ABSTRACT

Many pile-group groynes have been used on the rivers in Japan for bank protection purposes. The type of pile arrangement in a group significantly affects downstream flow structure, yet these effects have not been sufficiently studied. In this study, flow structure and turbulence characteristics around different pile-groups were investigated. The main purpose was to evaluate the effects of pile arrangement on the flow. Two types of pile-groups with in-line and staggered pile arrangements were assessed. The pile groups were studied along the bank and in the mid-channel to clarify the flow change mechanism in different locations. The results demonstrated significant impacts of pile arrangement on both flow structure and turbulence characteristics. The staggered type created a gradual deceleration of the flow from the mainstream toward the bank and drastically reduced turbulence in the downstream, compared to the in-line type. The presence of the sidewall in the side cases acted as the axis of symmetry of the mid-channel cases. In addition, flow structure and turbulence characteristics around the pile-groups were well simulated with a two-dimensional numerical model.