静钻根植竹节桩振动特性与应用研究

The objective of this research is to investigate the vibration characteristics of static drill rooted nodular pile considering the particularity of the pile structure and the complication of pile-soil contact condition. Firstly, theoretical calculation method, numerical simulation method and in-situ test are employed to analyze the application condition of one-dimensional wave theory in dealing with this kind of multiple variable cross-section pile. Then, by using proper models to simulate the dynamic interactions of pile-surrounding soil and pile-inner cement-treated soil, the dynamic response analysis model is built which can consider the non-homogeneity of the surrounding soil in both radial and vertical direction as well as the reaction of inner cement-treated soil. The influence of shallow defect on the dynamic response at the pile head is simulated by means of the equivalent stiffness method, and its detection by using low strain reflected wave method is investigated. Meanwhile, the influence of the timeliness of the hardening of cement-treated soil and the uniformity of grouting on the vibration characteristics of pile are studied and the inversion method is put forward. Finally, long-term load-bearing characteristics and deformation characteristics of static drill rooted nodular pile subjected to vertical harmonic load is investigated for the purpose of setting the dynamic design standard of this kind of pile. Based on all the above works, the facing problems in the integrity testing and dynamic design of static drill rooted nodular pile can be effectively solved and thus offers a foundation for the popularization and application of this new kind of pile.

针对桩身结构的特殊性和桩土接触条件的复杂性，深入研究静钻根植竹节桩这一新型桩的振动特性。首先，通过理论计算、数值模拟和现场试验的方式，分析一维波动理论在处理这类多次变截面桩时的适用条件；然后，采用合适的模型模拟桩-桩周土、桩-桩芯土之间的动力相互作用，建立完善的考虑桩周土体径向非均质性、竖向成层性以及桩芯水泥土作用的静钻根植竹节桩动力响应计算分析理论，并通过等效刚度法模拟桩身浅部缺陷对桩的振动特性的影响及其判别方法；同时，通过理论分析、模型试验和现场试验的方法研究水泥土硬化的时效性、注浆均匀性对桩的振动特性的影响及其反演判别方法；最后，研究竖向循环荷载作用下静钻根植竹节桩的长期承载特性和变形特性的发展规律，建立桩的动力设计标准。以期通过本课题的研究，有效解决静钻根植竹节桩在完整性检测和动力设计中面临的问题，加快其在工程中的推广应用。

由于现有桩型及其施工工法存在一定缺陷，在我国一种具有广泛应用前景的静钻根植竹节桩及其施工工法被引进，然而目前关于其振动特性的研究却很少。考虑到这种新桩型的桩身结构及桩土接触条件等方面与普通预应力管桩和灌注桩存在的显著差异，本课题的主要研究内容包括，针对桩-桩芯土相互作用的管桩纵向动力响应影响研究，针对桩-桩周土相互作用的静钻根植竹节桩纵向振动特性研究，复杂土层条件下变截面桩、缺陷桩纵向振动特性研究，竹节桩桩身结构和三维效应对竖向动力响应影响的研究，竹节桩桩身缺陷和桩周水泥土不均匀特性研究等五个方面。通过模型试验、理论推导和有限元分析等方法并考虑桩身三维效应、桩周土体竖向波动效应、横向惯性效应等方面展开研究，得出结果与主要结论如下： 桩身结构尺寸（包括内径、桩身壁厚、竹节内径和外径、竹节间距等）、桩周水泥土参数（龄期、粘结强度、模量等）、桩芯土不均匀性、桩周土的施工扰动（径向不均匀性）、桩身纵向缺陷的尺寸等因素对静钻根植桩的纵向振动特性影响显著；同时建立了基于考虑土体竖向波动效应的三维轴对称模型、考虑桩身三维效应影响的大直径薄壁管桩–桩端土塞耦合振动模型、基于桩内侧虚土桩的振动模型，针对静钻根植竹节桩提出变截面管桩模型、基于桩周土径向非均质的平面应变模型、桩外侧虚土桩模型、考虑桩周土竖向作用和施工扰动效应时大直径楔形桩的纵向振动模型等众多理论模型，并得到静钻根植桩纵向振动的理论解析解。本课题的系统研究，弥补了静钻根植桩纵向振动特性理论的空白，可为静钻根植桩的施工参数，尺寸构造、缺陷检测等实际工程方面的应用提供理论指导，为静钻根植竹节桩桩在全国范围内的进一步推广具有重要意义。