Prediction of scour depth versus time for bridge piers in cohesive soils in the case of multi-flood and multi-layer soil systems

Scour is the physical or chemical attack of flowing water which excavates and carries away material from stream beds and banks. Hydraulic structures such as bridge piers and abutments placed in the channel cause changes in the flow pattern such as acceleration, the formation of vortices, and scour around the structure. Channel scour, especially bridge pier scour, is the leading cause of bridge failures.;The scour phenomenon in cohesive soils is much different than that in non-cohesive soils. Scour in cohesive soils is much slower and more dependent on soil properties than that in non-cohesive soils. Applying the equations for non-cohesive soils to cohesive soils regardless of time appears to be overly conservative. Therefore, the scour analysis method for cohesive materials needs to consider the time effect and soil properties as well as hydraulic parameters.;The present study is based on the SRICOS method which was developed to predict scour depth z versus time t curve at bridge piers for a constant velocity and for a uniform soil. The SRICOS method was improved so that it can handle multi-flood and multi-layer soil systems, verified for 10 cases of full-scale scour measurements, and proposed as a meaningful and economic method for foundation design and maintenance. In addition, the simple SRICOS method was also developed. This method is very simple to use for obtaining the pier scour depth by hand calculations and is suggested as a useful method for design of bridge pier foundations.