SPWA Fall Rural Roads Workshop Gravel Roads Material Analysis, - - PowerPoint PPT Presentation

Manoj Jogi Saskatchewan Ministry of Highways & Infrastructure Saskatoon October 19, 2017

SPWA Fall Rural Roads Workshop

Gravel Roads Material Analysis, Surfacing and Maintenance

Basic Objectives of a Road

• 1. Support traffic loads
• 2. Protect roadbed from water infiltration
• 3. Minimize loss of surface material
• 4. Provide reasonable surface texture
• 5. Provide resistance to weathering

Typical gravel road section

Credit: FHWA

Crown

½ inch per foot or 4% crown recommended AASHTO recommends ½-1 inch foot crown

• 1. Drainage from the

road surface

• 2. Allow water to

leave the road as a shallow, non erosive sheet

Credit: Penn State University Center for Dirt and Gravel Roads Studies

Crown

Credit: Penn State University Center for Dirt and Gravel Roads Studies

Maintaining Crown

Credit: Penn State University Center for Dirt and Gravel Roads Studies

Sections without crown

Credit: FHWA

Parabolic crown

Credit: FHWA

• Less crown in the middle
• No room for drainage

Parabolic crown

Credit: FHWA

• Blade wear at center
• Modify usage to reduce

wear

Placement for Surface Aggregates

• Address all surface drainage issues before

placement

• Road instability issues must be addressed

before placement

• Flat ‘A’ crown profile, shape the subgrade

Credit: Penn State University Center for Dirt and Gravel Roads Studies

Crown gauge

Credit: FHWA Credit: Skorseth, 2015

Good vs Poor Construction

Credit: Maine

• Dept. of

environmental Protection

1 2 3

Aggregates / Soil Testing

• 1. Sieve Analysis Test
• Categorize coarse-grained soils in terms
• f particle size distribution.
• 2. Atterberg Limit Test
• Categorize fine-grained soils in terms of

the material’s consistency (plasticity index).

• 3. Percent fracture
• To determine percent fracture faces in

coarse portion of the material Organic soils are generally not tested unless they pose a risk to the failure on a project.

Sieve Analysis Test

Credit: Klimochko

Sieve Analysis Test

Procedure for describing a coarse-grained soil in terms of particle size (gradation).

Percent Passing 100% 92% 70% 40% 40% 52% 55% 8% 26% 48% 4% 12% 25% 1% 7% 7% 97% 82% 60% 0% Agg “A” Agg “B” Agg “C” Agg”D”

Importance of Sieve Analysis

Sieve analysis test results on a coarse- grained soil indicates the following:

• How clean or dirty the aggregate is.
• How well the aggregate can compact
• How will be the aggregate matrix in place
• How suitable the aggregate is.
• Confirm if aggregate is in ‘spec’?

Atterberg Limit Test

Atterberg Limit Test

Used for identifying soil’s water content causing the material to pass from one condition state to another.

• From liquid to plastic = Liquid Limit (wL)
• From plastic to plastic solid = Plastic Limit (wP)

Plastic Index (PI) = Liquid Limit (wL) – Plastic Limit (wP)

Atterberg Limit Test Apparatus

Liquid Limit Test Apparatus

Liquid Limit = soil moisture at which the bottom of the groove in soil sample closes approx. 12 mm after 25 rotations of crank.

Plastic Limit Test Apparatus

Plastic Limit = soil moisture at which the threads of soil sample start to break up when 3 mm in diameter.

In field roll the soil with water to thickness of a matchstick tip till it starts crumbling

Importance of Plastic Limit Value

• Plastic Limit (wP) value identifies the
• approx. optimum water content of a soil at

which it should be compacted.

• Soil goes into a plastic state – deforms

without rebound

Importance of Plasticity Index Value

• Plasticity Index (PI) value indicates the

relative compressibility of a soil.

• The higher a number, the more

compressible the soil.

• How well the soil can pack depends upon

plasticity index

• Good indication of binding characteristics

Determining Optimum Moisture

2160 2170 2180 2190 2200 2210 2220 2230 2240 2250 2260 5 6 7 8 9 Dry Density - kg/m3 Percent Moisture

Optimum Moisture = 6.7 % Proctor Dry Density = 2234 kg/m3

6.7%

Standard Proctor Test

2 1 3 4

Klimochko, 2008

Compaction vs. Optimum Moisture

• Wet of optimum moisture - dried to
• ptimum by blading or disking before

compacting.

• Dry of optimum moisture - it should be

sprayed with water to get the soil to

• ptimum before compacting.

Optimum Moisture vs. Soil Type

Optimum moisture contents for various soil types are as follows:

• Granular Base Course:  6 %
• Sandy Glacial Till:  13%
• Silty Glacial Till:  15 %
• Clayey Glacial Till:  17%
• Highly Plastic Clay:  30 %

3 Low Plastic Clay

Soil Compaction

• Proper compaction equipment is essential.
• Uniform water application is essential.
• Work zones should be kept short (≈ 500 m)

to help ensure uniform moisture application during compaction.

• If sections are too long, compacting soil at
• ptimum moisture content becomes more

difficult to achieve.

Soil Compaction

• Use sufficient amount of water.
• Use sufficient number of passes.
• Use proper equipment. Self propelled
• Pneumatic or steel wheel
• No steel rollers on steep grade

Soil Compaction

• Check densities (Quality Control)
• Check with Probe

Gradation Types

• Open graded – has only a

small percentage of aggregate particles in the small particle size range. This results in more air voids.

• Gap-graded - contains coarse

and fine-graded soil particles but no intermediate sizes.

• Well/Dense graded – has a

uniform distribution of all particles sizes.

Gradation

Open graded Gap graded Dense graded

Surface gravel

Stone + Sand + Fines (dust)

Good gradation is a good blend of stones, sand and fines.

Properties for surface gravel

• Very important property
• Crushing is needed for

this

• Better embedment than

rounded aggregates

• Resistance to movement

under traffic better than rounded aggregates Fracture Percent

Surface gravel

• Ideally some amount of

crushed stones (fractured faces)

• More gravel than sand

(excess sand = no stability)

• Blending different sizes

allows the pieces to lock together to form a strong tight surface Good gravel road can not be made with bad gravel

Credit: USDA Forest Service No fines Excess fines Right amount of fines

MHI Traffic Gravel Specifications

Sieve Designation Percent by Weight Passing Canadian Metric Sieve Series Type 101 102 103 104 105 106 108 109 75.0mm 100 50.0mm 55-85 100 40.0mm 63-92 31.5mm 100 100 22.4mm 63-92 63-92 100 100 100 18.0mm 63-92 63-92 63-92 100 5.0mm 0-40 0-40 0-40 40-70 0-40 0-60 40-70 45-80 2.0mm 0-25 0-25 0-25 20-45 0-25 0-45 20-45 25-60 400µm 0-20 0-20 0-30 Fractured Face % 50.0 Minimum

MHI Base Course Specifications

3505 - Jan 1996 Base Course Type Sieve Designation 31 33 35 Percent Passing (by weight) 50 mm 31.5 mm 100 25 mm 22.4 mm 18 mm 75-90 100 100 16 mm 12.5 mm 65-83 75-100 81-100 9 mm 5 mm 40-69 50-75 50-85 2 mm 26-47 32-52 32-65 900 µm 17-32 20-35 20-43 400 µm 12-22 15-25 15-30 160 µm 7-14 8-15 8-18 71 µm 6-11 6-11 7-12 Plastic Index 0-7 0-6 0-5 Fracture, Min (50/75 Blow) % Min 50 Lightweight pieces % Max 5

Properties for surface gravel

Sieve Designation C D E 75.0mm 100 100 100 50.0mm 100 100 100 25.0mm 100 100 100 9.5mm 50-85 60-100

• 4.75mm

35-65 50-85 55-100 2.0mm 25-50 40-70 40-100 400µm 15-30 25-45 20-50 75µm 5-15 5-20 6-20

AASHTO

• Minimum 8%

passing 71µm sieve and

• PI 4 – 9
• Maximum liquid

limit 35

Soil aggregate surface course

Recycled asphalt (RAP)

• Can be used but few issues
• In hot weather it behaves

as a weak pavement

• Hard to maintain and can

develop potholes

• Good idea to blend 50/50

with virgin gravel

• Good binding and

workability with 50/50 blend

Credit: Granite Construction Company

Properties for surface gravel

• Top size 1 – 1.5 inch
• Typical Ministry gravel is 22.5 mm (7/8

inch) top size

• Desirable 8 to 15 % passing 71µm sieve

(dust) – some amount of clay for binding

• Plasticity, PI 4 - 9 range
• Good abrasion resistance
• Wet conditions -- Less PI and fines
• Dry conditions -- Can have PI and fines on

higher side of the range

Surface Gravel

• Can be placed at in an 8” depth and compacted

to 6”,

• or in a 6” depth and compacted to 4½”
• Higher top size (Coarse)for wet area
• Lower top size (Finer) for dry area
• Pneumatic rollers, Wobbly or 10 tonne steel

roller can be used.

• Pneumatic / rubber rollers work on most gravel

surfaces and they do not crush the rock.

Aggregate Sampling

Make sure the sample obtained is:

• Representative (quartering)
• Not segregated by sampling
• Properly identified (label)

Poor sampling makes

test results misleading and worthless.

Credit: Skorseth, 2015

Jar Test

• Surface aggregate 8 – 15% fines (dust)
• Base aggregate (0 - 7% fines)
• More stones than sand desirable

Gradation for surface gravel

Poor surface aggregate

Credit: FHWA

Gradation for surface gravel

• Good blend for surface gravel

Coarse material Fine material

Credit: Klimochko, 2008

Gradation for surface gravel

• Mixing clay with aggregates

Credit: Klimochko, 2008 Credit: Skorseth, 2015

Gradation for surface gravel

• Gradation

makes a difference

Credit: FHWA

Poor gradation Good gradation

Culverts

• Culverts are critical for

natural flow of water

• Plugged or collapsed

culverts can cause serious damage

• Installation at correct

location and elevation- survey

• Reasonable

maintenance and cleaning for proper functioning

Install culverts as close as possible to the natural stream bed

Culverts

Install culverts at natural stream grade X X

Do not change stream bottom elevation Credit: USDA Forest Service

Culverts

Install culverts at natural stream grade

Right

Do not change stream bottom elevation Credit: USDA Forest Service

Culverts

• Culverts are critical for natural flow of water

Credit: USDA Forest Service

Culverts

Riprap

Riprap at inlet Riprap at outlet

Credit: USDA Forest Service

Culverts

Piping due to poor installation or lack of riprap

Credit: USDA Forest Service

Dust Control

• All gravel roads will give a certain amount of

dust under traffic

• Volume of dust depends upon

– Type of gravel – Volume and type of traffic – Precipitation

• Limestone based gravel tend to dust more
• Glacial deposits with a portion of clay tend to

resist the dusting

Dust Reduction

• A good gradation is

important

• Good amount of fines

(8-15%)

• Right plasticity (4-9)
• Chloride dust treatment is

not effective with poor gradation Through gravel specifications

Credit: FHWA

Dust Reduction

Prevent loose fines generation

• Good crown
• Shoulder drainage
• Strategies for less maintenance
• Loosen surface aggregate to sufficient

depth during grading

• Always ensure optimum moisture during

maintenance operations

Wash boarding

Wash boarding

• Poor quality gravel – low fracture percent,

low fines and plasticity

• Harsh breaking or acceleration
• Lack of moisture
• Motor grader too fast

Frost Heave

• Frost heave – upward movement of

subgrade due to expansion of accumulated moisture as it freezes

• Thaw weakening – weakening of subgrade

when moisture melts

Three conditions

• Frost susceptible soils - silt
• Water
• Temperature- freezing

Frost Heave

Water in void space freezes along plane of freezing Water in void space freezes along plane of freezing Water in void space freezes along plane of freezing

Credit: Washington DoT

Frost Heave Treatment

• Providing adequate drainage / Drainage

improvement

• Excavation of subgrade below frost depth
• Replacement of frost susceptible material
• Daylight
• Replace with 300 or more mm base course
• r pit run
• Geotextile filter cloth
• Insulation can also be provided

The use of granular, non-frost susceptible fill can also help to alleviate frost heave and subgrade softening problems

Frost Heave Treatment

Excavate Failure To Sideslope (Daylight) and Backfill with Granular Failure Note: Bottom of Excavation sloped down towards ditch. Daylight at Sideslope

Schematic showing typical deep patch used to repair small isolated areas experiencing various kinds of distress due wet base/subgrade.

Frost Heave Treatment / Deep Patch

References

• FHWA, Gravel Roads – Construction & Maintenance guide,

August 2015

• FHWA, Gravel Roads – Maintenance & Design Manual, SD-LTAP

November 2000

• Gravel Roads, Back to Basics. Montana State University, LTAP

2000

• Klimochko D, 2007 ATPC Presentation
• Gordon Keller & James Sherar Low Volume Roads Engineering,

USDA Forest Service/USAID

• Main Department of Environmental Protection, Gravel Road

Maintenance Manual, 2010

• Penn State University, Center for Dirt and Gravel Road Studies
• Skorseth K., 2015, SD-LTAP

. Managing Gravel Road Maintenance, 2015 NACE Conference, FL

• Joe Mahoney, 1985 Washington DoT

, Research Summary Report- Evaluation of Frost Related Effects on Pavements

Questions / Comments

Manoj.Jogi@gov.sk.ca 306-933-5227