Abstract
This study establishes a fully coupled thermo-hydro-mechanical (THM) finite element model based on non-equilibrium thermodynamics theory. The model innovatively introduces bound water temperature and particle temperature parameters to characterize microscopic thermal effects, thereby systematically revealing the influence mechanism of temperature gradients on PVTD consolidation behavior. Through comparison with experimental data for Bangkok clay from Abuel-Naga et al. (2006), the model demonstrates favorable accuracy in predicting temperature field distribution, temperature-induced deformation, and consolidation settlement in thermal PVD systems. The research findings indicate: (1) Temperature-driven optimization of hydraulic characteristics: elevated temperature (20–90°C) significantly reduces pore water dynamic viscosity (to one-third), thereby substantially enhancing hydraulic conductivity; (2) Consolidation acceleration mechanism dominated by thermal creep: temperature cycling induces irreversible volumetric contraction, with microscopic contributions comprising—thermal creep resulting from bound water migration to free water (77.7%), isothermal mechanical creep (17.7%), and particle packing effects (4.6%); (3) Critical influence of temperature gradient: simulations of various heat source positions demonstrate that consolidation efficiency is maximized when the heat source is concentrated around the PVD drain. Under this condition, thermal effects can act most effectively on critical drainage regions such as the smear zone, consistent with the experimental conclusions of Abuel-Naga et al. (2006). Non-uniform temperature distribution induces differential settlement; conversely, fixing the heat source on the drain board leads to reduced surrounding porosity and suppressed drainage; (4) Thermally induced excess pore pressure and settlement effects: superposition of particle and water thermal expansion with thermal contraction facilitates generation of thermally induced excess pore water pressure, thereby significantly increasing soil settlement magnitude. These results provide robust theoretical support for engineering optimization design of PVTD technology and profoundly elucidate the physical mechanism by which temperature gradients effectively mitigate smear effects and significantly accelerate consolidation through regulation of microscopic thermo-hydro-mechanical processes.
Full Text
Mechanisms of Thermal Gradient Effects on Soft Clay Consolidation in PVTD Systems
Binyuan Zhang¹, Hao Wang²
¹School of Construction Engineering, Dalian University of Technology, Dalian 116024, China
²School of Construction Engineering, Dalian University of Technology, Dalian 116024, China
Abstract
This study develops a fully coupled thermo-hydro-mechanical (THM) finite element model based on non-equilibrium thermodynamics theory. The model innovatively introduces bound water temperature and particle temperature parameters to characterize microscopic thermal effects, systematically revealing the influence mechanisms of temperature gradients on PVTD consolidation behavior.
Validated against experimental data from Abuel-Naga et al. (2006) on Bangkok clay, the model demonstrates good accuracy in predicting temperature field distribution, thermally induced deformation, and consolidation settlement in thermal PVD systems.
The research results indicate: (1) Temperature-driven optimization of hydraulic properties: temperature increases (20–90°C) significantly reduce pore water dynamic viscosity (to one-third of its original value), thereby substantially enhancing hydraulic conductivity. (2) Thermal creep-dominated consolidation acceleration mechanism: temperature cycling induces irreversible volume contraction, with microscopic contribution ratios of—thermal creep from bound water migrating to free water (77.7%), isothermal mechanical creep (17.7%), and particle packing effects (4.6%). (3) Critical influence of temperature gradient: simulations of different heat source locations show that consolidation efficiency is highest when heat is concentrated around the PVD drain. In this configuration, thermal effects maximize their action in critical drainage zones such as the smear zone, consistent with the experimental conclusions of Abuel-Naga et al. (2006). Non-uniform temperature distribution induces differential settlement; if the heat source is fixed to the drain board, it leads to reduced porosity around the drain and inhibits drainage. (4) Thermal-induced excess pore pressure and settlement effects: the superposition of thermal expansion of particles and water with thermal contraction promotes the generation of thermally induced excess pore water pressure, thereby significantly increasing soil settlement.
These findings provide solid theoretical support for the engineering optimization design of PVTD technology, elucidating the physical mechanism by which temperature gradients effectively suppress smear effects and significantly accelerate consolidation by regulating microscopic thermo-hydro-mechanical processes.
Keywords: Prefabricated Vertical Thermal Drain (PVTD); temperature gradient; thermo-hydro-mechanical coupling (THM); soft ground consolidation; smear effect; thermal creep; particle temperature