异形桩沉桩扩孔机理与承载力时效性研究

Since the non-cylindrical pile, such as the XCC pile, could improve the pile capacity and reduce the engineering cost, it is widely used in the construction of practical engineering. However, theoretical study is far behind the engineering practice, the potential mechanism is still not well understood. Particularly, the installation effect of non-cylindrical piles on the surrounding soil and the vertical capacity by considering the time effect is unknown. Based on the methods of theoretical analysis, model test and numerical study, this project aims to develop new critical state model based non-cylindrical cavity expansion and consolidation theories, which can then be used to reveal the mechanism of the non-cylindrical pile installation effect as well as the time effect of pile capacity. Subsequently, the transparent model test for the non-cylindrical piles installation, subsequent consolidation and the pile capacity are conducted to obtain the soil displacement induced by the pile installation, dissipation of the excess pore pressure and the variation of the pile capacity based on the transparent soil and PIV technique. Meanwhile, numerical study for the problem of non-cylindrical pile installation is conducted through the large deformation FEM using CEL technique. The proposed theoretical models are validated by comparing the results of transparent soil model test with the theoretical results. Finally, calculation methods are presented for the non-cylindrical piles vertical capacity by considering the pile installation and time effects based on the developed theories, which provides reference for the design of non-cylindrical piles in practical engineering.

现浇X形桩等异形桩因具有提高桩基承载力、降低工程造价等优点，近年来已经广泛地应用到工程建设中，但是理论的发展滞后于工程实践，其力学承载机理研究尚少见报道，尤其是针对异形桩沉桩扩孔过程机理以及考虑沉桩挤土效应的竖向承载力时效性亟需研究。本项目拟通过理论分析、试验研究和数值模拟等手段，建立考虑土体临界状态本构模型的异形扩孔理论和非柱对称固结理论，揭示异形桩沉桩扩孔机理以及承载力时效性；依托透明土和PIV模型试验技术，开展异形桩沉桩、沉桩后孔压消散以及承载力透明土模型试验，揭示沉桩挤土位移场、孔压以及承载力变化规律；开展基于CEL大变形有限元的异形桩沉桩贯入数值模拟，通过对比透明土模型试验与理论分析结果，验证本项目所提理论模型的可靠性，最终建立考虑沉桩挤土效应以及承载力时效性的异形桩竖向极限承载力的计算方法，为异形桩的工程应用提供参考依据。

采用模型试验、理论分析和数值模拟等方法对异形桩沉桩扩孔机理与承载力特性问题开展了系统的研究。主要成果包括：（1）采用洛朗级数有限项来表示任意形状洞口到单位圆外域的保角变换函数，基于最小二乘法并且根据边界对应原理，确定了洛朗级数的系数，建立了适用于任意异形孔洞的统一映射函数表达式；2）在异形扩孔模型中引入土体的临界状态本构模型，推导了考虑土体临界状态本构的异形扩孔解析解, 建立了考虑土体临界状态本构的异形扩孔理论；3）基于CEL大变形有限元方法，开展异形桩沉桩挤土数值模拟工作，获得了异形桩沉桩过程中桩周土体应力和位移变化规律，揭示了异形桩沉桩扩孔机理，验证了本项目提出的异形扩孔理论；4）开展了异形桩沉桩透明土模型试验，获得了异形桩沉桩挤土位移场等变化规律；5）同时开展了理论、数值、模型试验的对比分析，验证了考虑临界状本构的异形扩孔理论解释异形桩沉桩挤土效应的适用性；6）基于考虑临界状态本构的异形扩孔理论，建立了考虑沉桩挤土效应的异形桩竖向承载力计算方法。