浅埋富水隧道施工大变形原因分析与应对措施

Cause analysis and countermeasures of large deformation induced by shallow-buried tunnel construction under water-rich condition

为解决富水条件下隧道洞口浅埋段大变形问题突出、施工难度大的问题,依托在建福州市董奉山隧道项目,对隧道断面大变形的破坏特征及原因进行了详细分析,并提出针对性应对措施。结果表明:洞口浅埋富水地段受地层、地形、水环境及施工等因素影响,大变形以拱顶沉降为主,且在开挖后较短时间里变形急剧增加;隧道大变形表现为“急剧增长-缓慢增长-趋向稳定”3阶段变化规律,急剧增长阶段主要集中在下台阶开挖之前,其围岩变形量约占整个沉降变形的75%~80%。根据大变形分析情况提出:开挖前采用“超前帷幕注浆+井点降水”的辅助加固措施,改善掌子面前方围岩施工环境;开挖中采用钢架型号加强、中下台阶大直径锁脚及上台阶大拱脚等措施,可较大程度地控制隧道大变形发展,保证洞内施工安全。相关经验可供类似工程借鉴。

In order to solve the problems of prominent large deformation and difficult construction of shallow-buried section of tunnel entrance under water-rich condition,based on the Dongfengshan tunnel project under construction in Fuzhou City,the failure characteristics and causes of large deformation of tunnel section were analyzed in detail,and the corresponding countermeasures were put forward.The results showed that the large deformation was mainly caused by vault settlement due to the influence of stratum,topography,water environment and construction,and the deformation increased sharply in a short time after excavation.The large deformation of tunnel section presented a three-stage change rule of’rapid growth,slow growth and stable trend’.The rapid growth stage was mainly concentrated before the next step excavation,and the deformation of surrounding rock accounts for about 75%~80%of the whole settlement deformation.According to the analysis of large deformation,it was proposed that the auxiliary reinforcement measures of’advanced curtain grouting with well point precipitation’should be adopted before excavation,to improve the construction environment of surrounding rock in front of the working face.During excavation,the steel frame type strengthening,large-diameter locking foot at middle and lower steps and large arch foot at upper steps should be adopted,which can control the development of large deformation of tunnel to a large extent and ensure the safety of tunnel construction.The relevant experience can be used for reference in similar projects.