BCRA Poster

1
Subgrade Soil Support and Stabilization
OHARE Airport Modernization Research Project
Co-PIs Erol Tutumluer
Marshall R. Thompson RA
H.S. Brar
2
Introduction

• Subgrade performance is a key factor in the
  overall pavement performance

National Airport Pavement Test Facility -
Atlantic City, NJ

• This project provides testing and analysis to
  establish subgrade support and stabilization
  requirements for OHare airport pavements

3
Introduction (contd)

• The preliminary concrete pavement design for the
  OHare Modernization Program (OMP)
• 15 17 inches of PCC Surface
• 6-inch Hot Mix Asphalt Base
• 6-inch Asphalt Treated Permeable Base
• Stabilized Subgrade Zone (SSZ)
• Prepared Subgrade
• North Runway (9-27) paving is scheduled first for
  the Spring 2006
• Stockpiles of local soil on runway centerline
  (excavated from the Deep Pond nearby)
• Primarily fill and cut areas

4
Research Objectives

• Consider pavement design inputs for subgrade
  support
• Modulus of subgrade reaction, k
• Consider subgrade support and stabilization
  requirements with respect to
• Need for subgrade stabilization
• Stabilization admixture(s) stabilization
• Stabilization depth
• Estimate subgrade support for various
  combinations of subgrade stabilization treatments
  and prepared subgrade conditions

5
Project Tasks

• Task 1
• Establish the Best Demonstrated Available
  Technology (BDAT) for subgrade soil evaluation
  and stabilization
• Reports and publications collected submitted
  as Technical Notes on
• Subgrade strength/stiffness evaluation techniques
• Subgrade stability requirements IDOT Manual
• Working platform requirements for pavement
  construction

6
Project Tasks

• Task 2
• Evaluate currently available data for the
  subgrade test sections constructed in the Fall of
  2003 and the necessity/usefulness of constructing
  additional subgrade treatment test sections at
  OHare
• Plate load tests conducted (8/04) on the test
  sections
• Plate 1 12-inch stabilization/compaction no
  admixture
• Plate 2 12-inch quicklime fine (40 lb/yd2) fly
  ash (80 lb/yd2) stabilization
• Plate 3 12-inch quicklime fine stabilization (40
  lb/yd2)
• Plate 4 12-inch lime kiln dust stabilization (40
  lb/yd2)

7
Plate Load Tests
Modulus of Subgrade Reaction, k
8
Project Tasks

• Task 3
• Advise OMP on current and future test section
  monitoring and field test evaluation programs
• Various field tests may be useful to
  characterize the treated subgrade (OMP will
  arrange for testing)
• Dynamic Cone Penetrometer (8/04)
• Light-Weight Deflectometer (8/04)
• Clegg Hammer
• Geogauge
• Heavy Weight Deflectometer (HWD)
• Ground Penetrating Radar (GPR)
• Seismic Pavement Analyzer, SASW, etc.

9
Dynamic Cone Penetrometer
Light-Weight Deflectometer
10
Project Tasks

• Task 4
• Evaluate currently available geotechnical/subgrad
  e data for the North Runway with emphasis on the
  stockpiled Deep Pond soils. Recommend further
  soil sampling testing to be conducted (by an
  OMP designated testing firm)
• Routine tests to establish representative soils
  existing for the runway subgrade
• Grain size distribution (including hydrometer)
• Atterberg limits (LL and PL for PI)
• Moisture-density-CBR
• PH value calcareous content
• If needed, organic matter content

11
Project Tasks

• Task 5
• Based on the data and information gathered in
  Task 4, select (in consultation with OMP) the
  identified representative soils and recommend an
  admixture stabilization program
• Non-routine testing to be conducted at the UIUC
  Advanced Transportation Research and Engineering
  Laboratory (ATREL) on both untreated treated
  soils
• Triaxial testing for
• Shear strength
• Resilient modulus
• Permanent deformation

12
Project Challenges

• Properly sampling the Deep Pond stockpiled
  soils
• Selecting identifying representative soil
  samples
• Adequately characterizing the representative soil
  samples by conducting non-routine tests at the
  UIUC ATREL for
• Shear strength
• Resilient modulus
• Permanent deformation

13
Project Deliverables

• Technical Notes will be prepared and submitted to
  the OMP throughout the duration of this project
  to communicate specific findings and
  recommendations to OMP engineers as needed
• A Final Report will be prepared at the end of the
  one-year study
• Several of the Project Tasks are already pursued
  simultaneously, and the specific delivery of
  results will be contingent upon availability of
  OMP data and other factors that depend on
  coordination with OMP

14
Advanced Transportation Research Engineering
Laboratory (ATREL) - University of Illinois
15
Mechanical Behavior of Subgrade Soils

• Strength Maximum level of stress soil can
  sustain before it fails or excessively deforms
• Shear strength, tmax c snormaltanf
• c cohesion f internal friction angle
• Stiffness Stress obtained for a unit strain
• Resilient (MR) modulus,
• Poissons ratio (n)
• Resistance to Permanent Deformation Ability to
  resist a large number of load cycles without
  accumulating excessive deformations
• dp f(N, confinement, cyclic s or t, t/tmax)

16
Sample Preparation - Compaction

• Improve strength, reduce deformation, and prepare
• specimens close to field construction conditions
  
• (OMC Optimum moisture content)
• Laboratory Compaction Methods
• Static Standard for soils (AASHTO T-307-99),
  typically 5 layers
• Impact Proctor type (AASHTO T-99/180), several
  layers
• Vibratory Typically used for granular materials
• Vibration in several layers (vibratory hammer)

17
Std Modified Proctor Compaction (ASTM D698,
D1557)
Moisture-Density Relationship
130
126
gdmax
122
Dry Unit Weight (pcf)
118
114
wopt
110
5
6
7
8
9
10
11
12
13
14
15
Gravimetric Moisture Content ()
18
Typical Moisture-Density Results
120
Dupont Clay
115
100 Sr
90 Sr
(Gs 2.71)
110
105
Dry Density, pcf
100
95
ASTM D-1557
90
Intermediate
ASTM D-698
85
10
14
18
22
26
30
34
Moisture Content,
19
STRENGTH BEHAVIOR
20
AC

• Load stress
• distribution

Base
Subgrade
s
s



c
d
Confining stress
s
s
s
-
Deviator stress
c
d
v
c
c
s

Vertical stress
v
c
d
s
c
Triaxial Conditions/Tests
21
Triaxial Testing Equipment - Capabilities
22
Strength Tests Using Triaxial Setup

• Cohesive Soils (c, f0)
• Modified Proctor Procedure A (ASTM D1557)
• Unconfined Compression (ASTM D2166)
• Sandy Soils (c, f)
• Modified Proctor Procedure C (ASTM D1557)
• Rapid Triaxial Shear (UI Procedure)

t
sd s1 s3(0)
failure
C (s1f)/2 Qu/2
s1f
s3 0
s1
s
23
Typical Unconfined Stress-Strain Data
60
Dupont Clay
MC 23
50
DD 103.5 pcf
CBR 14
Qu unconfined compressive
strength peak s1
MC 26
DD 98 pcf
CBR 8
Axial Stress, psi
MC 28.5
DD 93.5 pcf
CBR 4
MC 30.5
DD 92.5 pcf
CBR 2.5
0
5
10
15
Axial Strain,
24
Strength Testing
tmax c sntanf
?d deviator stress
?3 cell pressure
FAA NAPTF P209 Aggregate
at 3 ?3 levels
6.9 kPa 1 psi
25
MODULUS BEHAVIOR
26
Elastic (Resilient) Behavior
Due To Repeated/Cyclic Load Application
?d
Elastic (Resilient) Modulus, E (MR ) Poissons
ratio, n
?3
Deformation
?3
MR ?d / ?r
?3
Recoverable Deformation
MR Resilient modulus
?d Repeated wheel load stress
?r Recoverable (rebound) strain
Permanent Deformation
Time
27
Resilient Modulus Overview

• Resilient Modulus (MR) is a fundamental material
  property
• Simulates repeated application of wheel loads
• MR testing is a rational test and is an
  improvement over CBR
• MR considers fundamental effects
• Stress condition, density, grading, fines, water
  content
• Evaluates rutting - very important

28
Determining Resilient Modulus

• Lab Testing AASHTO T 307-99 (SHRP TP46)
• Undisturbed
• Disturbed, remolded and compacted
• Input to mechanistic based pavement design
  procedures
• Estimate from various procedures
• Backcalculation from field FWD deflections
• Soil properties
• Unconfined compressive strength
• CBR

29
Resilient Modulus Test (AAHSTO T307-99)
Type I Unbound granular base and subbase
materials Type II Untreated subgrade soils, A-4,
A-5, A-6, A-7

• Repeatedly applied loads
• Similar to those from wheel loads
• Relates to elastic component of response only
• Resilient ( recoverable) deformation

30
Repeated Load Triaxial Test Stress States
?1 - ?3 Repeated (Cyclic)
Deviator Stress ?d
Total Axial Stress, ?1 (major principal
stress)
?3
?
Shear Stresses ????0
????0
MR sd / er
?3 Confining Pressure (minor principal
stress)
?2 ?3
Bulk Stress ?? ?1 ?2 ?3
?d 3?3
Vertical Specimen Deformations Measured Only!..
31
MR Tests Type II Soil Samples
Cylindrical specimens, 2 in. f by 4 in. high
Undisturbed soil samples Shelby tube (f 2.8,
4 in.)
32
Stress Sequence Type II Soils

• Haversine load waveform (pulse load duration
  0.1 sec., 5 Hz)
• Conditioning 1000 load applications
• at s3 41 kPa sd 28 kPa (s1 /s3 1.7
  only!..)
• Testing 100 load applications at 15 following
  stress states

s3 (kPa)
?d
AASHTO T307-99- SHRP Protocol P46
41
21
0
?3
141
146
1411
282
287
2812
sd
?3
413
418
4113
?3
554
559
5514
(kPa)
695
6910
6915
33
Subgrade Deviator Stress
P
Wheel
AC
Aggregate
sd
s3 low !..
Subgrade soil
34
University of Illinois MR Testing Procedure
- Type II Soils

• Haversine load waveform (pulse load duration
  0.1 sec., 5 Hz)
• Conditioning 200 load applications
• at s3 0, sd 41 kPa
• Testing 100 load applications at 8 following
  stress states

sd Repeated Deviator Stress
2-in. in f
?d
Unconfined s3 0
sd 14, 28, 41, 55, 69, also 83, 96,
110 kPa
35
University of Illinois Repeated Load Triaxial
Test System
36
Factors Affecting MR of Type II Soils
Fine-grained subgrade soils silts and clays

• Primary Factor
• Applied stress states, sd and s3
• Secondary Factors soil properties
• Moisture content, w (or Saturation, SR, )
• Suction f(depth to groundwater table)
• Plasticity index, PI
• Clay content, (smaller than 2mm)
• Dry density, gd
• Freeze-thaw effects

37
Stress Dependent MR Behavior

• Nonlinear stress dependent behavior
• Stress softening (fine-grained soils)
• Stress hardening (coarse-grained,
• aggregates)

s
cohesive soils
linear elastic
MR f (s)
aggregates
ep
e
38
Arithmetic or Bilinear Model
Cohesive Soils
MR f(sd ), Mainly Shear Stress
Typical Fine-Grained Soil Stress Softening
Behavior


-
s
s

• M

K
K
K
(
lt K
)
when
d
2
R
d
1
3
2

-
-
s
s

• M

K
K
K
(
)
gt K
when
d
2
R
d
1
4
2
1
where sd s1 - s3
K3
1
K4
K2
K1 Eri Breakpoint modulus
K1
K2 sdb Breakpoint deviator
stress (26 psi)
Thompson and Robnett (1979)
39
Typical MR Characterization for Soils
Greensboro, NC Airport Subgrade Soils
28
24
A-4 soil at OMC
A-4 soil at OMC3
20
Bilinear or Arithmetic Model
16
s
M
- 0.6274
1820

R
d
2
R
0.6617
12
8
4
s
M
- 0.4203
8.351


s
R
d
M
0.0408
4.9412

R
d

2
R
0.8715
2
R
0.8796
0
0
2
4
6
8
10
12
14
16
18
s
APPLIED DEVIATOR STRESS
(psi)
d
40
Empirical MR - CBR Correlations

• MR (psi) 1500 CBR
• (Heukelom and Klomp, 1962)
• MR (psi) 2555 CBR 0.64
• (2002 Design Guide Prepared for AASHTO)

Limited application for up to CBR 10-12
41
Empirical MR - CBR Correlations
The empirical correlations may not always work !..
Greensboro, NC Airport Subgrade Soils
42
PERMANENT DEFORMATION BEHAVIOR
43
Permanent Deformation Rutting
PRIMARY PERFORMANCE INDICATOR Base/Subbase
Materials and Subgrade Soils
Wheel Rutting!..
Permanent Deformation dp
44
Permanent Deformation Testing

• Much less advanced than resilient behavior
• No well-established test procedure exists
• Yet, soil performance is solely judged by its
  field permanent deformation or rutting potential
• Cohesive Soils U of I procedure
• Stress Levels 25, 50, 75 100 of Qu
• Subgrade Stress Ratio (SSR) sD/Qu
• N 1000 (Conditioning) up to 100,000
• For a given stress level
• Permanent strain (ep) is monitored
• ep versus N plots for various stress levels

45
Typical dp Test Results - Soils
0.10
Dupont Clay
0.08
q
28 psi
u
98 pcf
g
1.00 SSR
d
0.06
w
26
Permanent Strain, ep
0.04
0.75
0.02
0.50
0.25
0.00
1
10
100
1000
No. of Load Applications
46
Typical dp Test Results - Soils
0.07
moisture contents
Dupont Clay
0.06
23.0
0.05
26.0
28.5
0.04
30.5
Perm. Strain after N1000
0.03
0.02
0.01
0.00
0.00
0.25
0.50
0.75
1.00
Subgrade Stress Ratio
47
Factors Affecting Permanent Deformation dp of
Soils

• Primary Factors
• Applied stress states, sd, s3, and strength (Qu
  or tmax)
• Subgrade Stress Ratio, SSR ( sd / Qu)
• Number of Load cycles, N
• Secondary Factors soil properties
• Moisture content, w (or Saturation, SR, )
• Suction f(depth to groundwater table)
• Plasticity index, PI and clay content, (lt2mm)
• Dry density, gd
• Freeze-thaw effects

48
Permanent Deformation - Power Model
0.1
moisture contents
Dupont Clay
0.01
Permanent Strain, ep
epANB
0.001
1
10
100
1000
No. of Load Applications
49
Permanent Deformation - Power Model
1.E-03
Sand
-4
0.137
e
1.4x10
N
1.E-04
p
Permanent Strain, ep
2
R
0.96
s
45 psi
d
s
15 psi
3
1.E-05
1
10
100
1000
No. of Load Applications
50
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