【作者】 胡波；

【导师】 汪稔；

【作者基本信息】 中国科学院研究生院（武汉岩土力学研究所） ， 岩土工程， 2008， 博士

【摘要】 钙质砂是分布于热带海洋中的一种特殊岩土介质,由于其成因和组构上的特点导致其物理力学性质与常规的陆源砂有所区别。实践证明,颗粒破碎是影响钙质砂力学性质的主要因素。目前对于钙质砂的力学性质已经取得了很多的研究成果,但是能够准确模拟钙质砂颗粒破碎的本构模型不多见。本文通过大量力学试验对钙质砂在三轴条件下的剪切特性进行了阐述;对钙质砂颗粒破碎的影响因素和破碎机理进行了研究;在此基础上建立了钙质砂考虑颗粒破碎的本构模型,并对模型的模拟效果进行验证。具体的内容和结论如下:1、进行围压0.1至3.2MPa三轴条件下钙质砂的固结排水和固结不排水试验,对钙质砂三轴条件下的剪切特性进行分析。2、在介绍土体颗粒破碎分类和各种度量方法的基础上,分析了矿物成分、粒径大小、颗粒级配、应力水平和剪切应变等因素对颗粒破碎的影响;通过不同形状钙质砂颗粒在不同类型和应力水平试验前后的形态变化,分析不同形状钙质砂颗粒的破碎类型;给出了三轴试样中钙质砂的单个颗粒所受特征应力的公式。3、对钙质砂的颗粒破碎机理进行分析,给出了关于破碎消耗能量、摩擦角、剪胀与偏应力比的关系式。此公式有利于区别颗粒破碎、剪胀和滑动摩擦各部分对钙质砂或者其他无粘性土抗剪强度的影响。4、本文提出的考虑颗粒破碎的本构模型中,基于剪切变形中颗粒破碎的能量消耗提出了一种塑性流动准则。模型采用非关联流动准则和运动强化模型,考虑了颗粒破碎对塑性剪切变形与塑性体积变形的影响。在极限平衡条件下提出了应力-应变公式。模型能够准确模拟钙质砂在各围压下的应力-应变-体变特性,并且能够描述钙质砂的应力硬化和峰值后的应力软化特性。模型的特点是能够模拟各剪切应变阶段的颗粒破碎。更多还原

【Abstract】 Calcareous sand is a special marine geotechnical medium, which has unexpected physical and mechanical property due to its origin and fabric. It is demonstrated that the particle crushing is a main factor affecting the property of calcareous sand. Currently, the study on the mechanical behavior of calcareous sand has made great achievement, while the research on the constitutive model for calcareous sand incorporating particle breakage is not so much. In this study, serials of shear laboratory tests were carried out and the shear mechanical behavior of calcareous sand was presented thoroughly. Many parameters influencing particle breakage and the mechanics of grain rupture were analyzed. The constitutive model for calcareous sand incorporating particle degradation was developed and the verification of the model was also presented. The main work can be concluded as follows.1、Axisymmetric specimens of calcareous sand were tested in drained and un drained triaxial compression tests between confining pressures of 0.1 and 3.2MPa. The triaxial shear mechanical behavior of calcareous sand was presented.2、Based on the overview of the different modes of grain breakage and different definitions of existing particle breakage factors, many parameters influencing grain breakage were analyzed, such as mineral component, grain size, grain composition, stress level, and shear strain. The characteristic particle stress acting on a particle in a sample was calculated by a simple formulation.3、The grain rupture mechanics of calcareous sand was analyzed. A relationship between the energy consumption due to particle breakage, angle of friction, dilatancy, and deviator stress ratio was derived. It may be helpful to distinguish the effect of particle breakage, dilatancy, and the basic friction component of shear strength for calcareous sand and other cohesionless soils.4、In the current model, a plastic flow rule has been developed incorporating the energy consumption due to grain crushing during shear deformation. A non-associated flow and a kinematic type yield locus have been adopted in the model. The effects of grain breakage on the plastic distortional and volumetric deformations are incorporated in the current model. The stress-strain formulations are developed within the general critical state framework. The model can accurately predict the stress-strain and volume change behavior of coarse granular aggregates. The plastic dilation and contraction features of coarse aggregates at various confining pressures are well captured, and the strain-hardening and post-peak strain-softening behavior of calcareous sand adequately represented. A particular feature of the model is its capability to predict the degree of particle breakage at any stage of shear deformation.更多还原