浅埋偏压隧道进洞施工力学特性研究

Study on Construction Mechanical Properties of the Shallow Tunnel Entrance under Unsymmetrical Pressure

隧道进口段围岩常常具有浅埋、偏压、风化严重等特点,若施工处理不当,极易造成洞口边、仰坡滑动和洞内塌方等事故,从而影响隧道正常施工和人员安全。结合具体工程,对浅埋偏压隧道进洞施工开展了三维数值模拟,并结合监测数据分析了施工对围岩和支护结构力学特性的影响,主要结论如下:围岩变形具有非对称性,浅埋侧围岩变形量要小于深埋侧;随着隧道的逐步开挖,隧道深埋侧拱脚和浅埋侧拱肩处围岩易于发生剪切破坏,而且围岩的塑性区也主要位于这两个区域,并逐渐向拱顶上方贯通;初期支护结构的受力状态受偏压地形影响显著呈非对称性,而超前支护受偏压影响较小;现场实测围岩变形与计算结果较为吻合,且变形在22天后达到稳定状态。

The surrounding rock at tunnel entrance mostly has the characteristics of shallow,unsymmetrically loaded and serious weathering,etc. If improper construction measures are taken,it may trigger accidents of slope slide at tunnel entrance and collapse at tunnel face,which further affects the normal tunnel construction and the personnel safety. Three-dimensional numerical simulation was carried out to analyze the construction of a shallow tunnel entrance under unsymmetrically pressure. By comparing and analyzing the calculation results and the in-situ monitoring data,the construction mechanical properties of surrounding rock and support structure were revealed,and conclusions were drawn as following. Firstly,the deformation of the surrounding rock is asymmetric at the tunnel face,i.e. the deformation at the shallow is smaller than that at the deep side. Secondly,with the gradual tunnel excavation,the surrounding rock at the foot of deep side and the arch of shallow side is easy to be shear failure,what is more,the plastic zones of surrounding rock are mainly located at these two places,and it will gradually intercommunicate towards the tunnel arch. Thirdly,the stress state of the initial support structure is significantly affected by the unsymmetrically terrain,while the advance support structure is hardly affected by the asymmetric pressure. The in-situ measured deformation values of surrounding rock agree well with the calculation results,and the deformation will reach a steady state after 22 days.