岩溶区基桩竖向承载机理及其设计计算方法研究

Due to complex geological conditions of karst area, the characteristics of pile-rock and pile-soil interaction is more complicated than which of the common friction pile or rock-socketed pile. How to consider the influence of karst caves to the bearing capacity of piles becomes an urgent task. In view of the problems at home and abroad of this system have not been thoroughly and systematically studied and a whole body of design theory has not been proposed, this study intends to systematically conduct a series of laboratory tests about the characteristics of pile-rock and pile-soil interaction based on the existing research results, and the applicable load transfer model for piles in karst area will be presented. Then, through the analysis of potential energy increment varying process of pile-rock and pile-soil system, the only solution of streses and displacements distribution will be obtained, which can be a designing guide for piles in karst area. Furthermore, in order to ensure the rationality of design proposal of piles, the stability analysis of piles-rock and pile-soil system will be conducted by adopting the upper bound and lower bound finite element methods which belong to the limit analysis theory. Thus the whole design theory about the vertical bearing capacity of piles in karst area will be established. Finally, some relevant parameters will be determined by a field test of bridge piles in karst area and the applicability and rationality of the design theory will be verified.

岩溶区地质条件复杂，桩-岩、桩-土接触问题较一般摩擦桩或嵌岩桩更为复杂，且如何考虑溶洞的存在对基桩承载性状的影响更是亟待解决的问题。鉴于目前国内外尚未对此问题进行系统深入的研究，并未提出完整的岩溶区基桩设计计算方法，本研究拟结合目前已有研究成果，进行系统的室内桩-岩、桩-土接触特性分析试验，提出适用于岩溶区基桩的荷载传递模型；并通过分析基桩-岩溶承载体系势能增量变化过程，求解体系中应力与位移分布的唯一解，由此指导岩溶区基桩方案设计；然后采用基于极限分析理论的上限、下限有限元法对基桩-岩溶承载体系进行稳定性分析，确保基桩设计方案合理可行；由此建立完整的岩溶区基桩竖向承载力计算方法及基桩设计计算理论。最后，拟结合某岩溶区桥梁基桩工程现场试验确定部分相关参数，并验证该分析理论的适用性与合理性。

本研究从试验研究、数值研究、理论研究三方面展开。试验研究方面，提出了梁板结构的岩溶区基桩承载力计算模型，并探讨了不同跨度、厚度溶洞顶板对基桩极限承载力的影响；数值研究方面，以工程实例为背景，探讨了不同岩性、厚度、跨度溶洞顶板下基桩的极限承载力，得到了一般性的规律，并用于指导工程实践；在理论研究方面，基于极限分析，根据基桩与溶洞的距离，推得了溶洞发生冲切破坏、冒顶破坏、不破坏三种情况的限定条件，并对溶洞顶板发生冲切破坏研究展开更为深入研究，包括冲切破坏体母线方程及溶洞顶板安全厚度的求解，此外，在复变函数的基础上，提出了基桩作用在不同位置时，溶洞稳定性评价方法及基桩桩端极限承载力计算方法。