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Peer Editing - Milesbd (Gravel Road)

EDITING NOTES - by Madelaine Dobson

1. I have proofread the draft updates and provided grammar & spelling suggestions - in italics below (copy-pasted from Miles' sandbox 02-APR-2019)
2. This draft looks very good. I like the technical focus which provides more foundational support to the existing content.
3. Is there any way to tie in commentary on sustainability or innovation? I liked the innovative models you presented in your poster/seminar presentation. It would be complementary to bring some of the environmental perspective in as well as the technical information.
4. Was there any thought given to updating the rest of the page? There are some grammatical errors etc. For now I just focused on your new content (not proofing existing content).
5. The overall page is a bit long with that massive table. Is there any other way to present that data?

{ From Gravel Roads for sandbox Editing---START}:

• • Note to reviewers for HENV680 - My changes appear in bold below - bolding is removed during the publishing phase to current article.

Construction

Compared to sealed roads, which require large machinery to work and pour concrete or to lay and smooth a bitumen-based surface, gravel roads are easy and cheap to build. However, compared to dirt roads, all-weather gravel highways are quite expensive to build, as they require front loaders, dump trucks, graders, and roadrollers to provide a base course of compacted earth or other material, sometimes macadamised, covered with one or more different layers of gravel. Graders are also used to produce a more extreme camber compared to a paved road to aid drainage, as well as to construct drainage ditches and embankments in low-lying areas. Cellular confinement systems can be used to prevent the washboarding effect.

Construction of a gravel road begins with the base or subgrade layer. The expected road traffic volume and the average daily truck passage must be considered during the design process as they will influence the thickness and composition of this layer. Geotextile fabric may be laid to improve the stability of the subgrade layer. When geotextile fabric is used, a gravel layer with a minimum thickness of 6" (15 cm) is suggested to ensure the fabric remains unexposed. Road construction guidelines suggest that the crown in the road surface begins at the center point in the road, and does not exceed a 4% gradation from the center to the edge of the roadway.

The surface layer is constructed atop the subgrade layer. The amount of precipitation is taken into consideration for the selection of gravel size distribution. The surface layer will follow the crown established by the subgrade layer. Scarification of the subgrade layer prior to application of the surface gravel layer can be performed to increase the mixing and adherence between layers. Construction of the road surface is done gradually through multiple applications of layers of gravel, with compaction prior to the addition of the following layer. During reparation of a damaged road, ensuring that any washboarding, rutting, potholes, and erosion is adequately removed will minimize future need for reparation. Windrowing can be performed along the edges of roads in dry climates to allow easy access to gravel material for small repairs.

Materials

The gravel used consists of varying amount of crushed stone, sand, and fines. Fines are silt or clay particles smaller than .075 millimetres (0.0030 in), which can act as a binder. Crushed stone is used because gravel with fractured faces will stay in place better than rounded river pebbles. A good gravel for a gravel road will have a higher percentage of fines than gravel used as a subbase for a paved road. This often causes problems if a gravel road is paved without adding sand and gravel sized stone to dilute the percentage of fines.

A gravel road is quite different from a 'gravel drive', popular as private driveways in the United Kingdom. This uses clean gravel consisting of uniform, rounded stones and small pebbles.

Laterite and murram roads

In Africa and parts of Asia and South America, laterite soils are used to build dirt roads. However laterite, called murram in East Africa, varies considerably in the proportion of stones (which are usually very small) to earth and sand. It ranges from a hard gravel to a softer earth embedded with small stones. Not all laterite and murram roads are therefore strictly gravel roads. Laterite and murram which contains a significant proportion of clay becomes very slippery when wet, and in the rainy season, it may be difficult even for four-wheel drive vehicles to avoid slipping off very cambered roads into the drainage ditches at the side of the road. As it dries out, such laterite can become very hard, like sun-dried bricks.

Maintenance

Gravel roads require much more frequent maintenance than paved roads, especially after wet periods and when accommodating increased traffic. Wheel motion shoves material to the outside (as well as in-between travelled lanes), leading to rutting, reduced water-runoff, and eventual road destruction if unchecked. As long as the process is interrupted early enough, simple re-grading is sufficient, with material being pushed back into shape.

Segments of gravel roads on grades also rut easily as a result of flowing water. When grading or building the road, waterbars are used to direct water off the road. As an alternative method, humps can be formed in the gravel along the road to impede water flow, thereby reducing rutting.

Another problem with gravel roads is washboarding — the formation of corrugations across the surface at right angles to the direction of travel. Narrow-spaced washboarding can develop on gravel roads, leading to inconsistent moisture levels in the gravel, poor quality gravel, and vehicular stress to the road. Another way washboarding can occur is during the construction or maintenance phase, when gradation is done at high speeds causing the blade to bounce off the surface, creating a pattern of widely-spaced corrugations. They can become severe enough to cause vibration in vehicles so that bolts loosen or cracks form in components. Grading removes the corrugations, and reconstruction with careful choice of good quality gravel can help prevent them reforming. Additionally, installing a cellular confinement system will prevent the washboard-like corrugations from occurring.

Gravel roads are often found in cold climates because they are less vulnerable to freeze / thaw damage than asphalt roads. The inferior surface of gravel is not an issue if the road is covered by snow and ice for extended periods.

//add section:

Dust Control

Dust control is routine practice on gravel roads in order to reduce the need for frequent maintenance, mitigate health concerns, and prevent roadside plants from damage. Some common dust-suppression techniques are the application of a chloride solution (Calcium Chloride, Magnesium Chloride, Sodium Chloride), the application of a resin compound, or the incorporation of natural clay into the gravel mixture during the construction phase.

Calcium Chloride as a Dust Suppressant

Calcium Chloride provides dust suppression through it's hygroscopic properties, allowing moisture to be drawn in and retained by the compound. Calcium Chloride can be applied in either dry (pellet or flake) or wet (dissolved pre-prepared solution) form. Machinery such as a grader is used to "blade" the road's surface (pass frequently to mix and distribute the gravel). Then what happens? How is this relevant to the overall process?

Dry application of this type of dust suppressant is begun by first preparing the road surface through grader passes, moving the top 5-8 cm of gravel creating windrows on the edges of the road. Calcium Chloride is then applied to the road surface, and the road is then sprayed with water until the compound is dissolved. A grader "blades" the surface in numerous passes to ensure a uniform distribution of the compound. Compaction and the forming of the road surface is then performed to finalize the process.

Wet application begins by spraying the road surface with a Calcium Chloride solution. Mixing of the top 5-8 cm of gravel is done through numerous passes of a grader after the solution is applied. The road is then formed and compacted.

Length of Unpaved Roads by Country Country Length of unpaved roads (km)

{ From Gravel Roads for sandbox Editing---END:

Sources

Length of roads in Canada

Chapter 500 - roads in BC

CIA World Factbook

Chapter III gravel roads

References

Gravel Roads: Construction and Maintenance Guide. Washington: Department of Transportation (DOT), Federal Highway Administration (FHWA). 2015. ISBN 9780160929915.

BC supplement to TAC geometric design guide. – 2007 ed. British Columbia: British Columbia. Ministry of Transportation. 2007. ISBN 978-0-7726-5800-5.

Skorseth, Ken; Selim, Ali A. (November 2000), "Section III: Surface Gravel" (PDF), Gravel Roads: Maintenance and Design Manual (PDF), FHWA, Federal Highway Administration - South Dakota Local Transportation Assistance Program, pp. 39–49

Ken., Skorseth, (2005). Gravel roads : maintenance and design manual. South Dakota Local Transportation Assistance Program (Box 2220, Harding Hall, Brookings, 57007-0199). ISBN 2005410659. OCLC 62208163.

Caouette, Leo. 2013. APPLICATION METHODS CALCIUM CHLORIDE AS A DUST SUPPRESSANT. Nunavut: Nunavut Municipal Training Organization. https://www.nmto.ca/sites/default/files/application_of_calcium_chloride.pdf.

Statistic Canada. (2009). Envirostats. Ottawa. Retrieved from https://www150.statcan.gc.ca/n1/pub/16-002-x/16-002-x2009001-eng.pdf

BC Ministry of Transportation. (2007). 500 - Low Volume Roads Chapter. In B.C. Supplement to TAC Geometric Design Guide for Canadian Roads (p. 500i–500.13). Victoria: BC Ministry of Transportation. Retrieved from https://www2.gov.bc.ca/assets/gov/driving-and-transportation/transportation-infrastructure/engineering-standards-and-guidelines/highway-design-and-survey/tac/tools/low_volume_roads-interim_guidelines.pdf

Central Intelligence Agency. (2016). The World Factbook (2016th–2017th ed.). Washington: Central Intelligence Agency. Retrieved from https://www.cia.gov/library/publications/the-world-factbook/index.html

Skorseth,Ken Ali, A. S. (2000). Section III: Surface Gravel. In Gravel Roads: Maintenance and Design Manual (pp. 39–50). Washington: US Department of Transportation. Retrieved from https://www.epa.gov/sites/production/files/2015-10/documents/2003_07_24_nps_gravelroads_sec3_0.pdf