More Like this

1. C7. (2021). “Performance of prefabricated thermal drains in soft clay.” Geosynthetics 2021. Kansas City. Feb. 21-23. IFAI, Roseville, MI. 1-12.

   Samarakoon, R. ; McCartney, J.S. ( February 2021 , Proceedings of Geosynthetics 2021)

   Nicks, J. and (Ed.)

   This paper focuses on the behavior of prefabricated thermal drains used to improve saturated clay layers using heating. A prefabricated thermal drain can be formed by integrating a closed-loop geothermal heat exchanger within a conventional prefabricated vertical drain (PVD). Prefabricated thermal drains can be installed in a similar way to a PVD but operate by circulating a heated fluid through the heat exchanger tubing to induce an increase in temperature of the soft clay. This increase in temperature will lead to thermal consolidation, which can be accelerated by drainage through the PVD. Although thermal drains have been tested in proof of concept field experiments, there are still several variables that need to be better understood. This paper presents numerical simulations of the coupled heat transfer, water flow, and volume change in layers of kaolinite, illite and smectite clays within a large-scale oedometer with a prefabricated thermal drain embedded at the center. Thermally induced excess pore water pressures and a slight initial expansion was observed for clay layers with lower hydraulic conductivity. However, the overall volume change resulted in contraction where the rate as well as the magnitude of settlement was greater for a thermal PVD compared to a conventional PVD. A further analysis of kaolinite layers with different initial porosities indicated that the increase in the magnitude of settlement observed when using a thermal PVD was independent of the hydraulic conductivity of the clay whereas the increase in the rate of settlement was more pronounced for clays with lower hydraulic conductivity. 

   more » « less
2. A Study on Thermal Consolidation of Fine Grained Soils Using Modified Consolidometer

   https://doi.org/10.1061/9780784482117.014  

   Joshaghani, Mohammad ; Ghasemi-Fare, Omid ( March 2019 , Geo-congress 2019)

   In order to fully understand the thermo-hydro-mechanical behavior of the geotechnical infrastructures, the effects of temperature variations on soil properties and soil behavior have to be studied. Hydraulic conductivity, strength, volume change, moisture content, and pore pressure generation and dissipation rates depend on temperature variations. Thermal loading might induce excess pore water pressure and volumetric changes. Temperature changes in the fine-grained soils will cause expansion in water and soil particles. Since the coefficient of expansion for soil particles is much smaller than that for water, a generation of pore water pressure is expected. This thermally induced pore water pressure and then its dissipation during the relaxation period results in a time dependent consolidation. Thermal consolidation in fine grained soil is more dominant and can be irreversible in normally consolidated clay. However, the volumetric changes of highly over consolidated soil caused by temperature increment is reversible by temperature reduction. In this research, a modified consolidation testing device is used to study the effect of temperature increments (e.g., increasing step by step temperature increments to 80ºC) on the consolidation of fine grained soils. In another words the effect of temperature increments during the test on the consolidation process is studied. Time of applying the heating, target temperature, and initial void ratio are parameters affecting the rate and the amount of consolidation in the samples. 

   more » « less
3. Numerical Analysis on Feasibility of Thermally Induced Pore Fluid Flow in Saturated Soils

   https://doi.org/10.1061/9780784482124.009  

   Tamizdoust, Mohammadreza Mir ; Ghasemi-Fare, Omid ( March 2019 , Eighth International Conference on Case Histories in Geotechnical Engineering)

   The exact heat transfer mechanism in the soil media can be understood by analyzing the soil behavior surrounding the heat sources. In literature, heat conduction has been considered as a main heat transfer mechanism in soil, and less attention has been given to the natural heat convection in saturated soils. There is only limited research in the literature which shows the presence of thermally induced pore fluid flow in soil media. It has been observed that heat convection through pore fluid flow in sand facilitates heat transfer in the ground. Therefore, both heat conduction and heat convection must be considered to accurately model the heat transfer mechanism in soil. In this paper, the presence of natural convection of water in a 2D axisymmetric domain of soil with a vertical heat source has been numerically investigated in steady-state condition. The soil thermal response and heat transfer mechanism for different soil types are compared. Feasibility of thermally-induced pore fluid flow is analyzed for different soil types. The results determine the presence of thermally driven pore fluid flow in high permeability soil (e.g., coarse sand) and confirm that the effect of heat convection in low permeability silt and clay is negligible. 

   more » « less
4. Coupled Thermo-Hydro-Mechanical Modeling of Saturated Boom Clay

   https://doi.org/10.1061/9780784482827.038  

   Tamizdoust, Mohammadreza Mir ; Ghasemi-Fare, Omid ( February 2020 , Geo-Congress 2020)

   Temperature variations in low permeable soil (e.g. clay) induce pore pressure, which is known as thermal pressurization. Previous research showed that thermal pressurization highly depends on thermal pressurization coefficient. This coefficient depends on the soil type and changes with temperature due to temperature dependency of thermal expansion coefficient of water. Thermal pressurization is often investigated through thermo-hydro-mechanical (THM) numerical modeling. THM process, with respect to thermal loading, has been examined in the literature to justify the field observations by incorporating advanced thermo-mechanical constitutive models. However, result of numerical simulations using advanced thermo-elastoplastic models still show some discrepancies with experimental and field observations. In this study, the assessment of thermal pressurization in Boom clay is scrutinized through employing a relatively simple while practical thermo-poroelastic finite element model with careful consideration of the temperature-dependent thermal, hydraulic, and mechanical properties of the medium and saturating fluid (i.e. water). The numerical model is carried out using COMSOL Multiphysics and the results of the numerical simulations are compared and validated with the ATLAS project, a large-scale experimental facility in Belgium. The results confirm that thermal and hydraulic coupling parameters are the key factors to change thermal pressurization. 

   more » « less
5. Effects of pore scale and conjugate heat transfer on thermal convection in porous media

   https://doi.org/10.1017/jfm.2022.491  

   Korba, David ; Li, Like ( August 2022 , Journal of Fluid Mechanics)

   The study of thermal convection in porous media is of both fundamental and practical interest. Typically, numerical studies have relied on the volume-averaged Darcy–Oberbeck–Boussinesq (DOB) equations, where convection dynamics are assumed to be controlled solely by the Rayleigh number ( Ra ). Nusselt numbers ( Nu ) from these models predict Nu – Ra scaling exponents of 0.9–0.95. However, experiments and direct numerical simulations (DNS) have suggested scaling exponents as low as 0.319. Recent findings for solutal convection between DNS and DOB models have demonstrated that the ‘pore-scale parameters’ not captured by the DOB equations greatly influence convection. Thermal convection also has the additional complication of different thermal transport properties (e.g. solid-to-fluid thermal conductivity ratio k s / k f and heat capacity ratio σ ) in different phases. Thus, in this work we compare results for thermal convection from the DNS and DOB equations. On the effects of pore size, DNS results show that Nu increases as pore size decreases. Mega-plumes are also found to be more frequent and smaller for reduced pore sizes. On the effects of conjugate heat transfer, two groups of cases (Group 1 with varying k s / k f at σ  = 1 and Group 2 with varying σ at k s / k f  = 1) are examined to compare the Nu – Ra relations at different porosity ( ϕ ) and k s / k f and σ values. Furthermore, we report that the boundary layer thickness is determined by the pore size in DNS results, while by both the Rayleigh number and the effective heat capacity ratio, $\bar{\phi } = \phi + (1 - \phi )\sigma$ , in the DOB model. 

   more » « less