软岩公路隧道紧急停车带变截面段变形特征及加固方法

软岩公路隧道紧急停车带变截面段变形较正常段往往较为显著,易发生变形侵限,是软岩公路隧道施工的难点。以渭源至武都高速公路木寨岭隧道为依托,总结了隧道紧急停车带变截面段的变形特征,分析了其变形破坏原因；在此基础上,提出采用小孔径预应力锚索对变截面段围岩进行加固,利用FLAC3D有限差分软件对变截面段的开挖施工过程进行模拟,对比了不同小孔径预应力锚索加固方案的变形控制效果,并对选定方案进行了现场试验验证。研究结果表明：隧道由紧急停车道向正常段施工时,正常段距离紧急停车带端头约15m范围内一侧的围岩变形明显大于另一侧,位移最大值出现在上台阶拱脚,且出现了喷射混凝土开裂、钢架扭曲和局部变形侵限现象；紧急停车带变截面一侧围岩受到了爆破施工的多次扰动,同时紧急停车带端头所受支护的约束作用较弱,加上地下水对围岩的软化作用,是变截面一侧围岩产生大变形的主要原因；采用纵向预应力锚索+环向预应力锚索对紧急停车带端头附近围岩进行加固,可以有效提高变截面一侧围岩整体稳定性,减小变截面段围岩非对称变形。研究成果可为类似软岩公路隧道紧急停车带变截面段的变形控制提供重要借鉴。

Deformation Characteristics and Reinforcement Methods in Variable Cross-section at Emergency Parking Belt in Soft Rock Mass Highway Tunnel

The deformation of variable cross-section at the emergency parking belt in soft rock mass highway tunnel is significant than that of the normal section. The deformation related disasters are prone to occur, which is difficult to maintain normal construction in soft rock mass highway tunnels. By taking the Muzhailing Highway tunnel in the section from Weiyuan to Wudu as the research object, the deformation and failure characteristics of variable cross-section at the emergency parking belt was summarized and analyzed. On this basis, the prestressed anchor cable with small diameter was proposed to reinforce the rock mass. The excavation process of variable cross-section was simulated by using FLAC3D finite difference software. The deformation control effects of different reinforcement schemes were compared, and the support effect of selected scheme was verified by field test. The research results show that the deformation of rock mass on the sudden-change side was obviously larger than that on the other side in the range of 15 m at the variable cross-section, when the tunnel was constructed from the emergency parking belt to the normal section. The maximum deformation occurred at the arch foot of the upper bench and the shotcrete cracking, distortion of steel ribs and local deformation intrusion occurred. The rock mass on the sudden-change side has been disturbed many times by the blasting construction. Meanwhile, the restraint of the support structure on the end of the emergency parking belt was weak and the rock mass was softened by groundwater. These were the reasons for the large deformation of rock mass on the sudden-change side. By adopting longitudinal prestressed anchor cable +circumferential prestressed anchor cable to reinforce rock mass at the end of emergency parking belt, the stability of rock mass was enhanced and the deformation was basically symmetrical. The research results provided an important reference for the deformation control of variable cross-section at the emergency parking belt of soft rock mass highway tunnel.