Geothermal systems and geostructures, as sustainable energy sources, undergo daily and seasonal temperature fluctuations that significantly influence their mechanical response. Reliable prediction of thermally induced deformations therefore requires advanced thermo-mechanical constitutive models. Existing approaches often address constant elevated temperatures but fail to capture multiple thermal cycles or the coupled effect of mechanical cycling under heating. This study presents a hypoplastic thermo-mechanical model enhanced with the extended intergranular strain anisotropy concept to reproduce small-strain behaviour. Experimental evidence shows that normally consolidated fine-grained soils, when subjected to repeated thermal cycles, exhibit a transition to an overconsolidated state after the first heating–cooling cycle. To capture this, the model introduces a temperature-dependent preloading surface, enabling the evolution of the three-dimensional overconsolidation ratio under thermal cyclic loading. In addition, the original viscous strain-rate mechanism at ambient conditions is preserved, ensuring a consistent representation of rate effects under coupled thermal and mechanical actions. The proposed model is validated against diverse thermo-mechanical loading paths, including monotonic and cyclic scenarios, across different soil types. The results demonstrate its capability to capture key aspects of the complex response of fine-grained soils under combined thermal and mechanical loading, indicating its potential applicability to energy geotechnical problems.
Thermal disturbances induced by explosions or fires can rapidly alter the stress and temperature fields in surrounding rock masses, triggering strongly coupled thermo-hydro-mechanical processes that accelerate rock degradation, weaken structural integrity, and may ultimately threaten tunnel stability, posing a significant risk to long-term operational safety. In this work, the thermo-hydro-mechanical response of a cylindrical tunnel embedded in saturated soil subjected to thermal loading is investigated. Conventional thermoelastic models may not fully capture the finite-speed heat propagation, memory-dependent thermal transport, and delayed deformation behavior of soils under transient thermal shocks. Therefore, a fractional-order three-phase-lag generalized thermoelastic model incorporating strain relaxation effect is proposed to describe the coupled thermo-hydro-mechanical responses of saturated soils. The governing equations are solved using the Laplace transform method to obtain the corresponding solutions. The influence of fractional-order parameter, thermal relaxation time, strain relaxation time, and the magnitude of thermal loading is systematically examined. Results show that fractional-order and relaxation parameters significantly affect the evolution of temperature, pore water pressure, and displacement fields, while thermal loading mainly amplifies their magnitudes near the tunnel wall without changing the overall distribution patterns. The proposed model provides insight into the coupled heat and mass transfer under transient thermal shocks and offers guidance for mitigating stress concentration and improving tunnel stability.
Wei Peng, Qing-Meng Wu, A. Sur et al.· Mathematics and mechanics of...· 0 citations
Granular materials are routinely subjected to thermal cycling due to natural and anthropogenic phenomena. Despite the ubiquity of this occurrence and its relevance for science, engineering, and technology, the long‐term thermo‐mechanical response of granular materials to repeated heating and cooling remains poorly understood. In this work, we employ large‐scale discrete element simulations to investigate the evolutionary response of granular materials subjected to cyclic thermal loading, with the aim of understanding whether these materials deform indefinitely upon thermal cycling or undergo particle rearrangement towards a stabilized structural state. By considering the response of such materials under isotropic and laterally restrained (oedometric) conditions, the study explores the influence of temperature amplitude, mean effective stress, initial relative density, and material properties like Young's modulus, interparticle friction coefficient, particle thermal expansion coefficient, and particle size distribution. The simulations show that the consideration of a sufficient number of thermal cycles always brings granular materials to a stabilized structural state through plastic shakedown, regardless of their boundary conditions, stress state, or material properties. This evidence suggests that plastic shakedown is a fundamental mechanism governing thermally induced strains in granular materials subjected to cyclic heating and cooling, in much the same way it happens with cyclic mechanical loading.
N. Mehraeen, A. F. Rotta Loria· International journal for nu...· 0 citations
Concrete exposed to sub-zero and elevated temperatures exhibits strongly non-monotonic mechanical behavior governed by different physical mechanisms. Existing thermo-mechanical constitutive models commonly account for temperature-dependent degradation, but many are formulated for a specific temperature regime, and explicit treatment of reversible freezing-induced strengthening and irreversible high-temperature damage within a single constitutive structure remains limited. This study develops a unified thermo-elastoplastic damage model for concrete over the temperature range from −40 to 800 °C within the framework of irreversible thermodynamics. Plasticity is formulated in the effective-stress space, while compressive damage is driven by the damage energy release rate. Temperature effects are incorporated through evolution laws for compressive strength, elastic modulus, peak strain, and the shape parameters of the ascending and descending branches. Ice-induced strengthening is represented through reversible modifications of stiffness and strength thresholds, whereas high-temperature dehydration and microcracking are represented through irreversible thermal damage. The model was calibrated using published low-temperature compression data for C30–C50 concrete and complete high-temperature stress–strain curves for normal-strength concrete. The normalized curve-shape laws were subsequently assessed using high-strength concrete curves after normalization by their measured peak stress and peak strain, while selected components of the three-dimensional extension were assessed using residual HSC60 true-triaxial data. The calibrated model represented the freezing-point strength valley, sub-zero strengthening and embrittlement, non-monotonic strength evolution at intermediate temperatures, and progressive high-temperature ductilization. Complete high-temperature normal-strength concrete curves were reproduced with R2 values of 0.94–0.99, while the normalized multiaxial strength assessment yielded an average relative error of approximately 8%. These results support the internal consistency of the formulation and the limited cross-strength-grade applicability of the normalized curve-shape laws, rather than unrestricted predictive capability. Further independent experiments are required before application beyond the material, moisture, thermal-history, and loading conditions represented by the available datasets.
Clayey slip surfaces control the reactivation and long-term deformation of slow-moving landslides and may experience thermal fluctuations from climate, seasonal ground-temperature changes, or subsurface heat sources. Experiments show that residual shear strength depends on temperature and shearing rate, yet most numerical approaches use temperature-independent strength parameters. We present a non-isothermal viscoplastic constitutive model for clayey slip surfaces implemented with zero-thickness interface elements. It includes temperature-dependent normal and tangential stiffness, progressive degradation of cohesion and friction angle, and rate-dependent viscoplastic slip governed by a non-associated flow rule. Coupling with hydraulic and thermal balance equations allows the interface response to evolve with stress state, temperature, aperture, and accumulated irreversible displacement. Validation against temperature-controlled drained ring-shear tests on bentonite and smectite-rich soils covers heating--cooling, cooling--heating, and combined thermal paths. The simulations reproduce thermal strengthening at slow shearing rates and thermal weakening or limited sensitivity at higher rates. Application to the Congress Street cut benchmark shows that zero-thickness elements improve the representation of strain localization and progressive failure. Increasing temperature progressively degrades interface strength, increases displacement, joint aperture, and shear strain, and accelerates sliding. Temperature-dependent interface degradation can therefore reduce the apparent stability margin of clayey slopes and should be included in slope-stability assessments involving thermal fluctuations.
S. Tourchi, E. Badakhshan, Milad Jabbarzadeh et al.· 1 citation
Understanding the thermo-mechanical behaviour of clay–sand mixtures is critical for the design and long-term performance evaluation of geotechnical and geoenvironmental infrastructures exposed to elevated temperatures. This study systematically investigates the mechanical and microstructural responses of binary mixtures with varying bentonite contents (25%, 50%, 75%, and 100%) and different initial states under isothermal conditions (20, 40, and 60 °C) by temperature-controlled multi-stage oedometer tests. Upon initial heating, non-preconsolidated mixtures exhibit pronounced thermal contraction, with the magnitude of volumetric strain increasing with bentonite content, while preconsolidated specimens display thermal expansion. For preconsolidated specimens, the normal compression lines (NCLs) at different temperatures remain parallel, consistent with previous findings. Interestingly, NCLs of non-preconsolidated mixtures at different temperatures are non-parallel and intersect at a transitional stress, resulting in a temperature-dependent increase in compressibility, particularly for mixtures with higher bentonite fractions. The proposed equations incorporating the combined effects of temperature and bentonite content can accurately predict compression and swelling indices of bentonite–sand mixtures. The creep coefficient of binary mixtures is positively correlated with the bentonite content. Meanwhile, three-dimensional
C
αe
surface with the consideration of bentonite content and vertical stress is plotted and shifts up with the increasing temperature. Scanning electron microscope (SEM) observations corroborate the macro-scale findings, showing that elevated temperatures densify the microstructure of non-preconsolidated mixtures but disrupt the structure of preconsolidated specimens. These findings highlight the pivotal role of initial state and bentonite content in governing the thermo-mechanical and time-dependent behaviour of bentonite–sand mixtures.
An Li, Ze-Jian Chen, Wei-Qiang Feng et al.· Acta Geotechnica· 0 citations
Geothermal energy extraction using existing wellbore systems provides a promising approach for sustainable heat utilization; however, the long-term thermo-hydro-mechanical (THM) responses associated with different working fluids remain insufficiently understood. In this study, a three-dimensional coupled THM model was developed to compare geothermal heat extraction using water and pressurized CO2 under identical geological and operational conditions. The model integrates Darcy flow, heat transfer, and linear elastic deformation to investigate the evolution of hydraulic, thermal, and mechanical fields over a 100-year operation period. The results show that the hydraulic fields rapidly reach quasi-steady states, whereas thermal responses continuously evolve due to cold-front propagation from the injection well. Compared with water, pressurized CO2 exhibits stronger fluid mobility and produces a larger thermal influence region, resulting in different heat extraction characteristics under the same mass-flow-rate condition. Thermal cooling induces reservoir contraction and stress redistribution; however, the calculated stress and displacement variations remain within a stable range throughout the simulation period. The comparison demonstrates that pressurized CO2 can enhance long-term thermal utilization while maintaining acceptable geomechanical stability under the investigated conditions. These findings provide insights into the selection of working fluids for wellbore-based geothermal systems and highlight the importance of coupled THM evaluation for long-term reservoir performance assessment.
Donghuan Han, Yan Xia, Xiang-Yang Wang et al.· Energies· 0 citations
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