陡坡条件下小净距隧道不同开挖顺序的安全性与破坏模式分析

Analysis of Safety and Failure Mode for Excavation of Tunnel with Interval and Steep Slope based on Strength Reduction

基于有限元强度折减理论,考虑地表坡度变化以及小净距隧道不同的开挖顺序两大因素,通过对围岩发生极限破坏时的安全系数与塑性区进行分析,探究坡度变化条件下不同开挖顺序对隧道开挖安全性与破坏模式的影响。结果表明,随着坡度的增加,隧道不同开挖顺序下的安全系数越来越小,且先开挖浅埋侧的安全系数明显高于先开挖深埋侧;随着坡度的增加,浅埋洞单独开挖时隧道外侧竖向剪切破裂面发生小幅度偏转并出现与其近似垂直的向下贯通地表的破裂面,深埋洞单独开挖时隧道外侧竖向剪切破裂面发生小幅度偏转并逐渐消失,且将出现隧道外侧拱脚向地表坡脚发展的滑坡破裂面。

Based on finite element strength reduction theory,considering two factors of the variations of the surface slope ratio and the excavation sequence of the tunnel with small interval,through analysis of the safety factor and plastic zone of the surrounding rock mass destruction,the influence of different excavation sequence on the safety and failure mode of the tunnel under the condition of slope ratio varying are discussed.The results show that with the increase of slope ratio,the safety factor of tunnel under different excavation sequence is getting smaller and smaller,and shallow buried side tunnel excavation is higher than that of deep buried;and with the increase of slope ratio,the lateral vertical shear rupture surface of the tunnel under the excavation of shallow buried tunnel is slightly deflected,and the fracture surface which is near to the ground surface is approximately vertical.When the deep hole is excavated separately,the outer tunnel vertical shear rupture surface appears small amplitude deflection and gradually disappear and will appear rupture surface when outer tunnel arch foot develops towards the ground slope foot.