Experimental study on flow structure of island-tunnel bonding zone and flow force during sinking the immersed tube

East and west artificial islands are used to realize the transition from bridge to tunnel for Hong Kong-Zhuhai-Macao Cross-sea Tunnel. Immersed tunneling method is applied in sea tunnel and the total length of the sinking section is 5 664 m. The tube sections of E1-E33 are arranged from west artificial island. The standard pipe section is 180 m long,37.95 m wide,11.4 m high and weighs about 80 000 tons. The connection area of the island and tunnel is affected by the deflecting flow and the sudden change of the water depth during the foundation trough excavation,and the flow pattern is complicated. Moreover,the flow pattern will be changed when the sinking joint is subsided. It is necessary to obtain the magnitude of water flow force to guarantee the safe sinking and accurate docking of the immersed tube. By using the undistorted model in a wide flume with the geometric scale of 1:100,the experimental study on the flow distribution and water flow force during the sinking process of the island tunnel is carried out. The results indicate that,when there is no protective measure at the head of the island,the deflecting flow would affect the middle part of tube E1 and the flow velocities on the surface and at the bottom layers are larger than that of the middle layer. When sinking tube E1,the maximum longitudinal flow force can reach 4 601 kN,and the averaged longitudinal flow force of tube E2 is 5 149 kN. After sheltering tube E1,the flow velocity at tube E1 decreases significantly. The middle part of tube E2 is mostly affected by the sheltering body,the maximum increment in the flow velocity reaches to 40%,and the flow velocity of the middle layer is larger than those on the surface and at the bottom layers. The average longitudinal flow force of tube E2 is 5 240 kN. When the sinking tube is completely immersed into the water,the flow velocity in the foundation trench is relatively small,and the water flow force during the sinking process decreases gradually. The vertical distribution of water flow in the connection area of island and tunnel is not exponential one,and the velocity distribution along the length of the pipe section is not uniform due to the influence of deflecting flow on the island head wall. The formula of floating water flow force at the pipe section is not suitable for calculating the magnitude of the water flow force during the sinking process of immersed pipe.