SRICOS: PREDICTION OF SCOUR RATE AT BRIDGE PIERS

Abstract

A new method called SRICOS is proposed to predict the scour depth versus time around a cylindrical bridge pier of diameter founded in clay. The steps involved are: 1. taking samples at the bridge pier site; 2. testing them in an erosion function apparatus (EFA) to obtain the scour rate versus the hydraulic shear stress applied; 3. predicting the maximum shear stress that will be induced around the pier by the water flowing before the scour hole starts to develop; 4. using the measured scour rate versus hydraulic shear stress applied curve to obtain the initial scour rate corresponding to the maximum shear stress; 5. predicting the maximum depth of scour for the pier; 6. using the scour rate and the maximum depth of scour to develop the hyperbolic function describing the scour depth versus time curve; and 7. reading the scour depth versus time curve at a time corresponding to the duration of the flood to find the scour depth that will develop around that pier. A new apparatus is developed to measure the scour rate versus time curve of step 2, a series of advanced numerical simulations are performed to develop an equation for the maximum shear stress value of step 3, and a series of flume tests are performed to develop an equation for the maximum depth of scour value of step 5. The method is evaluated by comparing predictions and measurements in 42 flume experiments. The method is extended to include a random velocity-time history and a multilayer soil stratigraphy; it is called the extended SRICOS or E-SRICOS. The algorithms to accumulate the effects of different velocities and to sequence through a series of soil layers are described. The procedure followed by the computer program to step into time is outlined. A simplified version of E-SRICOS called S-SRICOS is also presented. Calculations for the S-SRICOS method can easily be done by hand. Eight bridges in Texas are used as case histories to compare predictions by the two new methods (E-SRICOS and S-SRICOS) with measurements at the bridge sites.