| The thermo-hydro-mechanical(THM)coupling problems of saturated geomaterials have been one of the difficult and hot topics in the research field of geotechnical engineering.Based on the theory of Granular Solid Hydrodynamics,the Tsinghua Thermodynamic Soil(TTS)model provides a new approach for the analyses and predictions of such problems.Different from traditional elasto-plastic theories,the TTS model use terms such as Onsager migration coefficients,which are defined in thermodynamics,for the quantitative description of energy dissipations.The first objective of this dissertation is the investigation and development of TTS,including its rate-dependency and thermal-mechanical properties.Based on the constitutive equations of TTS,a THM coupling axisymmetric finite element code is developed,and a systematic research on the thermal consolidation and thermal creep of saturated clay materials is carried out,which serves as the second objective.The main achievements and conclusions can be summarized as follows.1.A systematic study on the rate-dependent behaviors of the TTS model is carried out.The quantitative expression of the viscous stress in TTS is proposed,which enables TTS to consider both viscous dissipation and non-viscous dissipation.The proposed model presents good simulations and physical explanations to the rate-dependent problems of a variety of geomaterials.2.Based on the TTS model,a THM coupling axisymmetric finite element code is developed using Matlab.Five numerical examples are carried out which indicate the validity and accuracy of the code,including the bearing capacity of surface footings,the one-dimensional consolidation solution,and the THM process of saturated soil.The code provides a new approach for analyzing complicated THM coupling problems of geotechnical engineering.3.A series of numerical simulations on exited consolidated drained heating tests of saturated clays is carried out using the newly-developed THM coupling finite element code.It is found that the inhomogenous distributions of temperature and the accumulation of pore pressure within the clay samples have significant influence on the thermally induced volume change.The research shows that the volumetric deformation of saturated clays during temperature increase is a combination effect of(a)the principle of thermal expansion,(b)the constitutive thermal-plastic mechanism which is also known as the thermal creep,(c)the consolidation effect due to excess pore pressure which is known as the thermal consolidation,and(d)the decrease of effective stress due to the existence of excess pore pressure.4.Based on the theory of surface forces,a quantitative expression for the micro-scale effective stress of saturated clays is derived.It is shown that the disjoining pressure of bound water increases with temperature,leading to a decrease of effective stress and a visco-plastic redistribution of clay particles,which macroscopically behave as volume contractions.This theoretical research provides a new micro-scale mechanism explanation for the special thermal-mechanical properties of saturated clays such as thermal creep.5.The TTS model is applied for the analyses of thermal-mechanical properties of rock materials for the first time.Based on the model,a two-dimensional finite element analysis for the deep geothermal well system is presented,which indicates that the thermally-induced mechanical stresses at interfaces between different materials are non-monotonic during the monotonic thermal loading.The results of the simulation are of important significance for the engineering design of oil and gas wells and geothermal wells.6.By means of a fifth-order Runge-Kutta formula,The TTS model is implemented into finite element softwares ABAQUS and Code_bright,and simulations on the rate-dependent and confining-pressure-dependent properties of soils are carried out.The work enables the application of TTS in general finite element softwares. |
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