关键词: 水底隧道, 饱水地层, 衬砌作用荷载, 限量排放

Abstract:

Being different from general mountain tunnel by NATM, the lining of underwater tunnels built by mining method may be sustained heavy external water pressure; and underwater tunnels are more affected geological uncertainties and risks, particularly when passing through the saturated stratum such as the weathering deep slot stratum F4 in Xiamen undersea tunnel. Based on fluid-mechanical interaction model for saturated ground conditions, the three dimensional numerical analyses are conducted to investigate the relationships between the pressure behind the lining and the discharge water inflow for different drainage conditions. The results show that the water pressure trapped behind the support depends on the discharge capacity of the drainage system relative to the water inflow from the ground, even the reduction of 80% external water pressure is obtained while the discharge water flow being controlled about one-third of the full water inflow from the ground. From the view of reasonable design of seismic water loads behind the lining, the reduction coefficient of 0.2 is regarded as the acceptable level for controlled drainage underwater tunnel. The emphasis is placed on introduction of grouting circle in support system for weathering deep slot stratum F4，but if competent ground conditions are anticipated to be encountered during underwater tunnel construction; then grouting circle may not necessarily be required. In view of the disadvantageous distribution of deformation and internal forces occurred in the invert, particularly in the corner position of invert connected with the side-wall; therefore, whether it is waterproof-type tunnel or drainage-type tunnel, more attention is paid on design of invert form and support.

Key words: underwater tunnel, saturated stratum, load of lining, controlled drainage