Developing TxDOT Design Guidelines for Riprap Rock Size and Apron Limits at Culverts

Current design practices for bridge-class culverts often use bridge-centric or outlet-focused rip-rap rock size design equations, which do not adequately address inlet contraction scour, multiple culvert types, velocity amplification in wide structures, and varying soil erodibility. This project will develop defensible, culvert-specific rock sizing equations and apron design criteria tailored to varying culvert types (with-bottom and bottomless) and soil conditions. Researchers will: (1) perform literature review, survey, and site visits to synthesize design practice, identify research gaps, inspect Texas Department of Transportation's (TxDOT’s) data, and identify typical failure modes and vulnerable locations; (2) establish culvert-specific rock sizing equations for both with-bottom and bottomless culverts, with calibrated amplification factors for inlet and outlet culvert hydraulics and for both cohesive and non-cohesive soil conditions; (3) develop apron limits design criteria, including layout rules and quick-reference guidelines, that explicitly incorporate soil erodibility categories and address multiple vulnerable inlet and outlet transitions; and (4) produce ready-to-use design aids (charts, worksheets, and design examples), implementation recommendations, and quality assurance/quality control (QA/QC) checklists compatible with existing specifications and scour analysis procedures tailored for designers and maintenance personnel. These outcomes will provide TxDOT with scientifically robust design procedures compatible with the Specifications for the National Bridge Inventory (SNBI), enhancing infrastructure resilience and optimizing construction and maintenance expenditures.

• Record URL:
  • https://library.ctr.utexas.edu/Presto/project=0-7281

Language

• English

Project

• Status: Active
• Funding: $371,295.72
• Contract Numbers:

  0-7281

• Sponsor Organizations:

  Texas Department of Transportation

  125 E. 11th Street
  Austin, TX  United States  78701-2483
• Project Managers:

  Smith, Anne

• Performing Organizations:

  Center for Multidisciplinary Research in Transportation (TechMRT)

  Texas Tech University
  Box 41023
  Lubbock, TX  United States  79409-1023

  Texas A&M Transportation Institute

  Texas A&M University System
  3135 TAMU
  College Station, TX  United States  77843-3135
• Principal Investigators:

  Lu, Yimin

• Start Date: 20260901
• Expected Completion Date: 20280831
• Actual Completion Date: 0

Subject/Index Terms

• TRT Terms: Culverts; Design; Erosion; Quality control; Riprap; Size
• Identifier Terms: Texas Department of Transportation
• Subject Areas: Bridges and other structures; Design; Geotechnology; Highways;

Filing Info

• Accession Number: 02001120
• Record Type: Research project
• Source Agency: Texas Department of Transportation
• Contract Numbers: 0-7281
• Files: RIP, STATEDOT
• Created Date: Aug 28 2026 10:02AM