【作者】 李立军；

【导师】 梁仁旺；

【作者基本信息】 太原理工大学 ， 岩土工程， 2013， 博士

【摘要】 随着我国经济的迅速发展和城市化进程的加快,高层、超高层建筑、城市地铁隧道项目大量的建设,都遇到一个共同的问题：深基坑的设计及施工问题,如基坑支护、降水、开挖等等。特别是,近年来有关基坑土方坍塌的事故频频发生,给人民的生命及财产安全造成巨大的影响。因此,如何解决好城市建设项目中的基坑支护及环境效应问题成为岩土工程的热点与难点,技术安全、经济合理的基坑支护结构体系是基坑工程的主要发展方向及研究重点。双排桩支护结构由于具有整体刚度大、侧向位移小、不需要设置支撑、施工方便、速度快、不需要工作面等优点,目前广泛应用于边坡加固、边坡抗滑、基坑支护等工程中。但是,双排桩的作用机理及受力特征目前还不清楚,双排桩的设计理论不成熟,主要依靠工程经验。本文在总结前人研究的基础上,以数值模拟与现场试验为研究手段,理论分析方法与工程实践相结合,全面研究双排桩支护结构的要素设计和复合式双排桩的受力及变形特征,研究双排桩的作用机理、探讨土压力的分配规律、分析支护结构的内力及变形规律、对比不同支护方案下的安全性、经济性,为双排桩支护结构的广泛应用及优化设计提供理论支持与工程经验。本文的主要研究内容如下：1.回顾总结双排桩支护结构的理论计算方法,对比总结各自的特点及应用范围。2.采用FLAC3D数值法模拟双排桩结构的受力状态,研究双排桩支护结构的要素设计,包括：桩距、排距、直径、长度、连梁截面及刚度、基坑深度、土体抗剪强度指标等,寻求双排桩设计最优参数。3.采用FLAC3D数值法模拟复合式双排桩支护结构的受力特征,研究不同复合方案下支护结构的内力及变形规律,分析基坑工程的安全系数,并将研究成果应用于太原市平阳景苑的深基坑支护工程中。4.将理论研究应用于实践工程中,详细阐述了平阳景苑深基坑支护工程的设计思路、支护选型、模拟计算、方案比选,并最终确定支护方案,为该地区同类基坑工程支护设计提供借鉴。5.针对平阳景苑的深基坑支护工程进行现场试验研究,编制详细的试验方案,分析研究了土层的侧向位移、桩体的内力及位移、地表的沉降及位移、锚索拉力、地下水变化、周围建筑物沉降等,并与计算结果对比。6.采用不同三轴试验方案,重点研究了土体抗剪强度指标对支护结构受力的影响,并将不同试验方案下测定的指标值带回计算模型中,将计算结果与实测值进行比较。通过上述内容的研究,本文在以下方面取定一些研究成果：1.研究结果表明,双排桩支护结构的内力及变形特征明显区别于单排桩,最大位移不是发生在桩顶,而是桩顶下2-4m,弯矩曲线出现反弯点,正负最大弯矩差值在减小,受力更加合理。对比结果表明,在桩数相同的条件下,采用双排桩支护结构可以明显减少位移,使结构受力更加合理。2.首次全面分析了双排桩支护结构要素设计变化对双排桩的影响,并得出最佳设计参数：排距4～6d(d为支护桩直径),桩距2-4d,桩长1.5～2倍基坑深度,深度在10m以内采用双排桩支护比较合理,连梁必须具有足够刚度,才能发挥其协调的作用。3.研究发现,土体抗剪强度指标c,(?)值是影响支护结构内力及变形的最重要两个因素。计算结果显示,c,(?)值变化与支护桩最大水平位移呈双曲线关系,这是本文研究的一大亮点。4.首次将复合式双排桩支护结构引入太原地区,工程实践表明是成功的,并节约造价约3000万元,为该地区同类支护工程提供借鉴。5.对比分析不同复合方案下双排桩支护结构的受力特点,全面研究不同组合方案的内力及变形规律。研究结果显示,设置锚索、支撑可以明显改善双排桩的受力,限制侧向位移。而同样条件下,设置支撑的支护效果优于锚索,增加锚索或支撑的排数,支护结构的内力及变形没有明显改善,最佳的锚索或支撑的排数为2排。否则的话,前排桩成为主要受力构件,整个体系类似于拉锚结构,发挥不出后排桩的作用,这是本文研究的又一亮点。6.关于锚索的作用点位置在本文中也作了重点研究,结果显示：最佳位置是冠梁处,双排桩结构受力最合理。7.现场试验显示,深基坑存在显著的空间效应,中间桩体侧向变形大于端部桩体,位移曲线呈“中间大、两头小”的鼓肚状。8.对比分析多样单级加荷和单样多级加荷三轴剪切试验测定c,(?)值,研究结果显示,单样多级加荷下测定的c,(?)值偏大,内力及变形值的计算结果与实测结果更接近。查阅文献,还没有找到类似的研究。更多还原

【Abstract】 With the acceleration of the process of China’s rapid economic development and urbanization, the construction of a large number of high-rise, high-rise buildings, urban subway tunnel project, have encountered a common problem:the design and construction of deep foundation pit, Pit Supporting, precipitation, excavation, and so on. In particular, in recent years frequently occur the collapsed accidents of pit earthwork, it give a huge impact on people’s lives and property safety. Therefore, how to solve the problem of the foundation pit support and environmental effects in the urban construction projects become a hot and difficult geotechnical technology, security economic rationality Pit Supporting Structure system is the main direction of development and research priorities of the foundation pit engineering.Double row pile retaining structure has the overall stiffness, small lateral displacement and do not need to set up support, besides, its construction is convenient, fast, no face, etc. They are widely used in slope reinforcement, slope skid, pit support and other projects. However, the mechanism of double-row piles and force characteristics is unclear, double-row piles immature design theory, mainly relying on engineering experience. On the basis of previous studies, using numerical simulation and field test research methods, combined theoretical analysis methods and engineering practice, the paper study the design elements of the double row pile retaining structure and composite double the force of the pile deformation characteristics, to study the mechanism of double-row piles、distribution of earth pressure、the analysis the internal forces and deformation law of supporting structure, comparing different support schemes under the security, economy, and provide theoretical support and engineering experience for double row pile retaining structure widely used and optimize the design. The main contents of this paper are as follows:1. Reviewed the theory calculation method of double row pile retaining structure, comparative summary of each of the characteristics and scope of application.2. Using the FLAC3D numerical methods to simulate the stress state of the structure of the double-row piles to study the design of double row pile retaining structure elements, including:pile spacing, row spacing, diameter, length, coupling beam cross-section and stiffness, pit depth, soil shear strength indicators. Seek the optimal parameters of double-row piles to design.3. Using the FLAC3D numerical methods to simulate the characteristics of the composite structure of double-row piles and study the different composite program under the supporting structure of the internal forces and deformation law, meanwhile, analyze the safety factor of the excavation project, and applied research for Taiyuan City Garden deep foundation pit support engineering.4. The theoretical research applied to practice engineering, and elaborate Pingyang Jingyuan deep foundation pit support engineering design ideas, supporting selection simulation calculation scheme comparison, and ultimately determine the support program, providing a reference for the similar foundation pit support design of the area.5. Pingyang Garden for deep foundation pit engineering field tests, making detailed test plan, analysis of soil lateral displacement, pile internal force and displacement, ground surface settlement and displacement, cable tension, the groundwater level change, settlement of surrounding buildings, and compared with the calculated results.6. Adopted different triaxial test program, focuses on the impact force on the supporting structure of the soil shear strength index, and the index value measured under different test programs back to the computational model, the calculated results with the measured values comparison.Through the above research, this paper takes some research achievements in the following aspects:1. Research results show that the double row pile retaining structure of the internal forces and deformation characteristics significantly different from the single row of piles, the maximum displacement does not occur in the top of the pile, but the top of the pile under2～4m, bending moment curve inflection point is, positive and negative difference of maximum bending moment is reducing,the force is more reasonable. The comparison results show that, in the same number of piles, double row pile retaining structure can significantly reduce the displacement, make the structure more reasonable stress.2. For the first time, comprehensive analysis of the double-row pile retaining structure elements of design changes on the double-row piles and optimum design parameters:row spacing:4～6d (d diameter for supporting piles), pile spacing:2～4d, the pile length:1.5to2times pit depth, depth of less than10m double row pile retaining is more reasonable, Even beam must have sufficient stiffness to play its coordinating role.3. The study found that soil shear strength index value c,φis the internal force and deformation of supporting structure the two most important factors. Calculations showed that c,φ values change with the support piles maximum horizontal displacement was a hyperbolic relationship, which is a major highlight of this study.4. The first time the introduction of the composite double row pile retaining structure in Taiyuan area. Engineering practices show it is successful, and save the cost of about30million yuan, and provide references for the region similar support engineering.5. Comparative analysis of double-row piles supporting the mechanical characteristics of the structure under different composite program, a comprehensive study of the different combinations of internal forces and deformation law. The study results showed that, setting the anchor rope, the support can be significantly improved the force of double-row piles, and limited the lateral displacement. Under the same conditions, supporting effect under setting support better than the anchor cable, but increasing the number of rows of the anchor rope or support is no significant improvement in the internal forces and deformation of the supporting structure, the best anchor cable or supporting rows is2. Otherwise, the front row piles to become a major force member, the entire system is similar to anchor the structure, not to play the role of rear pile, which is another highlight of this study.6. On the anchor position, in this paper also made a key research, results showed that, the best position is crown beam, at this time, the double-row piles structure stress is the most reasonable; Back row piles can bear the soil pressure; The lateral deformation is the minimum.7. Field tests, deep foundation pit has space effect significantly, the pile deformation of between pile is greater than the end pile, displacement curve is " big in the middle, two small " drum belly shape.8. Comparative analysis of diverse single-stage loading and single-sample multi-level triaxial shear test measuredc,φ values, the results show that a single kind of multi-level loading measurementcφ value is too large, the internal forces and deformation calculated values c,φ is closer the measured results. Consulting literature, similar studies have not yet found.更多还原