An Experimental Study on the Effect of Under-Scouring Depth and Horizontal Spacing between Two Bed Protection Blocks on the Stability of Frontal Block

摘要

Stability of river-bed protection block at flood event is affected by under-scouring of the block. Block spacing effects for block stability was investigated with different under-scouring conditions. Three blocks were placed at the bottom in a flume with changing under-scouring depth of frontal block and spacing between the first and second block. Drag and lift forces were measured directly in each experimental condition. PIV technique was used for visualizing flow and evaluating streamline pattern. The experimental results show that for same under-scouring gap, the lift and drag coefficient decreases with increasing spacing between two blocks. In addition, if the under-scouring gap increases under the same horizontal spacing, then the lift coefficient increases and the drag coefficient decrease. These results demonstrate that, wider spacing is suitable for stability of frontal block for under-scouring condition.