Gravel Road Design & Maintenance. Minneapolis, MN

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1 Gravel Road Design & Maintenance 2011 NACE Conference Minneapolis, MN by Ken Skorseth SDLTAP Program Manager

2 Critical Issues Roadway Shape Drainage Surface Gravel Selection Preservation

3 Design Issue Basic Geometrics: Be familiar with the AASHTO publication: Geometric Design of Very Low-Volume Local Roads (ADT < 400) Commonly called the Little Green Book.

4 Gravel Rds Maint & Design Green Book and Little Green Book

5 Gravel Rds Maint & Design Nearly 80% of the roads in the US have traffic volumes of 400 vehicles per day or less.!! (quote from Little Green Book) It becomes very difficult to construct and maintain these very low-volume roads to a high geometric standard.

6 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) Design speed (km/h) Major access Minor access Recreational & scenic Industrial/ commercial access Resource recovery Agricultural Access Note: Total roadway width includes the width of both traveled way and shoulders.

7 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.

8 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.

9 Design Issue Crown: (con t) There are conflicting views on crown: 1/3 to 1/2 in. per ft. recommended by NACE manual Blading Aggregate Surfaces 1986 edition. 2 to 6% for low-type pavements recommended by AASHTO Green Book pg edition.

10 Design Issue Crown: (con t) 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%.

11 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 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 Design Issue Surface Gravel (con t) Too often, surface aggregate is perceived as not important, hence quality suffers. In study completed in Canada in 2003 samples were taken from several aggregate supplier s stockpiles being marketed as surface aggregate--- (con t next slide)

14 Design Issue Surface Gravel (con t) Only 14% of the samples met the companies own specifications when tested by independent labs! Quality control was almost nonexistent. Information from Material and Performance Specifications for Wearing Course Aggregates on Forest Roads by G. Legere & S. Mercier.

15 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.

16 Design Issue Surface Gravel (con t) Similar ADT, Similar geometrics, but different surface materials!

17 Design Issue Surface Gravel (con t) Corrugation or washboarding which is surface distress that is directly related to surface aggregate specification.

18 Premium Gravel!

19 Design Issue Surface Gravel (con t) Sample specifications comparison:

20 Design Issue Surface Gravel (con t) Another sample spec: WisDOT CRUSHED AGGREGATE SHOULDER COURSE Gradation No. 3 SIEVE SIZE CRUSHED GRAVEL CRUSHED STONE 1 inch /4 inch /8 inch No No No No

21 Design Issue Stage Construction In my experience, if a road/street is to be maintained three years or more as an unpaved road, use material and crown specification for gravel roads. If less than three years, use base aggregate and crown specification for pavement. (It will be hard to maintain in the interim).

22 Design Issue Stage Construction (con t) Little Crown and poor surface aggregate, but road is to paved in three years.

23 Design Issue Perfect Gravel Road Coarse aggregate base, few fines, 6-12 inches thick Surface layer with ¾ inch topsize stone and good percentage of plastic fines minimum 3 inches thick Prepared subgrade Not the real, but the ideal!

24 Gravel Roads Managing Maintenance There are two primary issues: Managing frequency of blade maintenance. Keeping control of shape on traveled way and shoulder.

25 Crown One of the biggest challenges in gravel road maintenance.

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27 Some roads have too little crown, some have too much.

28 Imagine a cattle trailer on this road.

29 The road has 13 inches of crown on a 20 top

30 Two Track Road

31 Crown Gauge is Helpful

32 Electronic Slope Reading

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36 Manageable Road Width

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38 Crown should be near ½ inch per ft (or 4%) Example: 24 ft roadway should have approx. 6 inches of crown.

39 The Next Challenge High Shoulders!

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41 Outstanding example!

42 Shouldering Operations

43 Dramatic Contrast Similar ADT, Similar roadway shape, but different surface materials!

44 Option: Geotextile Separation

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47 Six years of performance

48 A Remarkable Contrast! A Chloride Stabilized Road Since 1994!

49 Without Adequate Funds for Base Improvement and Paving Stabilized Gravel is an Alternative.

50 Maitland Rd Lawrence Co, SD

51 Heavy Residential Traffic & Continued Development

52 A Model of Successful Gravel Stabilization for 23 Years

53 One Section of Maitland Rd With Asphalt Surface

54 Get ready to face the challenges of maintaining gravel roads in the future! Thanks!