【作者】 朱庆科；

【导师】 莫海鸿；

【作者基本信息】 华南理工大学 ， 结构工程， 2013， 博士

【摘要】 双排桩支护结构是近年来兴起的一种新型深基坑支护结构,其侧向刚度大,能有效控制支护结构的变形,而且受力条件和整体稳定性好、施工方便,逐渐成为深基坑支护结构的优选方案之一。国内外学者对双排桩支护结构进行了大量的研究,研究成果对实际工程中的许多方面具有很好的指导意义,但由于双排桩支护结构受力复杂,在一些方面实践先行,理论滞后,从而限制了该种支护结构的发展。目前阶段而言‘,在考虑桩顶冠梁平面外实际刚度计算方面、空间效应冠梁的影响长度方面、不同潜在滑动面安全系数的极限平衡数值积分求解方面、滑动面的分布规律以及基坑加固等方面研究有所欠缺,本文在归纳整理了现有双排桩支护结构体系的国内外研究成果基础上,基于均质粘性土层的地质条件,通过理论推导、分析和数值模拟等方法,对深基坑双排桩支护结构体系研究中存在的上述薄弱环节进行了有益的补充和完善,本文主要开展的研究工作和成果如下：1.提出了考虑冠梁平面外实际刚度计算双排桩支护结构的内力和变形的理论计算方法,并对比分析冠梁平面外假设无限刚与实际有限刚对桩身内力和位移的影响。该方法基于winkle假定,引入冠梁平面外实际刚度的影响因素,对双排桩支护结构进行理论分析,在此基础上建立各段桩体的挠曲微分方程,然后根据各段桩体端点在几何变形和内力上的连续性关系以及相应的边界条件,采用数学近似方法幂级数求解各段挠曲微分方程,并求导各段挠曲方程的解得出双排桩各点的内力及变形,通过分析冠梁平面外假设无限刚与实际有限刚的计算结果可以得出：1)冠梁的刚度增大可减少前、后排桩的位移,但会增大前、后排桩桩身弯矩；2)冠梁刚度的变化对后排桩桩身弯矩的影响比前排桩稍大；3)冠梁的刚度变化对桩身弯矩的影响幅度和对位移的影响幅度比较接近。该方法与现行假设冠梁无限刚的理论计算方法相比更符合工程实际情况,为考虑冠梁实际刚度求解双排桩的变形和内力提供了一种可行的理论计算方法；2.对双排桩支护结构进行了三维数值模拟,研究了双排桩支护结构在空间效应下的受力和变形特性,在此基础上,研究了冠梁与支护桩的刚接和铰接连接方式、基坑的长边长度、短边长度、开挖深度、冠梁刚度、土层粘聚力和摩擦角、支护结构排距和桩距等主要设计参数与空间效应冠梁影响长度的关系,通过分析不同参数变化下的冠梁影响长度的规律得出：基坑短边长度、开挖深度和支护结构排距的变化对冠梁影响长度都有较大影响；基坑长边长度、粘聚力、摩擦角、冠梁刚度以及支护结构桩距的变化对冠梁的影响长度影响很小。3.提出了双排桩支护基坑在不同潜在滑动面的简化整体稳定安全系数积分计算方法,该方法以Bishop法原理为基础,建立适用于深基坑双排桩支护结构稳定分析的简单平面直角坐标系,推导出潜在滑动面经过基坑底部与前排桩交点圆弧等位置的简化整体稳定分析的安全系数积分表达式,并考虑可能出现的主动区、桩间土和被动区加固的情况,完善了安全系数在不同积分区间的积分表达式,然后编制了相应的计算程序计算基坑稳定安全系数,通过计算结果的分析可以得出,滑动面经过基坑底部与前排桩交点圆弧的安全系数为F1,滑动面经过前排桩桩底圆弧的安全系数为F2,滑动面经过后排桩桩底圆弧的安全系数为F3,而F1略大于F2,F2略大于F3,与有限元计算结果进行对比分析,验证了所提出方法的可行性,完善了极限平衡法数值积分求解安全系数在深基坑双排桩支护结构中的应用。4.对双排桩支护结构的基坑稳定性进行了数值分析,系统研究了基坑稳定安全系数随土层的粘聚力、摩擦角以及支护结构的桩长和排距等设计参数而变化的规律得出：基坑的稳定安全系数随着粘聚力、摩擦角、支护结构桩长和排距的增加而增加,稳定安全系数受粘聚力和摩擦角的影响最大,受支护结构桩长的影响较大,受支护结构排距的影响较小。并且,总结了滑动面的分布特点和规律。5.对双排桩支护的基坑进行加固分析,系统研究了主动区、桩间土和被动区加固对桩身内力和变形特性的影响后得出：1)对于主动区加固,当加固深度超出基坑深度,加固效果不明显；2)对于被动区加固,加固深度或宽度约为基坑深度的一半时最有效。6.在以上工作基础上提出进一步开展相关研究工作的建议。更多还原

【Abstract】 In recent years, double-row pile structure has emerged as a new type of supporting structure for deep foundation pits. Because such structure has high lateral stiffness, which can effectively control its deformation, and exhibit good load conditions and overall stability with ease of construction, it has gradually become one of the optimal solutions for supporting structures of deep foundation pits. Scholars worldwide have conducted considerable research on double-row pile structure, and the results have provided significant guidance to actual engineering applications in many aspects; however, because the mechanic behavior of double-row pile structure is complex, practice has advanced ahead of theory with respect to some aspects, and thus the development of such supporting structures has been restricted. At present, research is lacking in various areas, including the calculation of the actual out-of-plane stiffness of the pile top beam, the affected length by top beam under spatial effects, the numerical integral solving for safety factors of different potential slip surfaces using the limit equilibrium method, the distribution rules of slip zones, and reinforcement of the foundation pit. After summarizing the existing research results worldwide of double-row pile structure, we offer a beneficial supplement to and improvement upon the above weaknesses existing in research on double-row pile structure for deep foundation pits by means of theoretical derivation, analysis, and numerical simulation, in the context of the geological conditions of homogeneous cohesive soil layers.The main works and achievements of this research are as follows:1. A theoretical algorithm was proposed to calculate the stresses and deformation of a double-row pile structure with the actual out-of-plane stiffness of the top beam being taken into account, and the influences of assumed unlimited out-of-plane stiffness and actual limited out-of-plane stiffness of the top beam on the stresses and displacement of the pile body were compared. This method is based on the Winkle assumption, and influential factors of the actual out-of-plane stiffness of the top beam were introduced to conduct a theoretical analysis of double-row pile structure. Thereby, the deflection differential equation of every section of the pile body was established and then solved by using power series by mathematical approximation according to the continuity of geometrical deformation and internal force at the ends of the pile section and corresponding boundary conditions. Afterward, the solution of the deflection differential equation of every section was derived to obtain the deformation and internal force at every point of the double-row piles. Through analysis of the calculation results in the context of assumed unlimited out-of-plane stiffness and actual limited out-of-plane stiffness of the top beam, the following can be obtained:1. The increase in stiffness of the top beam can reduce displacements of the front-and rear-row piles but will increase the bending moments of the pile bodies of the front-and rear-row piles.2. The influence of the variation in top beam stiffness on the bending moments of the pile bodies of the rear-row piles is a little greater than that on the front-row piles.3. The influence of the variation in top beam stiffness on the bending moments of the pile bodies is close to that on the pile top displacement. Compared with the current theoretical calculation method under the assumption that the top beam has unlimited stiffness, this method better conforms to practical engineering situations, providing a feasible theoretical calculation method for solving for deformation and stresses of double-row piles with the actual stiffness of the top beam being taken into account;2. Three-dimensional numerical simulations were conducted to study the stresses and deformation characteristics of double-row pile structure under spatial effects. On this basis, we studied the relationships between the affected length by top beam under spatial effects and major design parameters, such as the rigid or hinge joint mode between the top beam and the supporting pile, the long side length, the short side length and excavation depth of the foundation pit, the top beam stiffness, the cohesive force and friction angle of the soil layer, and the row spacing and pile spacing of the supporting structure. Through analysis of the rules governing variations in the affected length by top beam with different parameters, the following results were obtained:Variations in the short side length and excavation depth of the foundation pit and in the row spacing of the supporting structure have a significant influence on the affected length by top beam under spatial effects; in contrast, variations in the long side length, in the cohesive force and friction angle, in the top beam stiffness, and in the pile spacing of the supporting structure have a very small influence on the affected length by top beam under spatial effects.3. An integral method for calculating the safety factor for simplified integral stability was proposed for a foundation pit supported by double-row piles at different potential slip surfaces. In this method, based on the Bishop method, a simple plane rectangular coordinate system suitable for stability analysis of double-row pile structure in a deep foundation pit was established, and we derived the integral expressions of the safety factor for a simplified integral stability analysis of the potential slip surface when passing the arc at the intersection point between the foundation pit bottom and the front-row piles, etc. With possible reinforcement of the active zone, interpile soil, and passive zone being considered, we improved the integral expressions of the safety factor in different integral intervals and developed a corresponding computing program to calculate the stability safety factor of the foundation pit. Analysis of the calculation results shows that, if the safety factor of a slip surface passing an arc at the intersection point between the foundation pit bottom and the front-row piles is expressed as F1, that of the slip surface passing an arc at the bottom of the front-row piles is expressed as F2, and that of the slip surface passing an arc at the bottom of the rear-row piles is expressed as F3, then F1is slightly greater than F2, and F2is slightly greater than F3. Comparative analysis of these results with finite-element calculations verifies the feasibility of the proposed method, and the method improves the application of numerical integral solving for safety factors using the limit equilibrium method in double-row pile structure of deep foundation pits.4. After an analysis of the stability of foundation pits with double-row pile structure and a systematic study on the relationships between foundation pit stability and major design parameters such as the cohesive force and friction angle of the soil layer and the pile length and row spacing of the supporting structure, we concluded that the stability factor of the foundation pit increases with increases in the cohesive force and friction angle of the soil layer and in the pile length and row spacing of the supporting structure, with the influence of cohesive force and friction angle being the largest, followed by that of the pile length of the supporting structure, and finally by that of the row spacing of the supporting structure. Furthermore, the distribution characteristics and rules of the slip zones were also summarized.5. After analysis of reinforcement of a foundation pit supported by double-row piles through systematic study on the influences of the reinforcement of the active zone, interpile soil, and passive zone on the internal force and deformation characteristics of the pile body, we concluded that:1) For reinforcement of the active zone, when the reinforcement depth is larger than the foundation pit depth, the reinforcement effect is not evident;2) For reinforcement of the passive zone, the reinforcement is most effective when the reinforcement depth or width is about half of the foundation pit depth.6. On the basis of the above work, suggestions are given for conducting further relevant research.更多还原