BACKGROUND

The Federal Highway Administration, U.S. Army Corps of Engineers, and state DOTs have developed or used methods of sizing riprap for use in protecting bridge abutments, piers, channels, guidebanks, dams, embankments, and other structures vulnerable to erosion. Most of the methods are based on, or have been derived from, methods originally presented by Isbash or Shields in the 1930s. Other methods of sizing riprap have resulted from empirical studies that have been designed to protect specific structures such as piers and abutments.

Existing techniques and procedures for design of riprap protection can be confusing and difficult to apply. A brief review of the literature indicates that many different techniques are used to determine the size and extent of a riprap installation. Depending on the technique used to size riprap, the required size of stone can vary widely. Most states have their own specifications for classifying riprap size and gradation and there is not a consistent classification system or set of specifications that can be used when preparing plans or assembling a specification package for a project. There is a need for a consistent specification that could be used from location to location.

Various construction practices are employed for installing riprap; many of them are not effective and projects requiring the use of riprap historically have suffered from poor construction practices and poor quality control. Standard construction practices and techniques are needed to ensure proper placement and performance of riprap countermeasures.

OBJECTIVE

The objective of this research is to develop design guidelines, material specifications and test methods, construction specifications, and construction inspection and quality control guidelines for riprap at streams and riverbanks, bridge piers, bridge abutments, guidebanks, and other locations requiring scour countermeasures.

Accomplishment of the project objective will require at least the following tasks.

TASKS PHASE I (1.) Review the technical literature from domestic and foreign sources and assess the adequacy and extent of existing information used to design, specify, and construct riprap. Specifically, review riprap design equations and techniques for determining (1) the size of stone, for riprap design, (2) the gradation requirements, (3) the material quality tests, and (4) the thickness requirements. (2.) Survey federal agencies, state departments of transportation, and other agencies to determine practices used to design, specify, and construct riprap. The survey shall collect data on riprap design equations, classification systems, specifications, standard plans, and construction guidance. The survey shall be submitted to the NCHRP panel for review and approval prior to distribution. Based on the survey results, interview selected agencies to acquire detailed information. (3.) Based on the findings of Tasks 1 and 2, synthesize the current state of practice for designing, specifying, and constructing riprap at stream and river banks, bridge piers, bridge abutments, guidebanks, and other locations requiring scour countermeasures. Perform a critical evaluation of all commonly used design equations, material specifications and test methods, and construction practices. Based on the critical evaluation, determine equations, specifications, test methods, and construction practices to be developed in Phase II. (4.) Submit an interim report documenting the information developed in Tasks 1, 2, and 3. Specifically, the interim report shall include the following:

• A summary of the findings of the literature review;
• Results of the survey;
• Results of the critical evaluation, including a detailed report of the design equations, material specifications and test methods, and construction practices evaluated; and
• An updated work plan as a separate appendix on how the research team intends to complete Phase II. Specifically, equations, specifications, test methods, and construction practices to be developed in Phase II should be identified.

Meet with the NCHRP panel to discuss the interim report and updated work plan. Work on Phase II will not begin until the interim report and updated work plan are approved by NCHRP.

PHASE II (5.) Based on the panel's guidance during the interim meeting, determine or develop the following:

• Design equations and methodologies to use for each different design application;
• Guidance on proper determination of design variables (e.g., velocity multiplication factors, design flood frequency and freeboard, flow velocities, characteristics, and flow depths);
• Sensitivity of equations and methods being evaluated to ranges in flow parameters, flow depths, flow velocities, side slopes, and other important variables;
• Limitations on using the recommended equations and methods;
• Filter requirements, design methods, and types;
• Vertical and lateral extent and configuration of filter and riprap; and
• Durability and susceptibility to ice and debris damage.

(6.) Develop material specifications for riprap and test methods for riprap gradation and material quality. Contact riprap producers (e.g., quarry operators and national associations) to evaluate the feasibility of producing recommended gradations. (7.) Develop construction guidelines and specifications with consideration of the practicality of constructing riprap using the recommended procedures ( e.g., at piers and abutments, under wet or dry conditions, on side slopes, in deep water, or at sites requiring dewatering). Contact experienced construction contractors, state and federal construction agency personnel, and national and state construction associations to evaluate the practicality and constructability of the guidelines and specifications. (8.) Submit a final report that documents the entire research effort. The design guidelines, material specifications and test methods, construction specifications, and construction-inspection and quality-control guidelines shall be included as stand-alone appendices.

Status: Research is complete.

Product Availability: NCHRP Report 568: Riprap Design Criteria, Recommended Specifications, and Quality Control. Typical details for the riprap applications investigated in this study are available for download below.

Guide bank typical details
•  Web-viewable file in PDF format
•  AutoCAD format for download
•  Microstation format for download

Revetment riprap typical details
•  Web-viewable file in PDF format
•  AutoCAD format for download
•  Microstation format for download

Riprap apron at vertical wall abutment typical details
•  Web-viewable file in PDF format
•  AutoCAD format for download
•  Microstation format for download

Riprap at piers typical details
•  Web-viewable file in PDF format
•  AutoCAD format for download
•  Microstation format for download

Riprap at spill-through abutments typical details
•  Web-viewable file in PDF format
•  AutoCAD format for download
•  Microstation format for download

Riprap spill-through slope and apron typical details
•  Web-viewable file in PDF format
•  AutoCAD format for download
•  Microstation format for download

Sand-filled geocontainers as filter for pier riprap typical details
•  Web-viewable file in PDF format
•  AutoCAD format for download
•  Microstation format for download