCl mixtures accurately with consideration of dissolved NaCI and brine properties at high pressure and temperature conditions.Verifications show that it can be applied up to the pressure of 100 MPa and temperature of 150℃.The module was implemented in the linked simulator TOUGH2MP-FLAC3 D for the coupled hydro-mechanical simulations.A simplified three-dimensional（3D）1/4 model（2.2 km×1 km×1 km） which consists of the whole reservoir,caprock and baserock was generated based on the geological conditions of a gas field in the North German Basin.The simulation results show that,under an injection rate of 200,000 t/yr and production rate of 200,000 sm3/d,CO2breakthrough occurred in the case with the initial reservoir pressure of 5 MPa but did not occur in the case of 42 MPa.Under low pressure conditions,the pressure driven horizontal transport is the dominant process;while under high pressure conditions,the density driven vertical flow is dominant.Under the considered conditions,the CO2-EGR caused only small pressure changes.The largest pore pressure increase（2 MPa） and uplift（7 mm） occurred at the caprock bottom induced by only CO2injection.The caprock had still the primary stress state and its integrity was not affected.The formation water salinity and temperature variations of ±20℃ had small influences on the CO2-EGR process.In order to slow down the breakthrough,it is suggested that CO2-EGR should be carried out before the reservoir pressure drops below the critical pressure of CO2.
基金supported by the 13th Five-year Informatization Plan of the Chinese Academy of Sciences,Grant No.XXH13506 and XXH13505-220Data sharing fundamental program for Construction of the National Science Technology Infrastructure Platform(Grant No.Y719H71006)。
文摘Snowfall in the Tianshan Mountains in China is frequent during winter;thus,avalanches have become a severe issue in snow-covered areas.Accumulation and metamorphosis,as well as hydrothermal exchanges with the environment,considerably affect the stability of snow on slopes.Therefore,a hydrothermal model of snow cover and its underlying surfaces must be developed on the basis of meteorological data to predict and help manage avalanches.This study adopted the conceptual model of snow as a porous medium and quantitatively analysed its internal physical processes on the basis of the thermal exchanges amongst its components.The effects of local meteorological factors on snow structure and the redistribution of energy and mass inside the snow cover in the Tianshan Mountains were simulated.Simulation results showed that deformation as a result of overlying snow and sublimation of snow cover at the bottom is the main cause of density variation in the vertical profile of snow cover.Temperature drives water movement in snow.The low-density area of the bottom snow is the result of temperature gradient.The simulation results of the long-term snow internal mass distribution obtained by the method established in this study are highly consistent with the actual observed trend of variation.Such consistency indicates an accurate simulation of the physical characteristics of snow cover in small and microscale metamorphism in the Tianshan Mountains during the stable period.
基金supported by the National Natural Science Foundation of China (NSFC) (Grant No. 51609081)
文摘In this paper,the thermo-hydro-mechanical(THM)response of claystone is studied via a series of parametric studies,considering the evolution of mechanical properties and deformation behavior of corroded steel.The numerical simulations are performed by using a coupled THM finite element code and two different constitutive models:a visco-elastoplastic model for geological formation and a von Mises type model for steel liner.The mechanical properties and deformation behavior of corroded steel are described in a conceptual model.Finally,a disposal tunnel supported by a steel liner is studied and a series of parametric studies is defined to demonstrate the corrosion effects of steel liner on the THM response of the claystone.The comparison of different numerical calculations exhibits that the volumetric expansion related to corrosion products has an important impact on the stress and displacement fields in the claystone surrounding the disposal tunnel.However,the evolutions of temperature and liquid pressure in the claystone are essentially controlled by its THM properties and independent of the steel corrosion.
基金This research was supported in part by Grant-in-Aids for Scientific Research(A,16H02360)and(B,17H03307)from the Japan Society for the Promotion of Science(JSPS)KAKENHI.
文摘Damage caused by frost heave leads to costly maintenance in cold regions, like Hokkaido, Japan. Therefore, thestudy of the frost mechanism with experimental and numerical methods has been of great interest. Numerousmodels have been developed to describe the freezing process of saturated soil, which differs from the partiallysaturated conditions in the field. In fact, most subsurface soils are unsaturated. The freezing process of partiallysaturated soils is more complex than saturated soils, as the governing equations show strongly nonlinear characteristics. This study proposes a thermo-hydro-mechanical coupled model considering the heat transfer, waterinfiltration, and deformation of partially saturated soil to reproduce the freezing process of partially saturatedfrost susceptible soils distributed in Hokkaido. This model better considers the water-ice phase change and soilfreezing characteristic curve (SFCC) during freezing under field conditions. The results from the multiphysicssimulations agree well with the frost heave and water migration data from frost heave tests of Touryo soil andFujinomori soil. In addition, this study discussed the influence of the various factors on frost heave amount,including temperature gradients, overburden pressures, water supply conditions, cooling rates, and initial saturation. The simulation results indicate that the frost heave ratio is proportional to the initial degree of saturationand is inversely proportional to the cooling rate and overburden pressure.Moreover, simulation under the open system generates much more frost heave than under the closed system.Finally, the main features of the proposed model are revealed by simulating a closed-system frost heave test. Thesimulation results indicate that the proposed model adequately captures the coupling characteristics of water andice redistribution, temperature development, hydraulic conductivity, and suction in the freezing process. Togetherwith the decreased hydraulic conductivity, the increased suction controls the water flow in the freezing zone. Theinflow water driven by cryogenic suction gradient feeds the ice formation, leads to a rapid increase in total watercontent, expanding the voids that exceed the initial porosity and contributing to the frost heave.
基金the Natural Sciences and Engineering Research Council of Canada(NSERC)Discovery Grant Canada(NO.RGPIN-2024-05104).
文摘This study numerically investigates the thermo-poromechanical effects in a Canadian geothermal reservoir caused by long-term fluid production and injection.Using finite element modeling,it explores pore pressure diffusion and thermal dynamics,incorporating both the geological structure of the rock mass and faults.The simulations utilize the IAPWS(International Association for the Properties of Water and Steam)equations to model fluid density and viscosity,ensuring realistic representations of heterogeneous pressure fields.The system replicates a doublet configuration within a faulted zone,featuring two hydraulically stimulated fractures.The primary aim is to assess the likelihood of fault reactivation under varying in-situ stress conditions over a 100-year geothermal operation.Results show that stress distribution is largely influenced by thermal stresses along the fluid circulation pathway,with fluid velocity and temperature gradients affecting reservoir stability.Minimal pore pressure changes highlight the dominant role of thermal stresses in controlling fault behavior.The analysis indicates no potential for fault reactivation,as slip tendency values remain below the critical threshold,even when accounting for reduced mechanical properties using the Hoek-Brown criterion.Thermal effects continue to influence the surrounding rock throughout the operational period,suggesting that the reservoir maintains mechanical stability conducive to sustained geothermal production and injection.These findings provide valuable insights into the long-term safety and behavior of geothermal reservoirs,offering important implications for future geothermal energy development and management strategies.
