【作者】 王旭军；

【导师】 龚剑；

【作者基本信息】 同济大学 ， 土木工程施工， 2014， 博士

【摘要】 上海中心大厦基坑工程为近年来上海软土地区罕见的超大、超深基坑工程。其周边环境复杂，变形控制要求高；且因该地区隔水性好的第⑧粘性土层的缺失，导致第⑦和第⑨砂土承压含水层贯通，地下连续墙未能隔断坑内外承压水层的水力联系，且水头降深大、降水时间长，从而导致承压降水对基坑变形影响显著。该基坑工程采用“主楼顺作+裙房逆作”的总体施工方案，采用圆形地墙将主楼区和裙房区临时隔开，先行施工主楼区基坑，后再逆作施工裙房区基坑。由于工程的特殊性，针对此类裙房基坑变形特性的研究甚少。同时，现采用逆作法施工的深大基坑工程普遍采用盆式土方开挖技术；但在实际施工过程中，相关施工参数通常只根据施工经验确定，甚至有时较为随意，从而容易导致基坑变形过大。另外，基坑工程总体施工方案合理与否，对工程施工的安全性和经济性起到关键作用。由此，本文通过理论分析、数值模拟和实测数据分析等手段，对基坑降水对基坑变形的影响、本裙房基坑工程的变形特性、深大基坑的盆式土方开挖技术、及本工程的总体施工方案合理性验证等方面内容，作了较深入的研究。主要内容包括以下几个方面：（1）基于FLAC渗流分析模块对不同土层分布的孔压场进行了研究，定性把握了不同土层及渗流边界条件下的孔压分布规律；并依此规律，针对上海软土地区常见三类深基坑降水情况，给出了相应的考虑渗流作用的水压分布计算简化方法，且对此合理性作了相应论证；同时结合本裙房基坑工程实例，对给出的水压分布简化计算方法的合理性给予了验证。（2）依据实测数据详细分析了围护墙侧移的整体变形性状、最大侧移值及发生位置和三维空间效应，并分析了基坑开挖宽度和出入口进出施工车辆对围护墙侧移的影响；同时着重分析了混凝土垫层的设置和水平梁板及大底板的混凝土结构收缩对围护墙侧移的影响，指出混凝土垫层对围护墙具有较好的支撑作用，及超长水平混凝土结构的收缩对围护墙变形影响显著。另外，围护墙顶竖向位移、立柱的隆沉、墙柱之间的差异沉降、墙后地表沉降及基坑周边历时建筑和临近管线沉降作了详细分析。突出说明了承压降水对基坑变形的显著影响。（3）基于FLAC有限差分软件对基坑变形特性进行了研究。在模拟中，结合水土分算原则，土体物理参数采用有效应力指标，并根据实际施工过程降水情况，及前面考虑渗流作用的水压分布研究成果，考虑了土中孔压变化对基坑变形的影响。在分析过程中，首先讨论了主楼区与裙房区之间的临时隔断圆形地墙的简化方式、是否考虑地下水和工程桩的作用等因素对计算结果的影响；分析了基坑开挖宽度及水平支撑刚度对基坑变形的影响；并对裙房基坑中间部位的变形特性做了较全面的计算分析，且比较了计算值和实测值之间的关系，特别说明了基坑北侧部分地表测点有所隆起的原因；同时采用不同计算方法对作用在围护墙上的水土压力大小进行了分析，并与实测值进行了对比，说明了采用前面提出的考虑渗流作用的水压分布计算方法用于水土压力计算的合理性。（4）为合理确定逆作法深大基坑工程的盆式土方开挖方案，依据悬臂和带撑两种不同条件的特点，对土方开挖的分块大小、盆边开挖深度、盆中开挖深度、盆边留土宽度和坡度及分块开挖顺序等施工参数的确定进行了较为详细的分析说明。并提出了盆边开挖路径向相关区和盆中开挖路径非相关区的概念及划分。且对盆式开挖盆边留土宽度的对基坑变形影响作较深入的研究，并给出了合理确定的方法和建议。（5）为论证背景基坑工程现行总体施工方案的合理性，首先详细分析了该基坑工程的特点；在此基础上，提出了四个比选方案：中间大开口全顺作、中间大开口全逆作、主楼区顺作+裙房区顺作、主楼区顺作+裙房区逆作等方案；接着从工期、经济成本、周边环境影响、技术方法等方面进行方案了比较分析。同时对现行所采用方案的优点作了进一步说明。更多还原

【Abstract】 The excavation of Shanghai Tower project is a rare oversized and ultra-deepexcavation in Shanghai soft deposit in recent years. The surrounding environment isvery complex, so the strict control of deformation is required. And due to lack of the8thlayer of cohesive soil in Shanghai soft deposit, which leads to the7thand9thlayerof confined aquifers are connected directly. But the diaphragm wall failed to isolatethe hydraulic connection of confined aquifer between the inside and outside of theexcavation, and the water head drawdown is large, the time of dewatering is long, sothat the affection of the dewatering on the pit deformation is significantly. The overallconstruction program of the excavation uses the bottom-up construction for the mainbuilding pit and the top-down construction for the podium pit. Circular wall is used asthe temporary partition between the main building and the podium construction areas,the main building pit is constructed firstly, and then the podium pit is constructed withtop-down method. Because of the particularity of the excavation, few studies havebeen made to study the deformation characteristics of similar podium pits. Andgenerally, basin excavation method is commonly employed in the top-downexcavations, but in the actual construction process, construction parameters of thebasin excavation techniques are usually determined only according to the constructionexperience, even sometimes more casual, so it easily leads to excessive deformation.Therefore, in order to study the affect of dewatering on the deformation of theexcavation, the deformation characteristics of the podium pit, the basin excavationtechniques of deep and big excavations, and the reasonable verification of the overallconstruction scheme of foundation pit, intensive studies on these aspects are carriedout using the tools of theoretical analysis, numerical simulation and experimental dataanalysis and so on. The main contributions of this thesis are described in thefollowings:(1) Using the basic flow scheme of FLAC program, the pore pressures in thecondition of different soil layers and different fluid flow boundary conditions arestudied, and the laws of the field distribution of pore pressure are qualitativelygrasped. In accordance with the law, for the three types of dewatering situationscommonly encountered in Shanghai soft deposit, simplified calculation methods of the water pressure distributions is given, and the rationality of the calculation methodsis reasoned. Meanwhile, rationality of the calculation methods is proofed, based onthe experimental data of the podium pit.(2) Based on the measured data, general trends of lateral displacement of wall,maximum lateral displacement of wall and location of its occurrence,three-dimensional effect of wall displacement are analyzed with details. Factors thataffect wall deflection such as excavation width, heavy traffic adjacent to wall,concrete cushion, and the shrinkage of overlong horizontal concrete structure, arestudied. Meanwhile, it highlights that the confinement effect of cushion todeformation of retaining wall is significant, and the concrete shrinkage of overlonghorizontal concrete structure leads to big increment of lateral displacement of wall.Additionally, vertical displacement of the top of wall and piles, differential settlementof wall and piles, ground surface settlement, settlement of temporary buildings andpipelines surround foundation pit are analyzed with details. Furthermore, theremarkable influence of confined water dewatering on settlement of foundation pit isespecially replied.(3) Deformation characteristics of foundation pit studies using explicit finitedifference program (FLAC) are conducted. Based on the principle of the separatedcalculation method for water and soil pressure, the soil physical parameters useeffective stress indicators, and according to dewatering conditions during the actualconstruction process and the earlier research results of water pressure distributionwhich considering seepage, the influence of changes of the soil pore pressure on pitdeformation is considered. Meanwhile, some factors affecting on the results ofcalculation are studied, such as the simplified form for the circle wall between themain building construction area and the podium construction area, and whetherconsidering pore pressure in soil and piles. And the influence of excavation width andthe stiff of horizontal strut on displacement of pits are analyzed. The deformation ofthe podium pit in the middle part is overall computational analysis with simplified2Dnumerical models and measured values, the reasons for the project phenomena whichsome surface measuring points on north pit show some heave is specially instructed.Furthermore, it also carries out analysis of the soil and water pressure on the wall bydifferent methods and compares with measured data, which testes and verifies that using the previously proposed method for calculation water pressure to calculatewater and soil pressure is reasonable.(4) To determine the rational program for large and deep top-down foundation pitusing basin excavation technique, some construction parameters of basin excavationare studied. These include block size of excavation, basin excavation depth of sideportion, basin excavation depth of middle portion, width of berm, slope of berm edge,and block excavation sequence and so on. Meanwhile, this thesis first presents theconcept of excavation path-dependent area for side portion of basin excavation andexcavation path-independent area for middle portion of basin excavation, and themethod of boundary division is proposed. Furthermore, the effect of width of berm onthe displacement of foundation pit is detailed studied, and the method for determiningthe width is proposed.(5) In order to demonstrate the rationality of the overall construction program forthe foundation pit, a detailed analysis of the characteristics of the pit is carried out.And based on the characteristics, four alternative schemes are proposed: scheme1,total bottom-up construction method with large opening in the middle; scheme2, totalup-down construction method with large opening in the middle; scheme3, with circlewall as the temporary partition between the main building and the podiumconstruction areas, bottom-up construction method both for the two pits; scheme4(current scheme), as mentioned earlier. Then, the schemes are compared from theaspects of deadline, economic cost, the influence on surrounding environment,technological factors and so on. Finally, the current scheme is given and its advantageis further explained.更多还原