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There is extensive data to show that heating and cooling produces irrecoverable deformations in clays under fully drained conditions. The effects are most pronounced for normally and lightly overconsolidated clays that undergo significant compression. Most constitutive models have key limitations for predicting the thermo-mechanical response of clays through long-term (seasonal) cycles of heating and cooling. The Tsinghua ThermoSoil model (TTS; Zhang and Cheng in Int J Numer Anal Methods Geomech 41(4):527–554, 2017) presents a novel theoretical framework for simulating the coupled thermo-mechanical response of clays. The model uses a double-entropy approach to capture effects of energy dissipation at the microscopic particulate contact level on continuum behavior. This paper proposes a simple procedure for calibrating input parameters and illustrates this process using recent laboratory data for Geneva Clay (Di Donna and Laloui in Eng Geol 190:65–76, 2015). We then investigate capabilities of the TTS model in simulating familiar aspects of thermal consolidation of clays as well as the long-term, progressive accumulation of strains associated with seasonal heating and cooling processes for shallow geothermal systems installed in clays. The model predicts the existence of a long-term steady-state condition where there is no further accumulation of strain. This state depends on the consolidation stress and stress history but is independent of the imposed range of temperature, Tcyc. However, the value of Tcyc does affect the rate of accumulation of strain with thermal cycles. Simulations for normally consolidated Geneva Clay find steady-state strain conditions ranged from 2.0 to 3.7% accumulating within N = 10–50 thermal cycles.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2016., Cataloged from PDF version of thesis. Page 370 blank., Includes bibliographical references (pages 281-295)., The use of ground source heat pumps to transfer heat to and from the ground via borehole heat exchangers is among the most energy efficient techniques for space heating and cooling. Designs for seasonal heat exchange systems are becoming increasingly popular in urban environments to reduce energy costs and contribute in decreasing carbon emissions. Broader applications require more careful evaluation of hydro-mechanical behavior of soil to understand the long-term ground response to seasonal cycles of heating and cooling and the impacts on adjacent structures. The goal of this thesis is to develop reliable methods for studying the coupled thermo-hydro-mechanical (THM) response of clay to long-term seasonal heating and cooling induced by vertical heat exchanger arrays in clay. The research investigates and implements a new class of constitutive models based on the work by Zhang and Cheng (2013). The proposed Tsinghua Thermosoil (TTS) model is capable of simulating the cyclic thermo-mechanical response more realistically than other available constitutive models and can describe the accumulation of volumetric strain due to cyclic heating and cooling. Irreversible deformations in the TTS model are simulated through the conversion of bound to free water, a process that has been studied via laboratory measurements of specific gravity variations with temperature for three clays of differing mineralogy. The thesis describes the calibration of the TTS model in detail, using recently published cyclic thermal tests on Geneva clay (Di Donna and Laloui, 2015). The TTS model is integrated within a finite difference framework to solve coupled THM problems in 1-D and axisymmetric spaces. The FD simulator is applied to a prototype project that uses an array of borehole heat exchangers for seasonal heating and cooling. The ground conditions represent typical stress history profiles found in Geneva, Switzerland. An extensive parametric study is undertaken to study the long-term THM re, by Despina M. Zymnis., Ph. D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2009., This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections., Includes bibliographical references (p. 227-229)., An in depth study was undertaken to evaluate the effectiveness of analytical solutions in describing ground movements induced by soft ground tunneling. The analytical solutions that were examined consider both isotropic and anisotropic stiffness parameters and were proposed by Pinto and Whittle (1999) and Chatzigiannelis and Whittle (2001) respectively. Computed ground movements were compared to field measurements from five published case studies of tunnels around the world that involved different excavation methods (open and closed face tunneling) and varying soil properties. A Least Squares Solution procedure has been employed in each case for selecting model input parameters that best describe the field data. The control study of the thesis involves the westbound tunnel of the Jubilee Line Extension project in London. The use of anisotropic stiffness parameters improved significantly the agreement with surface and subsurface field measurements. Moreover, the volume loss computed by the analytical solutions is significantly reduced comparing with previous published interpretations of volume loss that were based on empirical methods. The analytical solutions prove to be a very powerful tool for describing ground displacements induced by different methods of tunnel excavation through various soil types. They are practical, since they require minimal information on soil properties, while at the same provide a complete framework for understanding the relationships between the distribution of far-field deformations, construction methods and ground conditions., (cont.) Pinto's proposed design method proved to be effective in selecting appropriate input parameters for most tunnel cases apart from the tunnels excavated in London Clay., by Despina M. Zymnis., S.M.