上海中心大厦裙房深大基坑变形特性及盆式开挖技术研究

发布时间：2019-05-18 10:26

【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。
[Abstract]:The foundation pit project of Shanghai Center Building is a rare and super-deep foundation pit project in Shanghai soft soil area in recent years. The surrounding environment is complex, and the deformation control requirement is high; and due to the absence of the second sticky soil layer in the area, the first and the second sandy soil pressure-bearing water-bearing layers are communicated, the underground continuous wall can not block the hydraulic connection of the inner and outer bearing water layers of the pit, the water head is deep in depth and the precipitation time is long, So that the pressure-bearing precipitation greatly influences the deformation of the foundation pit. The general construction scheme of the "The main building is in the direction of the + skirt." is adopted for the foundation pit engineering, and the main building area and the skirt building area are temporarily separated by a circular floor wall, and the foundation pit of the main building area is firstly constructed, and then the foundation pit of the construction apron area is inverted. Due to the particularity of the project, there is little research on the deformation characteristics of the foundation pit of this kind of skirt. At the same time, the deep foundation pit works which are constructed by using the reverse construction method are generally adopted in the basin-type earth excavation technology, but in the actual construction process, the relevant construction parameters are usually determined according to the construction experience, and even at random, so that the deformation of the foundation pit is easily caused to be too large. In addition, the overall construction scheme of the foundation pit works is reasonable or not, and plays a key role in the safety and economy of the construction. In this paper, by means of theoretical analysis, numerical simulation and actual data analysis, the influence of the foundation pit dewatering on the deformation of the foundation pit, the deformation characteristics of the foundation pit engineering of the present skirt, the basin-type earth excavation technology of the deep foundation pit and the rationality verification of the overall construction scheme of the project are discussed in this paper. A more in-depth study was made. The main contents include the following aspects: (1) Based on the FLAC seepage analysis module, the pore pressure distribution of different soil layers is studied, and the distribution of pore pressure in different soil layers and seepage boundary conditions is determined qualitatively. In view of the three types of deep foundation pit dewatering in the soft soil area in Shanghai, the paper gives a simplified method for calculating the water pressure distribution of the seepage, and proves the rationality. At the same time, the foundation pit engineering of this skirt is combined. In this paper, the rationality of the simplified calculation method of the water pressure distribution is given. (2) According to the measured data, the whole deformation character, the maximum lateral displacement value and the position and the three-dimensional space effect of the side-shift of the enclosure wall are analyzed in detail, and the excavation width of the foundation pit and the access and exit of the access and exit construction vehicle to the side of the enclosure wall are analyzed. The effect of the shrinkage of the concrete cushion on the side of the enclosure wall is analyzed, and the effect of the shrinkage of the concrete structure on the side of the enclosure wall is analyzed. It is pointed out that the concrete cushion has a good supporting effect on the enclosure wall, and the shrinkage of the super-long horizontal concrete structure can be used for the deformation of the enclosure wall. In addition, the vertical displacement of the top of the enclosure, the uplift of the column, the differential settlement between the wall columns, the settlement of the ground surface after the wall and the settlement of the surrounding of the foundation pit and the settlement of the adjacent pipelines Fine analysis. The effect of pressure-bearing precipitation on the deformation of foundation pit is highlighted. The Influence of (3) on the Deformation of the Foundation Pit Based on the Finite Difference Software of FLAC In the simulation, the effective stress index is used in the physical parameters of the soil, and according to the actual construction process and the water pressure distribution of the seepage, the change of the pore pressure in the soil to the foundation pit is considered. In the process of the analysis, the paper first discusses the simplified way of the temporary partition of the circular floor between the main building area and the skirt building area, and whether the influence of the factors such as the role of the ground water and the engineering pile on the calculation results is considered, and the excavation width and the horizontal support stiffness of the foundation pit are analyzed to the foundation pit. The influence of deformation is made, and the deformation characteristic of the middle part of the foundation pit of the skirt is calculated and analyzed, and the relation between the calculated value and the measured value is compared. The reason of the bump is that the water and soil pressure on the wall of the enclosure is analyzed by different calculation methods, and compared with the measured value, the water pressure distribution calculation method considering the seepage effect is used in the water and soil pressure gauge. The rationality of calculation is as follows: (4) In order to reasonably determine the basin-type earth excavation scheme of the deep foundation pit project of the reverse practice, the block size of the earth excavation and the depth of the basin edge are excavated according to the characteristics of the two different conditions of the cantilever and the belt support. The determination of the construction parameters such as the depth of the excavation in the basin, the width of the retaining soil at the side of the basin, the sequence of the excavation of the block and the like is carried out. The detailed analysis shows that the excavation path of the basin edge is not related to the excavation path in the relevant area and the basin The concept and division of the area are studied, and the effect of the soil width on the deformation of the foundation pit is studied. (5) In order to prove the rationality of the current general construction scheme of the background foundation pit engineering, the characteristics of the foundation pit project are analyzed in detail. On the basis of the above, four selection schemes are proposed: the middle large opening is the whole and the middle large opening is the whole and the main building The area is in the direction of the + skirt building, the main building area is in the reverse direction of the + skirt building area, and then the construction period, the economic cost, the surrounding environment impact, the technical method and the like are followed. The comparison and analysis of the scheme are carried out. At the same time, the current scheme is adopted.
【学位授予单位】：同济大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU753

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