静钻根植竹节桩承载性能与沉降特性研究

The precast pile and bored pile are the commonly used pile foundations in China, while they both have their own disadvantages. Severe compacting effect occurs during the construction process of the precast pile, which is harmful to the surrounding facilities; for the bored pile, the existence of mudcake around the pile shaft and the soft sediment beneath the pile base reduce the bearing capacity, moreover, large amounts of mud is produced during the construction process. The construction of the static drill rooted nodular pile can be summarized as follow: a special drilling machine is used to drilling and grouting firstly, then the precast pile is put into the hole filled with cemented soil to form a complete composite pile. Therefore, this construction method will not cause compacting effect, and mudcake effect as well as base sediment effect will not occur. Moreover, mud emission will largely be reduced, and the cost of this composite pile can be reduced about 10% compared to the bored pile. This subject is mainly on experimental and theoretical investigation of the static drill rooted nodular pile, and field tests, model tests, shearing tests on pile-soil interface, laboratory soil tests, analytical calculation as well as numerical simulation will be used to investigate the bearing capacity, failure mechanics and settlement characteristic of this composite pile. Finally, computing method for bearing capacity and settlement of the static drill rooted nodular pile in different geological conditions can be obtained, which will offer theoretical basis for promotion and application of this composite pile foundation.

预制桩和钻孔灌注桩是我国应用最为广泛的两种桩基础，然而它们在使用过程中都存在着明显的缺陷。预制桩施工过程中会产生挤土效应，对周边已有建筑产生不利影响；钻孔灌注桩存在桩侧泥皮效应以及桩端沉渣效应，而且会产生大量泥浆。静钻根植竹节桩是采用一种特殊钻机喷浆搅拌形成水泥土至设计深度，然后将预制桩植入到充满水泥土的钻孔中形成的一种组合桩基；它既可以避免预制桩施工过程中的挤土效应，也能够消除钻孔灌注桩的泥皮效应和桩端沉渣效应，同时泥浆排放大量减少，而且其造价相比钻孔灌注桩能减少10%左右。本课题将对这种新型组合桩基进行较系统的试验和理论研究。拟通过现场原型桩静载试验，室内模型桩试验，室内桩土接触面剪切试验，室内土工试验及解析计算，数值模拟等理论研究来揭示这种新型桩基的承载性能、破坏机理和沉降特性，得出不同地质条件及不同规格静钻根植竹节桩的承载力和沉降计算方法，为这种新型桩基的设计和推广提供理论依据。

本课题运用模型试验结合现场实测和理论分析方法等，对静钻根植竹节桩多方面进行了研究，得出了许多重要的结论：通过静钻根植竹节桩的桩-水泥土-桩周土接触面剪切试验对混凝土与水泥土接触面、水泥土与砂土接触面的摩擦性质进行了研究，得到了水泥土性质对混凝土-水泥土接触面和水泥土-桩周土体接触面摩擦性能的影响；通过对静钻根植竹节桩抗压、抗拔现场静载试验并结合有限元计算，研究了影响静钻根植竹节桩抗压和抗拔承载性能的因素；通过将预制桩和水泥土的复合弹性模量作为其桩身弹性模量，同时考虑桩身弹性模量沿桩身改变以及桩端水泥土扩大头的作用，采用理想弹塑性荷载传递函数提出了一种在均匀地基中静钻根植竹节桩单桩沉降计算方法；在此基础上建立了同时考虑桩-水泥土-桩周土接触面作用的静钻根植竹节桩简化沉降计算方法。通过在自主设计的大型模型槽中的静钻根植竹节桩、静钻根植管桩和混凝土桩模型试验对静钻根植竹节桩、静钻根植管桩和混凝土桩这三种桩型的承载特性进行了详细的对比分析与研究；并利用模型槽研究了不同应力水平下的静钻根植竹节桩的桩侧摩擦特性。本研究内容能帮助研发地基处理新技术，同时对静钻根植竹节桩浙江省设计规范以及行业规范的编制工作、东南沿海软土地区的静钻根植竹节桩应用推广也有帮助作用。分阶段将研究结果进行总结，先后发表/录用了专业论文15篇，其中8篇SCI检索，7篇EI检索，申请了国家发明专利5项。