桩基础荷载对邻近已有隧道影响的有限元分析

目前，城市密集的高层建筑桩基础对临近隧道的影响问题越来越突出，为了更好地理解桩群荷载对已建成隧道的影响，主要进行了两方面的研究：（1）利用平面应变有限元方法分析了桩列荷载作用对邻近已有隧道的变形及受力影响，并研究了桩群参数变化（包括桩间距以及桩基础与隧道结构净距）对现存隧道的影响；（2）分析计算了上海太平洋2期广场工程对邻近地铁1号线隧道的影响。分析结果表明：隧道单侧存在桩列荷载作用时，隧道变形以沉降为主，水平位移较小，同时隧道结构向桩基础方向产生一定扭曲，这对于运营地铁是十分不利的；桩基础荷载造成隧道所受弯矩分布向桩基础方向偏转；随着桩间距、桩与隧道净距的增加，隧道拱顶下沉量以及弯矩变化最大值相应减小，沿隧道方向桩间距变化影响大于垂直隧道方向桩间距变化影响。

Finite element analysis of influence of pile group loading on existing neighboring tunnels

The influence of pile group loading on existing neighboring tunnels is assessed by using the finite element method with the aim of furthering the understanding of the interaction problems. Firstly, some parametric studies including foundation layout and clear distance between piles and existing tunnels are carried out using the 2-D plane strain approach. Then a case study of Pacific Square Ⅱ of which minimum distance between pile foundations from Metro No.1 in Shanghai is only 15m, is analyzed by using this approach. According to the results, this approach can satisfy the pile rows loading problems. The loading of piles causes global downward movement and squatting of the tunnel lining. And the horizontal displacement of tunnel lining is much smaller than vertical displacement. The tunnel diametrical distortions are occurred in this case. It is very disadvantageous because of the differential movement of the two rails of the subway tunnel. The bending moment distribution behaves clockwise rotation due to pile loading. The crown settlement of tunnel lining and maximum bending moment change reduce with the increasing of pile space and clear space between pile and tunnel.