Study On The Failure Mechanism Of Ancient Sea Wall Of Qiantang River

The Qiantang River locates at southeast china, which is famous for its unique tidal bore. The tide works day and night. However, the ancient seawall along Qiantang River works as a defense against flood, tide,typhoon and other forms of disasters. Undergone 250 years,280 kilometers of ancient seawall was built along Qiantang River. Because of river reclamation and change of river way, much of the ancient seawall was disappearing, there is only 40 kilometers ancient seawall remaining. Local problems of ancient seawall and frequent natural disasters bring about a lot of thoughts for us. Thus, it is important to do some researchs about failure mechanism of ancient seawall. Discussing the dynamic responses of different water impacts will provide basis for further understanding of existing condition of ancient seawall, which is significant for further protection of the ancient seawall.This paper based on the large wave flume test, which simplifys the tidal bore as wave impact. Through the model test, we discuss the impact of wave on the main body of ancient seawall and interaction of wave, main body and soils under seawall. Regarding the apron as the focus, we analyze the change formations of apron under different impacts of wave, stream and interaction of wave and stream, which provides the reference of prototype apron protection.First of all, through historical reference review and engineering exploration, we get geological conditions and structure types of the ancient seawall.Secondly, we simply review the characteristics of Qiantang tidal bore, simplifying the tidal impact as wave impact in the model test; and also, sketching up the wave theory involved in apron test. Under shallow water condition, the wave near coast is diving wave, the water mass points of which flow the same direction with the current on the river bottom. The movement of water mass points provide dynamic conditions for the scouring of particle.Furthermore, the we conduct a water wave physical model test to simulate the impacting pressure on the surface of the ancient seawall and the change of the pore pressure of the soil under the main body under different engineering conditions. Through the analysis of the test data, getting the wave pressure on the ancient seawall, movement tendency of main body and the pore pressure of soil under mian body under different wave heights and wave periods. During certain conditions, the main body has the forward tendency, the pore pressure rises. After a wave impact, the main body undergo positive wave impacting and negative suction pressure.Finally, aiming at the apron, we conduct a physical model test to do study about the structure disorder of apron stone and the change of pore pressure of the soils under the apron under different engineering conditions.