In the test of hydraulic model with equal Froude number, the Reynolds number is decreased, due to the reduced structure of pile group according to model scale, and the model-prototype resistance coefficient of piles is not equal. In order to solve this problem and study the drag force of water flow around piles, an experimental work was conducted in a re-circulating flow tank(30 m long,3 m wide,0.26 m deep). Results revealed the relationship between piles resistance coefficient and pile number, pile spacing and pile arrangement. Based on the experimental results and achievements of related literature, the piles resistance similarity theory was developed for the piles physical model test. Research results showed that the physical model test which considered the resistance similarity of piles can offer more accurate predictions of the water flow and sediment movement.
