Revision of Local Socavation Around a Pier with Different Roughness Through Numerical Simulation and Predictive Equations

Failures in bridges are multifactorial, however, among those that occur in bridges over rivers, the local scour in piers and abutments can be considerate as one of the main causes, it is common that happens during major floods. Even when there is a large number of equations to determine the scour depth there is no single solution, there are methods that are based on laboratory data that according to (Farias et al, 2009) exhibit important limitations, such as restricted ranges of parameters, scale effects and even inadequate adjustments of the mathematical equations to describe the observed trends. Also some based on field data do not show consistent results.

Several authors have carried out reviews of the scope of the most used methodologies, both with laboratory and field data, among them (Rodríguez and Bustillos, 2015) and others such as (Nalluri Chandra, et al, 1999) have proposed modifications to these. The comparison of the values of the local scouring obtained by numerical modeling and through the general and modified equations registered in (Nalluri Chandra, et al, 1999) and that are based on 134 laboratory data is presented.

In the present document, this phenomenon is studied in flow around two types of piers, the first one smooth, the second with roughness imitating the surface of a golf ball, waiting to see an effect in the mitigation of the turbulence and therefore in the depth of scour, since it is known that this kind of surface decreases the friction with the medium.

To obtain numerical results, a three-dimensional CFD software was used, a laboratory-scale channel measuring 7.65 m long by 0.60 m wide was modeled with a pier at the center and whose bottom is composed of non-cohesive material, sand quartz of 1.5 mm, for two representative flow rates the lower of 0.02545 m³/s and the greater of 0.06 m³/s, with hydraulic depths of 0.13 m and 0.362 m respectively.

The results show that the scour depth around the pile with roughness increased by about 30%. As expected, the background patterns formed around the smooth stack were more extensive in the transverse direction than in the vertical one. Regarding the comparison of numerical results with the laboratory data equations, the results show very little agreement between them, they are closer when compared with the modified equations, especially the ones proposed by Arunachalam and Shein version I, both methods have in common that they are ones of the simpler and that the variables involved in them are hydraulic parameters and the geometry of the pier (Rodríguez and Bustillos, 2015).