Study on Stability of the Foundation Trench at Island-Tunnel Connection Section

The construction of Hong Kong-Zhuhai-Macao bridge submarine tunnel applied immersed tube method. The hydrodynamic conditions of the foundation trench at the island-tunnel connection section are complex. The seabed of tunnel is silty clay. The construction of tunnel may cause the local scour and sediment deposits of the foundation trench. In both cases, the sinking of immersed pipes may not work properly. The construction company need to master stability of the foundation trench before the sinking of immersed pipes. Under different conditions, the stability of the foundation trench is studied by normal model in the flume of reciprocating flow. The normal model with a geometric scale of 100 can simulate the flow characteristics at the connection section of island-tunnel. The experimental velocity is 1.2m/s when the immersed pipe does not sink after foundation trench excavation. The flow velocity is 0.6m/s during the sinking process of immersed pipe. The range of scouring and siltation of the foundation trench is within 0.20m after laying the gravel cushion with a block diameter of 5cm in the foundation trench of E1 and E2 pipe. When there is shelter at the head of the artificial island and the seabed is also protected, the scouring and silting range of the foundation trench is smaller, the gravel cushion is more stable. The test shows that the siltation of foundation trench caused by local scour can be reduced effectively after the implementation of protective measures. The safety construction risk of immersed tube can be reduced.