【作者】 徐中华；

【导师】 王建华；

【作者基本信息】 上海交通大学 ， 固体力学， 2007， 博士

【摘要】 由于在变形控制、可持续发展等方面的诸多优点,支护结构与主体地下结构相结合已成为建设多层地下结构的一种有效方法,是上海软土地区近年来迅速发展和应用的新型支护型式。在支护结构与主体地下结构相结合的深基坑工程设计中,最关切的问题是预测基坑的变形,但目前尚缺乏对其变形性状的系统研究。由于基坑工程的高度复杂性,采用常规的弹性地基梁法或平面有限元法已难以分析支护结构与主体地下结构相结合深基坑的复杂变形性状,因此本文采用三维有限元建模和大量的基坑实测数据分析并结合三个大型基坑工程的实践对上海地区支护结构与主体地下结构相结合的深基坑变形性状进行了系统的研究。主要内容包括如下几个方面:1.对支护结构与主体地下结构相结合的深基坑建立了考虑土、围护结构、水平支撑体系和竖向支承系统共同作用的三维有限元模型;采用弹塑性的修正剑桥模型模拟基坑开挖过程中土体的非线性特性;基于面-面接触模型实现了连续墙与土体之间的接触算法,用以真实地模拟连续墙与土体的相互作用;进而实现了对基坑施工过程的仿真模拟。系统地分析了均质地层中支护结构与主体地下结构相结合深基坑开挖的变形行为、应力和应变行为及其空间效应。研究了墙体与土体之间设置接触面与否及接触面参数对基坑变形的影响。分析了修正剑桥模型各参数对基坑变形的影响。2.在上海地区典型土层条件下,采用前面提出的三维有限元模型,对影响支护结构与主体地下结构相结合基坑的变形进行了系统的参数研究。研究了连续墙的厚度、水平支撑楼板的厚度、水平支撑楼板的竖向间距、悬臂开挖深度、坑底加固、基坑的长宽比及连续墙接头对基坑变形的影响。结合支护结构与主体地下结构相结合基坑的特点首次研究了工程中非常关心的出土口留设位置、盆式和岛式开挖、分块放坡开挖、工程桩的存在等因素对基坑变形的影响规律。探讨了在广泛的参数影响下基坑的变形特征变量包括连续墙的最大侧移、地表最大沉降、墙后土体最大侧移及坑底回弹的一般变化规律,得到了其变化范围的上限,并讨论了各变形特征变量的相互关系,从而为实测统计提供了理论支撑。3.收集了上海地区315个基坑工程的详细资料,在对大量的基坑实测数据分析的基础上研究了支护结构与主体地下结构相结合深基坑的有关变形性状。给出了围护结构最大侧移的变化范围及平均值,对其影响因素如墙底以上软土厚度、围护结构插入比、支撑系统刚度、坑底抗隆起稳定系数、桩土面积比及首道支撑的位置进行了定量分析。给出了墙后地表最大沉降的变化范围及平均值、分析了墙后地表沉降的分布模式、建议了地表沉降包络线的方程。对影响地表最大沉降的因素进行了分析并与常规顺作法基坑进行了对比。分析了坑底回弹、墙顶及立柱竖向位移的变化范围及其相关规律。研究了上海地区连续墙类、灌注桩类、钢板桩类、SMW工法类、搅拌桩类及复合土钉类等常规顺作法基坑围护结构的变形规律,并将其与支护结构与主体地下结构相结合基坑的围护结构变形规律进行了对比,揭示了后者与常规顺作法基坑在变形规律上的异同。研究得到的有关变形的规律为基坑变形的预测提供了实用图表,可直接应用于上海地区深基坑工程变形的预测。4.对由由国际广场、兴业银行大厦和上海铁路南站北广场三个采用支护结构与主体地下结构相结合深基坑工程的变形进行了实测研究。对实测结果的分析表明,围护结构各个测斜点在各个工况下的最大变形均在理论分析给出的范围之内,且平均最大侧移与理论研究得到的平均最大侧移吻合得很好,表明理论研究结果能较好地预测围护结构的最大变形。实测得到的墙后地表沉降、管线沉降和建筑物的沉降分布均位于理论研究得到的支护结构与主体地下结构相结合基坑的地表沉降包络线之内,表明该包络线可用来较好地预测基坑开挖对周边环境的影响。研究了基坑开挖引起的水平梁板支撑体系的沉降或回弹的分布规律及基坑变形的时间效应。分析了基坑开挖引致的周边建筑物的三维沉降形态。更多还原

【Abstract】 Due to its many advantages such as the capability of deformation control and being of benefit to sustainable development, the construction method of deep excavations supported by permanent structure is an efficient way to build multi-storied underground structures. It is a new type of retaining system which has developed quickly and become more and more widely used in Shanghai soft deposit in recent years. A major concern in the construction activities of this type of retaining system is to predict the wall deflections and surface ground settlements in the design stage. However, a fundamental study of the deformation behavior of this type of retaining system is relatively limited and infrequently reported in the literature. As deep excavations supported by permanent structure are in nature very complex, it is insufficient to analyze their deformation behavior by using conventional methods such as the method of beam on elastic foundation and the plane finite element method. This thesis evaluates the deformation behavior of deep excavations supported by permanent structure in Shanghai soft deposit, based on a series of 3-D finite element analysis as well as data analysis from a large number of case histories. The main contributions of this thesis are described in the following:(1) A three dimensional finite element model considering the interactions between the soil and structures is setup to simulate the construction procedures of a deep excavation supported by permanent structure. The elastic-plastic Modified Cam-Clay constitutive model is used to present the behavior of the soil. The interaction between the soil and the diaphragm wall is simulated by surface-based contact. Deformation behaviors and stress and strain responses due to deep excavation in homogeneous soil are investigated in details. Results of analyses considering and without considering the interfaces between the diaphragm wall and the soil are compared to investigate the influence of the wall-soil interface on the deformation caused by excavation. Effect of input parameters of the wall-soil interface and the Modified Cam-Clay model on the response of deep excavations is also discussed.(2) Extensive parametric studies are performed by a series of 3-D finite element analyses of deep excavations supported by permanent structure in typical Shanghai stratum to investigate their influence on excavation-induced deformations. The analyzed parameters include the thickness of the wall, the thickness of the horizontal slabs, the vertical strut spacing, cantilever excavation depth, soil reinforcement, the ratio between the excavation length and excavation width, and the wall connection. Moreover, some factors affecting the deformations of deep excavations such as the location of access openings, bermed excavation,‘Island-type’excavation, blocked excavation and the existing of piles are also evaluated. General trends of the maximum lateral displacement of wall, maximum ground settlement, maximum lateral displacement of ground and bottom heave are obtained by collecting them from the numerical experiments. Relationships between these deformation variables are analyzed and their upper limits are also proposed. The general trends of these deformation variables provide a guideline to the analysis of data from a large number of case histories in the following chapter.(3) A database of 315 case histories of deep excavations in Shanghai soft deposit is presented. Deformation behavior of deep excavations supported by permanent structure is analyzed based on these deformation data. The range and mean value of the maximum lateral displacement of wall are proposed. Some factors which affect the maximum lateral displacement of wall are analyzed. These include the thickness of soft soil above wall toe, the embedded depth ration of wall, the system stiffness, the factor of safety against basal heave, the ratio between the sectional area of piles and the excavation area, and the location of first level strut. The range and mean value of the maximum ground settlement are also proposed. An equation is proposed to describe the boundary of ground settlement based on the analysis of ground settlement profile. Factors affecting the ground settlement are studied. Ground deformation behavior of deep excavations supported by permanent structures is compared with that of conventional bottom-up method. Ranges of bottom heave, vertical displacement of top of wall and piles are evaluated. Deformation behavior of other retaining system (constructed using bottom-up method) such as diaphragm wall, bored pile wall, sheet pile wall, SMW, soil cement columns, and compound soil nail wall are studied and are compared with that of deep excavations supported by permanent structure. Many figures obtained trough these theoretical analysis offer a practical approach for geotechnical engineers to predict deformations of deep excavations in Shanghai soft deposit.(4) Comprehensive monitoring systems were installed on three excavations which were supported by permanent structure. Emphases are put on the analysis of deformations of these three excavations. Results show that maximum lateral displacements of all the inclinometers in walls at different stages fall in the range proposed by theoretical analysis. Furthermore, mean values of measured maximum lateral displacements of wall agreed quite well with that proposed by theoretical analysis. This confirms the validity of the theoretical analysis results to predict maximum wall deformations. Monitored ground settlements, pipeline settlements, and buildings settlements fall within the range defined by the boundary equation proposed by theoretical analysis. This shows that the boundary equation can be used to evaluate the influence of deep excavation on adjacent facilities. Vertical deformations of the horizontal slabs are analyzed based on the monitored data. Time effects on lateral wall deflections and 3-D settlements of buildings caused by excavation are also studied.更多还原