饱和岩土体多场耦合热力学本构理论及模型研究

发布时间：2019-05-07 13:16

【摘要】：本文基于物理守恒定律及非平衡态热力学理论,建立了一种针对饱和岩土体的温度场-渗流场-应力场(THM)完全耦合问题的理论模型。该模型从理论上确定了热力学体系的耗散力构成,并采用经典非平衡态热力学理论,将能量的耗散归结为一系列迁移系数模型的确定。本文从理论上统一地给出了所有物理场所应遵循的物理规律,包括一种无需屈服面、流动法则、加卸载准则和硬化/软化准则等概念的应力场本构模型。本文模型考虑了温度和变形对各相密度及土体渗透性的影响以及渗流和热传导之间的相互耦合,并推导得到了一个饱和岩土体渗流公式的一般形式。采用熵增方程作为温度场控制方程,考虑了热弹耦合和能量耗散过程(如非弹性变形发展)对温度场的影响。本文考虑了暂态弹性和颗粒涨落这两种颗粒固体材料特有的能量耗散机制,引入了颗粒熵及颗粒熵温度的概念对颗粒涨落剧烈程度进行描述,并得到了非弹性变形发展规律与颗粒涨落和暂态弹性之间的定量关系。弹性势能密度函数给出了有效应力与弹性应变的关系,并在有效应力空间上唯一确定了一个极限应力状态面。同时,弹性势能密度函数也反映了岩土体的粘性、应力引起的各向异性和弹性模量和强度的状态相关性等重要特征。分析表明,本文得到的应力场本构模型具备统一考虑岩土体类型(砂土和粘土)、密实程度、排水条件、超固结度和加载速率等因素对力学行为的影响,且有较好的预测能力。本文模型给出了一种与临界状态土力学中相似但又有区别的临界状态;引入了等效修正应变的概念,可合理反映岩土体的滞回特性,如滞回环的发展、残余应变的累积、有效应力的衰减和卸载刚度的退化等。通过考虑结合水相和自由水相间随温度变化的相互转化及其激发的颗粒涨落,可较好地模拟饱和岩土体的非等温固结现象。分析表明,非等温固结过程具有显著的OCR值依赖性和不可逆性。本文模型也可反映温度荷载作用下的热破坏现象。在不排水条件下,当饱和土体存在较大剪应力时,在循环温度荷载作用下,孔压将迅速累积,热剪切应变将发生急剧增长。本文通过将温度对饱和岩土体剪切性质的影响归结于非等温固结过程引起的干密度变化和温度对某些重要参数的影响,可较好地模拟饱和岩土体排水和不排水剪切性质的温度效应。对不同土体类型、不同OCR值和不同排水条件的剪切性质温度依赖性进行了研究,并给出了统一的机理解释。
[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.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU43

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