平顶直墙暗挖通道临时支撑的拆除分析

Analysis on Demolition of Temporary Support in a Flat-roof Straight-wall Mined Channel

长沙地铁5号线高桥南站3号出入口地下通道具有地质环境复杂、下穿多种地下管线等特点。地下通道施工采用CRD工法开挖,其中临时支撑的拆除是初期支护最不利受力阶段。为保证现场施工安全并指导后续施工,基于有限元数值模拟,分析了临时支撑拆除对地表沉降和初期支护受力状态的影响。研究表明:暗挖通道施工时,地表沉降变化存在3个快速增长阶段,分别是左洞上台阶开挖、右洞上台阶开挖和临时支撑的拆除,其中,临时支撑拆除引起的地表沉降占施工过程地表总沉降的54.6%,拆撑长度对地表沉降影响较小;临时支撑的拆除会引起初期支护两侧轴力和弯矩大幅增加,并改变拱顶跨中受弯状态。为保证施工安全性,建议在二次衬砌未闭合成环前增设中部支架,再拆除临时支撑,待二次衬砌闭合成环达到强度后,拆除中部支架,或者不拆除中部临时竖撑且待二次衬砌闭合成环达到设计强度后,再拆除中部支撑。

The underground channel at the No.3 entrance of Gaoqiao South Station of Changsha Metro Line 5 features a complex geological environment and an underpass of various underground pipelines.The underground channel was constructed using the CRD excavation method,and removing temporary supports was seen as the worst stress phase for the initial support.To ensure that construction safety and guide the subsequent construction,finite element analysis was performed to assess the impact of temporary support removal on the ground subsidence and stress response of initial support.The results show that there are three rapid growth stages of the surface settlement during the construction of the underground tunnel,which are the excavation of the upper bench of the left tunnel,the excavation of the upper bench of the right tunnel and the removal of the temporary support.According to the research result,temporary support removal induced ground subsidence accounts for 54.6%of the total ground subsidence during mined channel construction.The effect of support removal length on ground subsidence is limited;temporary support removal induces an increase in axial force and moment on both sides of initial support and changes the bending state of the vault span center.Adding center support before forming a complete second lining structure is recommended to ensure construction safety.Once the second lining reaches the target strength,center support can be removed.Another option is to maintain the temporary vertical center support until the second lining reaches the target strength,then remove the center support.