大断面公路隧道临近大型溶洞围岩稳定性分析

依托某高速公路隧道，运用有限元分析软件，对大断面公路隧道临近溶洞不同尺寸的围岩稳定性及钢拱架内力进行了分析。结果表明:①洞周位移随溶洞尺寸的增大均有所增加，溶洞尺寸显著影响掌子面挤出；②掌子面临近溶洞位置的塑性应变最大；③初期支护整体承受的弯矩以正弯矩为主（内侧受拉），墙脚位置出现小范围的负弯矩（外侧受拉），并伴随应力集中现象，是受力的薄弱环节，随着溶洞尺寸的增大，临近溶洞位置的弯矩出现不同程度的减小；④初期支护的轴力整体呈上大下小的分布，随着溶洞尺寸的增大，初期支护临近溶洞位置的轴力显著增加，加剧了轴力分布的不均匀性。

Analysis on Stability of Surrounding Rock of Large Section Highway Tunnel Approaching to Large Karst Cave

The stability of surrounding rock and internal force of steel arch frame of large section highway tunnel approaching to different cave sizes are analyzed by using finite element analysis software based on the tunnel of an expressway. The results show that:① the peripheral displacements are increased with the size of cave and the face extrusion is significantly affected. ②Maximum plastic strain appears in the tunnel face approaching to the karst cave; ③ the bending moment of the initial support is mainly the positive moment (tension inside) while the corner position bears negative moment (tension outside). The corner position of the tunnel is the most unfavorable position because of stress concentration. The bending moments approaching to the cave are decreased in various degrees with the increased size of cave. ④The axial force of the initial support is big on the top and small at the bottom. With the increase of the size of cave, the axial force of the initial support approaching to the cave position increases significantly, which intensifies the inhomogeneity of the axial force distribution.