Experimental Study Of Horizontal Wave Force On A Perforated Caisson With Rubble Foundation

As a new type breakwater, perforated caisson is taken more attention because its structure can effectively reduce the wave reflection and the wave energy. There have been many systematic researches on the interaction between waves and perforated caissons, but most of these researches are based on the constant water depth in front of the caisson. However, in actual projects, the perforated caissons could be built on the rubble foundations. A detailed analysis and research, which is considered the influence of the foundation, is few, so it becomes important to take a systematic research on the perforated caisson with rubble foundation.Through 2D experiment in the wave flume, the reflection coefficient and the horizontal wave force between waves and perforated caissons with rubble foundation have been investigated. At the same time, use and compare with the previous test data of the perforated caisson without foundation in the same experimental conditions. The physical model test was carried out in the wave tank for suspension material test at the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. Regular and irregular wave parameters are selected in the range of engineering practice. The JONSWAP spectrum suggested by Goda is used to simulate irregular waves. The main factors influencing the reflection coefficient and the total force are considered in the test model design, such as the width of chamber, the porosity of perforated wall and the height of the rubble foundation. In order to compare with each other, the solid conventional structure and the perforated caisson each with low and middle foundation were tested separately.The relationship between the reflection coefficient of perforated caisson with rubble foundation and their effect factors are obtained, and it can be known that the influence of the relative foundation height and the influence of the relative chamber width are the most dominant factors. The reflection coefficient of perforated caissons with middle foundation is smaller than those without foundation. The phase difference between the total horizontal force and the total vertical force has been investigated, and the total vertical force reaches its extremum before the total horizontal force. The phase difference of crest values make for the stabilization of perforated caissons, on the contrary, the phase difference of trough values make against the stabilization.By use of the Ordinary Least Square Estimation, the empirical formulae of reflection coefficient, the phase difference between the total horizontal force and the total vertical force, the ratio of the total moment are presented for theoretical study and practice. The results of empirical and the experimental data show good consistency with each other.