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Application of a Thermo-Plastic Constitutive Model for Coupled THM Analysis of Behavior of Saturated Soils

Afshari, Kioumars | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 42490 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Pak, Ali
  7. Abstract:
  8. Effects of temperature on the behavior of soils and rocks have been studied widely in recent years. Following the need for understanding the effects of temperature on the behavior of clayey soils, several experimental and numerical studies on thermo-mechanical behavior of clayey soils have been carried out and a number of thermo-mechanical constitutive models have been developed for saturated and unsaturated clayey soils. In this research, a two-yield surface thermo-plastic constitutive model developed by Abuel-Naga et al. (2007, 2009), has been chosen for THM analysis of the behavior of saturated clayey soils. This constitutive model is based on Modified Cam-Clay (MCC) model. The MCC model and Abuel-Naga et al. (2007, 2009) model are added in a finite element program ‘PISA’© which has the capability of conducting fully coupled Thermo-Hydro-Mechanical (THM) analysis for a wide variety of geotechnical problems. In addition, in this study, the effect of temperature on viscosity and thermal expansion coefficient of pore water has been considered. According to the chemical characteristics of water, at elevated temperatures, viscosity of pore water decreases and thermal expansion coefficient increases. Therefore, in order to simulate the generation of thermally induced pore water pressure accurately, the effect of temperature on the thermal expansion coefficient of water should be considered (Kell, 1968). In addition, thermally induced decrease in viscosity of water (Hillel, 1980), leads to an increase in hydraulic conductivity, and a higher hydraulic conductivity, in turn, causes the excess pore water pressure to dissipate in a shorter time. After verification of the program against a number of benchmark problems as well as non-isothermal triaxial and odeometer tests in the literature, the program has been used for simulation of the large-scale non-isothermal odeometer test by Abuel-Naga et al. (2006) and ATLAS in-situ experiment by François et al. (2009). In large-scale non-isothermal odeometer test, thermal and thermo-mechanical consolidation around a heat source have been studied at different stress histories. In these numerical analyses, the effects of temperature on the amount and rate of consolidation have been studied in details. The results of comparison between the amount of thermally-induced settlement and preloading-induced settlement at different overconsolidation ratios, show that at a certain amount of OCR, the proportion of thermally-induced settlement becomes maximum. In addition, the effects of using PVDT (an innovative method including Prefabricated Vertical Drains in addition to a U-tube to circulate hot water in the drain) on the increase in OCR in clayey soils soils has been studied at different stress histories. In the numerical modeling of ATLAS test, a similar attempt for the numerical simulation of the test has also been carried out by François et al. (2009), in which, another thermo-plastic constitutive model called ACMEG-T developed by François et al. (2008) has been used. In this research, a comparison between these two numerical simulations in prediction of changes in pore water pressure and stresses in the saturated soil mass has been made, and the results of two numerical simulations have been compared with the experimental data
  9. Keywords:
  10. Constitutive Model ; Thermal Expansion ; Viscosity ; Coupled Thermohydromechanical (THM)Analysis ; Prefabricated Vertical Drain ; ATLAS in-situ Test

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