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PE 2019
Compaction Quality Assurance of Geomaterials Using the Light Weight
Deflectometer
By
Sadaf Khosravifar, PhD, PE
Dynatest North America, Inc.
PE 2019
Research Team at University of MarylandProfessor Charles W. SchwartzNiosha Afsharikia, PhD
Undergraduate AssistantsNicolas AlvarezChristopher PlattBen GeerstmaYunpeng ZhaoGregory KoeppingRamiz VatanMateus CoelhoMarcus Watson
LWD ProvidersDynatest, Zorn, Olson
Material ProvidersLuck Stone
Technical Advisory Committee of TPF 5(285)Maryland SHA (lead agency)Technical DirectorAdministration
FHWATechnical LiaisonDelMar Division
Sponsoring AgenciesFloridaMichiganMissouriNew YorkNorth CarolinaSouth CarolinaVirginia
Others Minnesota Indiana
Dan SajediRodney Wynn
Michael ArastehAzmat Hussain
David HorhotaDavid Gauthier John Donahue Brett Dening K.J. KimJesse ThompsonShabbir Hossain
John SiekmeierNayyar Zia Siddiki
Acknowledgement
PE 2019
Introduction
• First Light Weight Deflectometers (LWD) date back to the early 1970’s
• Specifically designed for unbound or lightly bounded pavement layers
• In-situ tool for measuring Surface Stiffness
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• Surface Modulus
• Determine the Non-linearity
• Calculate the modulus of 2 layers
• with Dual Plate System (DPS) and additional geophones
• Calculate overlay
• Determine layer thickness
• Quality Control/Quality Assurance (QC/QA)
What can be determined from the Dynatest LWD?
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• Reflects engineering properties of material
• Avoid nuclear QC/QA methods
• Better testing of stabilized materials
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
0 1 2 3 4 5 6 7 n
E/Eo
pt
Days since Placement
FASB layer
GAB layer
0
10
20
30
40
50
60
70
80
0 1 2 3 4 5 6 7 n
E (k
si)
Days since PlacementKhosravifar et al. 2013
Why LWD for Compaction QA
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Stress effects Confining stress stiffening effects on MR
Deviator stress softening effects on MR
Moisture effectsCompaction moisture effects on MR
Drying profile history (limited time duration)
Drying (post-compaction moisture) effects on MR (stiffening)
Layered systemSubgrade only
Stiff base over soft subgrade
Stiff base over stiff subgrade
Key Issues for LWD-based Compaction QA
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Individual LWD device detailsPlate diameterPlate rigidityContact area stress distributionLoading rateDeflection measurement type and
location(s)
Moisture measurement devicesReliabilitySpeed in giving the results
PE 2019
What is an Ideal Modulus-Based Specification
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1) Smooth transition from density-based methods to
modulus-based QC/QA
2) Applicability to a variety of geomaterials
3) Cost efficient for organizational implementation
4) Based on field moisture and modulus measurements
immediately after placement
5) Easy-to-determine target modulus values
FHWA Transportation Pooled Fund Study (TPF 5-285)
LWD testing on Proctor molds
PE 2019
ELWD_Mold atmultiple
MC and P/Pa
EstablishELWD_Target =f(Structure, MC, P/Pa)
Measure:- ELWD_Field
- MC
Lab Field
CompactionCriteria:
ELWD_Field
ELWD_Target
> 1
PWL > 80%
MC = OMC + Δ
FHWA TPF 5-285 LWD - Proctor Method
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Limit post compaction QA to two hours
PE 2019
1- Laboratory Determination of Target Modulus
Using LWD drops on Compacted Proctor
Mold:• Sample preparation
• Testing procedure
• Determination of optimum MC
• Determination of target ELWD_Target
2- Compaction Quality Control Using LWD• In-situ LWD testing procedure
• In-situ LWD testing frequency
• In situ MC testing
• Adjustment of ELWD_Target for two-layer systems
• Evaluation of in situ MC for acceptance
• Evaluation of ELWD_Field/ELWD_Target for acceptance
FHWA TPF 5-285 LWD - Proctor Method
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PE 2019
f=Parabolic– for flexible soil-plate system f=8/3
f= Uniform– for semi-flexible soil-plate f=2
f= Inverse Parabolic– for rigid soil-plate system f=pi/2
LWD TESTING IN FIELD (SEMI-INFINITE)
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+ Determination of Moisture Content𝐸𝑜 =𝑓 1 − 𝜐2 𝜎𝑜𝑟𝑜
𝑑𝑜
𝐸𝑜= Surface LWD modulus𝑓=Stress Distribution Factor𝜐= Poisson’s Ratio𝜎𝑜=Peak Stress Under the Plate𝑟𝑜 = radius of the LWD plate 𝑑𝑜=Peak Center Deflection
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Target Modulus for 1-Layer System
Form Quarterly
(08/2011)
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Table 7. Matching LWD pressure in the field and on the mold.
Plate size P/Pa P Force Drop
Height
[inch] - [kPa] [kN] [inch]
Field LWD 12 0.94 95.25 6.73 33.00
Lab LWD 6 0.94 95.25 1.68 4.16
Figure 2. Dynatest LWD average applied load from different drop heights on the mold.
y = 0.2914x + 0.4712
R² = 0.9845
0.00
0.50
1.00
1.50
2.00
2.50
3.00
0 1 2 3 4 5 6 7 8 9
Avg
load
[kN
]
Drop height [inch]
𝐸 = (1 −2𝑣2
1 − 𝑣)4𝐻
𝜋𝐷2 𝑘𝑠peak
s
peak
Fk
w
𝜎1
𝜎3 =𝜗
1 − 𝜗𝜎1
Plate Diameter (D)=150 mm
Condition: Confined compression
Drop height: Adjusted to Achieve the SAME Pressure as in Field~4.16 in for 95.25 kPa
PE 2019
Esurface−Corrected Target = 1/1
E2 1 +hr0
3 E1E2
2+
1 −1
1 +hr0
2
E1
in which:E1 = Target modulus of the top layer (GAB, base, etc.) from LWD on MoldE2 = surface modulus of the underlying layer (subgrade, fill, subbase, etc.)h = thickness of the top layerr0 = D/2= radius of the LWD plate
Corrected Target Modulus for 2-Layer System
E1 BaseTarget from LWD on Mold
E2 Subgradefrom LWD in field prior to base
placement
hD
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Easy setting of the desired drop heightMovable release handleLaser engraved scale on the shaft
Dynatest LWD and App
Easy Switch between Plate Sizes w DPS6 in Diameter for Lab12 in Diameter for Field
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Dynatest LWD and App
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Dynatest LWD and App
2.47 %
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Location Soil TypeAASHTO
ClassificationUnified Classification
1 Virginia Subgrade A-3 SP-SM Poorly graded sand with silt
2
Maryland
MD5 Waste contaminated embankment
A-1-a SW Well graded sand with gravel
3 MD5 Subgrade A-2-7 SP Poorly graded sand with gravel
4 MD337, Deep GAB A-2-7 GW-GM Well graded gravel with silt and sand
5MD404 sand overlaying
SubgradeA-2-7 SP Poorly graded sand
6 MD404 Subgrade A-2-6 SP Poorly graded sand7 MD404 GAB A-2-7 GP-GM Poorly graded gravel with silt and sand8 New York Embankment A-3 SP Poorly graded sand9
IndianaCement modified Subgrade A-2-4 SW Well graded sand with gravel
10 Virgin Subgrade A-2-4 SW-SM Well graded sand with silt and gravel11 GAB A-1-a GW Well graded gravel with sand12
MissouriSubgrade A-3 SP Poorly graded sand with gravel
13 Base A-3 GW Well graded gravel with sand14
FloridaSubgrade A-2-7 SP Poorly graded sand
15 Base A-3 SP Poorly graded gravel with sand
Evaluated sites– TPF 5-285
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Evaluated sites- Maryland Follow-up Study
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Pooled fund
Dynatest LWD
y = 0.9191x0.0834
R² = 0.5807
0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.05
1.10
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
PC
Efield/Etarget, Dynatest LWD
MD5 Fill
MD337 GAB
FL Base
NY SG L1
NY SG L2
MD404 GAB
95 PC
Power (All)
f factor= 8/3
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LWD based Compaction QA Results
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MDSHAfollow-up
Study
f factor= 8/3
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LWD based Compaction QA Results
PE 2019
FHWA TPF 5-285 LWD - Proctor Method
• Target Modulus defined using LWD testing on Proctor Mold
• Uses existing contractors/agency equipment
• Accounts for moisture variation
• Accounts for stress levels
• Accounts for pavement structure
• Bridges the gap between QC and Design
• Simple and requires some degree of expertise
• The Compaction Module in the Dynatest app makes the process easy
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PE 2019
Contact Information
Sadaf Khosravifar, PhD, PEDynatest North America, IncCell: +1 530-531-5030 [email protected]
Niosha Afasharikia, PhDWood [email protected]
Professor Charles W. SchwartzUniversity of [email protected]