【作者】 王俊林；

【导师】 王复明；

【作者基本信息】 郑州大学 ， 水工结构工程， 2011， 博士

【摘要】 大直径扩底桩具有施工设备简单、成桩质量可靠、承载力大、无噪音干扰和经济效益显著等优点,已成为多层及高层建筑、桥梁工程、大型设备和重型厂房等工程中重要的基础形式。本文通过现场载荷试验,数值模拟、理论分析,对水平荷载作用下大直径扩底桩的承载力、荷载传递机理及变形机理开展了研究工作。(1)从加荷级别、变形观测、测试元件的埋设、受力点设置、数据测读时间、加卸载方法等方面对水平静载试验方案进行了研究,为大直径扩底桩水平载荷现场试验提供了可行的方案,使现场载荷试验得以顺利完成。对4根水平荷载作用下的大直径扩底灌注桩进行了现场静载荷试验,确定了其临界荷载、极限荷载和水平承载力特征值及相应位移量；同时进行桩身内力测试,在对试验数据进行整理,对试验结果进行分析的基础上,研究了水平荷载荷载传递机理及桩身剪应力和弯矩沿深度变化的规律。结果表明：大直径孔桩的H-Y0,曲线和H-ΔY/ΔH曲线,可分为三阶段：弹性阶段、弹塑性阶段和破坏阶段；地基土水平抗力系数的比例系数与桩顶位移是具有明显的非线性关系,可近似用双曲线来拟合；桩身弯矩最大截面处,钢筋应力随荷载的增加而呈线性增加,当水平荷载达极限值时应力突变,桩身断裂,这说明其极限水平荷载由桩身强度控制；桩身弯矩由上至下逐渐变大,深度为3-4D时最大,然后变小,桩变截面处仍有弯矩产生,尤其是较短的S22桩,这说明扩底对桩身弯矩分布有较大的影响。(2)利用有限差分程序,采用摩尔-库仑破坏准则,对水平荷载作用下大直径扩底桩进行了数值模拟计算,分析了桩身位移沿桩身埋深的分布规律和表层土弹性模量及扩底尺寸对桩身位移的影响。结果表明：上部土层的弹性模量对桩身水平位移的影响比较显著。为了保证大直径扩底桩有良好的水平承载性能,表土层弹性模量宜在10MPa以上；为充分发挥大直径扩底桩的水平承载性能,桩长宜为7D左右,不宜大于10D。(3)提出了基于地基反力和桩身强度的大直径扩底桩水平承载力计算方法,分析了桩身尺寸(桩直径、扩底直径、桩长和扩底段高度)、桩周土和桩端土性质对桩水平承载力的影响。计算分析表明：大直径扩底短桩属刚性桩；基于不同的临界状态,推导的基于力平衡、力矩平衡和桩身强度的三种大直径扩底短桩水平承载力计算公式,具有概念清楚、意义明确的特点,可以方便地求出大直径扩底桩的水平承载力；通过与规范法和工程实测值进行对比,基于桩身强度的水平承载力计算公式与实测结果较吻合。本文的研究成果对大直径扩底桩的设计、施工提供了理论依据具有积极的指导意义。更多还原

【Abstract】 Large diameter belled pile has been widely used in Multi-storey and high-rise buildings, bridges, factories and other large equipment and heavy engineering for its simple construction, reliable and easy to check, large capacity, no noise interference and the advantages of significant economic benefits. In this paper, the level of load on the large diameter hand-dug hole pedestal pile deformation mechanism and the load bearing characteristics of the work are studied in details based on the static load test, numerical simulation and theoretical analysis.(1) After the static load test scheme is studied from the loading level, deformation, test devices planted, set of working point, time of data readings and loading-unloading method, a feasible plan is achieved for horizontal load field test of the large diameter hand-dug hole pedestal pile. On-site static loading test for the four root level load enlarged end of large diameter pile is carried out to determine its critical load, limit load bearing capacity, horizontal bearing capacity eigenvalues and corresponding displacement. Meanwhile, the internal force test of pile body is carried on for getting the test data and experimental results to further research the horizontal load transfer mechanism of shear stress and bending moment and pile body along the depth change rules.The results are included in the below:a) the H-Yo curve and H-△Y/△H curve of large diameter pile can be divided into three stages, namely elastic stage, elastic-plastic stage and destroy stage; b)there exsits the obvious nonlinear relationship, which can be approximated to fit a hyperbolic line, between the horizontal resistance coefficient of the foundation soil proportion coefficient and the displacement of pile top.; c)at the largest cross-section bending moment, the reinforced stress linearly increases with the load increasing. When the horizontal load reaches limit, strain value mutations that pile body fractures. This shows that the limit of the horizontal load is controlled by the strength of the pile; d)Bending moment distribution is evenly larger from top to bottom when it is getting a depth of 3-4D maximum, and then smaller. A moment in the cross-section place of pile is still produced, especially in the shorter S22 pile. This shows that the belled has great influence on the distribution of bending moment.(2)Through FLAC3D program and Mohr-Coulomb criterion, a numerical simulation calculation for the large diameter belled pile under horizontal loads is carried out to analyze the displacement rules of pile body along the buried depth of pile body regularity of distribution and the influence of the surface soil modulus of elasticity and enlarged end of pile body size on the displacement of pile body. It can be showed that the result has a good consistency with the test results, and that the upper layers of elastic modulus has notable influence on to the influence of pile body horizontal displacement of the pile body. In order to ensure a good level of pile bearing capacity, the topsoil elastic modulus is above in appropriately lOMPa. To fully play to the horizontal bearing capacity of large diameter belled pile, Pile length should be around for the 7D, but should not be greater than 10D.(3)The horizontal bearing capacity calculation method of large diameter belled pile based on the foundation counterforce and pile body strength is proposed to analyze the impact of the pile body size (pile diameter, belled diameter, the pile length and the height of pedestal), soil around the pile and properties of pile tip soil on the horizontal bearing capacity of pile. The calculations show that the large diameter belled pile is rigid pile. Based on different critical conditions, the three horizontal bearing capacity calculation formula of large diameter belled pile,, clear concept and clear meaning, is derived according to force balance, moment balance and strength of pile, by which the horizontal bearing capacity of large diameter belled pile can be easily computed. Through the comparison with standardized method and measured value of engineering, it shows that the results from the calculation formula of pile body strength for the level of the bearing capacity are nearly identical to the on-site measured results.The results of this paper provide a theoretical basis for design and construction of large diameter belled pile, and also have the positive significance for theorectical research.更多还原