SRICOS: Prediction of Scour Rate at Bridge Piers (7-2937-1)

A new method called SRICOS is proposed to predict the scour depth z versus time t around a cylindrical bridge pier of diameter D 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 z versus the hydraulic shear stress applied t ; 3. predicting the maximum shear stress Tmax that will be induced around the pier by the water flowing at Vo before the scour hole starts to develop; 4. using the measured z versus t curve to obtain the initial scour rate z corresponding to Tmax; 5. predicting the maximum depth of scour Zmax for the pier; 6. using z and Zmax to develop the hyperbolic function describing the scour depth z versus time t curve; and 7. reading the z versus t 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 z versus t curve of step 2, a series of advanced numerical simulations are performed to develop an equation for the Tmax value of step 3, and a series of flume tests are performed to develop an equation for the Zmax 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.