The Principle of Interaction between Plastic Volumetric and Shear Strains for Unsaturated Soils

The principle of interaction between plastic volumetric and shear strains for rock and soil has been extended to the field of unsaturated soils.Two new interactions of suction-plastic volumetric strain and pore air pressure-plastic volumetric strain appear in the unsaturated state of a soil except the interaction between plastic volumetric and shear strains.It is very important to find that the suction possesses a dual property,which is the origin of generating its special functions.Thereby the effect of the suction on volumetric strain includes two opposite aspects.By means of this property of suction,the physical significance of effective stress parameter,effects of suction on volume change and preconsolidation pressure,and the mechanism of collapse upon wetting all can be explained.In addition,it is theoretically proved by application of this principle of interaction that the critical state line for unsaturated soils exists,and is unique and independent of the stress history.

CONSOLIDATION HEORY OF UNSATURATED SOIL BASED ON THE THEORY OF MIXTURE(Ⅰ)

Unsaturated soil is a three-phase media and is composed of soil grain,water and gas.In this paper,the consolidation problem of unsaturated soil is investigated based on the theory of mixture.A theoretical formula of effective stress on anisotropic porous media and unsaturated soil is derived.The principle of effective stress and the principle of Curie symmetry are taken as two fundamental constitutive principles of unsaturated soil.A mathematical model of consolidation of unsaturated soil is proposed,which consists of 25 partial differenfial equations with 25 unknowns.With the help of increament linearizing method,the model is reduced to 5 governing equations with 5 unknowns,i.e.,the three displacement components of solid phase,the pore water pressure and the pore gas pressure.7 material parameters are involved in the model and all of them can he measured using soil tests.It is convenient to use the model to engineering practice.The well known Biot's theory is a special case of the model.

Effective stress in soils under different saturation conditions

BISHOP’s effective stress or two state stress variables are unsatisfactory for unsaturated soils where one of fluid phases is discontinuous, so new expressions of effective stress should be founded. The approach for derivation was according to the principle of equilibrium of forces (i.e., the stress-sharing principle), and it was firstly validated by demonstrating TERZAGHI’s principle of effective stress. And then, the derivations were subdivided into four parts according to different pore air states: 1) air bubbles were spherical and suspended in pore water; 2) air bubbles were bound on soil skeleton; 3) air bubbles held almost the single section of pore; 4) air phase was continuous. The different formulae of effective stress were presented. Conclusions are drawn as follows: 1) For nearly-saturated soils, the "real" effective stress would be a little smaller than TERZAGHI’s effective stress; 2) For soils in which air phase is discontinuous in the form of bubbles, a new concept of pore air elastic pressure is put forward, and the total stress can be constituted by effective stress, pore water pressure and pore air elastic pressure; 3) For soils in which air phase is continuous, effective stress is equal to the value of the total stress plus suction; 4) Suction can be divided into two parts: one is the effect caused by additional pressure, and the other is the contract action by the "skin".

Study on one—dimensional consolidation of saturated soil with semi—pervious boundaries and under cyclic loading

The variation of effective stress ratio of stratfied soil with semi pervious boundaries and under cyclic loading was analyzed on the basis of Terzaghi's one dimensional consolidation assumptions. A solution by Laplace Transform was obtained for the case when the soil was under time varied loading. With numerical inversion of Laplace Transform, some useful results were obtained for several kinds of commonly encountered loadings. The results can be meaningful in engineering practice.

Derivation of the work expression and discussion on the effective principle and the phase separation theorem in unsaturated soil

Based on the balance equations for mass, linear momentum, energy in porous media theory and some hypotheses in unsaturated soil mechanics, an expression of the total deformation work W is derived, and with the help of the specific ex-pression of the work, the effective stress conjugated with the displacement of the soil skeleton is suggested by the authors, which has the similar form as the expressions proposed by Wheeler (2003) and some other researchers according to their experience and intuition, but the effective stress presented in this paper is derived on the basis of porous media theory and its assumptions, whose premise and hypothesis are clear. It is also pointed out that due to the complexity of the physical mechanism and various influencing factors, it is impossible in unsatu-rated soil mechanics to determine the deformation of solid skeleton by the effective stress only, like in the saturated soil mechanics. Besides, by using the expression of the deformation work and the free energy Aα for each phase, the applicability of the Phase Separation Principle proposed by Passman (1984) in unsaturated soil is discussed, and it is considered that the principle should not strictly apply to un-saturated soil mechanics.

非饱和成层土稳态渗流问题的解析计算

广泛存在的成层土非饱和稳态渗流的解析计算研究相对薄弱。基于达西渗流定律和土层界面的连续性条件,构建了描述非饱和成层土稳态渗流过程的数学模型。使用分离变量技术和数学归纳思想,获得了成层土同一剖面的基质吸力、有效饱和度与吸应力沿高程分布的解析表达式。基于COMSOL数值分析平台对解析算法进行了验证计算,从而实现了非饱和成层土稳态渗流过程的解析求解。而后,探讨了土层界面的存在对渗流过程的影响并开展了参数敏感度分析。分析表明:(1)相同入渗条件下相同高程处砂土的基质吸力最大,黏土最小;地表渗流速率的不同对粉土层有效饱和度分布影响最大,砂土最小。(2)黏土层中吸应力近乎线性增长,砂土的吸应力则沿高程先增大后减小;土层界面的存在会影响基质吸力沿高程的增长速率,可使有效饱和度和吸应力沿高程分布发生突变。(3)Gardner模型参数α值越小,相同高程处基质吸力值越大,饱和土渗透系数(ks值)越小,基质吸力增长速率越慢;α与k_(s)取值越小,有效饱和度降低速率越慢;α取值越小或ks取值越大,地表处的吸应力值越大。研究成果可为诸如边坡稳定等工程地质问题提供一定的理论支撑。

含毛细饱和区土层中有效自重应力的快速计算方法

毛细饱和区的存在,使得有效自重应力的计算相对烦琐。尤其在考察有效自重应力分布时,很难直接绘制出各土层的分布曲线。为解决上述问题,以包含毛细饱和区的各土层有效自重应力计算为例,推导得出了可以快速计算土层中有效自重应力的方法,解释了毛细饱和区土体有效自重应力变化的本质。应用该方法,可以快速、高效地计算、绘制土层中有效自重应力的分布,对于土力学毛细饱和区相关知识点的理解和应用起到了积极的作用。

新工科背景下岩土工程本研协同的实践型教学:以微型三轴仪的研发为例

技术的飞速发展和产业的不断变革为工程教育的改革提出了新的要求和挑战,也促进了新工科建设理念的生成。在土木工程领域人才的全过程培养进程中,教学与实践的有机结合可以实现激发学生创新思维、提升工程实践能力和培养专业综合素养。针对土力学课程教学中关于土工测试环节存在的问题,组织相关科研方向的研究生和正在学习该知识点的本科生,自主研发了一套微型三轴仪作为随堂教具并运用于教学实践,旨在优化教学模式、加强课堂互动。微型三轴仪体积小、重量轻、便于携带,可模拟实际三轴仪的固结、剪切和控制排水条件等功能,有助于学生掌握不同类型常规三轴压缩试验的关键操作步骤,直观地体会有效应力决定土的强度和变形特性,激发学生学习热情,培养综合实践能力,提升课堂教学效果。基于理论知识掌握与实践能力提升的导向,对岩土工程教育过程中的理论和实验教学改革进行了探索与实践。以教学促进实践,以开发促进研究,打通了不同阶段的专业知识衔接,通过仪器研制和课堂反馈夯实专业理论知识,构建了本研学生协同联动的实践型教学模式,探讨了微型设备类教具在研发过程中的难点,实现了专业能力高、创新思维强的人才培养。

有效应力原理解析

分析了关于饱和土有效应力原理的一些错误理解,基于土颗粒-水相互作用分析,给出了土体中有效应力的物理含义,是单位截面的土体中土颗粒骨架所传递的有效荷载,其大小等于总应力与孔隙水压力之差。利用土体的力平衡方程,一方面证明了Terzaghi饱和土有效应力原理,并分析了该原理的适用范围;另一方面证明了Bishop非饱和土有效应力原理,解释了参量χ的物理含义,将二原理统一在一个力学框架下,从理论上说明了Terzaghi有效应力原理是Bishop有效应力原理在有效饱和度χ=1时的特例,并分析了Bishop非饱和土有效应力原理的适用范围。研究表明,从荷载条件和土性条件两个角度分析有效应力原理,清晰地解释了有效应力的物理概念,并且提出孔隙水压力影响土体力学特性的机理。

考虑吸力效应的非饱和黏土回弹模量预估模型

回弹模量是反映路基弹性支撑能力的重要指标,并受运营期间基质吸力变化的显著影响。通过3种压实黏土试样的土-水特征曲线试验和重复动三轴试验,研究了回弹模量与基质吸力的相关性,并基于非饱和土有效应力原理,提出了考虑吸力效应的回弹模量预估模型。结果表明:基质吸力与回弹模量之间具有较强的非线性相关性,可采用指数形式进行两者的拟合;含水率由最佳含水率-4%提升至最佳含水率+4%时,受基质吸力减小的影响,回弹模量降幅达到29.1%~39.0%;在土-水特征曲线过渡区,采用以饱和度表征的有效应力参数,可较好地反映基质吸力对于回弹模量的贡献,预估效果优于采用残余含水率或进气值相关的有效应力参数;在相同饱和度的情况下,黏粒含量越多、塑性指数越高,基质吸力对有效应力的贡献比例越小。

土力学有效应力及其作用的讨论

讨论了饱和土有效应力的作用及其使用中应注意的问题,以及土力学预测中存在的不确定性的几种情况.从土的各相平衡方程出发推导得到了非饱和土的总应力和各相应力之间的关系,以及非饱和土的平均骨架应力的表达式,并定义该式为非饱和土的有效应力;该表达式与变形功推导得到的有效应力公式是一致的.文中还就非饱和土有效应力的一些问题进行了探讨.

饱和多孔介质流固耦合渗流的数学模型

将基于多孔介质的有效应力原理引入流固耦合渗流中 ,并根据平衡条件得出了应力场方程 ;充分分析流固耦合渗流的物理特性 ,建立起孔隙度和渗透率动态模型 ;依据流体力学连续性方程 ,考虑流固耦合情形下多孔介质骨架变形特性和流体的可压缩性 ,得到了孔隙流体的连续性方程 ,即渗流场方程。在以上诸方程的基础上辅助以定解条件 ,建立起了完备的饱和多孔介质流固耦合渗流的数学模型。本文还对模型进行了简化分析 ,并与经典一维固结理论作定性对比 ,分析表明 ,经典的固结理论可认为是本文模型的一种简化。

滑坡体基质吸力的观测试验及变化特征分析

降雨是影响滑坡稳定性的主要因素之一,在一个降雨周期内,滑坡体会呈干湿循环变化,坡体的基质吸力和暂态孔隙水压力会随着降雨过程和时间呈现不同的变化趋势。为研究这一复杂的变化趋势和规律,在三峡库区泄滩滑坡体上建立一个深为20 m的观测井,对滑坡体基质吸力、孔隙水压力和滑坡区降雨量进行长达2 a的观测研究,取得大量的第一手监测数据,分析总结了滑坡体基质吸力、孔隙水压力随时间、空间及降雨的变化规律。这一研究成果为进一步分析降雨对滑坡的影响程度提供了真实而科学的依据。

非饱和土固结的混合物理论(Ⅰ)

非饱和土是由土粒、水、气组成的三相介质,本文以混合物理论为基础研究了非饱和土的固结问题.文中导出了各向异性多孔介质及非饱和土的有效应力的理论公式,把有效应力原理和Curie对称原理作为非饱和土的两个重要的本构原理,建立了非饱和土固结的数学模型:由25个方程求解25个未知量.在增量线性化的情况下,本模型简化为5个控制方程求解5个未知量:3个固相位移、孔隙水压力和孔隙气压力.模型中包含7个材料参数,都可由试验测定,便于工程应用.Biot理论是本模型的特例.

饱和砂土爆炸液化模型研究

运用有效应力原理 ,建立了用于描述三相饱和砂土爆炸动力分析的实用模型。模型既可用于非饱和砂土 (与外界连通的气体、水和土颗粒 )、完全饱和砂土 (水和土颗粒 )和三相饱和砂土 (含有少量封闭气体、水和土颗粒 )的爆炸效应及其后效应如液化问题研究 ,也可用于地震荷载及其它动荷载问题的研究。

一个高饱和度非饱和土的本构模型

高饱和度的非饱和土中由于气体处于封闭状态,其内部气压的变化必将对土体的行为产生影响。首先,对高饱和度非饱和土特性进行探讨和研究,随后,在已有非饱和土模型框架基础上,采用广义有效应力原理,建立一个适用于高饱和度条件下的非饱和土的弹塑性本构模型。模型中引入气相耗散的影响,在硬化方程中考虑封闭气体压力改变的影响。最后,利用已有的试验结果来对模型进行验证,并将模型预测结果与前人模型进行对比,表明模型预测可以很好地预测土体的行为,尤其是在高饱和度条件下其结果比其他模型更加接近实际情况。

饱和土中爆炸应力波传播特性研究

在饱和土地层中建设了大量的工程项目,由于安全和防卫的需要,这些重要的工程必须考虑爆炸应力波荷载的作用,研究饱和土中爆炸应力波传播特性有着重要的意义。基于应力波传播理论,初步分析了爆炸荷载作用下饱和土介质的变形特性、压缩特性和强度特性;采用有效应力动力分析方法,推导了爆炸应力波在饱和土介质中传播的有效应力运动方程。研究结果可以为饱和土介质中建筑设施的抗爆安全评估提供理论依据。

土中有效应力概念的起源与发展

Terzaghi于1922年提出的有效应力概念是土力学的基石性概念,其历史迄今已有百年。值此百年之际,有必要对有效应力的概念起源、物理意义、方程形式及其力学作用进行总结和分析。可知饱和土Terzaghi有效应力方程已得到了广泛的认同,而非饱和土Bishop型有效应力方程的具体形式尚未统一。有效应力方程中应力变量的物理意义仍未形成共识。通过进一步的分析,认为存在于土骨架上的应力可以分为3类,第1类是由总应力引起的沿土骨架传递的应力,即有效应力;第2类是由孔隙流体压强引起的作用在土颗粒横截面上和土颗粒间接触面上的应力,它们不沿土骨架传递;第3类是由范德华引力、双电层斥力、收缩膜表面张力(对非饱和土而言)和胶结物作用引起的颗粒间局部应力,它们也不沿土骨架传递。因此,这3类应力对土体抗剪强度和体变的贡献应分别考虑。

湿吸力及非饱和土的有效应力原理探讨

提出并阐述了湿吸力的概念,分析了非饱和土的孔隙水压力与由于表面张力而产生的土颗粒之间的湿吸力的定量关系及其根本区别,探讨了湿吸力的变化规律及其主要的影响因素,分析了现有非饱和土有效应力原理存在的问题。基于湿吸力概念,分析并给出了有效应力公式,建议了非饱和土的状态分类及有效应力原理。文中明确解释了Bishop有效应力公式中经验参数χ的物理意义、表达式及其适用范围和影响因素。最后,讨论了非饱和土状态分类原则及其力学分析方法,并指出:非饱和土变形理论的研究,首先应采用细观土力学方法。

考虑非Darcy渗流和自重应力的一维固结分析

基于饱和黏土中渗流的非Darcy特性和变形的非线性,考虑土体埋深和自重应力的影响,修正了Terzaghi 1维固结方程.为简化计算,建立了以有效应力为求解对象的非线性控制方程,并采用有限差分法建立隐式差分格式对方程进行求解.探讨了综合考虑土体渗流非Darcy特性、埋深、自重应力和变形非线性时的固结特性.计算结果表明:考虑土体自重应力时的孔压消散速率和地基沉降速率都要大于不考虑土体自重时的情况;综合考虑土体自重、非Darcy渗流特性和变形非线性的孔压消散速率和地基沉降速率都可能出现前期快于Terzaghi固结理论解而后期相反的情况.