Scouring is defined as the waterways erosion of the bed and sides because of crossing water flows, as bed erosion in downstream of hydraulic structures because of flow high intensity, and as bed erosion because of the creation of local turbulent flows. Because of the intensity of the secondary flows in this part of the river, noting the subject of erosion and sedimentation and rendering suitable solutions for its controlling in the arches is highly important. Among the simple and economic methods of protecting the bridge abutment against scouring is the usage of riprap coverage. The aim of this research is to study the impact of riprap diameter size on the instability depth. To do the experiments, a flume with 180 degree arch from Plexiglas was used. Experiments were performed in clear water conditions using two types of ripraps with two densities with four diameter sizes around abutment with arched wall located in 70 degrees from arch with four discharges. Experiments started from upstream flow depth and by decreasing the flow depth and by movement of the first riprap the movement threshold depth was recorded and by the ripraps group movement the failure threshold depth was recorded. The results obtained from experiments show that in stable density and discharge, the instability depth decreases in both movement and failure thresholds by increasing the riprap diameter.
展开▼
