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Geo-Sustainable Stabilization of Collapsible Loess soil Deposits

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Presentation on theme: "Geo-Sustainable Stabilization of Collapsible Loess soil Deposits"— Presentation transcript:

1 Geo-Sustainable Stabilization of Collapsible Loess soil Deposits
James Mahar, Ph.D., LPG, PG, PHG Department of Civil & Environmental Engineering

2 Presentation Outline Introduction Scope of Work
Research Soil Characterization Soil Stabilization Methodology Results Conclusions and Recommendations

3 History of Development Lime (CaOH, CaO) Fly Ash (Class C, Class F)
I. Introduction History of Development Lime (CaOH, CaO) Fly Ash (Class C, Class F)

4 Lime stabilization II. Background Fly Ash stabilization
Lime-Fly Ash (LFA) stabilization Reduced Plasticity Higher strength Increased CBR values Lower thickness of pavement

5 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

6 Research Soil Characterization, Cont’
Idaho soil distribution dominated by Silt soil Research soil is representative of Southeast Idaho soil distribution Best suited soil for LFA stabilization

7 Location of the site Courtesy City of Pocatello

8 Location of the site Courtesy City of Pocatello

9 Research Soil Characterization
Soil properties considered Plasticity Index (PI) Proctor Compaction test Gradation Soil PH Unconfined Compression Test (UCC) California Bearing Ratio (CBR)

10 SOIL CHARACTERIZATION UNTREATED SOIL - BENCHMARK I
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 2 STP-3 B-3/1 1.42 14.3 29 5 A-4(2) CL-ML 32 6 109.0 12.0 2.7 7.1 33 9 3 STP-5 B-5/1 13.7 38 27 11 A-4(10) 82.3 99.5 19.5 1.25 20.3 36 109.5 16.0 2.58 39 B-5/3 40 13 A-7-6 4 B-5/4 10.7

11 ENGINEERING PROPERTIES OF THE UNTREATED SOIL
TABLE 2 - DATA SUMMARY ENGINEERING PROPERTIES OF THE UNTREATED SOIL TEST # 1 2 3 4 SOIL LOCATION TEST PIT # STP-5 SOIL # B-5/4 B-5/3 B-5/1 SP-1 DEPTH OF SOIL DEPTH, FT 0.5FT FT 2 FT 1.25 FT MOISTURE CONTENT NATURAL ω% 11% ATTERBERG LIMIT TEST LIQUID LIMIT, ωL 40 38 36 PLASTIC LIMIT, ωP 27 PLASTICITY INDEX, PI 13 11 9 AASHTO A-7-6 A-4 (10) A-4 USCS ML CL GRADATION TEST SIEVE ANALYSIS, % 82.3% SOIL PH PH AT NATURAL ω% 7.9 PH AT OPTIMUM ω% 8 STANDARD PROCTOR COMPACTION TEST MAX γdry 109.5 PCF OPTIMUM ω, % 19.5% CALIFORNIA BEARING RATIO TEST CBR, UNSOAKED CBR, SOAKED UNCONFINED COMPRESSION TEST UCC, qu 48 PSI 46 PSI 56 PSI Cohesion, c 24 PSI 23 PSI 28 PSI SOIL DESCRITPTION SOIL DESCRIPTION BROWN

12 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

13 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

14 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%

15 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

16 V. Results Atterberg Limit Test

17 Results Cont’d Standard Proctor Compaction Test
TABLE 4 - STANDARD PROCTOR COMPACTION Location Depth QL+FA"F" Standard Proctor (ft) Percentage Opt ω% Max γd (pcf) STP-5 2 ft 0% 19.5% 99.5 4% 21.4% 97.1 20.2% 98.6 Figure 3 – Standard Proctor Compaction Curve for treated and Untreated Soil

18 Results Cont’d… Soil pH Test

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22 TABLE 4 - CBR VALUES VERSUS LIME-FLY ASH PERCENTAGES
CBR RESULT CHART LFA CBR VAULES PERCENT UNSOAKED SOAKED (%) 0% 4 3 2% 16 28 3% 25 58 4% 26 56 6% 86 8% 30 91 10% 31 96 12% 46 173

23 Correlation between CBR and Subgrade Modulus

24 Correlation between CBR and Subgrade Modulus
NOTE – Correlation between CBR and R-value was made based on: CBR = 1500 Mr Mr = R (Papaginannakis, 2008) (Pavement Design and Materials) Figure 4 Correlation Curve among LFA percentage, Unsoaked CBR and R-Value

25 VI. Conclusions and Recommendations
LFA stabilization increases CBR values significantly Improves soil strength Reduces Plasticity Reduces pavement thickness Improves Subgrade Modulus values

26 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

27 Questions ?


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