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Geomechanics and Engineering
  Volume 23, Number 6, December25 2020, pages 561-573
DOI: http://dx.doi.org/10.12989/gae.2020.23.6.561
 


Thermal volume change of saturated clays: A fully coupled thermo-hydro-mechanical finite element implementation
Hao Wang and Xiaohui Qi

 
Abstract
    The creep and consolidation behaviors of clays subjected to thermal cycles are of fundamental importance in the application of energy geostructures. This study aims to numerically investigate the physical mechanisms for the temperature-triggered volume change of saturated clays. A recently developed thermodynamic framework is used to derive the thermo-mechanical constitutive model for clays. Based on the model, a fully coupled thermo-hydro-mechanical (THM) finite element (FE) code is developed. Comparison with experimental observations shows that the proposed FE code can well reproduce the irreversible thermal contraction of normally consolidated and lightly overconsolidated clays, as well as the thermal expansion of heavily overconsolidated clays under drained heating. Simulations reveal that excess pore pressure may accumulate in clay samples under triaxial drained conditions due to low permeability and high heating rate, resulting in thermally induced primary consolidation. Results show that four major mechanisms contribute to the thermal volume change of clays: (i) the principle of thermal expansion, (ii) the decrease of effective stress due to the accumulation of excess pore pressure, (iii) the thermal creep, and (iv) the thermally induced primary consolidation. The former two mechanisms mainly contribute to the thermal expansion of heavily overconsolidated clays, whereas the latter two contribute to the noticeable thermal contraction of normally consolidated and lightly overconsolidated clays. Consideration of the four physical mechanisms is important for the settlement prediction of energy geostructures, especially in soft soils.
 
Key Words
    thermal consolidation; thermal creep; saturated clay; thermodynamic constitutive model; thermo-hydro-mechanical; finite element
 
Address
Hao Wang: 1.) Department of Civil Engineering, Tsinghua University, Beijing 100084, China
2.) Beijing Key Laboratory of Urban Underground Space Engineering, School of Civil and Resource Engineering,
University of Science and Technology Beijing, Beijing 100083, China

Xiaohui Qi: School of Civil and Environmental Engineering, Nanyang Technological University, Singapore 639798, Singapore
 

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