基坑开挖与降水对支护结构受力及地面变形影响的研究

发布时间：2018-03-20 06:45

本文选题：深基坑工程　切入点：渗流　出处：《太原理工大学》2013年博士论文　论文类型：学位论文

【摘要】：在地下水位较高的场地进行深基坑工程的设计及施工,降水开挖引起局部水文地质条件的变化与支护结构及周边环境之间是相互制约、相互作用的。本文首先对太原市汾河低阶地地层进行了分类整理,按照地层变化规律、粒径组成、渗透性质及帷幕底部可能嵌固进入地层透水性质的不同,将基坑止水帷幕分为三类嵌固模式。每种模式给出了相应的渗流变化特征及其对支护结构及地面变形的影响程度。本文对太原市中环壹号深基坑工程监测资料进行整理分析,依此为模拟基础,以比奥固结理论为基础利用Flac3D的cysoil模型进行数值模拟,深入研究了止水帷幕为第二类嵌固模式时,水头边界条件下分别采用侧向和上部两种不同水头补给位置时,降水回灌四种组合方式的渗流条件与支护结构及地面变形之间的相互作用；并对地下水位改变、土体性质改变、渗透系数改变、回灌条件改变引起基坑周边地面沉降的影响规律进行了分析研究。最后对渗透系数与降水前后土体的力学性质测试的试验方法及参数的变化规律进行了深入的分析研究。通过以上分析研究获得的主要认识及结论为： 1、材料本构关系cysoil模型是摩尔-库仑的衍生模型,采用定律为增量弹性法则、破坏准则和流动准则。运用该模型将降水回灌的渗流变化与土力学有机地组合起来,与比奥固结理论相结合能很好反映地下水的渗流特征及开挖应力改变之间的作用。模拟结果与中环壹号监测资料对比,地面沉降的模拟吻合率高达90%以上,地下连续墙墙体水平位移的吻合率为60%-80%,水平支撑的撑力吻合率达80%以上,说明该模型适用于本论文研究的基坑开挖降水工程。 2、通过对各项水文参数改变的模拟得出： 1)水头边界条件的侧向固定水头补给位置适用于第一类、第二类嵌固模式,上部固定水头补给位置适用于第三类嵌固模式。 2)分步降水加回灌的降水开挖工况对基坑周边地面变形控制最为有利。回灌是控制地面沉降的有效手段,回灌井位置在基坑开挖深度(0.5～1.0)H范围内最佳。 3)根据正交水平原理提供了回灌井深度、回灌压力、回灌井数量及排数、帷幕深度各因素及因素组合对地面沉降的贡献系数表,来评价各参数及参数组合对地面沉降的影响程度,以便设计施工中采用最优最经济的回灌组合方式。 4)降水引起基坑外地面沉降曲线为“凹”形：从基坑边至最大沉降点处为对数曲线,从最大沉降点至降水影响范围的最外边界处为线性关系。利用回归关系给出第二类嵌固模式下基坑外地面变形与渗透系数变化关系的计算公式。 5)考虑回灌渗流应力场作用比不考虑渗流作用,地表沉降降低50%,坑底隆起增35%,支护结构的水平位移增加30%,水平支撑轴力增加15%。设计中需考虑回灌渗流作用,以降低支护结构的风险。 6)墙体水平位移受水平侧向支撑的限制,同一断面出现两头小中间大的鼓肚子挠曲形状。墙体的最大水平位移位置在墙顶下0.85H处,在开挖深度(0.4-0.85)H水平位移增量大,该段落为支护结构的最薄弱部位,是设置支撑及施工监测的重点部位。 7)地表沉降量随着土体弹性模量的增大而减小；地表最大沉降和弹性模量曲线大致呈折线形分布。随着土体模量的提高,土体变形滑移面的斜率在增大,滑移面越来越陡,土体的变形影响范围在减小。但土体模量的提高对支护结构的变形影响不大。 3、对水文参数的试验研究得出： 1)综合考虑取样过程中土样的扰动程度、取土深度、土样应力释放情况、孔隙水压力消散程度及渗透系数对土层影响的权重等因素,提出对室内试验测出的渗透系数的修正公式。 2)降水过程相当于给土体一个预压加固作用,降水后土体压缩模量ES1-2增大25%；粘聚力增大33%；内摩擦角增大8%。 3)高压固结多级卸荷回弹试验土体均出现“回滞圈”,卸荷曲线的斜率不一致,但回弹的路径几乎是一组平行线。本文的研究成果是对太原市中环壹号工程的支护体系研究中得出的,对水位较高的河流一级阶地基坑开挖的设计及施工具有一定的借鉴和指导作用,对深大基坑中渗流场与支护结构、周边环境的相互作用理论的研究具有一定的意义。
[Abstract]:In the design and construction of deep foundation pit at high groundwater level, the change of local hydrogeological conditions caused by precipitation and excavation is interdependent and interacted with supporting structure and surrounding environment.
This paper firstly classified the Fenhe River in Taiyuan city low terrace formation, in accordance with the law of change of formation, particle size composition, permeability properties and may be fixed at the bottom of the curtain into the formation permeability is different, the waterproof curtain is divided into three types of embedded mode. Each mode is given and the corresponding variation of seepage on supporting the structure and the ground deformation of the impact.
In this paper, Taiyuan city central one deep foundation pit monitoring data analysis, according to the simulation based on Biot's consolidation theory as the basis for the numerical simulation using cysoil Flac3D model, in-depth study of the waterproof curtain embedded into second patterns, head boundary conditions were used and two different lateral upper head supply position when the precipitation recharge seepage condition of four combinations and between the lining structure and ground deformation interaction; and change of groundwater level, soil properties, permeability coefficient, recirculation condition change induced effect of foundation pit surrounding ground settlement is studied.
In the end, the test method and the change law of the mechanical properties of soil mass before and after precipitation are analyzed and studied.
The main understanding and conclusions obtained through the above analysis are as follows:
1, the material constitutive model of cysoil is derived by using the Mohr Coulomb model, incremental elastic law rule, failure criterion and flow rule. Using this model, the precipitation recharge seepage variation and soil mechanics organically, combined with Biot's consolidation theory can well excavation and stress change between the role of reflect the seepage characteristics of groundwater. The simulation results are compared with the one central monitoring data, simulation of ground settlement agreement rate is more than 90%, the wall of underground continuous wall displacement of the anastomosis was 60%-80%, the level of support the supporting force of agreement rate reaches above 80%, indicating precipitation engineering excavation the model suitable for this paper.
2, through the simulation of the changes in various hydrologic parameters, the results are as follows:
1) the lateral fixed water head location of the head boundary condition is suitable for the first class and the second type of fixation mode. The upper fixed water supply location is suitable for the third type of fixation mode.
2) step by step precipitation and recharge irrigation and excavation operation is the best way to control the ground deformation around foundation pit. Recharge is the effective way to control land subsidence. The location of recharge well is the best in the depth of excavation (0.5 ~ 1) H.
3) according to the orthogonal principle provides a recharge well depth, pressure recharge, recharge well and the number of rows, the combination of different factors and factors of curtain depth on the ground subsidence contribution coefficient table to evaluate the impact of various parameters and the parameters of ground subsidence, so that the design and construction of the optimal economic return irrigation combination.
4) for concave curves of ground settlement caused by foundation pit precipitation from the foundation pit to the largest settlement point for a logarithmic curve from the outer boundary of the maximum settlement point to the precipitation affected area is linear regression. Given second kinds of embedded mode outside the foundation pit ground deformation and calculation formula of variation of permeability coefficient the relationship between.
5) considering the seepage recharge stress than that without considering the seepage effect, surface subsidence is reduced by 50%, 35% increase in heave, increase the horizontal displacement of the supporting structure 30%, increase in 15%. design should consider the seepage recharge support axial force level, to reduce the risk of supporting structure.
6) limit the horizontal displacement of the diaphragm wall under horizontal lateral support, the same section two small middle drum belly deflection shape. The maximum horizontal displacement of the wall under the top position at 0.85H in the wall, in the depth of excavation (0.4-0.85) H horizontal displacement increment, the paragraph is the weakest part of the supporting structure, is the key site set up support and construction monitoring.
7) decreases with increasing the elastic modulus of soil surface settlement; maximum surface settlement and elastic modulus curve is roughly polygonal shaped distribution. With the increase of soil modulus, deformation of slip surface in slope soil increases, slip surface becomes more and more steep, the extent of deformation of soil decreased. But soil modulus to improve the supporting effect of deformation supporting structure is small.
3, the experimental study of hydrologic parameters is obtained.
1) considering the disturbance degree of soil sample, the depth of soil sample, the release of soil samples, the degree of pore water pressure dissipation and the weight of infiltration coefficient on the soil layer, a correction formula for permeability coefficient measured in laboratory tests is put forward.
2) the precipitation process is equivalent to a preloading reinforcement. After precipitation, the compressive modulus of soil ES1-2 increases by 25%, cohesion increases by 33%, and the internal friction angle increases by 8%..
3) there is "hysteresis loop" in the soil of high pressure consolidation and multistage unloading test, and the slope of unloading curve is not consistent, but the path of rebound is almost a parallel line.
The results of this study is to draw on Taiyuan City Central No. 1 engineering support system, has certain reference and guidance for the design and construction of high water level of river terraces in the excavation of deep foundation pit, seepage field and supporting structure, has a certain significance to study the interaction theory of the surrounding environment the.

【学位授予单位】：太原理工大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU470;TU46

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