| Author | Abuel-Naga, Hossam M. |
| Call Number | AIT Diss. no.GE-05-01 |
| Subject(s) | Clay--Thailand--Bangkok--Testing
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| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. GE-05-01 |
| Abstract | Understanding the thermo-mechanical behavior of saturated fine grained soils has become a very important topic whenever the geotechnical problems involve thermal effects. Although many research works were directed to investigate the thermo-hydromechanical behavior of clays, there are still many inconsistencies surrounding some aspects in this field that need to be addressed by more experiments as well as an accurate analysis. The aim of this study is to investigate the thermo-mechanical behavior of soft Bangkok clay in terms of the effect of temperature up to 90°C on its engineering properties such as stiffness, compressibility, permeability, thermal conductivity, and shear strength and yielding behavior. Moreover, the aim of the study was extended to develop the constitutive model to enable the simulation of the observed behavior. Modified oedometer, modified flexible wall permeameter, modified thermal conductivity cell, and modified triaxial apparatus that can handle temperature up to 100°C have been utilized in this study. Finally, an endeavor to involve the thermo-mechanics of soil into the ground improvement field was conducted. The effect of raising the soil temperature on the performance of preloading with prefabricated vertical drain (PVD) ground improvement method was assessed by conducting large oedometer test program, where PVD and line heat source points were installed with several arrangements into the soil specimen. The thermally induced volume change is stress history dependent and stress level independent. There is irreversible compression for normally consolidated specimen while it is reversible expansion for highly overconsolidated specimen. The size of conventional elastic zone is temperature dependent; it contracts as the soil temperature increases and expands upon cooling. The hydraulic permeability increases as the soil temperature increases due to the reduction of the water viscosity. The peak undrained and drained shear strength and the shear stiffness increases as the soil temperature increases while the critical state line in the deviatoric plane (q-p) is temperature independent. The geometry of Roscoe surface is temperature dependent. The temperature also affects the flow rule. Thus, non-associative flow rule is recommended. The test results of thermal conductivity experimental program show that the thermal conductivity and volume fraction of the each soil phase, and the soil fabric are the major factors controlling the thermal conductivity of the saturated soil. A model equation for predicting the thermal conductivity of saturated soils ' that include the effects of these major factors was introduced based on onedimensional series-parallel heat flow theory. Finally, the test results of large oedometer experimental program show that the mechanical consolidation rate using PVD is improved at elevated temperature. Therefore, raising the soil temperature up to 90°C could enhance the performance of the PVD system. Based on the experimental results of soft Bangkok clay and the available test results on different saturated clay types, an improvement on the current state of the thermomechanics constitutive model of soils was conducted. An isotropic constitutive thermoelastic-plastic model that is able to reproduce the thermally induced volume change of saturated clay specimens under normally consolidated condition and overconsolidated condition, obtained by unloading process, in the temperature range of 20 to 95°C was introduced. Two volumetric yield limits, namely; loading yield limit and thermal yield limit have been employed to predict the plastic volume change. A new technique has been introduced to detect experimentally the thermal yield limit. Moreover, a thermo-elasticplastic model that can predict the shear strength behavior at elevated temperature in states wetter than critical condition was also introduced. The proposed model was developed within the framework of Critical State Soil Mechanics (CSSM) for the triaxial space. It is characterized by a non-associative temperature dependent flow rule which is introduced by adopting a yield surface different than the plastic potential surface. Moreover, besides the isotropic hardening rule of the yield surface, both surfaces (yield and plastic potential surface) were able to evolve according to a combined thermal distortional and rotational rule. The validity of the proposed models was investigated using the test results of soft Bangkok clay and test results of other suitable clay types reported in literature. Acceptable agreement between the proposed model prediction and the test results were observed. The originality of the proposed model rests on its capability to simulate the irreversible compressive the thermally-induced volumetric strain at low overconsolidation stress ratio obtained by unloading process, and the introduction of the combined thermal distortional and rotational rule for yield and plastic potential surface. Finally, the contribution of this study into the field of the thermo-mechanics of soils stand on three items; (i) the experimental results of soft Bangkok clay that enhanced the current state of the reliable database especially for the thermal behavior of soft soil where very few experimental evidences are available, (ii) the improvement of the current state of the thermo-mechanical constitutive model of saturated clays, (iii) the innovative idea that is directed to enhance the performance of the preloading with PVD ground improvement method by .raising the clay temperature up to 90°C |
| Year | 2006 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. GE-05-01 |
| Type | Dissertation |
| School | School of Engineering and Technology (SET) |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Geotechnical Engineering (GE) |
| Chairperson(s) | Bergado, Dennes T.; |
| Examination Committee(s) | Worsak Kanok-Nukulchai;Noppadol Phien-wej;Glawe, Ulrich.;Laloui, Lyesse.; |
| Scholarship Donor(s) | The Government of Japan; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2005 |