Abstract:
The spur dikes are widely used in the waterway regulation engineering. However, the emergence of complex three-dimensional flow fields around the groyne head usually leads to the develpement of a local sour hole which may cause failure of the whole works. In this paper, a new type of spur dike with stepped head is proposed to weaken the flow dynamics at the groyne head, and a series of flume tests have been conducted in order to study the hydrodynamic characteristics and the scour characteristics of this new structure. The analysis results show that with the stepped head, the concentrated flow and the down-flow at the groyne head is dispersed progressively, and the formation of the shedding vortex is also reduced effectively. All of these lead to a reduction of the flow dynamics around the groyne head, and consequentially, the local scour is reduced. In addition, the flow can be deflected by the countertop of the steps. As a result, the local scour hole is pushed away from the groyne head, which is favorable to the stability of the groyne head. The studies also show that the protective effect of this new structure is related to the number of the steps, the width of the countertop and whether there are steps set up at the downstream slope of the groyne body. Experimental analysis results indicate that as the number or the width of the steps increases, the effect to control the local scour increases. Also, steps set up at the downstream slope of the groyne body protect the site downstream of the groyne head directly where the shedding vortex and the down-flow act, which seems more favorable to the reduction of the local scour hole.