MINISTRY OF PUBLIC WORKS

WORKS SERVICES GROUP5TH ENGINEERING CONFERENCE

“Defending Guyana’s Development with Engineering Solutions”

Project Title: Chemical Stabilization of ClayDesign Department

Presenter: Stephan CheongDate: February 5,2015

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

Outline of Presentation

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.

Introduction to Soil Stabilization

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

Chemical Admixtures

Road Pavements

Foundations

Application of Soil Stabilization

Environmental Parameter

Sodium Hydroxide

Rice Husk Lime

PHYSICAL

Air: Dust Control measures when transported

Not Required Required Required

Water Quality Sodium toxicity results from high concentration of Sodium in water but decreases acidity of water due to low pH

Water quality is not affected

Ionizes to Calcium cations in water which is beneficial for human and fish health

Social

Health and Safety

Severely Hazardous Substance

Harmless Substance

Harmless Substance

Environmental Impacts

Their vulnerability to slow volume changes that can occur

independent of loading due to swelling or shrinkage.

The degree of weathering they have undergone

which leads to the destruction of interparticle bond.

Reductions in strength and elastic modulus with a general

increase in plasticity.

Engineering Properties of Clays

Standard Tests 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 Engineering Tests

Standard Tests Key Engineering Properties

Modified Proctor {ASTM D1557 -

00}

Compaction

California Bearing Ratio {ASTM D1883 -99}

Subgrade Strength

Settlement Potential of Cohesive Soils {ASTM D4546 -03}

Soil Permeability and Percent Settlement

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.

Project Limits

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

2.45235.75 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

California

Bearing Ratio

Subgrade Strength *Based on AASHTO

Pavement Thickness

Design Guide

Untreated Clay Soil

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

Results and Analysis

Soil Type Settlement Potential of Cohesive Soils {Remolded Samples}

Hydraulic Conductivity, kz (m/yr)

Untreated Clay Soil0.05755

Soil + 30% RHA0.80495

Soil + 8% Lime0.72524

Soil + 10% NaOH0.0938

Seating Pressure

σvo

(KPa)

Untreated Clay Soil

Soil + 8% Lime

Soil + 30% RHA

Soil + 10%

NaOH

- Percent Settlement /% of Remolded Samples

384 -13.0 -6.1 -8.2 -7.4- Percent Rebound Settlement /% of Remolded

Samples

24 -8.2 -4.3 -5.5 -4.7

Results and Analysis

Discussion

Increased CompactionStabilized Soil

% Variation from Clay

10% NaOH 5%

8%Lime -3%

30% RHA -17%

Increased Density

Stabilized Soil

% Variation from Clay

10% NaOH 10%

8%Lime -7%

30% RHA -9%

Discussion

Increased Load Bearing Capacity (Subgrade Strength)

Increased Hydraulic Conductivity

Stabilized Soil

% Variation from Clay

10% NaOH 60%

8%Lime 1160%

30% RHA 1300%

Stabilized Soil

% Variation from Clay

10% NaOH 90%

8%Lime 37%

30% RHA 7%

Stabilized Soil

% Variation from Clay (S)

% Variation from Clay (R.S)

10% NaOH 43% 43%

8%Lime 53% 48%

30% RHA 37% 33%

Discussion

Reduction in Settlement and Rebound Settlement

Flexible Pavement Design (AASHTO 1993)

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

Subgrade Type

Design Structural NumberSN (DES)

d1

(AC)

d2

(AB)

d3

(WS/SC)

d4

(WS)

SubgradeResilient Modulus/MPa

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

Structural Number and Layer Thickness (AASHTO 1993)

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 Considerations of Flexible Pavement

o Lane Width = 12Ft; Stabilized Depth = 12in; Road Length = 1mile

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

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.

Economical Benefits of Stabilization

Benefits of Soil Stabilization

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.

All three admixture can potentially stabilize Guyana’s coastal clays.

The Sodium Hydroxide admixture proved to be the most effective

investigated admixture.

Lime was slightly more effective in controlling settlement and

improving permeability.

Rice husk ash was more effective in controlling volume changes and

improving permeability.

Conclusion

A complete and thorough Environmental and Social Impact

Assessment will be required.

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

Recommendations

Thank You!For Your Attention

Questions???