Performance Study On Permeable Pile Breakwater

Pile breakwater is widely adopted in lake protection and beach reclamation, embankment protection engineering and so on, and its mechanics of attenuating wave energy is complex. Study detailedly the influencing factors to attenuate wave energy has important theoretical value and practical value.Based on retroactively study of the previous theories and engineering applications, a special-shaped cross section pile permeable breakwater, which is made from rectangular cross section with semi-circular shaped grooves on both sides were carried out, then the pile breakwater structures are researched on the influence of different permeable rate and wave period though physical model test. Compared with the rectangular cross section pile permeable breakwater the results show that the major factors influencing transmission coefficient are the permeable rateηand wave steepness Hi/L(or Hi/gT2), and the secondary factors is the relative width a/L. For these two different pile breakwater structures, variation of the transmission coefficient is consistent. When permeable rate less than 0.273, the influence of transmission coefficient with permeable rate is obvious. Comparing with this two pile breakwater structures by experiment results, it can be show that the wave attenuation performances of special-shaped cross section pile permeable breakwater is better than the rectangular cross section pile permeable breakwater. In the range of test, when the value of permeable rateηis near 0.2, transmission coefficient of special-shaped cross section pile breakwater is less than rectangular cross section pile permeable breakwater, at most it can decrease about 10%. Therefore, practical applications in projects, to reduce the wave height behind breakwater and resolve the problem of pile uplift in soft clay, this special-shaped cross section pile permeable breakwater can provide references for future design and application.Meanwhile, this paper set up mathematical model of the pile permeable breakwater base on two-dimensional wave source representation method. Then it is verified though the results of experiment. It is show that the results of mathematical model is nearly about physical model test, when the value of Hi/gT2 is more than 0.005. It indicates that this mathematical model can be used in this range. And then this model can be used to compute the transmission coefficient of two other different cross section pile permeable breakwaters (Rectangular groove cross section pile and triangle shaped groove cross section pile). By comparing with these results, it shows that when slotted section area fixed, the effect of shape of the section on transmission coefficient could be neglected, the transmission coefficient is related to volume of cross-section slotted. The more volume of cross-section slotted when permeable rate is smaller, the smaller transmission coefficient.But for the wave force, the cross section with semi-circular shaped caissons is the smallest than any other cross section.The results obtained in the paper are expected to be useful in coastal and offshore engineering.