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大量土工问题是具有不规则甚至不确定边界条件的多维问题,面临的荷载不仅限于明确定义的单调荷载,还包括时变与随机往复荷载。而土作为一种天然材料,其力学行为极为复杂。多相性、非均质性、各向异性、非线性、加载路径与历史的影响、压力敏感性、体积变形与剪切变形的强耦合等等均为岩土工程师们通常面临和需要处理的问题。当太沙基在80年前以他的划时代的有效应力原理奠定现代土力学基础时,现代计算技术与相应的基础理论并不存在。因而除个别问题如一维固结问题与渗流问题在适度简化后存在解析解外,大量问题的处理必须基于高度简化的面向问题的集总参数模型。这些模型结合工程师的经验对传统土工结构往往能给出合理的或保守的强度指标,但很少能提高和深化我们对问题的内在认识,而且在面对许多现代新型土工结构时,这些传统方法往往显得力不从心。自20世纪中期以来,在应用力学领域内有着一系列重要发展:多相连续介质理论与塑性本构理论趋于成熟,有限元与差分计算方法已成为通用的偏微分场方程求解器,数字计算设备的能力也已获几何级数的提高。以临界状态理论为标志土力学本身也有着重要发展。这一切发展已有可能将土力学的问题纳入一个统一的理论框架内予以系统的处理,而且事实上许多土力学与岩土工程的研究及分析也已在不同程度上基于这样的一个框架,而其中土的本构模型是一个关键。笔者力图从基本的物理和数学原理出发来勾划出一个土弹塑性本构理论框架,其大部分内容都来自经典文献。为避免不确定性,以太沙基有效应力原理为前提,所以该框架仅对饱和土有效。
A large number of geotechnical problems are multidimensional problems with irregular or even indefinite boundary conditions. The loads they face are not limited to well-defined monotonic loads, but also include time-varying and random reciprocating loads. Soil as a natural material, its mechanical behavior is extremely complicated. Polymorphism, Inhomogeneity, Anisotropy, Nonlinearity, Influence of Loading Path and History, Pressure Sensitivity, Strong Coupling of Volume Deformation and Shear Deformation are all problems that geotechnical engineers usually face and need to deal with . When Taishaji laid the foundations of modern soil mechanics 80 years ago with his epoch-making principle of effective stress, modern computing techniques and corresponding basic theories do not exist. Therefore, except for some problems such as one-dimensional consolidation problems and seepage problems with analytic solutions after moderate simplification, the handling of a large number of problems must be based on a highly simplified problem-oriented lumped parameter model. These models, combined with the experience of engineers, tend to give reasonable or conservative strength indicators to traditional geotechnical structures, but seldom improve and deepen our internal understanding of the problem and, in the face of many modern new geotechnical structures, these traditional methods Often seem powerless. Since the middle of the 20th century, there have been a series of important developments in the field of applied mechanics: the theory of multiphase continuous media and the plastic constitutive theory tend to mature, and the finite element and differential calculation methods have become common partial differential field equation solvers, numerical calculations The capabilities of the device have also been improved geometrically. Marked by the theory of critical state, soil mechanics itself also has an important development. All this development has made it possible to systematically address the problems of soil mechanics within a unified theoretical framework, and in fact many of the studies and analyzes of soil mechanics and geotechnical engineering have also been based in part on such a framework, Among them, the constitutive model of soil is a key issue. The author seeks to outline a theoretical framework of elasto-plastic constitutive theory from the basic physical and mathematical principles, most of which come from the classical literature. In order to avoid the uncertainty, the principle of effective effective stress is based on terbutaline, so the framework is only effective for saturated soil.