【摘要】：本文基于物理守恒定律及非平衡態(tài)熱力學理論,建立了一種針對飽和巖土體的溫度場-滲流場-應(yīng)力場(THM)完全耦合問題的理論模型。該模型從理論上確定了熱力學體系的耗散力構(gòu)成,并采用經(jīng)典非平衡態(tài)熱力學理論,將能量的耗散歸結(jié)為一系列遷移系數(shù)模型的確定。本文從理論上統(tǒng)一地給出了所有物理場所應(yīng)遵循的物理規(guī)律,包括一種無需屈服面、流動法則、加卸載準則和硬化/軟化準則等概念的應(yīng)力場本構(gòu)模型。本文模型考慮了溫度和變形對各相密度及土體滲透性的影響以及滲流和熱傳導(dǎo)之間的相互耦合,并推導(dǎo)得到了一個飽和巖土體滲流公式的一般形式。采用熵增方程作為溫度場控制方程,考慮了熱彈耦合和能量耗散過程(如非彈性變形發(fā)展)對溫度場的影響。本文考慮了暫態(tài)彈性和顆粒漲落這兩種顆粒固體材料特有的能量耗散機制,引入了顆粒熵及顆粒熵溫度的概念對顆粒漲落劇烈程度進行描述,并得到了非彈性變形發(fā)展規(guī)律與顆粒漲落和暫態(tài)彈性之間的定量關(guān)系。彈性勢能密度函數(shù)給出了有效應(yīng)力與彈性應(yīng)變的關(guān)系,并在有效應(yīng)力空間上唯一確定了一個極限應(yīng)力狀態(tài)面。同時,彈性勢能密度函數(shù)也反映了巖土體的粘性、應(yīng)力引起的各向異性和彈性模量和強度的狀態(tài)相關(guān)性等重要特征。分析表明,本文得到的應(yīng)力場本構(gòu)模型具備統(tǒng)一考慮巖土體類型(砂土和粘土)、密實程度、排水條件、超固結(jié)度和加載速率等因素對力學行為的影響,且有較好的預(yù)測能力。本文模型給出了一種與臨界狀態(tài)土力學中相似但又有區(qū)別的臨界狀態(tài);引入了等效修正應(yīng)變的概念,可合理反映巖土體的滯回特性,如滯回環(huán)的發(fā)展、殘余應(yīng)變的累積、有效應(yīng)力的衰減和卸載剛度的退化等。通過考慮結(jié)合水相和自由水相間隨溫度變化的相互轉(zhuǎn)化及其激發(fā)的顆粒漲落,可較好地模擬飽和巖土體的非等溫固結(jié)現(xiàn)象。分析表明,非等溫固結(jié)過程具有顯著的OCR值依賴性和不可逆性。本文模型也可反映溫度荷載作用下的熱破壞現(xiàn)象。在不排水條件下,當飽和土體存在較大剪應(yīng)力時,在循環(huán)溫度荷載作用下,孔壓將迅速累積,熱剪切應(yīng)變將發(fā)生急劇增長。本文通過將溫度對飽和巖土體剪切性質(zhì)的影響歸結(jié)于非等溫固結(jié)過程引起的干密度變化和溫度對某些重要參數(shù)的影響,可較好地模擬飽和巖土體排水和不排水剪切性質(zhì)的溫度效應(yīng)。對不同土體類型、不同OCR值和不同排水條件的剪切性質(zhì)溫度依賴性進行了研究,并給出了統(tǒng)一的機理解釋。
[Abstract]:Based on the law of physical conservation and the theory of non-equilibrium thermodynamics, a theoretical model for the (THM) complete coupling of temperature field, seepage field and stress field in saturated rock and soil is established in this paper. In this model, the dissipative force composition of the thermodynamic system is determined theoretically, and the dissipation of energy is reduced to a series of transfer coefficient models by using the classical non-equilibrium thermodynamic theory. In this paper, the physical laws that should be followed in all physical places are given theoretically, including a constitutive model of stress field, which requires no yield surface, flow rule, loading and unloading criterion and hardening / softening criterion, etc. In this paper, the influence of temperature and deformation on the phase density and soil permeability and the coupling between seepage and heat conduction are considered, and a general form of seepage formula for saturated rock and soil is derived. The entropy increasing equation is used as the governing equation of temperature field. The influence of thermal elastic coupling and energy dissipation process (such as the development of inelastic deformation) on the temperature field is considered. In this paper, the energy dissipation mechanism of transient elasticity and particle fluctuation is considered, and the concepts of particle entropy and particle entropy temperature are introduced to describe the intensity of particle fluctuation. The quantitative relationship between the development law of inelastic deformation and particle fluctuation and transient elasticity is obtained. The relation between the effective stress and the elastic strain is given by the energy density function of the elastic potential, and a limit stress state surface is uniquely determined in the effective stress space. At the same time, the elastic potential energy density function also reflects the viscosity of rock and soil, stress-induced anisotropy and the state-dependence of elastic modulus and strength. The analysis shows that the stress field constitutive model obtained in this paper has a unified consideration of the effects of the types of rock and soil mass (sand and clay), compactness, drainage conditions, overconsolidation and loading rate on the mechanical behavior, and has a good prediction ability. In this paper, a kind of critical state is given, which is similar to the critical state of soil mechanics, but also different from that in the critical state of soil mechanics. The concept of equivalent modified strain is introduced, which can reasonably reflect the hysteretic characteristics of rock and soil, such as the development of hysteretic loop, the accumulation of residual strain, the attenuation of effective stress and the degradation of unloading stiffness, etc. The phenomenon of non-isothermal consolidation of saturated rock and soil can be well simulated by considering the interaction of water phase and free water phase with temperature change and the fluctuation of particles excited by the interaction between water phase and free water phase, which can be used to simulate non-isothermal consolidation of saturated rock soil. The analysis shows that the non-isothermal consolidation process has significant OCR value dependence and irreversibility. This model can also reflect the thermal failure phenomenon under the action of temperature load. Under the condition of undrained water, when the saturated soil has large shear stress, the pore pressure will accumulate rapidly under the action of cyclic temperature load, and the thermal shear strain will increase rapidly. In this paper, the influence of temperature on shear properties of saturated rock and soil is attributed to the change of dry density caused by non-isothermal consolidation and the effect of temperature on some important parameters. The temperature effect of drainage and undrained shear properties of saturated rock and soil can be well simulated. The temperature dependence of shear properties of different soil types, different OCR values and different drainage conditions is studied, and the unified mechanism explanation is given.
【學位授予單位】：清華大學
【學位級別】：博士
【學位授予年份】：2013
【分類號】：TU43

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