Experimental study on a pile-supported structure built on a reef subjected to tsunamis

The shore structure whose deck is supported by piles was constructed for La Guardia Airport about 30 years ago in 1967 on the water in New York. The similar pile-supported structures consisted of a floating deck were also constructed, and has planed to be constructed on the reefs in Japan. The structures have several features such as a minimal environmental effect on surrounding current and seabed, small oscillations by winds or waves and easy removal. However they must be designed by taking the effect of tsunami into consideration. The deck elevation has to be determined so as the highest crest of tsunami running up the slope of the reef does not slam to the deck. In addition to this, how to assess the forces on piles resulting from the tsunami is unknown. Therefore we conducted 1/100-scale model set-up for a unit of the structure having a length of 75cm and a width of 45cm installed on a reef in a two-dimensional water tank which can generate solitary waves and currents. Then the following results were obtained: Firstly the drag coefficients of piles against solitary waves and currents are identical with those of a circular pipe obtained by Shilichting's chart. Secondly the height of the crest of the solitary wave depends on the slope angle of the reef as well as water depth. Therefore It should be carefully evaluated through model tests or numerical calculations by taking into consideration these items.