NEW METHOD TO DETERMINE THE SCOUR ON BRIDGE PIERS OVER RIVER COURSES
Physical models in a reduced scale are usually used in fluvial hydraulics, being able to solve problems of engineering where the equations of calculation, have not reached the necessary competition to replicate with sufficient exactitude the physical phenomenon that appears in the reality. However, these models have their limitations due to the scale factor and related to physics, so that parameters and phenomena appear so reduced that they can not be reproduced or measured.
Numerical models are a set of mathematical equations that are applied to a problem that is represented by means of nodes (meshes), which in turn represent reality. The resolution of the equations that make up the problem is complex, so specific computer programs and high-powered computers are used to reduce the time of calculations. In river engineering the progress of mathematical models is very considerable, but they have the disadvantage that field or laboratory measurements are needed to validate and calibrate them. It also requires a great technical knowledge to know how to structure the models and interpret the results.
The technological challenge of this innovation consists on combining both models to finally obtain a physical model, calibrated and validated by a numerical model, and at the same time, a numerical model that gave solution to the phenomena that the scale model was not capable of, and applying it to the particular case of the piles of the Danube bridge, which had been substantially modified with respect to the Customer’s solution.
Usually, channel scour caused by piles introduced into them is determined by analytical methods based on experimental formulas, which are conservative in nature and often lead to over-dimensioning of the foundation and its protection. The physical model made for the Danube had the particularity of being a “moving bed”, so it was possible to know with reasonable precision the scour processes caused by a complex pile for different analysis scenarios. As it was calibrated and validated by the numerical models, it was able to give more realistic scour results that led to the optimization of the foundations and their protections.
It was possible to analyze phenomena such as turbulence, vortices, particle trajectories, current line analysis and quantification of hydraulic pressures on the foundation. The model was also used to analyze phenomena that are not usually studied, such as the behavior of piles and foundations in front of debris and the qualitative study of floating around the piles and to rule out adverse effects for boats and bathers. The set of all these studies were of maximum use when it came to convincing the authorities and third parties that the designed solution was safe, as well as the non-affection to the navigation channel, getting the approval of the project.
In short, the set of studies carried out exceeds the usual scope in this type of action.