Study On The Construction Method Of The Shallow Portal Section Of Hejiachong Tunnel In CZT Intercity Railway

Many entrances of railway tunnel in hilly region are located in the intensively weathering zone, where the surrounding rock is generally crushing and the overburden is relatively thin,which is not conducive to tunnelling. Under the construction, how to make rational use of various construction methods, reduce project inputs, improve efficiency, needs to be solved urgently.Based on Hejiachong tunnel project of CZT intercity railway,which has shallow portal section,high-risking in tunnel construction,complex geological conditions and large-span characteristics, the pros and cons of different shallow construction methods and their applicable conditions were analyzed. The contents are mainly as follows:(1) With MIDAS-GTS, the construction process of CD method,CRD method and three-step temporary arch method of tunnelling in the different depth was simulated.The mechanical characteristics of supporting structure and deformation of surrounding rock in diffrent construction step were analyzed. It is concluded that using the CD method is suitable for the first40m and after it three-step temporary arch method can be used.(2) Combined with the engineering conditions of pipe shed support and small pipe grouting pre-consolidation in Hejiachong tunnel, on the basis of two-dimensional analysis, the construction process of tunnelling was simulated by establishing three-dimensional model.The displacement of surrounding rock,the mechanical characteristics of supporting structure and its changes in the process of construction were analyzed.The supporting effect was assessed.(3) Monitoring data showed that the selected construction methods can meet the construction requirements.