Vertical displacement of tube segment of immersed tunnels caused by sand flow construction

By using the full-scale model tests on the sand-flow method,the whole process of vertical displacement of tube segment in the construction of immersed tunnel foundation treated by sand-flow method is simulated.The relative elevation versus time-history curves of the tube segment model,the amount of vertical displacement and the morphological characteristics of the sand deposit are obtained.The test results show that the model tests have three processes,that is,normal expansion of sand deposit,slow-beating displacement and fast-smooth displacement.The displacement amount and displacement rate of model in the slow-beating displacement process are smaller than those in the fast-smooth displacement process.The vertical displacement makes the gap area small and the chutes thin and densely distributed on the top surface of the sand deposit.Sand particles cumulate on the sand-deposit top and form horizontal layers,which causes the vertical displacement directly.The displacement process significantly affects the expansion of the sand deposit.The process of the slow-beating displacement can be used to reduce the thickness of the gap and chutes in engineering practice,but measures should be taken to ensure that the sand deposit radius meet the design requirements before the vertical displacement.