Field Monitoring and Numerical Simulation Study for Mechanical Characteristics of Extra-long Highway Tunnel under Complex Geological Condition

For extra-long highway tunnel under complex geological condition, the existing design based on empirical analogue method could not accurately ensure the safety of tunnel construction. Taking Motianling tunnel in Chongqing as an engineering background, the monitoring and measurement schema was proposed for the extra-long tunnel under complex condition, and the field data and the numerical simulation results was analyzed. The results indicated that, the selected cross-section reflected overall state of the Motianling tunnel, and the structure safety monitoring during operation was considered; by tunnel internal and external observation,it was found that the tunnel face in F22 fault zone might not stay stability, because the monitoring information received feedback timely,and the supporting measures was proper, the surrounding rock stayed stability when excavating; for the typical section, the pressure was greater than interlayer pressure, primary lining sustained most of the load,and the secondary lining played an assistant role as safety reservation; the maximum of anchor axial force and surrounding rock pressure occurred at tunnel crown. By monitoring and numerical simulation, the dynamic excavation and design was realized, the Motianling tunnel was achieved safely and successfully at last, and the basic data are provided for safety monitoring during operation.