SCOUR AROUND BRIDGE PIERS APPLYING STREAM POWER APPROACH
The current research aims introducing the problem of scour around bridge piers from a new point of view. The classical approach for tackling this problem usually depends on applying empirical equations developed from the analysis of experimental results with the use of dimensional analysis. Thus, in the current research an intensive study for evaluating the existing scour predictor was performed. The comparison processes through comparing the results of some laboratory experiments performed for scour around bridge piers and the predicted scour depth from some selected available predictor equations. About 156 experiments were carried out to perform the current study in accordance with 15 predictor equations. The results show that the scour predictors have a low reliability for following a specific trend or giving accurate results. Thus, it has been considered that it is of great importance to study the scour problem around bridge piers through a new approach. Stream power approach has been selected for achieving this objective. A one dimensional numerical model for open channel hydraulic was selected to stimulate the problem of flow and scour around bridge piers. Stream power variation is studied versus several parameters such as scour depth, sediment type and flow conditions. Several laboratory experimental studies were tested and stream power values in these different cases were analyzed. Results show that there is a significant relationship between scour depth escalations and stream power value. The relationship between stream power and scour depth was found to have a specific trend through which a new predictor could be developed. The new predictor was applied on some experiments and the estimated scour depth was compared to the experimental results. It was found that there was a good agreement between the experimental results and the scour calculated using the stream power approach. Finally, it can be concluded that the new approach is considered more reliable than the classical methods for estimating the scour depth at bridge piers. However more studies are needed to perform an inclusive idea about the application of stream power approach for pier and abutment scour problem.
Bridge construction and river channel morphology—A comprehensive study of flow behavior and sediment size alteration of the River Chel, India
Human has always modified its surroundings for better adaptation which include the building of urban landscapes, dams, and engineering constructions like bridges and other infrastructures. It has been unveiled from the study of River Chel that when the rail bridge was constructed before 1913, the natural width of the river was nevertheless maintained but the problem was initiated and after the road bridge construction in 1970s when the river width was minimized,the morphological changes started in a large scale. Such modifications have affected nature as well as human communities both positively and negatively. This paper will try to portray the evolution of channel shifting and changes of sediment size regime that the River Chel is experiencing due to the construction of bridges across the middle part of its course. So, this study is concerned about the changes in channel pathway since last 100 years and field-based hydrological parameters and sediment size analysis reveals some distinct changes in the channel planform with alteration of sediment size regime. Simulation of the hydraulic modeling in HEC-RAS specifies the probable affected area with bridges and without bridges in both upstream and downstream of the river course. Hence, the study unveils the alteration of the river hydrology and sediment size caused due to anthropogenic effects and impact of such flow analysis has been evaluated through the bridge scour calculation by CUS method. The discussion concludes that the Odlabari road bridge construction (after 1970) has modified the normal hydrological behavior of the river with a higher probability of bank erosion in downstream and floods in upstream resulting river bottleneck condition.
TESTS OF SCOUR PROTECTION FOR BRIDGE PIERS
If flood velocities concentrated by the area constriction at bridges remove material from under the bridge pier foundations, the pier may settle or collapse. The maximum depth of scour occurring during the passage of a flood peak is difficult to ascertain or to estimate by empirical formulas or model tests. To explore further the method of limiting the depth of scour by surrounding the pier with prototype material, model tests were made covering a range of constriction percentages, depths of flow, and Froude numbers, using both round and elongated piers. After determining the extent of the scour hole formed during the passage of a simulated flood, the protection afforded by a layer of protective material was tested with a repetition of the same flood. If the material of the layer was large enough to resist being moved and had a grain-size distribution capable of preventing leaching, no scour hole formed. A special test showed protection remaining intact despite stream bed degradation.