Project Title: Chemical Stabilization of Clay
Design Department
Presenter: Stephan Cheong
Date: February 5,2015
Outline of Presentation
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Introduction to Soil Stabilization
Chemical Admixtures
Application of Soil Stabilization
Environmental Impacts
Engineering Properties of Clay
Standard Engineering Tests
Project Limits
Results and Analysis
Discussion
Flexible Pavement Design
Economical Consideration of Flexible Pavement
Benefits of Soil Stabilization
Conclusion
Recommendations
Introduction to Soil Stabilization

 Permanent physical and chemical alteration of soils to
enhance their physical properties.
 To create an improved soil material possessing the
desired engineering properties.
 Chemical stabilization relies on the use of an admixture to
alter the chemical properties of the soil.
Chemical Admixtures
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 The chemical additives used to modify the chemical
properties of a clay soil in this research are listed
below:
o Rice Husk Ash – Silicate Based
Chemical Admixtures

o Sodium Hydroxide – Sodium Based
o Lime – Calcium Based
Application of Soil Stabilization

 Road Pavements
 Foundations
Environmental Impacts
Environmental
Parameter

Sodium Hydroxide
Rice Husk
Lime
PHYSICAL
Air: Dust Control
measures when
transported
Not Required
Required
Required
Water Quality
Sodium
toxicity Water quality is Ionizes
to
results from
high not affected
Calcium cations
concentration
of
in water which is
Sodium in water but
beneficial
for
decreases acidity of
human and fish
water due to low pH
health
Social
Health and Safety
Severely Hazardous Harmless
Substance
Substance
Harmless
Substance
Engineering Properties of Clays

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Their vulnerability to slow volume changes that can occur
independent of loading due to swelling or shrinkage.
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The degree of weathering they have undergone
which leads to the destruction of interparticle bond.
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Reductions in strength and elastic modulus with a general increase
in plasticity.
Standard Engineering Tests
Standard Tests
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Key Engineering Properties
Liquid and Plastic Limit {ASTM D4318 00}
Plasticity Index
Shrinkage Limit {ASTM D4943 -02}
Shrinkage Potential
Specific Gravity {ASTM D854 -02}
Soil Density
Standard Engineering Tests
Standard Tests
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Modified Proctor {ASTM D1557 -00}
California Bearing Ratio {ASTM
D1883 -99}
Key Engineering Properties
Compaction
Subgrade Strength
Settlement Potential of Cohesive Soils Soil Permeability and Percent
{ASTM D4546 -03}
Settlement
Project Limits
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 Location of Disturbed Tested Sample: University of Guyana
 Selected Test Specimens: Soil mixed with 5%, 10%, 15%
NaOH, 3%, 5%, 8% Lime and 20%, 25% and 30% RHA.
 Soil mixed with 8% Lime, 30% RHA and 10% NaOH was more
effective in stabilizing clay soils.
Results and Analysis
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Soil Type
Specific
Gravity
Values
Plasticity
Index /%
Soil Type
*Plasticity
Chart
(ASTM D
2487)
Shrinkage
Limit/%
Untreated
Clay Soil
2.695
47.26
CH
13.62
Soil +
30% RHA
2.452
35.75
MH
3.90
Soil + 8%
Lime
2.504
26.87
MH
8.90
Soil +
10%
NaOH
2.956
24.09
MH
7.47
Results and Analysis
Soil Type
Maximum
Modified
Proctor Dry
Density /
lb/ft3
Untreated
Clay Soil
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California
Bearing
Ratio
Subgrade Strength
*Based on
AASHTO
Pavement
Thickness Design
Guide
105
3.01
Low
Soil + 30%
RHA
87.0
3.23
Low
Soil + 8%
Lime
101.6
4.12
Low
Soil + 10%
NaOH
110.6
5.71
Medium
Results and Analysis
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Soil Type
Settlement Potential of
Cohesive Soils
{Remolded Samples}
Hydraulic Conductivity, kz
(m/yr)
Untreated Clay Soil
0.05755
Soil + 30% RHA
0.80495
Soil + 8% Lime
0.72524
Soil + 10% NaOH
0.0938
Results and Analysis
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Seating
Pressure σvo
(KPa)
384
-
24
Untreated
Clay Soil
Soil + 8% Lime
Soil + 30%
RHA
Soil + 10%
NaOH
Percent Settlement /% of Remolded Samples
-13.0
-6.1
-8.2
-7.4
Percent Rebound Settlement /% of Remolded Samples
-8.2
-4.3
-5.5
-4.7
Discussion
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Increased Compaction
Increased Density
Stabilized Soil
% Variation
from Clay
Stabilized Soil
% Variation
from Clay
10% NaOH
5%
10% NaOH
10%
8%Lime
-3%
8%Lime
-7%
30% RHA
-17%
30% RHA
-9%
Discussion
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Increased Load Bearing
Capacity (Subgrade Strength)
Increased Hydraulic
Conductivity
Stabilized Soil
% Variation
from Clay
Stabilized Soil
% Variation
from Clay
10% NaOH
90%
10% NaOH
60%
8%Lime
37%
8%Lime
1160%
30% RHA
7%
30% RHA
1300%
Discussion
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 Reduction in Settlement
and Rebound Settlement
Stabilized Soil
% Variation
from Clay (S)
% Variation
from Clay (R.S)
10% NaOH
43%
43%
8%Lime
53%
48%
30% RHA
37%
33%
Flexible Pavement Design
(AASHTO 1993)
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Input Values for
Nomograph
•
•
•
•
•
•
•
Reliability (R)%=95
Overall Standard Deviation (So) =
0.40
Estimated Future traffic, 18 Kip
ESALs, w18= 10 × 106
m=1 (drainage provided)
Final Serviceability limit = 4.5
Initial Serviceability limit = 2.5
Design Serviceability loss = 2.0
Layer Coefficient
•
•
•
•
•
•
•
•
Asphaltic Concrete;
a1= 0.365, EAC = 300,000 psi
Aggregate base;
a2= 0.13, CBR = 70
White Sand/Sand Clay;
a3=0.11, CBR = 30
White Sand;
a4= 0.0925, CBR = 20
Structural Number and Layer
Thickness (AASHTO 1993)
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Subgrade
Type
Design
Structural
Number
SN (DES)
d1
d2
d3
d4
Subgrade
Resilient
Modulus
/MPa
(AC)
(AB)
(WS/SC)
(WS)
Clay
148.2
100
250
350
450
31.1
Clay +
30%RHA
145.1
87.5
237.5
350
450
33.4
Clay +
8%Lime
134.2
75
225
350
450
42.6
Clay +
10%NaOH
119.6
50
150
350
450
59.1
Economical Considerations of
Flexible Pavement
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o Lane Width = 12Ft; Stabilized Depth = 12in;
Road Length = 1mile
Subgrade
Cost of
Stabilized
Material/Mile
(GYD)
Cost of Road
Material / Mile
(GYD)
Total Road
Pavement
Cost per
Mile (GYD)
Clay
-
$133M
$133M
Clay + 30%RHA
0
$121.4M
$121.4M
Clay + 8%Lime
$10M
$100M
$110M
Clay +
10%NaOH
$27M
$79M
$106M
Economical Benefits of
Stabilization
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From a financial point of view, Stabilization produces the following
relevant benefits:
1) Increased Long-term performance of pavement structures
2) Saving of significant amounts of non-renewable resources
3) Transforms inexpensive earth materials into effective construction
materials
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Despite positive benefits of stabilization, the engineering properties
derived can vary widely due to heterogeneity in soil composition,
differences in micro and macro structure among soils.
Benefits of Soil Stabilization
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 Stabilization can:
o
increase the strength of a soil
o control the shrink-swell properties of a soil
o Replace mechanical methods of stabilization which can be
more costly.
o improve stress-strain properties, permeability, and durability.
Conclusion
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All three admixture can potentially stabilize Guyana’s coastal clays.
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The Sodium Hydroxide admixture proved to be the most effective
investigated admixture.
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Lime was slightly more effective in
controlling settlement and
improving permeability.
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Rice husk ash was more effective in controlling volume changes and
improving permeability.
Recommendations
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A complete and thorough Environmental and Social Impact
Assessment will be required.
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The following items which are not part of the scope of research are
recommended areas of further study;
1)
Correlation Between Laboratory Strength and In-situ Strength
2)
Impact of Subgrade Stabilization on Life-Cycle Cost of Pavements
3)
Mixing the Proportions of Two Stabilizers