北京地铁浅埋暗挖施工对既有桥桩的影响分析

在隧道施工影响下，建（构）筑物的上部结构及其桩基础、地层、隧道施工四者处于一个共同作用的完整体系中，每一部分的工作状态都是四者协同工作、相互影响的结果。因此，应综合考虑各影响因素。首先，岩土体是隧道与桩基相互作用的重要媒介。地铁隧道浅埋暗挖施工时必然扰动地层，地层将施工产生的变形传递到临近桩基导致桩基承载力的降低，荷载变化通过桩基向上传递使上部结构产生沉降和变形。当变形超过一定程度时，将影响上部结构的正常使用和安全。因此，在施工影响下，对既有桩基进行分析和控制以确保上部结构的安全是隧道施工穿越既有桩基的关键。在对上部结构-桩基-地层-隧道施工四者相互作用关系、桩基变形机制以及注浆加固机制进行详细论述的基础上，采用2D－Sigma有限元软件模拟北京地铁5号线雍和宫站－和平里北街站区间过桥段浅埋暗挖施工对既有桩基的影响，得出桩基变形的一般规律。同时比较分析注浆前后桩基的不同响应，提出注浆加固地层的必要性及相关的工艺参数。最后，将桩基变形的预测结果与现场实测结果进行对比分析，两者规律基本一致。研究表明，注浆加固地层对减小桩基变形、确保上部结构安全是非常有效的，这将对以后的地铁施工具有指导作用。

Analysis of effect on existing bridge piles induced by shallow tunneling construction of Beijing Subway

During tunnel construction, the superstructure and pile foundation of buildings, stratum, tunnel construction are in an interaction system. Functional mode of each section results in cooperating and interaction. So, they should be considered comprehensively. Firstly, soil is interaction medium of the tunnel and pile foundation. Constructing tunnel at shallow depth damages stratum. And stratum deformation is delivered to adjacent piles, which result in the reduction of pile foundation bearing capacity. Load fluctuation is transferred to the superstructure by pile foundation. Then sedimentation and deformation of adjacent structures is generated. Therefore, the crux in tunnel construction is to make the superstructure safety by analyzing and controlling for the existing pile foundation. Based on detailed discussion about the interaction of the superstructure and pile foundation of buildings, stratum, tunnel construction, pile deformation mechanism and grouting reinforced mechanism, the 2D－Sigma code is applied to simulate effect of existing pile foundation induced by shallow tunnel construction from Yonghegong Station to Hepingli North Street Station interval of line No.5 in Beijing. The universal law of pile foundation deformation is obtained; and necessity of grouting reinforced stratum and related processing parameters in construction are suggested by analyzing front-to-back response of pile foundation. Finally, based on analysis of comparison between numerical results and field measurement results for pile foundation deformation, their law is quite similar. Research shows that grouting reinforced stratum is effective for reducing deformation of pile foundation and making superstructure safety. The achievement will guide subway construction later.