Ultimate pier and contraction scour prediction in cohesive soils at selected bridges in Illinois.

Details

• Creators:
  Straub, Timothy D. ; Over, Thomas M. ; Domanski, Marian M.
• Corporate Creators:
  University of Illinois at Urbana-Champaign. Dept. of Civil and Environmental Engineering
• Corporate Contributors:
  United States. Federal Highway Administration ; Illinois. Dept. of Transportation. Bureau of Materials and Physical Research
• Subject/TRT Terms:
  • Bridge piers
  • Contraction (Thermodynamics)
  • Cohesive soils
  • Scour
  • Field studies
  • Mathematical prediction
  • Regression analysis
• Publication/ Report Number:
  FHWA¿ICT¿13¿025 ; ICT¿13¿025 ; UILU¿ENG¿2013¿2026 
• Resource Type:
  Tech Report
• Geographical Coverage:
  Illinois
• Corporate Publisher:
  Illinois Center for Transportation
• Abstract:
  The Scour Rate In COhesive Soils-Erosion Function Apparatus (SRICOS-EFA) method includes an ultimate scour prediction that is ; the equilibrium maximum pier and contraction scour of cohesive soils over time. The purpose of this report is to present the results of testing ; the ultimate pier and contraction scour methods for cohesive soils on 30 bridge sites in Illinois. Comparison of the ultimate cohesive and non-cohesive methods, along with the Illinois Department of Transportation (IDOT) cohesive soil reduction-factor method and measured scour are ; presented. Also, results of the comparison of historic IDOT laboratory and field values of unconfined compressive strength of soils (Qu) are ; presented. The unconfined compressive strength is used in both ultimate cohesive and reduction-factor methods, and knowing how the ; values from field methods compare to the laboratory methods is critical to the informed application of the methods. ; On average, the non-cohesive method results predict the highest amount of scour, followed by the reduction-factor method results; ; and the ultimate cohesive method results predict the lowest amount of scour. The 100-year scour predicted for the ultimate cohesive, non-cohesive, and reduction-factor methods for each bridge site and soil are always larger than observed scour in this study, except 12% of ; predicted values that are all within 0.4 ft of the observed scour. The ultimate cohesive scour prediction is smaller than the non-cohesive scour ; prediction method for 78% of bridge sites and soils. Seventy-six percent of the ultimate cohesive predictions show a 45% or greater reduction ; from the non-cohesive predictions that are over 10 ft. Comparing the ultimate cohesive and reduction-factor 100-year scour predictions ; methods for each bridge site and soil, the scour predicted by the ultimate cohesive scour prediction method is less than the reduction-factor ; 100-year scour prediction method for 51% of bridge sites and soils. ; Critical shear stress remains a needed parameter in the ultimate scour prediction for cohesive soils. The unconfined soil ; compressive strength measured by IDOT in the laboratory was found to provide a good prediction of critical shear stress, as measured by ; using the erosion function apparatus in a previous study. Because laboratory Qu analyses are time-consuming and expensive, the ability of ; field-measured Rimac data to estimate unconfined soil strength in the critical shear–soil strength relation was tested. A regression analysis ; was completed using a historic IDOT dataset containing 366 data pairs of laboratory Qu and field Rimac measurements from common sites ; with cohesive soils. The resulting equations provide a point prediction of Qu, given any Rimac value with the 90% confidence interval. The ; prediction equations are not significantly different from the identity Qu = Rimac. The alternative predictions of ultimate cohesive scour ; presented in this study assume Qu will be estimated using Rimac measurements that include computed uncertainty. In particular, the ultimate ; cohesive predicted scour is greater than observed scour for the entire 90% confidence interval range for predicting Qu at the bridges and soils ; used in this study, with the exception of the six predicted values that are all within 0.6 ft of the observed scour.
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• Format:
  PDF
• Funding:
  R27¿105
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/28794/dot_28794_DS1.pdf
• File Type:
  [PDF - 1.75 MB]
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha256:5454696222f8aa4c81428a5e31c3dba511ddbb89637aabcdd0f8cf9fd6638443