大跨软岩隧道施工动态监测试验研究

以内蒙古金盆湾大跨软岩隧道为工程背景,通过现场监测及数值分析,探讨围岩拱顶沉降、钢支撑内力、围岩与初期支护之间的内力、初期支护与二衬之间的内力随时间及开挖距离的变化规律,并用现有的理论及方法对其进行围岩稳定性分析。研究结果表明:对拱顶沉降数据的拟合函数进行求导分析并判定出围岩的稳定状况良好;围岩和初期支护压力在距离上台阶开挖面65 m后逐渐稳定;钢支撑外侧应力平均值大于内侧应力,最大应力值小于钢拱架的屈服强度,开挖过程安全级别始终处于安全或者基本安全状态;初衬和二衬间的接触应力在二衬浇筑后2天左右达到最大值,随后减小趋于稳定,且稳定值都小于0.1 MPa;数值模拟的围岩变形规律和实测围岩的变形规律相同且沉降实测值与模拟值差别不大,证明了模型的合理性。研究结论可为类似条件下工程的设计、施工和监测提供指导。

Study on Site Dynamic Monitoring of Soft Rock Tunnel with Large Span

Based on the engineering background of soft rock tunnel with large span in Inner Mongolia,a series of monitoring tests and numerical analysis were studied.Rules of measurement data changing with time and excavation distance were analyzed,including vault crown setdement,the stress of steel support,the stress between surrounding rock and initial support,the stress between initial support and secondary lining.In additional,the stability of surrounding rock was analyzed using the existing theories and methods.The results indicate:derivative analyses of the vault crown settlement fitting function illustrates the surroungding rock in good stability condition;The stress between surrounding rock and initial support reaches a constant value when the distance between this section and the highest step of tunnel face exceeds 65 m;The external stress of steel support is greater than the internal stress,the maximum value is less than the yield strength of steel support,and the steel support is always in the state of security or basic safety;The stress between initial lining and secondary lining reaches the maximum after the secondary lining pouting about two days,then it decreases and stabilizes,and the stable value is less than 0.1 MPa;In additional,the rule of surrounding rock displacement calculated with the numerical analysis is almost the same with that from the monitoring test,which proves the rationality of the model.The experiences and conclusions can be adopted in the design,construction and research of similar tunnels.