大型沉井基础承载性能计算理论研究

According to the analytical thinking of the theoretical modeling combined with numerical simulation, focus on the shortage of the computing theory of massive cassion. Based on different size and different buried depth of the model test of caission foundation, and combining the corresponding numerical simulation experiments, the relations between the bearing capacity and the both of the foundation size and the buried depth are established. The computation model of the foundation bearing capacity reflecting the nonlinear effect is suggested. The computation method of the ultimate bearing capacity of the caisson foundation is given. Considering the load condition and the buried depth and the form and the geological conditions of the anchorage foundation, and combining the results in the engineering monitoring and taking in the deformation characteristics of caission foundation in the whole process of construction, the numerical computation model and the corresponding computation method of forecasting the inhomogeneous subsidence and long-term deformation are established. According with the control requirements of the foundation subsidence and horizontal displacement in the construction period and operation period, the theory of the design computation based on the deformation control requirements of the caisson foundation is suggested.

以理论建模和数值计算相结合的分析思路，针对现有大型沉井承载性能计算理论的不足。基于不同尺寸和不同埋深的沉井基础实测数据，结合相应的数值模拟试验，建立承载力与基础平面尺寸和埋深的关系，提出反映非线性效应的地基承载力计算模型，给出沉井基础极限承载力的计算方法；考虑沉井基础受力、基础埋深、基础形式和地质条件，结合已有工程监测成果，计入锚碇基础施工全过程的各种变形特征，建立沉井位移计算模型与相应的计算方法；依据沉井基础在施工与运行期对沉降与水平位移的控制要求，提出基于变形控制的沉井基础设计计算理论。

随着大跨径桥梁的发展，原有深基础计算理论已无法满足大型沉井基础的设计需要。为掌握大型沉井的传力机制与地基变形规律，首先利用1:100模型试验方法获取沉井荷载-沉降变化关系，揭示埋置深度、地下水位对基础承载性能的影响；根据刚塑性体的平衡条件，在分别考虑粘聚力c和重度γ的情况下，推导了方形深基础地基极限承载力的理论解，再结合条形深基础地基极限承载力的理论解，叠加后得到矩形深基础地基极限承载力的通用解析解；以半空间问题的Mindlin解作为基本解，按弹性力学叠加原理求解沉井地基附加应力，建立适用于深置大型沉井基础沉降计算的分层总和法；根据沉井基础的受力特征，将地基分为主动土压力和被动土压力区域，利用土压力理论，推导沉井基础水平承载力计算公式；以库仑摩擦定律代替假想的弹簧模型，按Winker模型计算沉井基底井身水平反力，再根据接触面上的位移协调条件，推导得到沉井水平位移计算公式、滑移临界载荷以及沉井水平承载力增加系数与埋深的变化关系。利用位移计算理论所得成果，提出基于变形控制的沉井基础设计方法。