Engineering and Technological Sciences
Abstract
Based on non-equilibrium thermodynamics theory, this study establishes a fully coupled thermal-hydraulic-mechanical (THM) finite element model. This model innovatively introduces bound water temperature and particle temperature parameters to characterize microscopic thermal effects, systematically revealing the influence mechanism of temperature gradients on PVTD consolidation behavior. Through comparison with Abuel-Naga et al.'s (2006) experimental data on Bangkok clay, the model demonstrates good accuracy in predicting temperature field distribution, thermally induced volumetric deformation, and consolidation settlement in thermal PVD systems.
The research results indicate: (1) Temperature-driven optimization of hydraulic characteristics: temperature increase (20–90°C) significantly reduces pore water dynamic viscosity (to 1/3 of original), thereby substantially enhancing hydraulic conductivity; (2) Thermal creep-dominated consolidation acceleration mechanism: temperature cycles trigger irreversible volume contraction, with microscopic contribution ratios being—thermal creep due to bound water migration to free water (77.7%), isothermal mechanical creep (17.7%), and particle packing effects (4.6%); (3) Critical influence of temperature gradients: simulations of different heat source locations show that consolidation efficiency is highest when heat sources concentrate around PVD drainage bodies. Under this condition, thermal effects can maximize their impact on key drainage areas such as the smear zone, consistent with Abuel-Naga et al.'s (2006) experimental conclusions. Uneven temperature distribution will induce non-uniform settlement; if heat sources are fixed at drainage plates, it will cause reduced surrounding porosity and inhibit drainage; (4) Thermally induced excess pore pressure and settlement effects: the superposition of particle and water thermal expansion 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, thoroughly elucidating the physical mechanism through which temperature gradients effectively suppress smear effects and significantly accelerate consolidation by regulating microscopic thermal-hydraulic-mechanical processes.
Full Text
Mechanisms of Thermal Gradient Effects on Soft Clay Consolidation in PVTD Systems
Binyuan Zhang¹
Hao Wang²
¹ School of Construction Engineering, Dalian University of Technology, Dalian 116024, China
² School of Construction Engineering, Dalian University of Technology, Dalian 116024, China
Abstract
Based on non-equilibrium thermodynamics theory, this study establishes a fully coupled thermal-hydraulic-mechanical (THM) finite element model. 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. Through comparison with experimental data of Bangkok clay from Abuel-Naga et al. (2006), the model demonstrates good accuracy in predicting temperature field distribution, thermally induced volumetric deformation, and consolidation settlement in thermal PVD systems.
The research findings indicate that:
-
Temperature-driven hydraulic property optimization: Temperature increase (20–90°C) significantly reduces pore water dynamic viscosity (decreasing to 1/3), thereby substantially enhancing hydraulic conductivity
-
Consolidation acceleration mechanism dominated by thermal creep: Temperature cycles induce irreversible volume shrinkage, with the microscopic contribution ratios being—thermal creep due to bound water migration to free water (77.7%), isothermal mechanical creep (17.7%), and particle packing effects (4.6%)
-
Critical influence of temperature gradient: Simulations of different heat source locations indicate that consolidation efficiency is highest when the heat source is concentrated around the PVD drain. Under this condition, the thermal effect can be maximized in key drainage areas such as the smear zone, which is consistent with the experimental conclusions of Abuel-Naga et al. (2006). Uneven temperature distribution will induce non-uniform settlement; if the heat source is fixed at the drain, it will cause a reduction in surrounding porosity and inhibit drainage
-
Thermally induced excess pore pressure and settlement effects: The superposition of thermal expansion and thermal contraction of particles and water promotes the generation of thermally induced excess pore water pressure, thereby significantly increasing soil settlement
This achievement provides a solid theoretical foundation for the engineering optimization design of PVTD technology, thoroughly elucidating the physical mechanism by which temperature gradients effectively suppress smear effects and significantly accelerate consolidation through regulating microscopic thermal-hydraulic-mechanical processes.
Keywords: prefabricated vertical thermal drain (PVTD); temperature gradient; thermo-hydro-mechanical (THM) coupling; soft soil foundation consolidation; smear effect; thermal creep; granular temperature
This version posted 2025-09-02.