College of Engineering and Mines: CEM...

ALASKA GRAVEL

ROAD PROBLEMSIDENTIFY A PROBLEM

UNDERSTAND THE CAUSE(S)

MAKE EFFECTIVE REPAIRS

A Common Sense View Of

How Gravel Roads Work

Opening Comments• Cellphones

• Break At 1 Hour

• Questions During Presentation (why not?)

• Handout: Low-Volume Gravel Roads in Alaska – A Practical Guide for Owners & Others (version of April 2015)

• What If I Don’t Finish These Slides?

Objectives• Learn the form and function of a gravel road

• Learn the important requirements of a GOODgravel road — Gravel Road Rules-of-Thumb

• Learn how to recognize & fix gravel road problems

• Develop something of an engineer’s point of view—become “dangerous”

Advantages of a Gravel RoadGood reasons for gravel roads versus paved

ones.

1. Retain rural-ness (Dawson example)

2. Safety? (gravel road makes a poor drag strip)

3. Need for maintenance may not be as time-critical as for paved road.

4. Less easily damaged

5. Draw less traffic and fewer home buyer's interest. "Build it and they will come.

6. "Greener technology“

7. More easily repaired with lower- tech. equipment

8. No or little $

9. Permafrost

10. Materials for other surface type not available

11. Good source of slingshot ammo

Some Gravel Road Problems

Drainage Problems

Ruts & Potholes

Frost Boils

Potholes

Corrugations

Raveling / Segregation

Letter to the Editor, Fairbanks News-Miner, May 2016:

Mr. Weaver reports that some low-life so-and-so showed up at his home and stole thousands of dollars worth of gravel that he had used to surface his driveway.

What Is A Gravel Road

&

How Does It Work?

Gravel Road Material StrengthLimit Stresses at Various Depths to

What the Soil Can Withstand

We Can Do This By:Adjusting the Load orAdjusting the Soil

Just Common Sense ButA Very Important Concept!

Mountain Bike

Foot TrafficSmall Foreign Import

Dirt Bike

We’re talking about a gravel road built to handle a steady diet of this kind of traffic + occasional bigger stuff.

Expect 15 – 20 years good service with routine efforts at preservation.

Gravel Road Nomenclature & Function

• Describe the Gravel Road as aPavement Structure

• Describe How That Structure Works

Gravel RoadPavement Structure≈ 36 inches ±Subbase Material

SubgradeMaterial

Foundation

Gravel Surfacing Material ≈ 4 to 6 inches usually

In GeneralMaterial layers higher in a road must

be of better quality than the materials used lower in the road

Stress (σ) placed at the road surface

Causes

Strain (ε) “squish” in the gravel road

Stress (σ) placed at the road surface

Car tire: 1,000 lb @ 35psi -> 29 in2 of area6 inch diameter contact “circle”

Big truck tire: 5,000 lb @ 90 psi -> 56 in2 of area8.5 inch diameter contact “circle”

Causes

Strain (ε) in the gravel road that decreases with depth

Upper 20 Inches is Critical

Strain Decrease Through Pavement Structure’s Layers

Stress Decreases with Depth

Superposition Influence

Vehicle Affects On Road Life(some perspective)

Damage caused by 1 large truck ≈ 9,600 cars (on a paved road)

How is this Possible?

Trucks Heavy load/tire

Trucks High tire pressure

𝑅𝑒𝑙𝑎𝑡𝑖𝑣𝑒 𝐷𝑎𝑚𝑎𝑔𝑒 𝐸𝑓𝑓𝑒𝑐𝑡 =

𝑇𝑟𝑢𝑐𝑘 𝑇𝑖𝑟𝑒 𝑊𝑒𝑖𝑔ℎ𝑡𝐶𝑎𝑟 𝑇𝑖𝑟𝑒 𝑊𝑒𝑖𝑔ℎ𝑡

4.2

𝑇𝑟𝑢𝑐𝑘 𝑉𝑠 𝐶𝑎𝑟 𝐷𝑎𝑚𝑎𝑔𝑒 𝐸𝑓𝑓𝑒𝑐𝑡 = 5,000 𝑙𝑏𝑠∗

1,000 𝑙𝑏𝑠∗∗

4.2=862 !!

Trucks Many Tires

* 1 tire of a 20,000 pound dual axel @ 90psi** 1 tire of a 4,000 pound car @ 35psi

Soil Strength Can Vary Enormously With Season

Water (ice) Accumulation Due to Wintertime Freezing Process

Thaw-Weakening Due to Springtime Thawing Process

Wheel Load on Thaw-Weakened Pavement

IT’SSHOWTIME

U.S. Army Cold Regions Research & Engineering Laboratory (CRREL)

8 ½ minutes of movie aboutFrost Action in Soils

Show updated frost action video instead of following older video

No worry,because a gravel road is not made from silt.It’s made of gravel--

Right?

Not so fast

A gravel road is made of…

Aggregate Sizes• Boulder > 12”

• Cobble 3” – 12”

• Gravel .2” – 3”

• Sand .003” – .2”

• Silt .00008” – .003”

• Clay .00004” – .00008”– Surface area of kaolinite clay ≈ 18 Yd2/gram!

• Colloid smaller than 0.00004”– Will stay in suspensionG

rave

l Ro

ad M

ater

ial

Now you know that gravel road material is not simply gravel

What it is is:An aggregate gradation mostlycomposed of gravel, sand, and silt

So, what’s a gradation?

Statewide Research and Technology Transfer

Aggregate Gradation is Usually Defined by Sieving


Calculating an Aggregate Gradation:The % Passing Concept

Sieve Size Amount of Material on

Sieve (100 lbs total)

Percent Passing

1” 0 pounds 100 %

3/4” 4 pounds 96 %

1/2” 8 pounds 88 %

3/8” 8 pounds 80 %

#4 18 pounds 62 %

#8 18 pounds 44 %

#16 16 pounds 28 %

#50 14 pounds 14 %

#100 6 pounds 8 %

#200 2 pounds 6 %

pan 6 pounds

The “0.45 Power” Plot

The “0.45 Power” Plot

Two things important here:1. General shape of gradation curve2. Percent passing #200 sieve

Ideally Graded for Best Compaction

In addition to gradation, what other aspects of the aggregate

material are important?• Hardness

• Shape

– Angularity

– Sphericity

Particle Shape

Ideal Shape:Tetrahedron/Cube

In addition to gradation, what other aspects of the aggregate

material are important?

• Cohesion (Glue)—if clay, not too much

• Chemistry/Mineralogy

• Resistance to freeze/thaw cycle disintegration

• Color

More About Cohesion ?

Types of Cohesion:

1. Apparent cohesion

2. Real (permanent) cohesion• Example material–Brown’s Hill

Allowable Fines Content at Any Depth within Pavement Structure

12 to 14 % -#200 is ideal

Surfacing

Subbase

Subgrade

Gra

vel

Frost Boil (Bias Drive)

Bias Drive is a Usually GoodGravel Road within a FairbanksBorough Service Area

General Springtime Softeningof a Gravel Road (Bias Drive)

Iniakuk Avenue—Near UAF

`

View

“Good Surface Gravel” Video (about 4 min.)

Now We Know a Little About How A Gravel Road Works – We Might Feel Like Dancing!

But

Wait,

There’s

More…

Some UsefulRules-of-Thumb


Rules-of-Thumbfor

An Ideal Gravel Pavement Structure

• 4 - 6 inches of gravel surfacing– see rule-of-thumb for ideal gravel surfacing

aggregate

• 30 - 36 inches Subbase– limit minus #200 according to critical fines plot if

possible, compacts fairly well (see slide # 17 above)

• These materials types should be well compacted when placed.

• Material deeper than bottom of pavement structure can be almost anything that is not muck, highly organic, non-compactable.

Rules-of-Thumbfor

Layer Specifications

• For Surfacing Material: See Appendix* for surfacing material specifications

• For Subbase Material: See Appendix* for non-frost-susceptible fill specifications

• For Subgrade Material: Use ADOT&PF specification 703-2.07, Selected Material Type A, B, or C (whatever’s cheapest)

* Handout: Low-Volume Gravel Roads in Alaska – A Practical Guide…


Rules-of-Thumbfor

Ideal Gravel Surfacing Material

• high quality aggregate• particles not flat or elongated• 100 % minus 1 inch• 10 to 14 % minus #200 size

• (maybe 12 to 14% is best)

• contains up to 3 % clay (minus 0.002 mm) size—or other form of cohesion (glue)

• well graded aggregate (plots as straight line on 0.45 power paper)


Rules-of-Thumbfor

Getting Water Off of the Road Surface

• Proper cross section for road surface– “A” crown with 4 % cross slope– what about superelevation?

• A good crown must always be maintained.

• Allow no berms to form along downhill edges of roadway.– summer—for rain– spring—for snow/ice melt


Gravel Road Crown Explained

No Berms Along Downhill Edges

4 % Slope

Good Cross Secton

The recommended gravel road crown is 4 percent.

Superelevation Explained 1 of 2

Superelevation Explained 2 of 2

View

“Correct Roadway Shape” Video (about 4 min.)


Rules-of-Thumbfor

Getting Water Away from the Road

• A good ditch is a road’s best friend• Design to insure freeboard.

– 2 feet ±• Select a good ditch shape and maintain it.

– flat or modified “V” bottom may be best• Culverts must be compatible with ditch design• Keep ditches clean• Be aware of environmental issues with ditch

runoff.– whatever the requirements today, they will be more

strict tomorrow!

(continued from last slide)

Ditches AreSO IMPORTANT,

Here’s A Little More Information About

Them


Common Ditch Shapes


Flat-Bottom Ditch


U-Shaped Ditch


V-Shaped Ditch


Modified V-Shaped Ditch

Continue Tomorrow

Problems

Descriptions & Causes

Sources of Gravel Road Problems1. Poorly Designed Road Alignment & Safety

Features

2. Drainage Deficiencies

3. Ice-Rich Road Foundation Conditions

4. Substandard and/or Degraded Road Construction Materials (soil materials)

5. Poor Construction Practices

6. Poor Preservation Practices

Best times to examine a gravel road

• During or immediately after heavy rain event (to evaluate drainage)

• During spring thaw (to evaluate drainage and thaw-related problems)

• After a prolonged dry period (to evaluate dust)

• Examination of the gravel road during all three conditions is necessary for a full evaluation of its condition prior to major preservation efforts.

Problems Due to Poorly Designed Road

Alignment & Safety Features

(geometrics, obstructions, signs, lights, etc.)

•Accidents

•Corrugations(corrugations associated with the combination of steep grade + curve + high vehicle speed)

Accidents

Designed Too Narrow?

Via Con Dios Signor(El Camino del Muerte, La Paz – Coroico, Bolivia)

If the road is bad enough you may need extra “insurance”


TypicalCorrugations


Typical Corrugation Morphology

At Least There Are No Lines to Worry About

Problems Due to Drainage Deficiencies

(road surface and roadside)

• Erosion

– Rills

– Gullies

– Piping

• Potholes

• Ruts

• Soft Areas

A Rainy Day in Fairbanks

And a good day to look at

drainage


Poor Roadside Drainage

Not Enough Culvert

Now, this is a gully !!

Piping

Larry Bennett, Loreto, Baja Mexico

FBKS Gravel Road During Heavy Rain Event

Soft Area:Poor Drainage

Soft Area:It Can Get Worse

(Russian Secondary Road)


Potholes

Problems Due to Ice-Rich Permafrost Soil

Foundation(most common foundation problem

around the Fairbanks, AK area)

• Bumps / Dips

• Cracks

• Slope Failures

• Ruts

Ice in Permafrost Material(Farmer’s Loop Road just east of UAF)

Differential Thaw Settlement(Permafrost Area)

Longitudinal Crack Caused

By Thaw Settlement

Under Sideslopes &

Shoulders (Permafrost)

Problems Due to Substandard and/or

Degraded Road Construction

Materials

• Airborne Dust Production (could be in a class by itself)

• Loose Surface Rock

• Loss of Surfacing Material (usually to shoulders or sideslopes)

• Contamination (contaminated with underlying material) *

• Breakdown of Surfacing Material (abrasion, crushing, dissolution/weathering)

• Soft Areas (often with frost boils and water seepage at the road surface) *

• Ruts *

• Corrugations

* Associated with Seasonal Freeze/Thaw

Related to Surfacing Material

Dust Cloud Versus Speed

Loose Surface Rock


Raveling (Loose Surface Rock) & Dust


Corrugations


Rutting

Ruts(better & worse)

Very Soft Area w/ Ruts

• Soft Areas *

• Ruts *

* Associated with Seasonal Freeze/Thaw

Related to Pavement Structure Materials Below Surfacing Material

Soft Area / Frost Boil

Problems Due to Poor Construction Practices

• Specification Violations and Sloppy Materials Handling Affects:

All Other Problem Areas

Problems Due to Poor Preservation Practices(maintenance & reconstruction work)

• Most Commonly Related to Poor Preservation Work:– Contamination• dust• ruts• soft areas• corrugations

– Loss of crown– Loss of superelevation– Loss of adequate road surface drainage– Insufficient late-winter snow removal

• Specification Violations and Sloppy Materials Handling During Preservation Work Affects:

All Other Problem Areas


What Can Happen to Gravel Road Crown

No Berms Along Downhill Edges

4 % Slope

StartCondition

EndCondition ?

Hard Pavement CrownGravel Road No Crown

Preservation Methods

How to Fix, Repair, i.e., “Preserve” the

Gravel Road

Preservation Methods By Problem Type

• Poor Design & Construction (problem prevention)• Corrugations• Erosion (rills, gullies, piping)• Soft Areas / Rutting – Springtime• Soft Areas / Rutting – Summertime

– Road surface dry– Road surface wet

• General Minor Rutting• Potholes• Embankment Slope Failures, Cracks, Bumps / Dips• Poor Maintenance

Preservation Methods By Problem Type

See Pages 7 – 9 of Handout Titled:Low-Volume Gravel Roads in Alaska –

A Practical Guide for Owners & Others

One Example of a Preservation Method:

Corrugations

Corrugation Repair Recommendations• Recommended for Temporary Repair: Grade below

bottom of corrugations, and re-compact. Deep corrugations may require addition of new surfacing material (see Appendix, surfacing material).

• Recommended for Permanent Repair: If existing materials are to be left in place, first grade to below bottom of existing corrugations, then add soil stabilization agent (see Appendix, soil stabilization) and re-compact. A better alternative is to first grade out the corrugations, and then add 4’ to 6” inches of crushed, well graded gravel containing a cohesive binder (see Appendix, surfacing material). In areas where corrugations consistently reappear, permanent repair may ultimately require upgrading the offending roadway segment to asphalt concrete pavement.

• See Handout Page 6

Road Corrugation (Washboarding) Formation Isn’t as Simple as Most

People Think

“Scaling and Dynamics of Washboard Road”Anne-Florence Bitbol1,2, Nicolas Taberlet1, Stephen W. Morris3, Jim N. McElwaine21 Université de Lyon, ´ Ecole Normale Supérieure de Lyon,Laboratoire de Physique, 46 allée d’Italie, 69007 Lyon, France2DAMTP, University of Cambridge, Wilberforce Rd., CB3 0WA Cambridge, U.K.3Department of Physics, University of Toronto, 60 St. George St., Toronto, Ontario, Canada, M5S 1A7(Dated: June 19, 2009)

Examples of Things That Washboard

• Gravel Roads

• Paved Roads

• Train Tracks

• Hard Drive Disks

• Snowpack

Wintertime Washboarding of Packed Snow in Bob’s Driveway

Are these commonfeatures related to

corrugationphenomena?

Ever notice these?

Combinations of Problems

• When you evaluate gravel road condition, you will usually find that more than one problem exists. Common sense rules in deciding what sort of repairs to do.

• There are no hard, fast rules in this process, except that you are always trying to return the road to an acceptable standard at the least cost.

View 3

“Using Grader” Videos (about 2 ½ min. each)

Considering Geosynthetics• Many kinds of geosynthetics that might be usefully applied

to construction and/or repairs of gravel roads.– geotextiles (cloth-like materials)– geogrids, geocomposites– geomembranes– geocells.

• Search Internet or textbooks on geosynthetics– Holtz, Christopher, and Berg, “Geosynthetic Engineering”, 1997

• Don’t use geosynthetics on your gravel road project without consulting an engineer knowledgeable and experienced in the use of those products.

Planning to Upgrade From Gravel to Paved Surface?

A Literature Reference:

McHattie R.L., Evaluating and Upgrading Gravel Roads for Paving, Matanuska-Susitna Borough Engineering Guide, 2010

The Engineering Guide is a relatively small “PDF” file (less than 1 Megabyte). It is available for download from the Alaska University Transportation Center’s Internet URL:

http://ine.uaf.edu/autc/files/2012/07/Evaluation-of-Gravel-Roads-Final.pdf

http://ine.uaf.edu/autc/files/2012/07/Evaluation-of-Gravel-Roads-Final.pdf

Evaluating and Upgrading Gravel Roads for Paving

(Matanuska-Susitna Engineering Guide)From Preface:Fact: Given sufficient preparation, nearly any gravel road can be paved with a minimal-thickness hot mix asphalt concrete pavement or even a low cost asphalt surface treatment (AST), and it can be relied on to survive low-volume traffic for a decade or two. What does “sufficient” mean in terms of design and materials? And, perhaps more importantly, how much is “sufficient” going to cost?

This engineering guide provides tools to aid evaluation, development and management of Matanuska-Susitna Borough’s gravel-to-pavement projects.

The guide serves an additional purpose. It documents the engineering bases for design features and specification requirements used in certain Matanuska-Susitna Borough construction contracts in case of legal disputes.

Local Technical Assistance Program

• Provides assistance to local governments

• Run by Alaska DOT&PF

• Contact : David Waldo ([email protected])

• Contact: Simon Howell

([email protected])

• Webpage : http://www.dot.state.ak.us/stwddes/research/index.shtml

mailto:[email protected]


http://www.dot.state.ak.us/stwddes/research/index.shtml

University of AlaskaINE / AUTC

• Billy Connor, Director of AUTC

– [email protected]

• Dr. Jenny Liu, Associate Professor, AUTC

– [email protected]



With Respect to Gravel

Road Technology:

Has Your Confidence

Level Increased?

(if time permits)

More Examples of Preservation

Methods:

See Pages 7 – 11 of Handout Titled:

Low-Volume Gravel Roads in Alaska – A Practical

Guide for Owners & Others

Erosion(rills, gullies , piping)

Comments: This includes damage to the road surface as well as the embankment sideslopes. Lack of effective drainage. This problem can be minimized by simply getting stormwater or water from snow melt off of the roadway surface as quickly as possible without concentrating the flow.

Recommended: Establish or re-establish 4% crown wherever the road is not in superelevation. Late-winter maintenance should blade snow and hard pack to the embankment’s sideslope area prior to Fairbanks’ spring “breakup.”

Very Soft Areas and Deep RuttingSpringtime only

Comments: Usually related to loss of pavement structure strength due to thaw weakening during the springtime breakup period. A less serious form (usually less serious) of springtime softening can be caused by poor drainage of snow melt from the roadway surface or ponding of thaw water adjacent to the roadway. Assume that thaw weakening is the culprit if surface drainage or ponding problem is not obvious. Vehicle action on very soft surfacing material will most likely destroy the design properties of that material and require replacement of surfacing material as part of the repair.

Recommended for Snow Melt or Ponding: Improve drainage of road surface by re-establishing crown. Make sure that late winter maintenance clears ice pack and snow from road surface to prevent damming of melt water.

Recommended for Thaw Weakening: Remove approximately 18” of existing material. Replace with new surface course material and the remainder of the 18” thickness with non-frost-susceptible fill material (see Appendix sections on non-frost-susceptible and surfacing material).

Summertime Very Soft Areas and Deep Rutting

(road surface usually damp or wet appearing)

Comments: Constant or repeatedly reoccurring damp or wet areas are usually drainage related.

Recommended: Evaluate drainage conditions. Re-establish a 4% crown if it has been lost. Check that existing drainage features are functioning properly in the vicinity of the problem area. Ditches may need cleaning or other repairs. Culverts may need repair or replacement. Ponding adjacent to the roadway should be drained if possible, or the road should be raised to provide a minimum 24” of freeboard between the nominal road and pond surfaces.

Summertime Very Soft Areas and Deep Rutting

(road surface usually dry appearing)

Comments: Usually related to surface course degradation. Often presents a combination of visually-obvious problems. The following are almost always most noticeable during dry periods:

airborne dustminor rutting of sandy or silty appearing surface materialloose surfacing materialloss of surfacing materialbreakdown of surfacing material (abrasion, crushing, dissolving)

Recommended: The surfacing material requires some form of cohesion (glue). The cohesive agent can act temporarily or permanently. Examples of cohesive agents include: water, calcium chloride, proprietary soil stabilization additives, and clays. Replace or augment existing surfacing material with better surfacing material. An alternative is to treat existing surfacing material with soil stabilization additives. See Appendix sections on surfacing material, dust palliatives, and soil stabilization.

General Minor Rutting

Comments: Normal occurrence for most gravel roads.

Recommended: Non-aggressive routine grading when rutting exceeds about ¾”

Potholes

Comments: Usually associated with poor drainage of roadway surface

Recommended: Surface regrading is required that must include re-establishment of 4% crown (and re-establishment of correct superelevation wherever necessary).

Embankment Slope Failures, Cracks, Bumps/Dips

Comments: Caused by thawing of ice-rich permafrost foundation soils and subsequent settlements. Settlements are often highly variable in depth and spacing, as is the ice content of most foundation soils before thawing.

Recommended: Replace fill materials in settlement areas with gravel fill materials. Fill within the non-frost –susceptible subbase and surfacing layers must be suitable for those purposes. See Appendix sections on non-frost-susceptible and surfacing materials.

Poor Design and Construction

Read Page 10 of Handout

Poor Preservation Practices

Read Pages 10 & 11 of Handout

Controlling Dust

Dust Control

Field Guide

For GravelDriving

Surfaces

Contents

1. Introduction for the Manager or Operator ........................................................... 3

1.1. Why is Dust Control Important? .......................................................................... 3

2. Condition of Roadway Prior to Dust Control Application ............................ 5

2.1. Good Surfacing Material........................................................................................... 6

Use of the Existing Surfacing Material ..................................................................... 8

2.2. Good Cross Section ...................................................................................................... 8

2.3. Good Roadside Drainage ....................................................................................... 10

3. Determining Dust Control Benefits ......................................................................... 12

Advantage of Short Term Over Long Term Evaluation of Dust Control ...................................................................................................................................................... 12

Some Long-Term Analysis May be Useful ............................................................ 13

Short Term Evaluation of Dust Control ................................................................. 13

3.1. Quantified Measurement of Dust ...................................................................... 14

Estimating Dust Concentration Using a Visual Method ............................... 14

Estimating Dust Concentration Using a Machine ............................................ 17

EPA Dust Measuring Methods Beyond Casual Monitoring......................... 19

3.2. Determining the Initial Viability of a Dust Control Candidate ......... 20

3.3. Time-Value-of-Money (Life Cycle Cost) Analysis ..................................... 21

4. Dust Control Methods & Selection ........................................................................... 24

4.1. Managing Vehicle Speed ........................................................................................ 24

4.2. Introducing Types of Dust Control Palliatives .......................................... 25

4.3. Selecting a Dust Control Palliative ................................................................... 31

4.4. Alaska Experience with Dust Palliatives ...................................................... 33

Alaska Experience with CaCl2 ..................................................................................... 34

Dust control information is provided in the appendix of the class handout

booklet:

Low-Volume Gravel Roads in Alaska – A Practical Guide for Owners and

Others(Version of April 2015)

End of the Class—Almost

There’s Just A Little More

Questions:

• What’s the most important design & maintenance consideration for your gravel road?

• Why do higher gravel road layers have to be of better quality than lower layers?

• Why discourage a lot of heavy truck traffic on your gravel road?

• What does cohesion do for your surface material?

That’s all folks

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