卵石层小净距隧道关键参数研究

针对卵石地层小净距隧道围岩整体性与稳定性差、施工中易坍塌、围岩相互扰动大的问题，通过FLAC 3D数值模拟和现场监测，对卵石层小净距隧道左右洞合理净距和先后行洞掌子面安全纵向间距进行了研究。得到如下结论： 1）当净距不大于6 m时，隧道地表沉降槽呈“V形”，沉降最大点位于中夹岩顶部；随着净距大于6 m，隧道拱顶部位地表沉降逐渐超过中夹岩顶部，地表沉降槽呈 “W形”。2）当2洞间净距不大于6 m（约1倍洞跨）时，2洞开挖后围岩压力叠加效应明显，极易发生失稳；当隧道净距大于18 m时，可按分离式隧道进行设计； 3）随着先后行洞间掌子面纵向距离的增加，后行洞施工对先行洞的影响逐渐减少，当纵向间距达到30 m（4.6倍洞跨）时，这种影响基本可以不予考虑。

Study on Key Parameters of Small Spacing Tunnels in Pebble Layer

In order to solve the construction problem of small spacing tunnel in pebble layer, i.e. poor integrity and stability of surrounding rock, easy collapse in construction and great disturbance of surrounding rock, through FLAC 3D numerical simulation and field monitoring, the reasonable spacing distance for small spacing tunnel in pebble layer and the safety longitudinal distance between the exist and the following tunnel are analyzed. The results show that: 1) The soil surface settlement curve shows a V shape pattern and the largest ground settlement is located at the top of middle rock pillar when the spacing between two tunnels is less than 6 meters. When the spacing is larger than 6 meters, the ground settlement corresponding to the tunnel vault is greater than the top area of middle rock pillar, and the soil surface settlement curve shows a W shape pattern. 2) The pressure of surrounding rock after tunnel excavation exhibits an obvious superimposing effect and the tunnel is easy to collapse when the spacing is less than 6 meters (approximately equal to the tunnel span). The twin tunnel can be designed as two separated tunnels when the spacing distance is larger than 18 meters. 3) The construction of following tunnel has less influence on the existing tunnel with the increase of the longitudinal distance between the two working faces. When the longitudinal distance is greater than 30 meters(4.6 time the tunnel span), the effect between the two working faces can be ignored.