【作者】 李劭晖；

【导师】 徐伟；

【作者基本信息】 同济大学 ， 结构工程， 2007， 博士

【摘要】 随着我国桥梁建设的发展，在大跨度悬索桥的施工过程中出现了一些开挖深度和平面尺寸很大的锚碇基坑，其嵌岩支护结构设计和基坑开挖施工安全性方面还存在一些需要探讨的问题。本文结合实际工程，通过理论分析和现场监测资料总结了嵌岩地下连续墙的受力和变形特征，并与普通地连墙进行比较。研究表明，由于基岩的约束作用，嵌岩地连墙的变形可以控制在较低水平并且在嵌岩位置变形会出现反弯点，导致墙身在该位置会出现很大的负弯矩，对其设计起控制作用；分析表明，加大墙厚可以在一定程度上减少变形但是会大大增加墙身受力特别是嵌固段的负弯矩；一定的嵌岩深度有助于提高围护结构的稳定和减少变形，但达到一定深度后再增大嵌岩深度并不能改善支护结构受力；针对嵌岩地下连续墙的受力特点，本文提出了其正截面设计的新方法，建议考虑地连墙轴向压力的有利作用、将截面当作偏压结构进行设计，在保证地连墙安全的前提下减少了墙体配筋量并提高了墙身在嵌岩位置的塑性转动能力，该设计方法通过结构试验进行了检验。考虑到本次试验鲜有先例报道，所以本文通过数值方法进行了验证。数值计算的结果佐证了本次试验研究和设计方法的可靠性，并通过改变基岩弹性模量模拟了各类岩石对地连墙受力性能的影响，据此确定了墙身在各类岩层的嵌入深度。弹性地基梁法是目前基坑支护结构设计的主要方法，但是m值的确定还是依赖经验公式，而没有考虑基坑开挖施工的动态影响和圆形围护结构的拱作用。本文基于弹性地基梁理论，通过现场实测基坑变形，基于优化方法，对土体的m值进行反分析，并利用所得参数预报下一工况的支护结构变形。以润扬北锚为算例，对本文的方法进行了验证，并探讨了基坑开挖时，被动区土体m值的变化规律和取值方法；基于薄壳弯曲理论，推导了形式类似于弹性地基梁理论的圆柱形支护结构挠曲微分方程，建议将围护结构的拱作用通过分布弹簧来模拟，考虑到地连墙槽段间接头的削弱作用，分布弹簧的刚度应该有一定折减，最后以阳逻南锚为算例验证了该计算方法。基于现有的有限元理论和成熟的商业软件，建立了嵌岩地下连续墙支护深基坑开挖计算模型，可以模拟支护结构与土体的摩擦和基坑的分步开挖。以黄埔北锚为工程背景用本文模型进行分析，结果表明，圆形基坑主要依靠支护结构的环向拱作用来抵抗坑外水土压力，与常规的条形基坑有较大差别。圆形基坑的变形和应力都控制在较低水平，随着开挖的进行，墙身最大变形位置开始随开挖进程下移，但是在后几层开挖时，最大变形位置受基岩的约束作用并不进一步下移，而是稳定在开挖面以上，故而随深度增加而加强支撑的传统设计经验并不适用于该类支护结构。本文针对此特点，提出了该类基坑支护设计的优化方法，并给出了具体算例。通过对国内代表性的已建工程进行调研，总结了嵌岩地连墙施工成套技术、监测技术和施工优化技术的进展，提出了合理的信息化施工运行架构，并以实际工程为例，探讨了嵌岩支护结构施工期间的优化问题。最后，对本文工作进行总结并展望了下一步的研究方向。更多还原

【Abstract】 Anchor pit appears during the constrution of span bridge the depth and plan sizeof which exceed that of ordinary pits significantly. There are some problems in thedesign of rock-socketed retaining and construction safety for anchor pit.Load-bearing and deformation character of rock-socketed diaphragm isgeneralized from in-situ data of typical pits. It is different from conventionaldiaphragm that rock-socketed diaphragm resist negative moment on bedrock whichcontrols the design because of the restraint function of bedrock. The influence ofdifferent thickness and rock-socketed length on load-bearing character is given. Theresults show that thickening diaphragm can decrease deformation but increaseinternal force greatly, especially the negative moment. Proper rock-socketed length isbeneficial to stabilization of retaining structure and decrease deformation.According to mechanical character of rock-socketed diaphragm, new designmethod of normal section is presented in which the gravity of support system andrestraint function of bedrock are considered. Compared with traditional method, therebar ratio of diaphragm decreases obviously and plastic rotation of diaphragmsection near bedrock is guaranteed. This new design method is confirmed byexperiment and carried out in north anchor pit of Runyang bridge. Based on theappropriate material constitutive equation, failure criterion and model of cracking, thenumerical analysis is used to simulate experiment. The results justify the measureddata of experiment and compare the influent of elastic modulus of different bedrock,so proper rock-socketed length is presented.Elastic foundation beam method is widely used in the design of retainingstructure for foundation pit. Traditionally, the "m" of soil is determined by empiricalequation which does not consider the dynamic factors during excavation and archaction of round pit. Grounded on optimum method, the back analysis is used tocalculate the "m" of soils, which then are applied to predict the displacement of theretaining structure in next step and describe the variation of "m" during excavation. This method was carded out during the construction of north anchor of Runyangbridge; Based on the bending theory of shells, differential equation of the elasticsubgrade beam is derived which consider the arc action of retaining structure.Because of the influence of joint between diaphragm panels, the reduction factor ofring stiffness is presented through a typical round anchor pit.The excavation process of the south anchor pit of Huangpu bridge is simulatedby using spatial nonlinear FEM in which the interaction between soil and structure isconsidered. The stress and deformation of the support system during constructionprocess are performed and justified by measured value. The results show that thecylindrical retaining structure subjected mainly to the axial compressive anddeformation rule is different from that of strip one. Maximum lateral displacementdepth grows with excavation, and stops until it reaches a certain depth. So thetraditional design method which strength section of brace is not suited for therock-socketed cylindrical retaining structure and the optimal design is needed.Through investigation in several typical anchor pits, the packaged technology ofrock-socketed diaphragm is generalized, including panel construction, cut off water,observation system and joint between panels. Combined with practical engineering,the optimal method during construction is given.Lastly, author summarizes work of the paper and presents the further researchdirections.更多还原