岩溶区超大直径变截面桩的破坏模式与荷载传递机制

A new type of step tapered hollow pile with huge diameter has effectively solved the complex technical problems during the construction of the bridge foundation in karst strata. Nevertheless, there is still not impeccable design and calculation theory in default of clarifying load transfer mechanism of the pile. The purpose of this proposed scientific research program is to investigate the failure mode and load transfer mechanism of the step tapered hollow pile with huge diameter in karst strata. First of all, the creep model of the clayey soil and its program calculation module will be presented on the basis of the creep test results. The couple of model test and numerical simulation method will be used to analyze the progressive failure pattern of the pile foundation, and the characteristics of microstructure aging movement and macro mechanical response of the soil around the pile. On the basis, the relative motion rule and delaying characteristics of the pile-soil relative displacement will be clarified, and the time evolution process of both the bearing ratio and the relationship between side resistance and displacement will be studied. In addition, corresponding relationship between the potential failure mode and the induced factors will be given, which will offer the scientific basis for proposing the load transfer model and calculation theory of the pile. Moreover, the parsing algorithm of the side friction will be presented on the basis of disturbed state concept, and load-settlement relationship considering the side resistance delay will be proposed too. After analyzing the additional stress diffusion rule of the soil layer given the potential failure mode of the pile, the stress influence range in the soil layer will be identified and the modified computing method will also be given. The expected research achievements will provide the theoretical basis for the design and construction of the new type of step tapered hollow pile huge diameter in karst strata.

一种新型超大直径变截面空心桩，有效解决了复杂岩溶地层中桥梁桩基建设的技术难题。针对该新型桩基理论研究落后于工程实践的情况，急需弄清其潜在的破坏模式及荷载传递机制，由此形成完善的计算方法与技术体系。综合试验测试、理论解析和数值计算等方法，研究超大变径桩渐进破坏形态及土层细观时效运动与宏观力学响应特征，构建基于扰动状态概念的土体蠕变模型及程序计算模块，揭示桩-土界面的相对运动规律及位移迟滞性特点，摸清荷载分担比及侧阻-位移特征关系的时间演变过程，诠释超大变径桩潜在破坏模式及其诱导因子间的对应关系；研究超大变径桩的竖向荷载传递模型及承载计算理论，提出基于扰动状态理论的桩侧摩阻力解析算法，构建可考虑侧阻力延迟发挥的荷载-沉降特征关系；研究超大变径桩潜在破坏模式下土层附加应力扩散规律，明确应力影响范围并提出修正计算方法。成果可为复杂岩溶区该新型桩基的设计与施工工艺优化提供理论依据。

一种新型超大直径变截面空心桩，有效解决了复杂岩溶地层中桥梁桩基建设的技术难题。针对该新型桩基的理论研究落后于工程实践的情况，急需弄清其潜在的破坏模式及荷载传递机制，由此形成完善的计算方法与技术体系。本课题主要开展了以下方面研究：1）针对工程中常见的工况进行了相应的桩型以及施工工艺设计，采用数值模拟和室内试验等手段，深入开展超大直径变截面空心桩的桩型优势、承载性状以及桩-土相互作用机理研究；2）采用理论分析和数值模拟等方法，研究了超大直径阶梯型变截面桩的荷载传递机理，构建了桩-土间的荷载传递模型，提出了超大直径桩的沉降计算方法；3）采用理论分析、模型试验及数值模拟相结合的方法，研究了岩溶区阶梯型变截面桩的溶洞顶板破坏模式，提出了基于极限理论的安全厚度求解方法；4）基于透明土实验技术原理，开展超大直径变截面桩在竖向荷载下的承载性能与荷载传递机理室内模型试验；5）采用理论分析与数值模拟相结合的方法，对桩基荷载作用下串珠状隐伏溶洞的稳定性进行了较为系统深入的研究；6）针对桩基在静力以及地震作用下溶洞顶板稳定性，开展了理论分析和数值模拟，并结合计算机编程进行研究。研究成果为施工过程中避免了桩身强行穿越溶洞诱发的各类病害，有效解决了复杂岩溶地区桥梁桩基的建设问题等提出了新的思路与方法，有较为现实的经济和社会价值。