Soils 101: The Importance of Soil In Pavement Design and
Construction Part 1Soils 101: What to Know for a Successful Paving
Project
Presented By: National Ready Mixed Concrete Association
2
National Ready Mixed Concrete Association
• National Trade Association – Established in 1930 • HQ in
Alexandria, VA • 1,400+ Member Companies • NRMCA Represents ~75% of
North American Ready Mixed Production • Mission - Serve Industry
and Partners Through:
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• Structures and Sustainability: Build With Strength™
Initiative
Interested in becoming a member, visit:
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Your Instructors Today…
• Brian Killingsworth, P.E. – NRMCA Local Paving, Division Head –
28 Years in Practice – Pavement Design, Materials, Construction,
Forensics
• Luke McHugh, P.E. – NRMCA Local Paving, Northeast Region – 33
Years in Practice – Civil Design – Aviation Emphasis
More information at paveahead.com/experts/
5
NRMCA Disclaimer
• This presentation has been prepared solely for information
purposes. It is intended solely for the use of professional
personnel, competent to evaluate the significance and limitations
of its content, and who will accept full responsibility for the
application of the material it contains. The National Ready Mixed
Concrete Association and any other organizations cooperating in the
preparation of this presentation strive for accuracy but disclaim
any and all responsibility for application of the stated principles
or for the accuracy of the content or sources and shall not be
liable for any loss or damage arising from reliance on or use of
any content or principles contained in this presentation.
• Unless otherwise indicated, all materials in this presentation
are copyrighted to the National Ready Mixed Concrete Association.
All rights reserved. Therefore reproduction, modification or
retransmission in any form is strictly prohibited without the prior
written permission of the National Ready Mixed Concrete
Association.
• ©2015 National Ready Mixed Concrete Association.
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Instructions • Everyone is muted. • Webinar is being recorded and
posted at paveahead.com/education/. • Type questions in the
question box. • Download the handouts in the GoToWebinar control
panel. • Credit for course:
– Based on attendance. – Survey (Quiz) – In follow-up e-mail, not
required, but encouraged. – Attendance Certificate – In follow-up
e-mail 1 hour after webinar. – AIA members – Attendance registered
with AIA-CES if AIA number provided.
• AIA-CES Course SOIL101: 1.5 LU|Elective & 1.5 PDH for
Engineers
• Learning Objectives:
– Recognize how a soil sampling and testing plan is developed for a
paving project.
– Comprehend a geotechnical engineering report.
– Learn the various ways soil strength can be determined for use in
pavement design.
– Understand the importance of the soil moisture-density
relationship in construction.
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– ASTM – AASHTO
– Laboratory Methods – In-Situ Methods
• Field Compaction of Soils • Bases and Subbases
Source: www.cement.org
– ASTM – AASHTO
– Laboratory Methods – In-Situ Methods
• Field Compaction of Soils • Bases and Subbases
Source: www.cement.org
• Structure – Surface course – Base course – Subbase course –
Subgrade
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Subgrade stresses differ considerably.
Strength.
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+++ (Tensile Stress)
++ (Tensile Stress)
Transverse Cracking Joint Faulting
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Longitudinal Joint
Transverse Joint
Subgrade Subbase
Surface Texture
Concrete Materials
Tie bars
Concrete Pavement Design
• Thickness is a Function of Key Parameters: – Design life –
Traffic loads & frequencies – Concrete strength –
Subgrade/subbase support (strength characterization)
• Jointing & Reinforcement: – Load transfer considerations –
Prevention of uncontrolled cracking
• Other Design Considerations: – Reliability (Factor of Safety) –
Grades & drainage – Edge support conditions (e.g. curb &
gutter, shoulder…) – Pavement/subsurface interaction
Source: PavementInteractive.org
How Do We Evaluate The Suitability of Subgrade Soils?
Geotechnical Engineering Study and Report • Classification
(Gradation, Atterberg Limits, etc.) • Depth to Bedrock • Depth to
Water Table • Potential for Compaction • Presence of Weak or Soft
Layers or Organics • Susceptibility to Frost Action or Excessive
Swell • Soil Strength Characteristics – Critical Parameter For
Pavement Design
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Stay Tuned, More Details To Come…
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– ASTM – AASHTO
– Laboratory Methods – In-Situ Methods
• Field Compaction of Soils • Bases and Subbases
Source: www.cement.org
Data Collection Activities - Drilling
• Geotechnical Drilling (New Pavements) – Minimum 5 feet below
final top of subgrade elevation** – Spacing a function of roadway
type and soil conditions – High plasticity soils: increase drilling
depth to 10 to 15 feet – Strength testing must be representative of
subgrade soil supporting pavement materials – May require larger
augers at some boring locations for material collection
• Geotechnical Drilling (Existing Pavements) – Obtain existing
pavement thicknesses – Consider test pits if full depth reclamation
is possible – Spacing as stated above – Drilling depths as stated
above – Materials for soil strength as stated above
**Airport, Industrial, and Port Facilities may be different!
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• Standard Penetration Test (SPT) blows/ft • Material Descriptions
• Moisture and Water Table Depth (if encountered)
• Bedrock Depth (if encountered)
– Density – % Swell (freeze and/or moisture related) – Subgrade
Strength Characterization
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– ASTM – AASHTO
– Laboratory Methods – In-Situ Methods
• Field Compaction of Soils • Bases and Subbases
Source: www.cement.org
• Coarse or Fine Grained • Typically Classified as:
– Gravel – Sand – Silt – Clay (Lean or Fat: Based on Plasticity*) –
Or a combination of any of the above
• e.g. Sandy Gravel With Clay *Soil plasticity refers to the manner
in which water interacts with the soil particles.
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States of Consistency for Cohesive Soils (Soil Passing #40
Sieve)
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Atterberg Limits
• Liquid Limit (LL) • Plastic Limit (PL) • Plasticity Index (PI) •
PI = LL - PL
Albert Atterberg 1846-1916
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• AASHTO Classification System – (AASHTO M 145)
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Source: ASTM D 3282
– ASTM – AASHTO
– Laboratory Methods – In-Situ Methods
• Field Compaction of Soils • Bases and Subbases
Source: www.cement.org
• Water Effect – Capillary Forces
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10 11 12 13 14 15 16 17 18 19 20 21 22 23
gdry max
Chart1
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103.9
107.6
109.4
108.8
106
103
Sheet1
wc
gamma
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103.9
14
107.6
16
109.4
18
108.8
20
106
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Volume of Proctor Mold (ft3) 1/30 1/30 1/30 1/30 1/30 1/30
Weight of wet soil in the mold (lb) 3.88 4.09 4.23 4.28 4.24
4.19
Water Content (%) 12 14 16 18 20 22
Wet Unit Weight (lb/ft3) 116.4 122.7 126.9 128.4 127.2 125.7
Dry Unit Weight (lb/ft3) 103.9 107.6 109.4 108.8 106.0 103.0
Sheet2
Sheet3
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Soil Compaction
• Soil compaction is the process of “artificially” increasing the
density (unit weight) of a soil by compaction (by application of
rolling, tamping, or vibration).
• Moisture-density testing as practiced today was started by R.R.
Proctor in 1933. – His method became known as the “standard
Proctor” test.
Ralph Roscoe Proctor, PE (1894 -1962)
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Moisture and Density Relationships of Soils & Base – Laboratory
Methods
• ASTM D 698 - Standard Test Methods for Laboratory Compaction
Characteristics of Soil Using Standard Effort (12,400
ft-lbs/ft3)
• ASTM D 1557 - Standard Test Methods for Laboratory Compaction
Characteristics of Soil Using Modified Effort (56,000
ft-lbs/ft3)
• AASHTO T 99 - Moisture-Density Relations of Soils Using a 5.5-lb
Rammer and a 12-in. Drop • AASHTO T 180 - Moisture-Density
Relations of Soils Using a 10-lb Rammer and a 18-in. Drop
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Soil Strength is usually greatest at its maximum dry density.
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Total Compaction Energy Affects Maximum Dry Density and Optimum
Moisture
Typical Compaction Curves
• Compaction Increases Soil Strength
• Compaction Achieves Soil Support Uniformity
• Provides Stable Platform for Pavement Layers *To Optimum or Just
Above the Optimum Moisture Content
Source: Equipment World
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Soil Compaction in the Lab: 1- Standard Proctor Test 2- Modified
Proctor Test
Standard Proctor Test Modified Proctor Test
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Compaction Curve
Wet to Optimum
Dry to Optimum
Soil Compaction in the Lab: 1- Standard Proctor Test 2- Modified
Proctor Test
wc1 wc2 wc3 wc4 wc5 gd1 gd2 gd3 gd4 gd5
4 inch diameter compaction mold. (V = 1/30 of a cubic foot)
W = 5.5 or 10 pound hammer
25 blows per layer
Increasing Water Content
– ASTM – AASHTO
– Laboratory Methods – In-Situ Methods
• Field Compaction of Soils • Bases and Subbases
Source: www.cement.org
• Some Strength Parameters Require Complex & Expensive Testing
Devices.
• Some Strength Parameters Cannot Be Determined in the
Laboratory.
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(Not Commonly Used)
(More Commonly Used)
– California Bearing Ratio (CBR) • Measures shearing resistance •
Units: percent • Typical values: 0 to 20 for soils
– Resilient Modulus (MR) • Measures stress-strain relationship (an
engineering property)
• Units: psi or MPa • Typical values: 3,000 to 15,000 psi for
soils
– K-value (k) **Typically required for concrete pavement
design**
• Measures resistance to deflection • Units: psi/in • Typical
Values: 75 - 200 psi/in for soils
Source: FHWA
• Resistance of the material to uniaxial penetration.
• Measure of soil shear strength relative to standard crushed
stone.
• Field and laboratory test.
– An empirical test.
Source: www.dur.ac.uk/
Source: www.matest.com
ASTM D1883-Standard Test Method for CBR (California Bearing Ratio)
of Laboratory-Compacted Soils
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California Bearing Ratio (CBR)
• Load a piston (area = 3 in2) at a constant rate (0.05
in/min)
• Record load every 0.1 inch penetration
• Total penetration not to exceed 0.5 inch
• Draw load-penetration curve
0
100
200
300
400
500
600
700
Moisture Content
C B
R
Use relevant or saturated value for moisture content when assessing
soils under laboratory conditions.
Chart3
0.043
0.116
0.179
0.217
0.259
0.4
0.5
Typical Testing Machine Source: Humboldt
Surcharge Weights
• Simulate the weight of pavement.
• Prevent heaving up around the piston.
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Dynamic Cone Penetrometer (DCP)
• Originally developed in the Republic of South Africa (RSA) where
it has been used with related tools and analyses for over 25
years.
• Equipment can be purchased for about $1,000 to $3,000 (US).
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• Standard Test Method:
– ASTM D6951-Use of the Dynamic Cone Penetrometer in Shallow
Pavement Applications
– Equipment can come with different hammer weights:
• 8 kg (17.6 lb.)
• 4.6 kg (10.1 lb.)
– USACE CBR—DCP correlations in the ASTM standard test
method:
• e.g. CBR = 292 / ( DCP1.12 )
Mr
Source: www.GCTS.com
Source: Buchanan
Source: www.GCTS.com
Source: Buchanan
Source: FHWA
Define stress conditions at appropriate analysis depth to
determine resilient modulus for use in design.
Source: FHWA
• Falling Weight Deflectometer (FWD)*
Source: Cornell Local Roads Program
Source: Controls Group website
Falling Weight Deflectometer (FWD)
Heavy Weight Deflectometer (FWD)
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You can solve for (backcalculate): • Pavement Layer Moduli
FWD è Backcalculated Pavement Layer Properties
Backcalculation is an Iterative Process:
Source: Lytton
k-value = spring constant
Reaction
k (psi/in) = unit load on plate / plate deflection
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See ACPA Static (aka Effective or Composite) K-Value Calculator at
http://apps.acpa.org/applibrary/KValue/
() = [( × ) + (× ) + (× )]
keffective
keffective calculation is not quite this simple…but you get the
idea!
CBR % 2 - 80
k-Value psi/in 75 - 300
Equation Origin Limitations
Only for fine-grained non- expansive soils with a soaked
CBR of 10 or less.
Mr = 2555 x CBR0.64 AASHTO M-E Design A fair conversion over a wide
range of values.
See http://www.apps.acpa.org/apps/MRSG.aspx app library for Mr
& CBR correlation
Also a correlation for k-value and CBR:
MR vs CBR
CBR
Mr
Chart2
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1.5
1.5
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19.5
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– Strength
– ASTM – AASHTO
– Laboratory Methods – In-Situ Methods
• Field Compaction of Soils • Bases and Subbases
Source: www.cement.org
• Depth of Stabilization
Encountering Special Circumstances…
• Expansive Soils: – Frost Heave – High Plasticity Soils (PI >20
to 25)
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Pavements On Expansive Soils Soil Heave from an expansive clay
subgrade in this neighborhood resulted in a lawsuit between the
homeowners and the homebuilder.
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• Soil Treatment with Cement, Lime, or Fly Ash
• Geosynthetics: Geotextiles or Geogrids
• Drains or Barriers to Collect or Inhibit Moisture
Infiltration
• Chemical Injection of Soil
• Material Availability and Cost
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Don’t Forget…
• Mitigation Techniques: – May Need to be Combined, and – May Not
Completely Solve the Problem!
Treatment of Upper Native Soil
Water Native Expansive Soil (High PI)
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• There is a difference between Stabilization (sometimes referred
to as Modification) and Treatment.
• Additional laboratory testing and construction verification are
required for Stabilization (or Modification).
• Determining the correct Unconfined Compressive Strength (UCS)
value for stabilization is key (UCS of 150 – 300 psi at 7 days and
lab moisture cured is common).
• See Portland Cement Association or National Lime Association
(Mixture Design) for more info.
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• Lime-Fly Ash or Self-Cementing Fly-Ash Stabilization – Typically
Used with High Silt, Low Clay Soils
• Recycled and Waste Product Stabilization • Example: Cement Kiln
Dust (CKD)
• Deep Layer Subgrade Stabilization (Max 16”)
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Fly Ash Soil Stabilization
• Chemical Stabilizers – ROADBOND EN 1™
– EMC SQUARED® System
– FA = Chemical Stabilization
87
Subgrade
Stabilized
Pulverize, Shape, Add Cement, Mix In Place, Compact, and
Surface
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– ASTM – AASHTO
– Laboratory Methods – In-Situ Methods
• Field Compaction of Soils • Bases and Subbases
Source: www.cement.org
1- Rammers
Increasing compaction energy Lower OWC and Higher Dry Density
In the field: increasing compaction energy = increasing number of
passes or
reducing lift depthIn the lab: increasing compaction energy =
increasing number of blows/weight
92
• Compact granular materials near or even below optimum moisture. •
Density 95% or above of standard proctor or
• Density 98% or above of modified proctor
• Compact plastic soils at or slightly above optimum moisture: •
BUT do not exceed about 3% above opt.
• Density 95% or above of standard proctor
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103
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97
100
109
Max. Density
Opt. Moisture
D en
si ty
, l b/
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During construction of pavement layers, there is usually a
requirement to achieve a specified dry unit weight.
Moisture content
D ry
u ni
(a) > 98% of maximum dry unit weight, no moisture criteria
(b) >95% of maximum dry unit weight and moisture within ±2% of
mopt
Accept
Reject
94
• Stump holes
Nuclear Density Testing
In-Situ Moisture and Density of Soils & Base – Nuclear
Methods
• ASTM D6938 - Standard Test Method for In-Place Density and Water
Content of Soil and Soil- Aggregate by Nuclear Methods (Shallow
Depth)
• AASHTO T 310 - In-Place Density and Moisture Content of Soil and
Soil-Aggregate by Nuclear Methods (Shallow Depth)
98
Source: utest.com.tr
– Free Tutorials
– Regulatory Requirements
• Compact with proper moisture content.
• Check density with testing or proof rolling.
• Fine grading.
• Consider subgrade stabilization when extremely poor soils are
encountered.
• Insure adequate surface drainage.
• Uniformity is the key!
– ASTM – AASHTO
– Laboratory Methods – In-Situ Methods
• Field Compaction of Soils • Bases and Subbases
Source: www.cement.org
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Longitudinal joint
Tie Bar Eroded Subbase
Erosion
Water
Load
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Pumping and Joint Faulting
For control of pumping/faulting: • Short slabs • Proper jointing
design • Good load transfer • Good surface drainage • Use a
non-erodible subbase
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Potential for Erosion and Lifting
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When is a Subbase Needed?
• Subbases Have Little Influence on Required Concrete Pavement
Thickness, but do Affect Erosion and Faulting.
• What Conditions Need to Exist for Subbase Use?
– Heavy Loading (i.e. Trucks; ADTT > 100 to 200)
– Subgrade Susceptible to Pumping/Erosion (fine-grained)
– Water Available to Subgrade (infiltration or high water
table)
– Risk of Deep Frost Penetration & Heave
– Project Phasing and/or Need for Construction Platform
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• If Conditions Exists, What Kind of Subbase?
– Granular (Crushed Stone)
• Project Conditions Will Dictate…
• If Conditions Exists, Are There Other Options?
– Subgrade Stabilization
– Soil Mixing
– Subsurface Drainage
• Various Methods to Characterize – Classification
– Strength
– Stabilization
NRMCA Resources
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reviews for FREE • Cost comparisons including life cycle costs •
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– Conventional concrete (full depth and overlays) – Pervious
concrete – Roller compacted concrete – Cement slurry for full depth
reclamation (FDR)
123
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www.paveahead.com/education
– Each Thursday beginning at 2:00 pm EDT
– April 02 Designing Concrete Parking Lots and Streets
– April 09 Designing Concrete Industrial Pavements
– April 16 Soils 101: What to Know for a Successful Paving
Project
– April 23 Concrete Pavement Jointing and Details
– April 30 Materials and Construction Specifications for Concrete
Pavement Projects
– May 07 Concrete Street and Parking Lot Maintenance and
Repair
– May 14 Concrete Overlays of Existing Asphalt Surfaced Streets and
Parking Lots
– May 21 Concrete Trail Design
• Concrete Buildings Webinar Series:
buildwithstrength.com/education/
– Each Wednesday beginning at 2:00 pm EDT
Recordings available for previous webinars!
– Each Thursday beginning at 2:00 pm EDT
– May 28 Designing Pervious Concrete
– June 4 Specifying Pervious Concrete
– June 11 Installing Pervious Concrete
– June 18 Maintenance Guidelines for Pervious Concrete
• Portland Cement Association Webinar Series:
www.cement.org/learn/education
– Each Wednesday beginning at 9:00 am EDT
– April 22 Full-Depth Reclamation with Cement
– April 29 Lightweight Cellular Concrete for Geotechnical
Applications
– May 6 Roller-Compacted Concrete Pavements
– May 13 Cement Stabilized Subgrade Soils
– May 20 Cement-Based Water Resource Applications
Pervious Concrete Webinar Series!
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