Effects of estuary regulation engineering are related to structure type of its dykes, but it is difficult to study the effect of local complex structure with physical model directly. Taking NⅡC segment of the 2 nd phase project of Deep Water Channel at Yangtze Estuary as a case, the paper discussed the method of research on engineering effect of hollow block structure by combining flume experiment with physical model. The method makes it possible to research the effects on current and riverbed

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... nduced by complex local structure with large-scale physical model. By comparison of different schemes, it is derived that the scheme without 2600m-long training dike of NIIC segment do harm to the exit channel of North Passage, and there are little influence with the scheme of the height of 2600m-long training dike of NIIC segment debasing 1m or the scheme of adopting hollow-block mound breakwater structure. Waterproof and weakly water-permeable structure types such as caissons, rubble mound are widely used in estuary and coastal engineering. Two sorts of structures are popularly used in building seawall and designed training dike when the groundwork is of silt or soft clay: one is rubble slope mound on reinforced groundwork, including the rubble mound with artificial blocks; another is the pile structure (Xie,1996). The regulation engineering in the project of Deep Water Channel at Yangtze Estuary are mainly formed by three parts: south training dike, north training dike and spur dike groups between them. The south training dike is 48.077 km long, and the north designed training dike is 49.200 km correspondingly. N II C segment, which lies in the upper north training dike with the length of 2.6km, is on the groundwork of in argillaceous soil. The under putty surface elevation of groundwork is approximately-7.6~-8.6m (the Woosung basic plane). On this groundwork, with the failure field test of inserting big prestressed reinforcement concrete cylinder structure, more than 20 application schemes were proposed by many domestic designing departments. Among the 20 schemes including replacement of artificial block body mask in the slope mound or artificial block body mask packed in bags granulated substance core of bank mound breakwater on the sand groundwork; the in-depth cement mixes up (CDM) and in semicircle caisson mix dike the ground; stand erect dike with sunk reinforced concrete big cylinder and stand erect the dike with sunk steel cylinder, etc.. By comparing all the 20 schemes, the new developed hollow block mound breakwater(Xie et al. 2004) was adopted for the advantages of genius design, less weight, convenient construction, reasonable construction cost, well stability, and small risk. Since this new structure is being used in the domestic river and sea engineering for the first time, some key problems, which may determine whether or not a scheme will be adopted, need to be solved in laboratory in advance. The key questions include: character of water permeability, the influence of different hollow block structure and its place form to the character of water-permeable, whether the effect of regulation project will be influenced by water percolation, the influence of the water