【作者】 张春会；

【导师】 郭海燕；

【作者基本信息】 中国海洋大学 ， 港口、海岸及近海工程， 2007， 博士

【摘要】 随着我国城市建设的发展和大型水利工程的不断涌现,深基坑工程日益增多,且规模和深度不断加大。有限元法由于强大的适用性,正日益成为深基坑工程计算分析的强有力工具。以往基坑开挖有限元分析经验表明,有限元模拟结果的可靠性极大地依赖于所使用的土体本构模型和计算参数。然而,目前关于这方面的研究尚不完善。为此,本文以深基坑开挖有限元数值模拟为工程背景和研究内容,对其中的两个关键技术问题-土体本构模型和计算参数反演展开研究,研究工作成果如下:1.为了模拟基坑开挖卸荷过程中加载土体从初始应力状态开始持续地发生非线性弹塑性变形这一特性,将岩土弹塑性理论引入到Duncan-Chang模型中,将Duncan-Chang模型改进、发展成一种新的弹塑性土体模型(即改进Duncan-Chang模型)。2.详细分析了改进Duncan-Chang模型的数值计算技术,编制了基于改进Duncan-Chang模型的基坑开挖有限元计算程序MDC-Excavation。通过对某基坑开挖模拟,并与观测值比较,初步验证了改进Duncan-Chang模型的合理性。3.提出用五元件粘弹性土体模型模拟软土基坑开挖中土体的流变性,编制了相应的粘弹性有限元计算程序EV-Excavation。以上海某软土基坑开挖为例,预测了基坑开挖围护结构变形性状,通过与现场观测值比较,表明五元件粘弹性土体模型能较好地模拟软土基坑开挖变形的依时性特征。4.为了得到软土基坑开挖模拟的等效计算参数,将单纯形法引入到软土基坑开挖位移反分析中,编制了相应的位移反分析程序Back-EV。实例计算表明,在初值选择较好情况下,Back-EV能得到较为理想的计算结果。5.针对单纯形法易于陷入局部极值和严重依赖初值的缺陷,提出了随机单纯形法,然后将其应用到软土基坑开挖位移反分析中,开发了相应的计算程序RSMB-Excavation。数值实验和实例计算表明,随机单纯形法能更好地找到全局最优解或近似最优解,同时随机单纯形法也不依赖于单纯形初值的选取,因此随机单纯形法是基坑开挖位移反分析的一种有效方法。更多还原

【Abstract】 With rapid development of city construction and large hydraulic engineering projects springing up, deep pits increase by gradually, and the excavation depth and size become bigger and bigger. Because of better adaptability, Finite Element Method (FEM) is playing a much more important role for the design and analysis of pit engineering. The experiences of pits excavation numerical simulation indicate that the simulating results of FEM greatly depend on the soil constitutive model and the calculation parameters. However their studies have been not perfect as yet. Therefore, the FEM numerical simulation of deep pit excavation is taken as engineering background and study content in the paper, and two key techniques including the soil model and the back analysis of the calculation parameters are studied. Studying results and conclusions are listed as follows:1. In order to simulate the characteristic that loading soil continuously appears nonlinear elastic-plastic deformation from the initial stress state during pit excavation, the elastic-plastic theory of rock and soil is introduced into Duncan-Chang model, and Duncan-Chang model is improved and developed into a new elastic-plastic soil model (namely the improved Duncan-Chang model).2. The numerical calculation techniques of the improved Duncan-Chang model are thoroughly studied, and the FEM program (MDC-Excavation) of pit excavation simulation based on the improved model is developed. Through the simulation for a pit excavation and the comparison between the measured data and the calculating results, the improved Duncan-Chang model is proved to be reasonable and believable.3. The five-component visco-elastic soil model is advised to simulate the rheology of the soft pit excavation, and the visco-elastic FEM program (EV-Excavation) for pit excavation is developed. Taking the soft pit excavation in Shanghai as an example, the time effect of the retaining structure deformation is predicted. Through the comparison with the measured data, it is shown that the five-component visco-elastic soil model can better simulate the time effect of the soft pit excavation.4. In order to obtain the equivalent calculation parameters of the soft pit excavation, the simplex method is introduced into the displacement back analysis of the soft pit excavation, and the displacement back analysis program (namely Back-EV) is developed. Through case study it is indicated that the better and reasonable results can be observed by Back-EV when the initial values are reasonable.5. Facing up to the shortcomings of the simplex method such as easily losing in local extreme and serious dependence on the initial values, the random simplex method (RSM) is presented, then it is applied to the displacement back analysis of the soft pit excavation, and the correspondent displacement back analysis program(RSMB-Excavation) is developed. The numerical test and case study indicate that RSM can efficiently research for the overall optimum solution or the approximate optimum solution. Besides RSM does not depend on the initial values, so RSM is an efficient method for the parameter back analysis of the soft pit excavation.更多还原