【作者】 丁勇春；

【导师】 王建华；

【作者基本信息】 上海交通大学 ， 结构工程， 2009， 博士

【摘要】 随着软土地区城市建筑密度的增加,基坑工程常处于密集的既有建(构)筑物附近,基坑施工受到了更加严格的环境制约。预测基坑施工引起的变形及其对周边环境的影响,总结各种基坑变形控制技术措施并验证其实施效果,对于软土地区深基坑的设计与施工具有重要指导意义。本文结合上海软土地区深基坑工程实践,采用理论分析、数值模拟、原位试验和施工监测等方法,对软土地区深基坑围护结构(地下连续墙)施工和基坑开挖引起的变形及基坑变形控制方法进行了研究。总结并探讨了现行方法及软件应用于基坑分析的适用性,结合FLAC3D显式算法的计算特点并针对其构建复杂模型的不足,开发了相应的FLAC3D前处理程序。对FLAC3D基坑数值模拟涉及的模型尺寸与边界条件、初始应力条件、本构模型选用及参数确定、围护结构与土体相互作用、桩土相互作用、显式算法计算结果判断等技术问题进行了分析并提出了具体处理方法与经验建议,为复杂环境下深基坑施工变形预测提供了技术途径。对软土地区深基坑常用围护结构地下连续墙施工过程中的槽壁稳定与土体变形问题进行了研究。将地下连续墙槽壁稳定影响因素进行归类,分析了槽壁整体失稳、局部失稳及成槽前后槽壁土体的应力路径。编制了地下连续墙成槽原位试验方案,自主设计了土压力和护壁泥浆压力的测试装置与测试方法,对地下连续墙成槽作业进行了全过程监测并对试验结果进行了分析。通过对地下连续墙成槽开挖与混凝土浇筑的动态数值模拟,研究了槽壁水平应力分布、槽壁侧向变形与地面沉降的规律,并对槽壁加固、导墙施作、混凝土地坪、侧边已有墙体等施工条件对槽壁侧向变形与地面沉降的影响进行了参数分析,提出了相应的技术措施建议。根据建议的基坑围护结构侧向变形曲线和地面沉降曲线估算公式,通过引入水平位移传递系数和竖向位移传递系数,提出了预测坑外任意位置地层位移的简化计算公式,给出了基坑开挖对周边环境影响的简化分区图及相应保护对策。根据差异沉降作用下建筑变形的性态,建立了墙体变形的悬臂梁模型、简支梁模型和两跨连续梁模型,采用等代荷载法深梁理论分析了基坑沉降影响区内墙体参数对其受力和变形的影响,给出了建筑破坏等级的实用判断方法并进行了工程验证。根据桩基与基坑环境影响分区的关系,将基坑开挖对高架桥梁桩基的影响划分为无影响桩、短桩、中长桩和长桩四类,分析了不同桩基的变形规律及其保护对策。通过建立短桩、中长桩和长桩侧向变形的等代荷载法简化计算模型,提出了由桩身应力控制的桩基及基坑围护结构变形控制标准。针对基坑变形的产生、发展、传递和建(构)筑物保护等环节,提出了“源头控制、路径隔断、对象保护”的基坑变形综合控制理念,建议了基坑变形全过程控制流程。结合上海软土地区工程案例研究了深基坑工程中常用的基坑支护结构方案优化与调整、坑内被动区地基加固、坑外主动区地基加固与隔离、对象保护与加固等技术措施的变形控制效果,提出了基坑变形控制措施选择建议。将研究成果应用于上海地铁8号线西藏南路站6区深基坑工程并进行了合理性验证。采用基坑开挖环境影响简化分区图并根据高架桩基与基坑的相对位置关系,得出高架桩基的影响类型。对比分析了地下连续墙和钻孔灌注桩两种基坑围护结构施工的变形,通过建立考虑基坑周边高架基础在内的整体计算模型,动态预测了基坑变形及其对高架基础的影响。制定了基坑监测方案并对基坑开挖实施了跟踪监测,将主要监测结果与计算结果及上海地区已建地铁车站基坑监测数据进行了对比分析,既验证了变形预测结果的可靠性,又验证了基坑开挖环境影响分区图、桩基影响类型判断、由桩身应力控制的基坑变形控制标准及基坑变形综合控制措施的合理性。本文的研究具有一定实用价值,可为今后相关工程的设计与施工提供借鉴。更多还原

【Abstract】 Deep excavations with complicated environment conditions have sprung up during urban underground space developing process; these deep excavations are usually surrounded by buildings and utilities. More severe restrictions are required for these deep excavations in soft soil deposits. To ensure safety of those adjacent structures, ground movement pattern and the influence of deep excavation on environment are needed to be predicted in advance, thus providing guidelines to take appropriate deformation control measures. This dissertation carried out researches on deformation influence and control issues of deep excavation on environment in Shanghai soft soil deposits, by means of theoretical analysis, numerical simulation as well as in situ test and field observation.Conventional analysis methods and softwares for deep excavation were summarized and discussed. According to advantage of explicit calculation method and limitation of complex numerical model establishment based on FLAC3D, a pre-processing program for FLAC3D was developed. Some technical issues for numerical simulation, including boundary and initial stress conditions, choice of constitutive model and corresponding parameters, interaction between retaining structure and ground, interaction between pile and ground, and judgement of calculation results, were discussed and the corresponding treatment principles were proposed.Theoretical analysis, in situ test and numerical simulation were employed to study slurry wall stability and ground movement during slurry trenching and concreting for diaphragm wall. Influence factors on slurry wall stability were classified and discussed, meanwhile, global and local instability of slurry wall were investigated by theoretical analysis. Deformation mechanism of slurry wall during different construction stages were analyzed by in situ test. New testing equipments and methods for soil pressure and bentonite slurry pressure were designed, and the test results provided parameters for numerical simulation. The slurry trenching and concreting process were dynamically simulated by the established numerical model, and horizontal stress distribution, lateral deflection of slurry wall and ground settlement were investigated. The influence of slurry wall improvement, guide wall, concrete pavement, and existing side wall on lateral deformation of slurry wall and ground settlement was studied by parametric analyses.An empirical ground movement estimation expression for any point outside excavation was established based on lateral deflection of retaining wall and ground surface settlement profiles. The influence of deep excavation on surrounding environment was divided into three influence zones, and an simplified zone chart and environment protection countermeasures were put forward. A deep beam model was established to investigate stress and deflection of building wall subjected to differential ground surface settlement, and a practical method for estimating building damage degree was put forward and verified. The influence of deep excavation on adjacent pile foundation was divided into four types, and the corresponding deformation control criteria and protection measures were presented.A whole process deformation control idea of“source restriction, path isolation, and object protection”was proposed; the corresponding control flow diagram was also established. Some deformation control measures for deep excavation commonly adopted in Shanghai soft soil deposits, including optimization and adjustment of retaining scheme, ground improvement inside excavation, ground improvement and isolation outside excavation, protection and strengthening of adjacent structures, were investigated, and an integrated deformation control system for deep excavation was established.The main findings of the study were applied to a deep excavation project for metro station in Shanghai and validated by the field observation. The types of the nearby piles were classified by the proposed influence zone chart, and the corresponding protection countermeasures were emphasized. The deformation influence of diaphragm wall and bored pile construction on the environment was investigated and analyzed, and the influence of the deep excavation on the nearby pile foundations was dynamically predicted by the established numerical model taking into account the existing pile foundations. The excavation was extensively monitored by the designed observation scheme, and the observed results agreed well with the predicted data, meanwhile, the measured lateral deflection of retaining structures were only half of the collected case histories in Shanghai soft soil deposits. The reliability of this study and the effectiveness of the integrated deformation measures were proved.更多还原