软土地下开挖对被动桩水平承载力的弱化机理与安全控制方法研究

Soft soil is widely distributed along the big rivers and coastal areas in Chinese developed region. The excavation of underground space, represented by deep foundation pits and subway tunnels, has become a new norm of urban construction. It results in the passive horizontal bearing of the underground piles of the adjacent buildings or bridges, and causes the engineering safety problems, such as pile foundation tilting and additional deformation of structures. This project is aimed at the typical technical and theoretical problems of horizontal bearing capacity weakening of passive piles due to underground excavation in soft soils. Based on the technical route combining in situ DMT and CPTU tests, field full scale excavation tests, indoor model test and numerical simulation, the key contents of this project are studied as follows: The evaluation method for unloading characteristics of excavated soft soil based on in situ DMT/CPTU test parameters; The weakening mechanism and variation rules of horizontal bearing capacity of passive piles caused by typical soft soil excavation methods; The p-y relation of the horizontal bearing capacity of pile foundation considering unloading effects and the change laws of its characteristic parameters; The whole process analysis model of the horizontal bearing capacity of passive piles based on the DMT/CPTU in situ soil parameters and so on. Through the above research, the aim is to establish the weakening degree and safety evaluation method of the horizontal bearing capacity of passive piles under the condition of underground excavation and unloading in soft soil area, and put forward the corresponding safety control technologies. The research results have important theoretical and practical significance to ensure the safety of the underground space development and improve the technological level of the pile foundation engineering.

我国沿江沿海经济发达地区广泛分布软土，以深基坑及地铁隧道为典型代表的地下空间开挖已成为城市建设新常态，由此导致邻近建筑物或桥梁桩基被动水平承载，经常诱发桩基倾斜和构筑物附加变形等工程安全问题。本项目针对软土地下开挖弱化桩基水平承载力这一技术与理论问题，采用原位DMT和CPTU测试，现场足尺开挖试验、室内模型试验与数值仿真相结合的技术路线，着重研究下列内容：基于原位DMT/CPTU测试参数的软土卸荷特性分析方法；典型软土地下开挖方式对被动桩水平承载力的弱化机理与变异规律；考虑卸荷效应的桩基水平承载力p-y关系及其特征参数变化规律；基于DMT/CPTU原位土体参数的被动桩水平承载力全过程分析模型等。通过上述研究，旨在建立软土地区地下开挖卸载条件下的被动桩水平承载力弱化程度和安全评价方法，提出相应的安全控制技术。研究成果对保证我国地下空间开发安全，提高桩基工程技术水平具有重要的理论和实践意义。

我国沿江沿海经济发达地区广泛分布软土，以深基坑及地铁隧道为典型代表的地下空间开挖已成为城市建设新常态，由此导致邻近建筑物或桥梁桩基被动水平承载，经常诱发桩基倾斜和构筑物附加变形等工程安全问题。本项目针对软土地下开挖弱化桩基水平承载力这一技术与理论问题，采用原位CPTU测试，现场足尺开挖试验与数值仿真相结合的技术路线，进行了下列内容研究：基于 CPTU原位测试提出了基于 CPTU 原位测试的桩基 p-y 曲线分析方法和软土地区刚、柔性桩水平承载位移控制标准；通过设计邻坑开挖现场试验，结合 CPT 原位测试明确了基坑开挖卸荷对邻近既有桩基水平承载性能的影响机理；通过数值仿真计算分析方法建模，深入研究饱和软黏土中邻坑开挖和坑中坑开挖卸荷致被动桩水平承载弱化机理；基于开挖卸荷前后 CPT 测试 p-y 曲线，考虑开挖卸荷过程中土体应力释放及桩-土相互作用特征，提出了考虑邻近基坑开挖卸荷全过程的被动桩水平承载分析方法并开展了基坑开挖卸荷后邻近桩基水平承载力损失预测研究；对桩-隧道不同位置的桩侧响应进行了一系列的参数分析。确定桩周隧道影响区域，并提出了隧道邻近既有桩的保护方案；通过现场试验和理论计算，充分论证了软土地层后注浆技术与可液化地层共振法地基处理技术对桩基水平承载性能的提升效果。提出了基于开挖效应的被动桩水平承载主动控制方法，和开挖卸荷条件下被动桩承台设计参考标准。研究成果对保证我国地下空间开发安全，提高桩基工程技术水平具有重要的理论和实践意义。