|Title:||Pier and Contraction Scour Prediction in Cohesive Soils at Selected Bridges in Illinois
|Author(s):||Straub, T.D.; Over, T.M.
|Subject(s):||Bridge, Pier, Contraction, Scour, Cohesive, Soil, Illinois, SRICOS, HEC-18
|Abstract:||This report presents the results of testing the Scour Rate In Cohesive Soils-Erosion Function Apparatus
(SRICOS-EFA) method for estimating scour depth of cohesive soils at 15 bridges in Illinois. The SRICOS-EFA
method for complex pier and contraction scour in cohesive soils has two primary components. The first
component includes the calculation of the maximum contraction and pier scour (Zmax). The second component
is an integrated approach that considers a time factor, soil properties, and continued interaction between the
contraction and pier scour (SRICOS runs).
The SRICOS-EFA results were compared to scour prediction results for non-cohesive soils based on
Hydraulic Engineering Circular No. 18 (HEC-18). On average, the HEC-18 method predicted higher scour
depths than the SRICOS-EFA method. A reduction factor was determined for each HEC-18 result to make it
match the maximum of three types of SRICOS run results. The unconfined compressive strength (Qu) for the soil
was then matched with the reduction factor and the results were ranked in order of increasing Qu. Reduction
factors were then grouped by Qu and applied to each bridge site and soil. These results, and comparison with
the SRICOS Zmax calculation, show that less than half of the reduction-factor method values were the lowest
estimate of scour; whereas, the Zmax method values were the lowest estimate for over half.
A tiered approach to predicting pier and contraction scour was developed. There are four levels to this
approach numbered in order of complexity, with the fourth level being a full SRICOS-EFA analysis. Levels 1 and
2 involve the reduction factors and Zmax calculation, and can be completed without EFA data. Level 3 requires
some surrogate EFA data. Levels 3 and 4 require streamflow for input into SRICOS. Estimation techniques for
both EFA surrogate data and streamflow data were developed.
|Peer Reviewed:||not peer reviewed
|Sponsor:||Illinois Department of Transportation ICT-R27-19
|Rights Information:||No restrictions. This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161
|Date Available in IDEALS:||2013-10-22