【作者】 吴朝阳；

【导师】 李正农；

【作者基本信息】 湖南大学 ， 土木工程， 2015， 博士

【摘要】 我国是世界上已规划地铁项目最多的国家之一,目前已在35个城市中兴建地铁线路和车站。众多地铁车站的基坑施工必将对周边环境造成一定影响,主要是可能引起周边已有建筑的沉降和变形。由于地质条件、基坑方案、建筑结构等因素,基坑施工影响周边建筑的机理非常复杂,而传统的理论、经验方法难以全面地反映上述因素。因此,在基坑施工之前,很难准确地预测建筑的沉降和变形,也很难合理地评判建筑面临的风险状况。本文采用数值模拟与实测分析、参数反演、模糊风险评判相结合的方法,深入研究砂土/硬黏土层中的基坑施工对周边高层建筑的影响,并在地铁车站的基坑工程中展开了研究应用。在研究过程中,针对建筑沉降预测结果的不确定特性,大致按照“发现问题、实测验证、提高准确性、风险模糊评判”的技术路线来撰写。本文的主要研究内容和成果有：(1)数值模拟。总结并分析前人在基坑及建筑模拟方面的经验方法,确定了土体本构模型、建筑、模型计算区域、围护结构、地应力等对关键内容的模拟方案；对不能完全确定的内容则采用多种模拟方案的组合；采用Abaqus软件,对某地铁车站基坑建立3个有限元模型并展开模拟应用,得到了一些有意义的模拟结论。成果：提出了基坑模型的计算区域试算流程；对不能完全确定的土体弹性模量、基坑渗流、内支撑采用多种方案组合；根据工程应用的结果,揭示了建筑的模拟沉降量和倾斜度存在不确定的数值范围；影响建筑沉降计算值的模拟因素从大到小依次是降水方案、土体参数方案、支撑模拟方案；建筑沉降与土体的弹性模量可能成反比关系。(2)实测分析。对某车站基坑周边的地下水位、地下连续墙侧移、坑外地表沉降分布、周边建筑沉降变形的实测数据进行统计分析,并与有限元模拟结果、相关的统计经验进行对比。成果：验证了本文有限元模拟的方案和结论基本上是合理的；在砂土/硬黏土的二元结构土层中,基坑周边高层建筑的实测沉降量和倾斜度都较小；高层建筑的最大沉降值、差异沉降与建筑长宽比呈反比,而最大倾斜度、挠度比与其距基坑的距离呈正比。(3)参数反演及沉降预测。对比了多种试验设计方法的特点；根据原理和使用方法上的优点,采用均匀设计法来设计试验方案；根据土体弹性模量与坑外沉降模拟值之间的关系,选择了简单合理的参数回归方法；在某车站基坑的施工监测过程中,展开了数值模拟和参数反演应用,动态预测后续施工阶段的坑外沉降量。成果：首次在基坑土层参数的反演和地层位移的预测中引入了均匀设计法,减少了试验次数且不失精度,体现了均匀设计法与数值法相结合的优势；在其它条件不变的情况下,一些测点的沉降模拟值与土体弹性模量存在线性关系；通过参数反演来预测坑外沉降的准确性优于传统的经验方法。(4)建筑风险的模糊评判。选择了建筑的最大沉降值、最大倾斜度、损伤系数,来综合评判建筑的风险；针对评价指标的不确定性,引入三参数区间数来描述；根据建筑风险和三参数区间数的特点,提出了基坑周边建筑风险评判的流程；对距离某车站基坑最近的砖混结构进行了风险评判应用。成果：提出了评判基坑周边建筑风险的简化模型；引入损伤系数来描述建筑损伤状态,并按相关规程作了合理修正；引入三参数区间数来描述指标,并给出了可能度的积分解；提出了S型可变模糊隶属函数；引入并修正了超标加权法；在实际工程中的风险评判结果明确、统一且合理,优于传统的经验方法。更多还原

【Abstract】 Metro lines and stations have been built in35cities of China, which is one of the countries with the most metro projects in the world. The excavations of numerous metro stations have some impacts on the surrounding environment, especially the settlement and deformation of those existing building. For the geological conditions, excavation programs and building structures are difficult to be reflected by traditional theories and empirical methods, the influence principle of excavation to surrounding buildings is very complicated. Accordingly, it is difficult to predict the subsidence and deformation or judge the risk of those buildings.The impact of excavation in sand and stiff clay to surrounding high-rise buildings are studied based on numerical simulation, measurement and analysis, parametric inversion and fuzzy risk assessment, the methods of which are applied in the excavations of subway stations. Aiming at the uncertainty of prediction results of building settlements, this paper is written according to the technical route of "finding problem, measurement verification, increasing accuracy, fuzzy risk assessment", and the major contents and achievements of this study are as follows:(1) Numerical simulation. The empirical methods in simulating excavation and surrounding buildings were summarized and analysed to confirm the simulation schemes of key contents, such as soil constitutive model, building, computational domain, enclosure structure and ground stress. The combination of different schemes was used to simulate those uncertain contents. The software Abaqus was used to establish three finite element models of the excavation of a subway station, and some significant simulation conclusions were obtained in this application.Achievements:A procedure of dimension calculation of excavation model was proposed. Different schemes were used to simulate the uncertain elastic modulus of soil, seepage, inner support. The uncertain value ranges of building settlements and inclinations were revealed by the application results. The simulation factors of building settlements in descending order were the schemes of precipitation, soil parameters and inner support, and there might be inverse relationship between building settlements and elastic modulus of soil.(2) Measurement and analysis. The measured data of groundwater level, lateral displacement of diaphragm wall, ground settlements, building settlements and inclinations of a subway station were analysed statistically, and were contrasted with simulation results and relevant statistics experiences.Achievements:The simulation schemes and conclusions of this study were proved to be reasonable. The measured settlements and inclinations of buildings adjacent to excavation were smaller in the dual structure of sand and stiff clay. There were inverse relationship between the maximum settlements, differential settlements and the length-width ratios of buildings, but proportional relationship between the maximum inclinations, deflection ratios of buildings and the distances from buildings to excavation.(3) Parametric inversion and settlements forecast. The characteristics of different methods of experimental design were contrasted. Based on the advantage of principle and application, the simulation experiments were performed in terms of uniform design. Based on the relationship between simulation settlements and elastic modulus of soil, the simple and reasonable method was choised to regress parameters. To forecast the settlements outside excavation in subsequent construction stages, numerical simulation and parametric inversion were applied in the construction monitoring of a subway station.Achievements:Uniform design was introduced into parametric inversion and settlements forecast of excavation for the first time, and the advantage of uniform design and numerical simulation was reflected by reducing test number with high precistion. There were linear relationships between elastic modulus of soil and simulation settlements of some measuring points, when other conditions were unchanged. The accuracy of forecasting settlements outside excavation was higher than that of traditional experience.(4) Fuzzy risk assessment. The risk of building was synthetically evaluated by the maximum settlements, inclinations, damage coefficient of building. The interval numbers of three parameters were introduced to describe the uncertainty of evaluation indexes. Based on the characteristics of building risk and interval numbers of three parameters, an evaluation procedure of building risk was proposed. Risk assessment was applied in the masonry structure which was nearest to a subway station.Achievements:A simplified risk judgment model of buildings adjacent to excavation was proposed. The damage coefficient was introduced and revised by relevant standards to describe the damage condition of building. The interval numbers of three parameters were introduced to describe evaluation indexes, and the integral solutions of possibility degree were calculated. The fuzzy membership functions of S-type were proposed. The super weight method was introduced and revised. The clear, uniform and reasonable result in risk judgment application was better than that of traditional experience.更多还原