Mitigation of Expansive Soils Damages

Transcription

1 Mitigation of Expansive Soils Damages Joseph Muhirwa Richard Benda Robert Sargent REU Program University of Texas at Arlington

2 This presentation will focus on four main sections Introduction and Background Experimental Program Results and Conclusion Additional Work

3 Introduction and Background Experimental Program Results and Conclusion Additional Work

4 Clay is the most common particle that makes soils expansive because of its ability to retain large amounts of water. Very fine particles (less than 2 microns) Large surface area (plates with negative charge)

5 How expansive clay is depends on the minerals in the clay Illite Kaolinite Montmorillonite Montmorillonite is the most expansive mineral. One pound of it can have a surface area of 800 acres.

6 Expansive soil behaves like a sponge. It expands when it soaks up water and then shrinks back down when it loses water Water being attracted to the negatively charged clay plates

7 The damage to infrastructure by expansive soils costs close to 9 billion dollars per year Slope failure Pavement uplift and cracking structural damage

8 Austin, Texas is located in an area of highly expansive soil Austin USGS (1989)

9 The main objective of our research was to understand the concepts behind soil stabilization and determine the best percentage of lime to stabilize our soil UCS

10 Introduction and Background Experimental Program Results and Conclusion Additional Work

11 1. Atterberg Limits Test

12 The Swelling Potential of Expansive soils Can be determined indirectly from Atterberg Limits PI=LL-PL Plastic index (PI) Liquid Limit(LL) (ASTM 4318) Plastic Limit (PL)

13 2. Determination of Sulfate Content

14 Ettringite formation, Heave-inducing crystal, can be avoided by checking the sulfate content of Soil before lime stabilization Day 1: Sample Preparation Day 4: Final Weight of Soluble Sulfate Day 2: Filtration and Precipitation Day: Precipitate Filtration Modified UTA method (2000)

15 On the first day, Pulverization and Dilution of the soil are performed 1:10 Dilution Modified UTA method (2000)

16 On the second day, Stirring, centrifigution and Filtration of the soil solution are the major tasks Modified UTA method (2000)

17 On the Third day, The filtration of the precipitate solution is performed Start/End Modified UTA method (2000)

18 On the Fourth Day, The final Weight of the dry precipitate is determined. Removal Of Weighing Tin and precipitate from the oven Modified UTA method (2000)

19 3. Additive Selection/ Mix Design

20 Samples with different % of lime are tested to determine the most effective amount of lime Common % of Lime: 3%-8% OMC of control soil is the starting point Required mellowing time: at least 24 hrs Nelson and Miller (1992)

21 4. One-Dimensional Swell Test

22 A Direct Indication of Swell Potential can be obtained through 1-D Swell Test (ASTM 4546)

23 5. Unconfined Compressive Strength Test

24 The UCS Test helps to estimate the strength of Treated and Non-Treated Soils Extrusion Unconfined Compression

25 Introduction and Background Experimental Program Results and Conclusion Additional Work

26 1.Results and Discussion

27 53.50 Moisture content vs. Number of blows Austin s soil was found to be a highplasticity clay Moisture content (%) Number of blows Soil Property Results Liquid Limit (LL) 51.04% Plastic Limit (PL) 19.76% Plasticity Index (PI=LL-PL) 30.84% USCS Classification CH

28 The Sulfate content was within the Acceptable range Sample 1 Sample 2 Sample 3 *W 1 (grams) *W 2 (grams) Sulfate content (ppm) Avg. Sulfate content (ppm) W 1 = Mass of weighing tin and filter paper W 2 = Mass of weighing tin, filter paper, and precipitate 261 Acceptable Range = 1000 to 2000 ppm 1 1 Puppala et al. (1999) and Viyanat (2000)

29 In the time-displacement curve, 6% was observed to have reduced swell the most displacement (in) Time vs. Displacement Time (hr) 0 percent 2 percent 4 percent 6 percent All of the specimens with lime performed better than the control sample

30 In general, all lime treated samples had a higher shear strength than the control The 6% lime sample had the overall highest strength Stress, σ (lb/ft2) Stress vs. Axial Strain q u =8061 lb/ft 2 q u = 7368 lb/ft 2 q u =4952 lb/ft 2 Austin's soil with 0% lime Austin's soil with 2% lime Austin's soil with 4% lime Austin's soil with 6% Lime q u =3433 lb/ft Axial Strain, ԑ (%) Stiffer and softer specimens

31 2. Conclusions

32 Performance benefits from lime stabilization reduce maintenance costs

33 6% lime and 4% lime were found to be suitable to reduce swelling and increase bearing capacity 4% lime could be used in situations requiring reduced cost 6% lime could be used in situations requiring additional strength

34 For future research, additional additives could be tried in combination with lime (such as cement) + =

35 Introduction and Background Experimental Program Results and Conclusion Additional Work

36 1.Field Stabilization

37 Reduction of Slope and Embankment Failure at Grape Vine and Joe Pool Lakes Slope Testing Area Monitoring of Horizontal Movement by Inclinometer Monitoring of vertical Movement by surveying

38 2. Three-Dimensional Swell Test

39 The 3-D Swell Test can be Conducted Using Double Inundation

40 Lime Stabilization reduces the swelling potential considerably

41 3. Hydrometer Test

42 The size Distribution of Silt and Clay can be Obtained through Hydrometer Test

43 References Anand J. Puppala et al. (1999). Evaluation of a Sulfate Induced Heave by Mineralogical and Swell Tests. XI Pan-American Conference on Soil Mechanics and Geotechnical Engineering, Foz do Igacu, Brazil. Anand J. Puppala et al. (2002). Evaluation of a Modified Soluble Sulfate Determination Method for Fine-Grained Cohesive Soils. ASTM International, West Conshohocken, PA. ASTM. (n.d.). Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils, ASTM D4318, West Conshohocken, PA. ASTM. (n.d.). Standard Test Methods for One-Dimensional Swell or Settlement Potential of Cohesive Soils, ASTM D , West Conshohocken, PA. Miller, D. J., Nelson, J. D. (1992). Expansive Soils: Problems and Practice in Foundation and Pavement Engineering, John Wiley & Sons, Inc., Toronto, Canada. Viyanant, C., (2000). Laboratory Evaluation of Sulfate Heaving Mechanisms Using Artificial Kaolinite Soil. Masters thesis, The University of Texas at Arlington, TX.

44 Acknowledgements We are very grateful to all the people who made this research possible, especially Dr. Anand Puppala, Dr. Nur Yazdani, Dr. Yvette Weatherton, Dr. Stephanie Daza,Mr. Aravind Pedarla, Mr. Justin Thomey, Mr. Minh Lee and Mr. Naga Talluritinnu.

45 Questions???????