Geo-Sustainable Stabilization of Collapsible Loess soil Deposits

James Mahar, Ph.D., LPG, PG, PHG

Department of Civil & Environmental Engineering

Presentation Outline

I. Introduction

II. Scope of Work

III. Research Soil Characterization

IV. Soil Stabilization Methodology

V. Results

VI. Conclusions and Recommendations

History of Development Lime (CaOH, CaO) Fly Ash (Class C, Class F)

I. Introduction

II. Background

Lime stabilization Fly Ash stabilization Lime-Fly Ash (LFA) stabilization

Reduced Plasticity Higher strength Increased CBR values Lower thickness of pavement

III. Research Soil Characterization

Geologic setting of Eastern Idaho Soil properties based on USDA soil Survey

McDole Series Research Soil

Silt soil Other Soil units in Pocatello

Pocatello Silt loam Delphic Silt

Idaho soil distribution dominated by Silt soilResearch soil is representative of Southeast Idaho soil distribution Best suited soil for LFA stabilization

Research Soil Characterization, Cont’

Location of the site

Courtesy City of Pocatello

Location of the site

Courtesy City of Pocatello

Research Soil Characterization

Soil properties considered

Plasticity Index (PI) Proctor Compaction test Gradation Soil PH Unconfined Compression Test (UCC) California Bearing Ratio (CBR)

TABLE 1 - DATA SUMMARY SOIL CHARACTERIZATION

UNTREATED SOIL - BENCHMARK I

TEST PIT SOIL DEPTH NATU. PLASTICIY INDEX SEIVE STANDARD # # (ft) ω% ANAL. PROCTOR COMP. ωL ωP PI AASHTO USCS (%) max γdry opt ω% (pcf)

1 STP-1 SP-1 1.2 24.5 37 24 12 A-6 CL 77.3 102.5 16.5 SP-2 3.42 17.8 34 26 8 A-4 ML 77.3 102.5 16.5

2 STP-3 B-3/1 1.42 14.3 29 24 5 A-4(2) CL-ML 77.3 102.5 16.5 SP-1 1.42 14.3 32 26 6 A-4 ML 77.3 109.0 12.0 SP-2 2.7 7.1 33 24 9 A-4 CL 77.3 109.0 12.0

3 STP-5 B-5/1 2 13.7 38 27 11 A-4(10) CL 82.3 99.5 19.5 SP-1 1.25 20.3 36 27 9 A-4 ML 82.3 109.5 16.0 SP-2 2.58 13.7 39 27 12 A-6 CL 82.3 109.5 16.0 B-5/3 0.5-1.67 13.7 40 27 13 A-7-6 ML 82.3 99.5 19.5

4 STP-5 B-5/4 0.5-1.67 10.7 40 27 13 A-7-6 ML 82.3 99.5 19.5

TABLE 2 - DATA SUMMARY ENGINEERING PROPERTIES OF THE UNTREATED SOIL

TEST # 1 2 3 4SOIL LOCATION

TEST PIT # STP-5 STP-5 STP-5 STP-5SOIL # B-5/4 B-5/3 B-5/1 SP-1

DEPTH OF SOIL

DEPTH, FT 0.5FT - 1.67FT 0.5FT - 1.67FT 2 FT 1.25 FTMOISTURE CONTENT

NATURAL ω% 11% 11% 11% 11%ATTERBERG LIMIT TEST

LIQUID LIMIT, ωL 40 40 38 36PLASTIC LIMIT, ωP 27 27 27 27

PLASTICITY INDEX, PI 13 13 11 9AASHTO A-7-6 A-7-6 A-4 (10) A-4

USCS ML ML CL MLGRADATION TEST

SIEVE ANALYSIS, % 82.3% 82.3% 82.3% 82.3%SOIL PH

PH AT NATURAL ω% 7.9 7.9 7.9 7.9

PH AT OPTIMUM ω% 8 8 8 8STANDARD PROCTOR COMPACTION TEST

MAX γdry 109.5 PCF 109.5 PCF 109.5 PCF 109.5 PCFOPTIMUM ω, % 19.5% 19.5% 19.5% 19.5%

CALIFORNIA BEARING RATIO TESTCBR, UNSOAKED 4 4 4 4

CBR, SOAKED 3 3 3 3UNCONFINED COMPRESSION TEST

UCC, qu 48 PSI 46 PSI 46 PSI 56 PSICohesion, c 24 PSI 23 PSI 23 PSI 28 PSI

SOIL DESCRITPTIONSOIL DESCRIPTION BROWN BROWN BROWN BROWN

Summary of Properties of Untreated Soil

Very deep and well drained Wind-blown deposits Slope/stream wash on to Flood plain Liquid Limit ranges between 20 to 30% Plasticity Index ranges between 5 to 12% Soil classified as ML/A-7-6 Low plasticity soil

Summary of Properties of Untreated Soil

Low active clay content Fairly low undrained shear strength Alkaline Low strength soil Susceptible to moisture content change Ideal for Lime-Fly ash treatment

IV. Soil Stabilization

Mechanism of stabilization Pozzolanic reation of pozzolans (Al2O3, SiO2) with lime

(CaOH, CaO) in the presence of water Lime and Fly Ash Proportion Lime to Fly Ash ratio – 1:2 and 1:3 Lime-Fly Ash percentage by dry weight LFA – 2%, 3%, 4%, 6%, 8%,10% and 12%

Soil Stabilization Cont’d

Soil properties considered

Plasticity Index (PI) Proctor Compaction test Soil PH Unconfined Compression Test (UCC) California Bearing Ratio (CBR) Subgrade Modulus – R Value

V. Results

Atterberg Limit Test

TABLE 3 - INDEX PROPERTY OF TREATED SOIL

Depth QL+FA"F"(ft) Percentage ωL PI USCS AASHTO

STP-5 0.5-1.7 ft 0% 40 27 ML A-7-6STP-5 0.5-1.7 ft 2% 39 12 CL A-6STP-5 0.5-1.7 ft 4% 37 10 ML A-4STP-5 0.5-1.7 ft 4% 43 14 ML A-7-5STP-5 0.5-1.7 ft 6% 33 6 ML A-4STP-5 0.5-1.7 ft 6% 38 11 ML A-6STP-5 0.5-1.7 ft 6% 35 7 ML A-4STP-5 0.5-1.7 ft 8% 35 4 ML A-4STP-5 0.5-1.7 ft 8% 34 7 ML A-4STP-5 0.5-1.7 ft 8% 42 14 ML A-7-6STP-5 0.5-1.7 ft 10% NP NP - -STP-5 0.5-1.7 ft 12% NP NP - -

Location Atterberg Limit Test Soil Classification

Results Cont’d

Standard Proctor Compaction Test

TABLE 4 - STANDARD PROCTOR COMPACTION

Location

Depth QL+FA"F" Standard Proctor

(ft) PercentageOpt ω%

Max γd (pcf)

STP-5 2 ft 0% 19.5% 99.5STP-5 2 ft 4% 21.4% 97.1STP-5 2 ft 4% 20.2% 98.6

90

91

92

93

94

95

96

97

98

99

100

12 14 16 18 20 22 24 26 28 30

Dry U

nit W

eigh

t, γ d

, pcf

Water Content, ω%

Untreated Soil Treated Soil - QL+FA"F" - 4% with MC after mixing Zero Air-Void Line

Zero Air Void Line100% Saturation

Figure 3 – Standard Proctor Compaction Curve for treated and Untreated Soil

Results Cont’d…

Soil pH Test

TABLE 5 - Soil pH

Soil Type UntreatedLFA Percentage 0% 2% 4% 6% 8% 10% 12%

ω% 19.5% 19.5% 19.5% 19.5% 19.5% 19.5% 19.5%Soil pH 8 11 12 12 11 12 12

Treated- QL+FA"F"

TABLE 6 - CBR VALUES OF TREATED SOIL

Depth QL+FA"F"(ft) Percentage ω% γd (pcf) CBR ω% CBR Swell %

STP-5 0.75 - 1.4 ft 0% 20.5% 118 3 21.6% 2 1.1%STP-5 0.75 - 1.4 ft 2% 18.7% 103 16 21.9% 28 0.6%STP-5 0.75 - 1.4 ft 3% 16.5% 104 25 31.9% 58 0.2%STP-5 0.75 - 1.4 ft 4% 18.3% 100 26 26.7% 56 0.1%STP-5 0.75 - 1.4 ft 6% 17.9% 101 28 21.7% 86 0.3%STP-5 0.75 - 1.4 ft 8% 17.6% 100 30 23.4% 91 0.1%STP-5 0.75 - 1.4 ft 10% 16.6% 107 31 24.5% 96 0.2%STP-5 0.75 - 1.4 ft 12% 16.1% 104 46 24.1% 173 -STP-5 0.75 - 1.4 ft 20% 23.7% 97 17 28.6% 51 1.0%

Location Before soaking After Soaking

1625 26 28 30 31

4628

58 56

86 91 96

173

30

20

40

60

80

100

120

140

160

180

200

0% 1% 2% 3% 4% 5% 6% 7% 8% 9% 10% 11% 12% 13%

CBR

VALU

ES

LFA PERCENTAGE, %

SOAKED CBR

UNSOAKED CBR

Figure 1- CBR versus lime-fly ash percentages for untreated and treated soil

UNTREATED

0 1 2 3 4 5 6 7 8 90

5

10

15

20

25

SUBGRADE CBR

RE

QU

IRE

D T

HIC

KN

ES

S A

BO

VE

S

UB

GR

AD

E,

INC

HE

S

Figure 2- CBR based thickness design chart

0 5 10 15 20 25 30 35 40 45 505

10

15

20

25

SUBGRADE CBR

RE

QU

IRE

D T

HIC

KN

ES

S A

BO

VE

S

UB

GR

AD

E,

INC

HE

S

Figure 3- CBR based thickness design chart for treated and untreated soil

UNTREATED SOIL

TREATED SOIL

TABLE 4 - CBR VALUES VERSUS LIME-FLY ASH PERCENTAGESCBR RESULT CHART

LFA CBR VAULESPERCENT UNSOAKED SOAKED(%)

0% 4 32% 16 283% 25 584% 26 566% 28 868% 30 91

10% 31 9612% 46 173

Correlation between CBR and Subgrade Modulus

TABLE 7 - CORRELATION BETWEEN CBR AND SUBGRADE MODULUS

Depth QL+FA"F" Soaked(ft) Percentage CBR Mr (lb/in2) R

STP-5 0.75 - 1.4 ft 0% 2 3000 3STP-5 0.75 - 1.4 ft 2% 28 42000 74STP-5 0.75 - 1.4 ft 3% 58 87000 155STP-5 0.75 - 1.4 ft 4% 56 84000 149STP-5 0.75 - 1.4 ft 6% 86 129000 230STP-5 0.75 - 1.4 ft 8% 91 136500 244STP-5 0.75 - 1.4 ft 10% 96 144000 257STP-5 0.75 - 1.4 ft 12% 173 259500 465STP-5 0.75 - 1.4 ft 20% 51 76500 136

Location Correlation Values

Correlation between CBR and Subgrade Modulus

050100150200250300350400450500

05

101520253035404550

0% 2% 4% 6% 8% 10% 12%

R Valu

e

UnSo

aked

CBR

LFA QL+FA"F" Percentage, %

LFA versus CBR LFA versus R value

Figure 4 Correlation Curve among LFA percentage, Unsoaked CBR and R-Value

NOTE – Correlation between CBR and R-value was made based on: CBR = 1500 Mr

Mr = 1155 + 555 R(Papaginannakis, 2008)(Pavement Design and Materials)

VI. Conclusions and Recommendations

LFA stabilization increases CBR values significantly Improves soil strength Reduces Plasticity Reduces pavement thickness Improves Subgrade Modulus values

Conclusion and Recommendations cont’

LFA stabilization (CBR > 16) Lime stabilization (CBR > 21) Fly Ash stabilization (CBR > 23) Economic impact Environmental impact Type of soil Purpose of stabilization Availability of materials

Questions ?