挡土墙土压力非线性周期分布内变量梯度模型

发布时间：2018-03-22 15:06

本文选题：挡土墙　切入点：土压力　出处：《北京建筑大学》2017年硕士论文　论文类型：学位论文

【摘要】：大量的模型试验和现场实测数据均表明,挡土墙后土压力沿墙高呈非线性分布,并非经典土压力给出的线性分布假设。众多岩土工作者已经对土压力非线性分布现象达成了共识,并且提出了很多理论来解释这种现象。其中最著名的是卡岗在经典库伦理论的基础上提出的以水平条形单元为研究对象的水平层分析法。但是这种方法给出的只是墙后土压力抛物线形状的分布,更不能解释土压力中间状态和土体破坏的机理。更多的模型和实测数据也揭示了墙后土压力沿墙高的非线性分布呈现“R”形或者周期性波动的特点,这是现有的土压力计算理论无法的解释的。本文试图联系内变量梯度理论,利用内变量梯度理论在解释应变局部化、应力应变空间周期分布方面的显著优势,为土压力分布的研究提供一个新的思路。本文利用梯度理论研究了土压力沿墙高分布周期性波动分布现象,取得了如下主要成果:土体作为典型的散体材料,不同于一般的连续介质材料,在力学行为方面往往表现出非局部特性。经典的土压力理论是建立在传统弹塑性力学基础上,将土作为连续介质进行的研究,具有一定得局限性,不能解释土压力沿墙高周期性波动分布现象。(1)在经典Mohr-Coulomb破坏准则的基础上,考虑了一点的应力状态与相邻点的应变梯度的关系,用周围点的应力平均值来代替一点的应力值。引入应力张量第一不变量(静水压力)的二阶梯度项,利用平面应变假设,得到了挡土墙水平土压力沿墙高分布的解析解,结果表明该模型能较好的描述挡土墙后土压力沿墙高的周期性分布;(2)进一步讨论了内禀长度影响主动土压力分布的规律。作为表征材料内部尺寸而被引入的内禀长度,既保证了量纲平衡,也使得土体结构的自我组织和耗散、颗粒之间的长程相互作用的影响被引入到破坏准则中。墙后土体随着深度增加会越来越密实,内禀尺寸也会越来越大,土压力周期和波动都会随之增大;(3)在已经得到的内变量梯度模型的基础上,进一步考虑到土的应力应变关系的下降段,联系侧向应力-应变和土压力-位移的类似关系,将挡土墙的位移量引入到方程中去,得到了墙后土压力随挡土墙位移变化的分布变化;(4)在研究了平动模式下,挡土墙位移与墙后土体应力应变关系后,继续考虑挡土墙绕墙底转动(RB模式)和绕墙顶转动(RT模式)两种最基本的转动模式。利用转动参数定量地描述了挡土墙的转动状态,并将参数引入到内变量梯度模型中得到了墙后土压力在不同转动状态下的土压力分布。内变量梯度解联系了位移模式与层间等效内摩擦角的关系,能很好的描述挡土墙在转动状态下墙后土压力从主动极限状态到被动土压力状态或者过极限破坏状态整个过程的变化情况利用改进的土压力计算模型,将弹塑分区的概念引入到计算模型中去,进一步明确墙后土体破裂面形状和弹塑性分区形状,求出弹性区高度。内变量梯度模型中控制系数的确定吸收了广大学者在墙后土体弹塑性分区的成果,利用弹塑分区界点处土压力连续光滑作为边界条件。本文也借鉴了前辈学者在墙后土体弹塑性分区、土体软弱下降段、内摩擦角逐步发挥等概念和理论,是对传统土压力的继承和发展。
[Abstract]:A large number of model experiments and field data show that the earth pressure retaining wall along wall height distribution is nonlinear, the linear distribution assumption is not the classical earth pressure is given. Many geotechnical workers have reached a consensus on the earth pressure distribution of nonlinear phenomena, and put forward many theories to explain this phenomenon. The most famous is the post card based on the classical theory of Kulun on the horizontal bar unit as the research object of the horizontal layer analysis method. But this method gives only the earth pressure behind parabolic shape distribution mechanism not to destroy the earth pressure and explain the intermediate state of soil. More features of the model and field data also reveals the wall earth pressure along the nonlinear the wall height distribution showed the "R" - shaped or cyclical fluctuations, this is not the explanation theory to calculate the earth pressure existing. This article attempts to contact the internal variable Gradient theory, using the theory of variable gradient of strain localization in the interpretation, should be a significant advantage in periodic stress space, provide a new way to study the distribution of earth pressure of earth pressure along wall height distribution of the periodic fluctuation of distribution gradient theory in this paper, the main results are as follows: soil as a typical granular material, different from the continuous medium materials, in mechanical behavior often exhibit non local characteristics. Classical earth pressure theories are based on the traditional elastic-plastic mechanics on the basis of research on the soil as a continuous medium, has certain limitations, cannot explain the earth pressure along the wall of high cycle the fluctuation of distribution. (1) based on the classical Mohr-Coulomb criterion, considering the point of relationship between strain gradient stress and adjacent points, stress points around the mean value generation For a little stress value. The stress tensor invariants (hydrostatic pressure) of the two step, using the plane strain hypothesis analysis of retaining wall horizontal earth pressure distribution along the wall of the solution is obtained. The results show that the model can describe the soil pressure on retaining wall along the periodic distribution of the high walls; (2) further discusses the intrinsic length effect of active earth pressure distribution. The intrinsic length was introduced as an internal size characterization of materials, both to ensure the dimensional balance, but also the structure of the self organization and dissipation, influence between particles and Cheng Xiang interaction is introduced into the failure criterion. After the wall with the increase of the depth of soil will be more dense, the intrinsic size will be more and more, the earth pressure cycle and fluctuation will increase; (3) based on variable gradient model has been on the further consideration of soil stress strain Descending system, lateral contact stress and strain should be similar between the earth pressure and the displacement of the retaining wall, the displacement is introduced into the equation to get the wall soil pressure distribution with change of retaining wall displacement; (4) in the study of translational mode, the stress-strain relation of retaining wall displacement and after the wall, continue to consider retaining wall rotation around the bottom of the wall (RB) and rotation around the top of the wall (RT) of two kinds of the most basic rotation mode. Using the rotation parameters quantitatively describe the rotation state of the retaining wall, and the parameter into the internal variables in the gradient model of the earth pressure on the wall different rotation soil pressure under the condition of variable gradient distribution. Solutions between friction angle and interlayer equivalent displacement model, which can well describe the retaining wall in the rotating wall earth pressure from the active limit state to the passive earth pressure state or ultimate failure The calculation model of soil pressure improved the whole process of using state changes, will play the concept of plastic partition into the calculation model to further clarify the soil behind the wall rupture shape and elastic-plastic shape, calculate the height of the elastic zone. The absorption of the majority of scholars in the wall after the soil elastic-plastic results confirm the control the coefficient of internal variable gradient model, using elastic-plastic soil pressure at the partition point is continuous and smooth as boundary conditions. This paper also draws scholars behind the wall soil elastoplastic soil soft partition, descent stage, internal friction angle gradually play the concept and theory, is the inheritance and development of traditional earth pressure.

【学位授予单位】：北京建筑大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU476.4;TU432

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