sddot/sdltap gravel road experimental project
DESCRIPTION
SDDOT/SDLTAP Gravel Road Experimental Project. Ted Eggebraaten, SDLTAP Tech Assistance Provider Ken Skorseth, SDLTAP Program Manager . Reason for Project. More than 75% of local roads in SD are unpaved – managing them is a challenge! - PowerPoint PPT PresentationTRANSCRIPT
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SDDOT/SDLTAP Gravel Road Experimental Project
Ted Eggebraaten, SDLTAP Tech Assistance ProviderKen Skorseth, SDLTAP Program Manager
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Reason for Project• More than 75% of local roads in SD are
unpaved – managing them is a challenge!• Biggest complaints from public are: rough
condition (generally from corrugation or “washboard” in surface) and too much loose aggregate on the surface makes it hard to control a vehicle.
• How critical is gravel quality to this and how does it affect total cost of maintenance?
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• SDLTAP requested a research project on this matter to try to quantify effect of gravel quality on overall maintenance costs and road condition.
• SDDOT Research Review Board approved the project in 2009.
• SDLTAP was tasked with recruiting counties to build test sections and to advise.
• This presentation covers only SDLTAPs observation and documentation.
Project Background
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• Primary focus is on effect of gravel quality on life-cycle cost of gravel road maintenance
• Three types of gravel used in study:1. Substandard but commonly used – meets no
spec except top size control – one inch minus.
2. Barely meets SDDOT Gravel Surfacing Spec – percent passing #200 sieve is low and/or plasticity index (PI) at bottom of range at 4
3. Modified SDDOT Spec – higher minimums of 10% passing #200 sieve and PI at 7.
SDDOT Gravel Road Test Project
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SDDOT Gravel Road Test Project
• Three test sections were constructed in:– Hand County – northeast of Miller– Custer County – northwest of Custer– Brookings County – south of Volga
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Location of Sections:
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Substandard Gravel
SD Standard Specification
Modified Specification
Compacted and Uncompacted
Sections
Compacted and Uncompacted
Sections
Buffer Sections
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Each section was built with three to four inches of new gravel after existing surface was prepared and shaped. Compaction/non compaction comparison as well.
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One of the biggest challenges was finding gravel that meets the modified SDDOT Specification: “Shall have minimum plasticity index (PI) of seven”. (Even higher minimum was considered in project planning)
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One way to meet modified spec – blend different material from separate sources
This was done on one section in Brookings Co and one section in Custer Co
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More blending or “manufacturing” in the future?
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Processing material from a natural clay source
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Road mixing to get a high quality surface gravel
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Custer County Test Sections
Some sections showed contrast in performance quickly due to gravel quality
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Brookings County Test SectionsOnly one month after construction
Substandard Section
Modified Section
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Substandard gravel loosens in 31 days.Loose aggregate (or float) is 1 ¼ to 1 ½ inches between the wheel paths.
Modified material has only 1/4 to 3/8 inch of loose aggregate (float) between the wheel paths in the same 31 days.
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Current Status of Project• SDLTAP has accumulated photo documentation
on all sections over the past two years.
• Measurement and documentation has been done on these distress types in 2012:
1. Accumulation of loose aggregate (float)
2. Changes in top width from time of construction
3. Presence of corrugation (washboard) on surface
4. Change in roadway crown
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The float test
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Simply remove loose aggregate from a 10 inch cross section, weigh it and convert that to a one-mile section
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Change is top-width is measured on traveled way – grass line to grass line
XX ft.
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Corrugation (washboard): Hard to quantify in extent, fairly easy to measure severity
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Crown:measured with a laser level
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Summary of Loose Aggregate
• Brookings Section – measured 10-10-12:– Substandard Compacted: 383 tons per
mile
– Substandard Uncompacted: 405 tons per mile
– Standard Spec Uncompacted: 211 tons per mile
– Standard Spec Compacted: 203 tons per mile
– Modified Spec Compacted: 71 tons pre mile
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Brookings Section – Loose Aggregate
Substandard Compacted Uncompated
Standard SpecUncompated Compacted
Modified Spec
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• Hand Co Section – measured 9-11-12– Substandard Compacted: 430 tons per mile
– Substandard Uncompacted: 402 tons per mile
– Standard Compacted: 266 tons per mile
– Standared Uncompacted: 287 tons per mile
– **Modified Spec Compacted: 277 tons per mile
** Testing showed gradation and plasticity varied little from Standard
Summary of Loose Aggregate (Con’t)
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Hand Section – Loose Aggregate
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Summary of Loose Aggregate (Con’t)
• Custer Co Section – measured 10-16-12– Substandard Compacted: 134 tons per mile– Substandard Uncompacted: 134 tons per mile– Modified Compacted: 92 tons per mile
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Custer Section – Loose Aggregate
Substandard Compacted Uncompated
Modified Spec
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Change in Roadway Width
• Brookings Section:– Width ranges from 21 ft, 6 inches on the modified
section to 24 ft, 7 inches on the substandard section
• Hand Section:– Width ranges from 24 ft, 6 inches on the modified
spec section to 26 ft, 10 inches on the substandard section.
• Custer Section: No measurement due to uneven cross section
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Corrugation (Washboard)
• No corrugation observed on any sections meeting at least minimum standard specification.
• However, Brookings substandard section had corrugation on 100% of center wheel path at last observation.
• Custer substandard did not have corrugation.
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Concluding Points• Meeting basic SDDOT standard surface gravel
specification reduces loose aggregate by 1/3 to 1/2.
• Widest differential was in Brookings County near end of corn harvest with 405 tons of loose aggregate on substandard section to only 71 tons on modified section.
• Most interesting fact thus far: Brookings has done blade maintenance up to four times on substandard section to only once on modified!
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THANK YOU!
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Rainfall Data
• Data from July 1 to Oct 1, 2012– Brookings Section: 4.17 inches– Hand Co Section: 3.07 inches– Custer Co Section: 2.57 inches