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1. Role of initial effective stress on the thermal volume change of normally consolidated clay

   https://doi.org/10.1051/e3sconf/202020509001  

   Samarakoon, Radhavi ; McCartney, John S. ( January 2020 , E3S Web of Conferences)

   McCartney, J.S. ; Tomac, I. (Ed.)

   This paper focuses on the results from thermal triaxial tests on normally consolidated Georgia Kaolinite. The hypothesis evaluated in this study is whether the initial mean effective stress has an impact on the thermal volume change encountered during drained heating. To that effect, specimens at three different initial mean effective stresses were considered in this study. The clay specimens were first isotropically consolidated to a normally consolidated state, then subjected to a drained heating cooling cycle followed by further mechanical loading to higher effective stresses. The results indicate contractive volumetric strain during drained heating where the volumetric strain was found to increase with increasing initial mean effective stress. A rebound in volume was observed during subsequent cooling where the net change in volume transitioned from zero volume change of the specimen to net contraction of the specimen after a heating cooling cycle as the initial mean effective stress increased. The results indicate the need for considering the effect of initial mean effective stress when assessing in-situ heating as a method of soil improvement. 

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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. 

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3. 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. 

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4. Comparison of thermo-poroelastic and thermo-poroelastoplastic constitutive models to analyze THM process in clays

   https://doi.org/10.1051/e3sconf/202020504008  

   Mir Tamizdoust, Mohammadreza ; Ghasemi-Fare, Omid ( January 2020 , E3S Web of Conferences)

   McCartney, J.S. ; Tomac, I. (Ed.)

   Thermal pore pressurization in soil media has been investigated for the past few decades. It has been shown that temperature variations may significantly affect thermal pore pressure in clay soils confined deep into the ground. Moreover, thermal loading may lead to stress change and thermal deformation. Thermo-poroelastic and advance thermo-poroelastoplastic constitutive models have been formulated and incorporated numerically to simulate the thermo-hydro-mechanical process. However, the accurate response of soil media during THM process has not been completely understood. Although numerical modelling reasonably predicts the experimental observations, they still could not be used to completely justify the field observations. In this study, the main features of the thermo-poroelastic model are incorporated in a thermo-poroelastoplastic constitutive model (ACMEG-T) to further investigate the effect of different thermal and hydraulic properties on thermo-hydro-mechanical (THM) response of the soil media. 

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5. Regimes of Soil Moisture–Wet-Bulb Temperature Coupling with Relevance to Moist Heat Stress

   https://doi.org/10.1175/JCLI-D-23-0132.1  

   Kong, Qinqin ; Huber, Matthew ( November 2023 , Journal of Climate)

   Human heat stress depends jointly on atmospheric temperature and humidity. Wetter soils reduce temperature but also raise humidity, making the collective impact on heat stress unclear. To better understand these interactions, we use ERA5 to examine the coupling between daily average soil moisture and wet-bulb temperature (T_w) and its seasonal and diurnal cycle at global scale. We identify a global soil moisture–T_wcoupling pattern with both widespread negative and positive correlations in contrast to the well-established cooling effect of wet soil on dry-bulb temperature. Regions showing positive correlations closely resemble previously identified land–atmosphere coupling hotspots where soil moisture effectively controls surface energy partition. Soil moisture–T_wcoupling varies seasonally closely tied to monsoon development, and the positive coupling is slightly stronger and more widespread during nighttime. Local-scale analysis demonstrates a nonlinear structure of soil moisture–T_wcoupling with stronger coupling under relatively dry soils. Hot days with highT_wvalues show wetter-than-normal soil, anomalous high latent and low sensible heat flux from a cooler surface, and a shallower boundary layer. This supports the hypothesis that wetter soil increasesT_wby concentrating surface moist enthalpy flux within a shallower boundary layer and reducing free-troposphere-air entrainment. We identify areas of particular interest for future studies on the physical mechanisms of soil moisture–heat stress coupling. Our findings suggest that increasing soil moisture might amplify heat stress over large portions of the world including several densely populated areas. These results also raise questions about the effectiveness of evaporative cooling strategies in ameliorating urban heat stress.

   The purpose of this study is to provide a global picture of the relationship between soil moisture anomalies and a heat stress metric that includes the joint effects of temperature and humidity. This is important because a better understanding of this relationship will help improve the prediction of extreme heat stress events and inform strategies for ameliorating heat stress. We find a widespread positive correlation between soil moisture and heat stress, in contrast to studies relying on temperature alone. This raises the possibility that, over much of the world, and in the most populous regions, strategies like irrigation or “greening” that can reduce temperature might be ineffective or even harmful in reducing heat stress with humidity incorporated.

    

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