PROTECT THE BRIDGE PIERS AGAINST SCOURING
Product: Box Gabion, Reno Mattress.
Problem: The 426 km long Awash-Kombolcha-Hara Gebaya railway Project is being constructed by Yapı Merkezi as a single track starting from the northeast of the city of Awash including many bridges, viaducts and culvert structures.
Topographic, climate and precipitation characteristics are the main factors effecting the flow of the river bed along the railway line. If not mitigated, the energy of the flows will cause damage to the bridges and other hydraulic structures during maximum flow rate events. Flow shear force causes scouring problem under the footings. Moreover, bridge piers cause sudden contraction / expansion in the flow sections, resulting in energy loss which is seen as the water turbulence around the piers. Turbulenced flow create deep scour holes around the piers.
Solution: The project has been designed with Reno mattresses to protect the bridge piers against scouring which could result in a bridge collapse. Hydraulic model analyses were prepared for each of the 48 bridges within the scope of the project.
Water height levels were calculated using river bed terrain models, bridge geometry and discharges(Q100 and Q200). For example, the flow rates of each river were determined between 3 m/s and 7 m/s.
Analysis: The design discharge of the Sal River Q100 was defined as 562.5 m3 / s and the Q200 control flow rate was 736.70 m3 / s and the velocities around the bridge is between 3 m / s to 6 m / s. In the Darga River, Q100 design flow rate is defined as 297.50 m3 / s and the Q200 control flow rate is 387.60 m3 / s. According to these discharge, velocity around the bridge is between 3 m / s and 6.7 m / s. In addition, D50 material diameter, foot shape, foot angle was defined in the software.
The gabion was laid to cover the surface of the scour hole areas. The thickness of the gabions was chosen according to the velocity and share force of the flow. In the beds where rock movements are intense, extra steel wire lid covers are needed for protection over the mattress gabions. Cutoff walls with box gabions have been designed in the upstream and downstream from the right coast to the left coast.