Calculation of Bridge Pier Scour Using the Erodibility Index Method

摘要

This report explains concepts that can be used to understand the scour resistanceof earth materials such as rock, slickensided and cohesive clays, and non-cohesive granular material. A semi-empirical approach known as the Erodibility Index Method (Annandale 1995) that can be used to quantify the relative ability of these earth materials to resist scour is presented, concomitantly with a method that can be used to calculate the depth of scour around bridge piers. The first bridge pier scour analysis using the Erodibility Index was conducted for the Northumberland Strait Bridge (Anglio et al. 1996) (figure 1). This analysis entailed verification of the Erodibility Index Method by using material properties and estimates of the erosive power of water that resulted in scour of rock around one of the bridge piers. Laboratory studied were conducted to quantify the relative magnitude of the erosive power of water around the bridge piers. The verified relationship and estimates of the relative magnitude of the erosive power of water for design conditions were used to predict the likelihood of scour at other bridge piers and to design countermeasures. Subsequent research on the application of the Erodibility Index Method resulted in a general method to calculate the depth of scour at bridge pier foundations. This report explains the Erodibility Index Method, explains how to apply the method to calculate scour depth around bridge piers, and presents a case study.