基于双层永久衬砌结构的桩基托换施工力学行为研究

Study on Mechanical Behavior of Pile Foundation Underpinning Based on Double Layer Permanent Lining Structure

以西安地铁1号线矿山法区间下穿太平河桥工程为背景,运用有限元方法分析研究基于双层永久衬砌结构的桩基托换体系的施工力学行为,并论证超前注浆预加固地层的效果。研究结果表明:基于双层永久衬砌结构的桥梁桩基托换体系安全可靠、环境影响小,可为后续类似桩基托换提供宝贵的借鉴和参考;桥桩托换段桩基出露施工环节对桥跨结构的沉降变形影响较大,是衬砌结构洞内托换群桩基础的关键工序,故施工过程中应予以重点关注;基于双层永久衬砌结构的桥梁桩基托换体系在完成承载体系的有效转换后托拱结构节点处产生明显的应力集中现象,因此应适当加厚桩基托换节点处结构厚度并增加配筋量以满足结构安全要求;桩基托换施工过程中桩基开挖暴露长度愈短,托换体系施工引起的桥跨结构沉降变形及桩基托换节点区域主应力值愈小;洞内预注浆加固能够显著降低桥跨结构沉降变形及托拱结构受力,从而确保隧道修建时桥梁结构的安全性。

With reference to the project of Xi’an Metro Line 1 undercrossing the Taiping River Bridge constructed with mine tunneling method, finite element method is used to analyze the mechanical behavior of pile foundation underpinning system based on double-layer permanent lining structure, and the effect of advanced grouting to reinforce the stratum is demonstrated. Research results show that underpinning system of bridge pile based on double layer permanent lining structure is safe and reliable with minor environmental impact, which can provide valuable reference for similar pile foundation underpinning. The construction process of pile foundation exposure has great influence on the settlement and deformation of the bridge span structure, which is the key process of pile foundation underpinning and should be addressed. After the effective transformation of the bearing system of the bridge pile foundation underpinning system based on double-layer permanent lining structure, the stress concentration of the supporting arch structure node is obvious. It is necessary to appropriately increase the thickness of pile foundation underpinning structure and the reinforcing bar amount to meet the structural safety requirements. The shorter the exposure length of pile foundation excavation in the pile foundation underpinning construction, the smaller the settlement deformation of the bridge structure and the smaller the main stress value of the pile foundation underpinning area caused by the construction of the underpinning system. The pre-grouting reinforcement in the tunnel can significantly reduce the settlement deformation of the bridge span structure and the stress of the supporting arch structure so as to ensure the safety of the bridge structure during mine tunneling.