Construction Monitoring Analysis for Large Cross-section Tunnel Excavation of Passenger Dedicated Railway

A field monitoring programme was carried out for the cut and cover railway tunnel near Meilan Airfield in Hainan province,and varied laws on deflections and internal forces of excavation retaining and protecting were obtained. There are several monitoring on clusions as follows: 1) The horizontal displacements of retaining structure increases with the construction duration and tends to be stable gradually after the foundation pit excavation is completed. The largest displacement appears on about one third depth of the excavation. 2) The axial force of cables changes greatly during the excacation of the foundation pit,and sand and water effuse quickly between high-pressure rotating piles,which has great influence on the axial force of cables. 3) The steel supports adoptes strict control standards and has some potential bearing capacity. The axial force of steel support changes steadily and fluctuates very little.