Local scour around tandem square porous piles in steady current

Experimental study on the local scour around tandem square porous piles in steady current has been carried out in the live-bed flow condition. The influence of the porosity (P) of both front and rear piles in the tandem configuration (P = 0–38.5 %) and the gap ratios (G/D = 2–12) are quantified based on the measurement of the development of the local scour, time scale, three-dimensional scour profiles and the scour characteristics were analysed. Three regimes are identified regarding on the porosity distributions of the front and rear pile. The distinct features were found at the porosity of the front was small than its counterpart of the rear. The global scour can be recognized at G/D < 4. The dimensions of the scour hole for the rear pile decrease first as a trade-off is observed between the sediment deposit landed around the rear pile and its weak erosion. A critical gap ratio, at which the minimum scour dimensions were observed is strongly depend on the difference of the porosity between the front and rear piles.