降雨对小净距大跨度隧道开挖松动区的影响

Influence of Rainfall on Excavation Loosened Zone of Large-span Tunnel with Small Spacing

小净距大跨度隧道在洞口段易受到浅埋偏压作用,隧道开挖会造成上覆岩土体出现大范围松动区,在降雨条件下更易出现地表塌陷与拱顶塌方。本文改进了围岩切向应力扰动系数公式,依托广州龙头山双洞八车道隧道工程,利用有限差分软件FLAC 3D对隧道洞口段在是否考虑降雨2种条件下开挖产生的松动区进行分析。分析结果表明:运用工程实际采用的双侧壁导坑法模拟开挖,隧道围岩产生的松动区范围较大且在拱顶上部产生交汇区域,中部核心土开挖时影响较小;考虑降雨渗流场之后开挖,在流固耦合作用下左右2个隧道围岩松动区面积增长分别约为30%,42%;隧道围岩松动区不对称分布和雨水渗流作用加剧了隧道偏压变形,并导致上部地表沉降最大增长33%左右。

The portal section oflarge-span tunnel with small spacing will be likely shallow-buried and affected by bias pressure,tunnel excavation may cause large loosened zone in overlying rock and soil mass,and surface subsidence and vault collapse are more likely to occur under rainfall condition.Based on a two-hole eight-lane tunnel project in Longtou mountain of Guangzhou,this paper improved the tangential stress disturbance coefficient formula of surrounding rock and analyzed the excavation loosened zone in tunnel portal section under anhydrous and hydrous conditions by using finite difference numerical analysis software FLAC3D.The analysis shows that the loosened zone caused by tunnel surrounding rock is large and produces a convergence zone in the upper part of the vault and the central core soil excavation has little impact by using the both side drift excavation method applied in engineering practice,the surrounding rock loosened zone area ofleft-right holes under fluid-solid coupling condition increases about 30% and 42% by considering the rainfall and seepage field condition,asymmetric distribution of tunnel surrounding rock loosened zone and rainfall seepage effect aggravates the bias deformation of tunnel,which make the maximumgrowth of upper surface subsidence reach 33% or so.