【作者】 李建红；

【导师】 张丙印；

【作者基本信息】 清华大学 ， 土木工程， 2008， 博士

【摘要】 天然土体多具有一定的结构性,其力学特性与室内重塑土相比较为复杂。对结构性土应力变形特性的研究为目前岩土力学研究的一个热门课题。“21世纪土力学的核心问题是土体结构性的数学模型”。本文对胶结结构性土进行了系统的室内试验和细观胶结破损机理的分析研究工作。本文取得的主要新成果有:(1)采用人工制备的具有不同孔隙比和颗粒胶结强度的人工结构性土试样和相应的重塑土试样,进行了多种应力路径的常规三轴和真三轴试验。通过对比分析人工胶结结构性土和重塑土的试验成果,系统地分析和总结了人工胶结结构性土的应力和变形特性,分析了胶结强度和初始孔隙比对人工胶结结构性土应力变形特性的影响。(2)基于对胶结结构性土细观结构的观察和抽象,提出了以颗粒接触胶结特性区分胶结结构性土胶结元和摩擦元材料相的新方法,定义了可反映结构性土颗粒细观接触特性变化的破损变量。以离散介质力学宏细观积分方程为基础,推导了适用于胶结结构性土二元介质模型的基本方程。基于宏细观能量方程,利用能量平衡原理推导了破损变量的演化规律。(3)从胶结结构性土细观颗粒接触力的平衡方程出发,讨论了颗粒胶结接触发生破损的条件。通过分析颗粒接触力的构成和颗粒胶结的细观破损条件,建立了胶结元的破损准则。给出了等向压缩和三轴剪切条件下胶结元破损准则的具体表达式。推导了胶结元和胶结结构性土的强度包线。(4)应用上述有关胶结结构性土破损变量及其演化规律和胶结元破损准则的研究成果,基于岩土破损力学的理论框架,建立了一个胶结结构性土的二元介质本构模型。该模型认为,胶结结构性土的胶结元为弹脆性材料;摩擦元的本构方程满足修正剑桥弹塑性模型。该模型引入的结构性模型参数数量少,均具有明确的物理意义,且可以通过简单应力路径的室内常规三轴试验确定。通过与人工胶结结构性土试验结果的对比,表明该模型可以较好地反映胶结结构性土不同应力路径上的主要应力变形特性。更多还原

【Abstract】 The natural soil has many complex mechanical properties that are different from those of the remolded soil made in laboratory and the relevant study is a hot topic in geo-mechanics. It is said that“The establishment of mathematical model of natural soil is the key issue of geo-mechanics in the 21-th century.”In this thesis, a series of experiments of artificial bonded soil in lab have been carried out and the study on the micro-mechanism of particle bonding-breakage has been performed. The main achievements in this thesis can be summarized as following.The experiments on artificially bonded soil and remolded soil with different void ratio and bonding strength have been conducted in various stress paths on triaxial and truly triaxial conditions. On the basis of the comparison between experimental results of artificially bonded soil and remolded soil, the mechanical properties of artificially bonded soil have been comprehensively analyzed and summarized. The effects of bonding and initial void ratio on the mechanical property of artificially bonded soil have been studied.Based on the micro observation with SEM and some assumption, a new method to partition the bonding element and frictional element in artificially bonded soil has been proposed according to the contact property between particles. A new breakage parameter has been defined clearly with bonding element volume in micro level. The basic equation of the breakage mechanics have been deduced by the basic integrating equation of discrete medium mechanics from micro to macro level. The breakage-developing rule has been deduced based on the law of balance of energy principle in macro-micro level.Based on the equilibrium equation of contact force between particles in micro level, the breakage condition of bonding has been discussed. With the analysis of the composition of the bonded contact force, the criteria of bonding breakage have been established. The detailed equations of this criteria in isotropic loading and triaxial loading have been proposed. Based on this study, the strength envelop of bonding element and artificially bonded soil have been deduced.In the frame of the breakage mechanism, the new binary media model has been established with the breakage developing rule and breakage criteria. This model considers the bonding element as elasto-brittle material and the frictional element as elasto-plastic material which can be described by the modified Cam-clay model. The number of parameters in this model is moderate and all of them have the defining mechanical meanings. The value of these parameters can be calibrated by the conventional triaxial test with simple stress path in laboratory. The comparison between the results of calculation with this model and the experiments in this thesis show that this model can simulate the main mechanical properties of artificial bonded soil in various stress paths.更多还原