【作者】 冯勇；

【导师】 侍克斌；

【作者基本信息】 新疆农业大学 ， 水利水电工程， 2009， 博士

【摘要】 本文介绍了深基坑土钉支护工程的国内外研究现状,分析了寒冷地区深基坑施工、设计存在的问题,尤其是土钉支护设计没有考虑冻融循环后细粒土抗剪强度特性参数的变化的情况;结合具体实际工程采用信息化施工方法进行复杂环境条件下基坑支护工程的设计与施工;对有多个施工方案的深基坑支护工程进行多目标决策的方案优选;研究分析了基坑的变形现象、变形机理及相关变形的控制标准,对考虑冻融循环后基坑变形的时间效应和空间效应分别进行了分析,对基坑开挖引起地表沉降以及地表变形计算进行研究;使用FLAC3D对中天广场深基坑支护工程的开挖与支护进行了数值模拟研究。围绕寒冷地区深基坑土钉支护工程的环境事故及其防治技术为主要研究内容,主要进行了以下几方面的研究:(1)通过对南、北疆地区深基坑边坡的垮塌原因的调查,发现细粒土冻融作用是导致基坑边坡出现环境事故的主要原因。针对新疆地区土壤盐分较高的实际情况,选取含水率、密实度、粘粒含量和易溶盐四个影响因素,通过均匀正交试验研究细粒土边坡在四个影响因素经历不同冻融循环次数后抗剪强度特性参数C、Ф的变化,运用极差分析的方法,对试验结果进行分析,分别得出上述四个影响因素对C、Ф的影响的重要性排序,并且对试验结果的准确程度进行方差分析,验证试验数据的正确性,证明试验结果与工程实际情况基本符合,为控制深基坑环境事故的发生提供了理论上的依据。(2)通过参与目前西北最高楼中天广场深基坑支护工程的地质勘察、深基坑支护的设计、施工,以及基坑支护工程的变形监测四个阶段工作后,总结基坑土钉支护的设计方法,进行复杂环境条件下深基坑支护工程的土钉设计;为相邻建筑物不受深基坑开挖的影响而使其安全使用,保证已有建筑物不发生破坏,研究对原相邻建筑物基础进行基础托换并取得成功;为基坑支护工程的安全,对深基坑工程进行变形监测,由监测结果说明基坑支护是成功的。(3)多目标模糊综合评价是系统工程中对非定量事件作定量分析的一种简便方法,也是对人们的主观判断作客观描述的一种手段,利用多目标模糊综合评价指标的权数分配,可较大幅度地减少主观因素。研究深基坑支护施工方案的多方案优化决策选择问题时,对深基坑支护施工多方案的多层次、多目标建立评判数学模型,从而更加全面地反映了深基坑支护施工方案,使其优化更全面,更客观;针对以往多目标优化计算过程较繁锁的问题,运用模糊判断矩阵最小差法得出深基坑支护多目标优化的最佳满意解,开辟了施工方案多目标优化的新方法。(4)为减少基坑开挖对周围环境的影响,控制基坑开挖引起的地表沉降,本文分析了基坑的变形现象、变形机理及相关变形的控制标准;同时对基坑变形的时间效应和空间效应分别进行了分析;考虑对时空效应的被动土等效水平抗力系数Kh影响因素的分析,尤其是分析细粒土冻融循环前后抗剪强度特性参数C、Ф的计算公式,使基坑变形的时空效应考虑的因素更全面、合理;对基坑变形的预估研究,进行基坑开挖引起地表沉降以及地表变形计算,对于科学指导寒冷地区深基坑工程的设计与施工有一定的参考价值。(5)本文使用ITASCA公司的FLAC3D三维快速拉格朗日差分程序,对中天广场深基坑支护工程的开挖与支护进行了数值模拟研究,模拟结果显示基坑内土体沉降随着基坑开挖深度的增加而加大,基坑底部隆起位移也是随着基坑开挖深度的增加而加大,基底中部的隆起量最大,为70 mm,靠近基坑壁处较小,基坑土体水平位移同样是随着基坑开挖深度的增加而加大,基坑壁向坑内的水平位移变化趋势仍然是中间部分最大,边角处最小,而且基坑壁的长边由于开挖的范围相对较大,其变形量相对于短边也增大约19 mm,这充分体现了基坑开挖过程中的时空效应,本文的数值模拟计算结果可以为工程设计提供指导和参考。更多还原

【Abstract】 In this paper,the deep foundation soil nailing works at home and abroad are researched,the construction and design problems of deep foundation in cold regions are analyzed,especially the shear strength characteristics of fine-grained soil changes in the parameters after freeze-thaw cycle is not considered in the design of soil nailing;Light of the specific information of the actual project construction method is used to carry out the Foundation Pit Design and Construction under complex conditions;A number of construction programs of the Deep Foundation Pit multi-goal decision-making are optimized; the situation foundation deformation, deformation mechanism and the related deformation control standards are studied and analyzed, the freeze-thaw cycle time after the deformation effect and space effect are analyzed separately, the surface subsidence caused by excavation and the surface deformation are calculated;Using FLAC3D the Deep Foundation Pit excavation and support on ZhongTian plaza are studied in the method of numerical simulation. According to the research contents of deep foundation soil nailing environmental incidents and its control technology in cold region, the research are mainly carried out from following aspects:(1) Through the investigate of the cause of the deep foundation pit slope collapse in Xinjiang south and northern areas, the main reason is found that freezing and thawing causing environmental incidents of pit slope. Response to higher soil salinity in Xinjiang, the moisture content, density, clay content and soluble salt are selected as four factors. Based on the uniform orthogonal pilot study at the four fine-grained soil slope factors as well as experiencing different cold financial cycles, the changes of shear strength parameters C、Фare studied. In the methods of range analysis, the test results are analyzed. The importance of influence factor of above four factors on the C、Фare obtained separately, and the accuracy of the results are analyzed in variance to verify the accuracy of test data.The test results prove that the actual situation and in line with the project, and it provides a theoretical basis for controlling the occurrence of environmental incidents of deep foundation.(2) Through participating in four phases works of geological reconnaissance、design、construction and deformation monitoring on the northwest highest floor, the current transit plaza deep excavation works, the foundation soil nailing design methods is summarized. And the deep excavation of the soil nailing project is designed under complex environmental conditions. For the adjacent buildings safely use without disturbed by the deep excavation and buildings without damaged, the foundation of original adjacent buildings is studied and succeed. For the safety of deep excavation works, the deformation is monitored and the monitoring results show that the excavation is successful.(3) Multi-objective fuzzy comprehensive evaluation is a simple method in the systems engineering to analysis the case of non-quantitative, and it can be as a means for people to judge in an objective description. Using multi-objective fuzzy comprehensive evaluation index weights distribution can greatly reduce the subjective factor. Through research on optimization decision-making problems of deep foundation pit construction programs, the multi-objective mathematical model is set up. It can reflect the deep foundation pit construction plan more fully and to optimize the plan more comprehensive and objective; For the problem of the process of previous multi-objective optimization calculation more cumbersome, the least bad method of fuzzy matrix is used to get the best satisfactory solution of deep excavation multi-objective optimization. It opens up a new way for multi-objective optimization of construction plan.(4) In order to reduce the impact of excavation to the surrounding environment, excavation-induced ground surface settlement is controlled. The phenomenon of deformation, deformation mechanism and the related deformation control standards of foundation are studied in this paper. At the same time, deformation time effects and spatial effects are analyzed separately. Considering the influencing factors of Kh, which is the equivalent level resistance coefficient of passive soil, especially analysis the shear strength parameters C,Фformula of fine-grained soil before and after freeze-thaw cycles, the effect of deformation of the space-time factors are considered more comprehensive and reasonable. The research of deformation estimate, and the calculation of surface settlement and deformation caused by excavation will guide the design and construction of deep foundation works in cold regions.(5) In this paper, three-dimensional ITASCA’s Fast Lagrangian FLAC3D procedures are used to simulate transit plaza on Deep Foundation Pit excavation and support. The simulation results show that soil excavation in the settlement increase with the depth of excavation, and the uplift displacement of foundation at the bottom is also increase with the depth of excavation. In the central of basement, the uplift grows to the largest value of 70 mm, and near the pit wall is smaller. The horizontal displacement of soil excavation is also increase with the depth of excavation. The change trend of horizontal displacement from foundation pit wall to center is still the largest in the center and smallest in the corner, and because the long side of pit wall digs relatively in a large scope, and its deformation increases about 19 mm compared with the short side, which fully reflects the excavation in the process of space-time effects. The calculation results in this paper can provide guidance and reference for engineering design.更多还原