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Gravel Roads - Design and Maintenance Original Presentation for National ASCE Webinar

Gravel Roads - Design and Maintenance Original Presentation for National ASCE Webinar. Presented by : Ken Skorseth, Program Manager SD Local Transportations Assistance Program (SDLTAP) South Dakota State University. Gravel Rds Maint & Design. Overview of Presentation

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Gravel Roads - Design and Maintenance Original Presentation for National ASCE Webinar

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  1. Gravel Roads - Design and MaintenanceOriginal Presentation for National ASCE Webinar Presented by: Ken Skorseth, Program Manager SD Local Transportations Assistance Program (SDLTAP) South Dakota State University

  2. Gravel Rds Maint & Design • Overview of Presentation • Gravel Road Design Issues • Geometrics. • Surface Aggregate Specification. • Thickness Design Basics. • Stabilizing Gravel

  3. Gravel RdsMaint & Design • Design Issue – Basic Geometrics: • Be familiar with the AASHTO publication: GeometricDesign of Very Low-Volume Local Roads (ADT < 400) • Commonly called the “Little Green Book”.

  4. Gravel Rds Maint & Design 2001 Green Book and “Little Green Book”

  5. US CUSTOMARY Total roadway width (ft) by functional subclass Basic Geometrics Design speed (km/h) Major access Minor access Recreational & scenic Industrial/ commercial access Resource recovery Agricultural Access 15 - 18.0 18.0 20.0 20.0 22.0 20 - 18.0 18.0 20.0 20.0 24.0 25 18.0 18.0 18.0 21.0 21.0 24.0 30 18.0 18.0 18.0 22.5 22.5 24.0 35 18.0 18.0 18.0 22.5 22.5 24.0 40 18.0 18.0 20.0 22.5 - 24.0 45 20.0 20.0 20.0 23.0 - 26.0 50 20.0 20.0 20.0 24.5 - - 55 22.0 - 22.0 - - - 60 22.0 - - - - - Note: Total roadway width includes the width of both traveled way and shoulders. Guidelines for Total Roadway Width for New Construction of Very Low-Volume Local Roads in Rural Areas From: AASHTO – Guidelines for Geometric Design of Very Low-Volume Local Roads (ADT <400) Major Access road classification requires only 18 ft. (5.5 m) roadway width at 40 mph (64 km) design speed

  6. Gravel Rds Maint & Design Design Issue – Crown: An important design issue is crown on gravel road surfaces. Generally recommended crown for gravel surfaces is 4% which is double the crown used in pavements.

  7. Gravel Rds Maint & Design Design Issue – Crown: (con’t) Clear illustration of 2% crown on road to the left and 4% on the road to the right. Water will not drain off an aggregate surface with only 2% crown. This must be addressed in design and during construction.

  8. Gravel Rds Maint & Design Design Issue – Crown: (con’t) • There are conflicting views on crown: • 2 to 6% for “low-type pavements” recommended by AASHTO Green Book pg 387 – 2001 edition. • The FHWA Gravel Roads Manual recommends crown at or near 4%. • Note: in arid and semi-arid regions, gravel roads may perform with less crown, but don’t use less than 3 %.

  9. Gravel RdsMaint & Design Shoulder Maintenance is Important

  10. Gravel RdsMaint & Design Outstanding Shoulder Maintenance

  11. Gravel Rds Maint & Design Design Issue – Surface Gravel • The issue of good surface gravel (aggregate) cannot be emphasized enough!! • Good aggregate surfacing differs from base and other construction aggregates. • When it’s right, problems diminish!

  12. Gravel Rds Maint & Design Design Issue – Surface Gravel (con’t) • Material Specifications Discussion: • Many state DOTs do not have a surface aggregate spec. • Many specifications that do exist are quite loose and do not allow close enough control of gradation.

  13. Gravel Rds Maint & Design Design Issue – Surface Gravel (con’t) • Surface aggregate differs from base aggregate in two fundamental ways: • The need for more plastic fines to serve as binder. • Smaller top-sized stone that will remain embedded in the surface.

  14. Gravel Rds Maint & Design Design Issue – Surface Gravel (con’t) Corrugation or “washboarding” which is surface distress that is directly related to surface aggregate specification.

  15. Gravel Rds Maint & Design Design Issue – Surface Gravel (con’t) Similar ADT, Similar geometrics, but different surface materials!

  16. Gravel Rds Maint & Design Design Issue – Surface Gravel (con’t) Sample specifications comparison: Better when modified to 8 - 15

  17. Gravel Rds Maint & Design Value of Quality Surface Gravel Less corrugation (washboard) Less loose aggregate accumulating between wheel paths and on shoulder Less blade maintenance needed to keep road in good condition Less dust Less public complaint

  18. Gravel Rds Maint & Design A Current SDDOT Research Project Comparing Surface Gravel Quality • Three test sections have been constructed. • Each test section has three surface materials • Substandard, but commonly used • Meets SD Standard Specification for Gravel Surfacing – low percentage passing #200 (75 µm) sieve and low plasticity • Modified Specification having minimum 10% passing the #200 (75 µm) sieve and minimum plasticity index of 7

  19. Gravel Rds Maint & Design Construction done in Oct, 2011 Observations as of last week 7-27-2012

  20. Gravel Rds Maint & Design Performing loose aggregate or “float” test

  21. Gravel Rds Maint & Design 72 lbs (32.7 kg) removed from ten inch (250mm) cross section on surface

  22. Gravel Rds Maint & Design Only 12 lbs (5.4 kg) removed from same cross section on modified section!

  23. Gravel RdsMaint & Design -No Corrugation on modified section since construction-Blade maintenance has been averaging 4:1 on substandard vs modified sections

  24. Gravel Rds Maint & Design A gravel road stabilized with liquid MgCl2 in Meade County, SD. No blade maintenance was been done between construction in summer of 2011 and retreatment in July 2012! When gravel road geometry and material quality are understood and well managed, stabilization may be the next step when paving is not feasible.

  25. Gravel RdsMaint & Design From SDDOT Rural Road Design, Maint, & Rehab Guide Some Basics on Thickness Design 14.5 inches (370 Millimeters) of gravel needed to carry 25 to 50 trucks per day over weak subgrade!

  26. Gravel RdsMaint & Design What if you can’t build it?

  27. Gravel RdsMaint & Design Wind power generation tower construction

  28. Gravel RdsMaint & Design Medium sized crane used in tower const. How do you move it legally on a state or federal hwy?

  29. Gravel Rds Maint & Design General principles for managing gravel roads can be found in the FHWA Gravel Roads Manual. It can be found online by searching for “Gravel Roads Manual”

  30. Gravel Rds Maint & Design You may contact me at: Ken Skorseth SDSU/SDLTAP Box 2220-Harding Hall Brookings, SD 57007-0199 phone 800-422-0129 fax    605-688-5880 email: ken.skorseth@sdstate.edu

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