小净距公路隧道中岩柱对地表沉降变形规律研究

Law of Ground Settlement Caused by Middle Rock Pillar in Highway Tunnel with Small Clear Distance

为研究中岩柱对围岩稳定性与整个隧道的影响,依托重庆市九龙坡区新九路隧道为工程背景,通过MADIS-GTS模拟中岩柱在不同加固形态及不同加固高度下隧道地表沉降的变化规律,与实际施工监测数据进行对比分析。结果表明:1)小净距隧道地表沉降曲线受隧道埋深影响较大,当埋深较小时,双洞开挖后地表沉降曲线整体上呈不对称的"W"形,中岩柱在先行洞和后行洞之间起到杠杆支点的作用效应明显;当埋深较大时,整个沉降曲线大致呈对称的"U"形,在两隧洞上方一定高度形成共同压力拱,中岩柱被包围在压力拱内,从而导致地表沉降曲线中中岩柱支点效应被弱化,土拱效应明显。2)在小净距隧道施工过程中,浅埋隧道最优加固方案为中岩柱加固至地表且与拱顶为界;深埋隧道最优加固方案为以侧墙为界加固至拱顶。

To study the influence of middle rock pillar on the stability of surrounding rock and the entire tunnel,a case study is conducted on tunnel on Xinjiu road in Jiulongpo district,Chongqing,the variation law of surface settlement induced by middle rock pillars with different reinforcement forms and heights is simulated using MADIS-GTS,and the simulation results are compared with the monitoring data.The results show the following.(1)The surface settlement curve of the tunnel with small clear distance is greatly affected by the tunnel depth.When the burial depth is small,the surface settlement curve after the excavation of double holes shows an asymmetric W shape,and the middle rock pillar plays an obvious role as a lever fulcrum between the first and the second holes.When the burial depth is large,the settlement curve shows a roughly symmetrical U shape,a common pressure arch is formed at a certain height above the two tunnels,the middle rock pillar is enclosed in the pressure arch,which leads to the weakening of the pivot effect of the middle rock pillar in the surface settlement curve,and the soil arch effect is obvious.(2)In the construction process of tunnel with small clear distance,the optimal reinforcement scheme of shallow buried tunnel is that the middle rock pillar is strengthened to the surface and bounded by the crown.The optimal reinforcement scheme of deep buried tunnel is reinforced to the crown with the sidewall as the boundary.