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South Dakota Department of Transportation
Project Synopsis

Title: Evaluation of SRICOS Method for South Dakota Cohesive Soils
Project Researcher: Frances Ting,
Project Manager: Terry Jorgensen
Research Period: -
Status: Approved
Cost: $0.00

Problem Statement:The method currently used by SDDOT for designing bridge foundations is Hydraulic Engineering Circular No. 18 (HEC-18). This method is generally regarded as overly conservative due to the fact that scour prediction are based on laboratory experiments for cohesionless material. The greater scour resistance of cohesive soils may result in bridge foundation designs that are overly conservative. This increased cost could be avoided if more accurate scour prediction methods for cohesive soils were available to design engineers.

Work completed by Texas Transportation Institute in 2004 on NCHRP Project 24-15 and published in NCHRP Report 516 using the SRICOS (Scour Rate In COhesive Soils) method demonstrates that erosion rates for cohesive soils can be lower than for cohesionless soils. The scour depth in cohesive soils is also dependent upon the duration of the flow. The testing that this work is based on was done in Texas and one site on the Potomac River near Washington D.C. These results may be valid for cohesive soils in South Dakota, but no verification has been completed to confirm that this method is acceptable for use in South Dakota.

The SRICOS Method could provide potential cost savings and increased confidence levels if testing was done on cohesive soils in South Dakota. The method should also be examined with small water sheds and ungaged streams. Sensitivity analysis needs to be conducted to determine the critical input parameters.


Research Objectives:
1  Determine if scour prediction of SRICOS program is comparable with existing scour data in cohesive soils.
2  Evaluate sensitivity and determine critical input parameters to SRICOS program.
3  Determine applicability of SRICOS for use on small water sheds and ungaged streams.

Research Tasks:
1  Meet with the technical panel to review project scope, discuss issues, and review the work plan. Researchers will provide minutes of meeting.
2  Conduct a literature search which will include flow-frequency predictions for small water sheds and ungaged streams and compare the results with other states as they relate to use of SRICOS (Scour Rate In COhesive Soils) to evaluate bridge scour. At
3  Through collaboration with SDDOT and USGS identify three sites for verification of SRICOS method.
4  Conduct site investigations, collect minimum of four Shelby tube soil samples per site, and complete drilling log of sites identified in Task 3. All data collected will be included in final report. Continuous sampling will be conducted from flow line
5  Conduct Erosion Function Apparatus (EFA) testing, grain size analysis, soil classification with AASHTO standard designation, and Atterberg limits on Shelby tube samples.
6  Obtain hydrologic data (estimate if none existing) and run Hydrologic Engineering Center River Analysis System (HEC- RAS) on data to estimate flow velocity at bridge pier sites identified in task 3.
7  Run the SRICOS program using data obtained from previous tasks and sites identified in task 3. Compare these scour predictions with predictions from existing data.
8  Conduct sensitivity analysis on data from task 7 and identify critical input parameters in SRICOS program.
9  Meet with technical panel to review drilling information, soil testing results, SRICOS predictions, and other significant data collected to date.
10  Provide guidance on use of SRICOS for predicting bridge scour in small watersheds and ungaged streams.
11  Prepare a final report and executive summary of the literature survey, research methodology, findings, conclusions and recommendations.
12  Make an executive presentation to the SDDOT Research Review Board at the conclusion of the project.

Documents Available:

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