城市隧道上覆地层整体下沉的力学机制分析

 通过对北京和深圳地铁、厦门海底隧道、机场路等工程的现场监测结果的综合分析表明，浅埋暗挖隧道的受力机制与山岭隧道有较大不同，上覆地层变形体现出明显的整体下沉趋势，且带来的地层开裂、破坏更具突发性和破坏性。针对这种特征，对工程中地层滑动破裂角采用一种新的模型进行推导，其结果显示，地层滑裂角比传统结果大约15°，即滑裂面更陡峭、接近竖直方向，且该滑裂角是围岩参数、应力场、覆跨比、断面矢跨比的函数，一定程度上体现了围岩变形破坏类似的具几何效应，即浅埋暗挖隧道上覆地层的整体下沉、塌陷，突发性冒顶等特征，是由围岩的力学特性和几何特性共同作用的结果。另外，隧道结构下部土体的扰动、损伤、软化等，极易造成下部地层沉降和承载力的丧失，随之而来的即是隧道结构的整体下沉、支护效果恶化以及进一步的上覆地层整体沉降加剧。相应的采用理想弹塑性模型、修正剑桥模型的数值模拟分析，能部分反映这种上覆地层整体下沉的特征。研究结果还表明：对浅埋暗挖隧道围岩受力变形机制、本构关系的研究急需加强。

MECHANISM ANALYSIS OF INTEGRAL SUBSIDENCE OF UPPER STRATUM IN URBAN TUNNELS

By in-situ monitoring in Beijing metro，Shenzhen metro，Xiamen subsea tunnel，and Xiamen airport road tunnel etc.，its found that there are big differences between urban shallow-buried tunnel and mountain one both in stratum deformation and rock wall pressure. Upper strata in city tunnels subside as a whole，and the subsidence develops more suddenly and devastatingly. Faced with these complex situations，a new model for stratum slipping and cracking is established，and the deduced results show that stratum slipping angle is 15° higher than traditional one，thus relative slipping surface is steeper，closer to vertical direction. And the slipping angle is a function of rock properties，stress fields，tunnel depth versus span，and rise-span ratio，which to some extend testifies that the deformation and failure of rock wall embody scale effects，thats to say，the geometrical properties of rock wall jointing with mechanical parameters will call for stratum integral subsidence，collapse，and roof fall behavior. Besides，soil below tunnel structure，being disturbed，damaged，and softened，may easily drive under-stratum into subsiding and losing bearing capacity，further bringing integral subsidence of supporting structure，and finally sharpening integral subsidence of upper-stratum. Correspondingly ideal elastoplastic model and modified Cam-Clay numerical model can partially lead to the similar conclusion. Synthetically research shows that its vital necessary to acknowledge urban shallow-buried tunnel from rock wall mechanical behavior and its constitutive law.