文章针对骑跨于既有盾构隧道之上的基坑工程,按实际工况进行了开挖支护的平面应变有限元模拟,其中土体采用修正剑桥弹塑性模型.计算结果表明:隧道开挖致使周边土体呈X形的塑性区,且地下连续墙对于该塑性区开展有遮挡效应；当隧道位于基坑开挖中心线正下方时,隧道几乎不发生水平位移,且基坑开挖对位于其下方的已建隧道的竖向位移的影响较水平位移大,故当地下连续墙端部与隧道竖向间距足够大,隧道拱底与拱顶水平位移逐渐趋于相同.%Considering the construction of a foundation pit above an existing shield tunnel and its actual working conditions,a plane strain finite element simulation of the excavation and supporting measures was carried out and a modified Cam-clay model was employed for the soil body.The results show that due to the tunnel excavation,an X-shaped plastic zone emerges from the surrounding soil body,the diaphragm wall has a shelter effect on the development of this zone,almost no horizontal displacement occurs for a tunnel just below the excavation centerline,and the effect of the foundation pit construction on the vertical displacement of the tunnel built below is greater than that of the horizontal displacement.Thus,provided there is sufficient vertical distance between the end of the diaphragm wall and the tunnel,the horizontal displacements of crown and bottom tend towards equalization.
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