SRICOS-EFA Method for Complex Piers in Fine-Grained Soils

Abstract

The SRICOS-EFA method was developed by Briaud, Chen, and their students starting in the early 1990s to predict the scour depth versus time curve for a cylindrical pier in deep water subjected to a multiflood hydrograph and founded in a layered soil. Here, the SRICOS-EFA method is extended on the basis of flume tests and numerical simulations to the case of multiple rectangular piers lined perpendicularly to the flow, in any water depth, with a certain flow attack angle. The results show that the scour depth in shallow water can be much smaller than in deep water but does develop faster than in deep water, that there is a magnifying effect on the scour depth for piers that are spaced less than 3 pier diameters apart, that the scour depth for rectangular piers is about 10% larger than the one for a cylindrical pier except in the case of a wide and thin pier obstructing the flow where the scour depth can be significantly larger than for the cylindrical pier, and that the effect of the flow attack angle can be satisfactorily handled by using the projected width of the pier perpendicularly to the flow. The SRICOS-EFA computer program which automates these and other scour depth calculations can be downloaded free of charge from a website: http://ceprofs.tamu.edu/briaud/sricos-efa.htm. The SRICOS-EFA method recommended in HEC-18 offers a significant number of refinements compared to the method recommended for coarse-grain soils in HEC-18. It is site specific because it uses site specific samples that are not limited to coarse-grain soils, it includes the time effect through the use of a hydrograph, and it can handle layered soil systems. The coarse-grain soil approach presented in HEC-18 is typically conservative and sometimes very conservative when used for fine-grain soils.