考虑膨胀岩土地基应力路径及气候条件变化的基坑开挖对桩基影响研究

In actual engineering, pit excavation has significant effects on the working performance of piles beneath excavation bottom and adjacent excavation. However, there is little consideration on layered characteristic of strata, influence of different stress paths and climate change in recent research. Rely on the deep foundation pit of line 1 and line 2 of Nanning subway station and base on the characteristic of expansive soil foundation, theoretical analysis, laboratory experiment, the large-scale physical model test, centrifuge model test, numerical simulation will be applied in this project. And the characteristics of piles due to pit excavation will be studied, including the engineering characteristic and settlement rule of expansive soils under climatic conditions change, the deformation and strength property of expansive soils under unloading stress path, the vertical bearing behavior of piles beneath excavation bottom considering pit excavation effect in expansive soil foundation, the influence of pit excavation on adjacent piles in expansive soil foundation. The application of this research results is expected to accurately predict the effects to piles from pit excavation in expansive soil zone. The working performance of piles beneath excavation bottom and adjacent excavation will be effectively evaluated, and some corresponding protective measures will be taken. Furthermore, this research is hopefully to provide important guiding significance for the optimization design of pit engineering and pile foundation, the control influence on surrounding environment in expansive soil zone.

针对基坑开挖对坑底工程桩及邻近建筑物桩基有明显影响的工程实际及目前相关研究存在“忽略地基的层状特性”、“忽略地基的应力路径”和“忽略气候条件变化”等不足，本课题拟以广西南宁地铁 1#、2#线车站基坑为工程依托，针对膨胀岩土的工程特性，分别采用理论分析、室内实验、大型物理模型试验、离心模型试验和数值模拟等多种研究手段，系统研究基坑开挖对桩基的影响。主要包括：气候因素变化条件下膨胀岩土的工程特性及沉降规律；基坑开挖卸荷路径下膨胀岩土的变形、强度特性；膨胀岩土地基中基坑开挖条件下坑底桩基的竖向承载特性；膨胀岩土地基中基坑开挖对邻近桩基的影响。本项目的实施可更准确地预测膨胀岩土区域基坑开挖对桩基的影响，进而有效评估坑底及邻近桩基的工作性能，从而采取针对性的防护措施。成果对膨胀岩土地区基坑、桩基优化设计及对周边环境影响的控制，将具有重要的指导意义。

以广西地区代表性膨胀土为研究对象，通过室内试验获得了膨胀土基本物理特性和浸水前后力学特性。开展了膨胀土地基中桩基模型试验和理论分析，提出了膨胀土地基中竖向单桩及水平单桩受力变形的非线性分析方法，揭示了膨胀土地基中竖向和水平荷载作用下刚性桩筏基础受力和变形的关系以及桩的内力和变形沿桩身分布规律，在此基础上获得了膨胀土浸水后竖向和水平荷载作用下桩筏基础的受力和变形特性。结合现场监测和数值模拟方法，揭示了基坑开挖对邻近桩基、支护结构及周边地表和建筑物变形的影响规律。.截止2019年12月31日，共发表（含收录）科技论文30篇；申请发明专利2项，其中授权1项，在审1项。项目提出了膨胀土地基中单一水平和竖向荷载下单桩的非线性计算方法，获得了水平和竖向荷载同时作用时桩伐基础的内力、位移变化规律，揭示了基坑开挖对邻近桩基、支护结构及周边地表和建筑物变形的影响规律。可根据本成果有效评估坑底及邻近桩基的工作性能，从而采取针对性的防护措施，对膨胀岩土地区基坑、桩基优化设计及对周边环境影响进行控制，保证建（构）筑物的安全，降低工程损失，具有重要的指导意义。