Experimental Study on the Influence of Polypropylene Fibres on the Strength and Swelling Behaviour of Lime Stabilized Clayey Soil

Abstract

Black cotton soil is a prevalent soil type in India, known for its significant swelling and shrinking behavior when exposed to changes in moisture content, making it particularly challenging for engineering purposes. This soil is highly clayey, predominantly composed of the Montmorillonite clay mineral. Given its unstable properties, this soil is not ideal for construction at the site. As a solution, the engineer may consider replacing or stabilizing the soil to ensure the stability and integrity of the structure. Soil stabilization is employed to enhance the geotechnical properties of black cotton soil, making it suitable for various engineering applications such as embankment protection, road construction, minor-loaded structures, parking lots, factories etc. In this study the Black cotton soil is treated with lime and reinforced with polypropylene to increase the strength and decrease the expensive behaviour. This thesis examines various soil properties like optimum moisture content (OMC), dry density, UCS , swelling pressure and shear parameters. Different quantities of lime (3%, 6%, and 9% by weight) are used to significantly decrease the expensive behaviour and plasticity of black cotton soils and polypropylene fibers (0.25%, 0.5%, and 0.75%) were mixed with black cotton soil to enhance its load-bearing capacity and reduce settlement, making it more suitable for construction. A series of experiments were conducted on these mixtures to evaluate their effectiveness in improving the soil\'s geotechnical properties. The tests conducted include liquid limit, plastic limit, optimum moisture content (OMC), maximum dry density (MDD), bulk density, dry density, and grain size analysis. The goal of this study is to improve the engineering properties of black cotton soil, ensuring that structures built on it can effectively withstand applied loads. The test results revealed that the Liquid limit, Plasticity index, differential free soil index and swelling pressure significantly on addition of lime and on further addition of polypropylene fibers resulted in increased strength of BC soil.

Introduction

1. Background & Problem Statement

• Soil improvement is crucial due to the challenges posed by expansive soils, especially Black Cotton Soil (BCS) found widely in Indian states like Madhya Pradesh, Maharashtra, Karnataka, etc.

• BCS has problematic properties:

  • High compressibility

  • Swelling and shrinkage with moisture variation

  • Low bearing capacity

  • Low shear strength

2. Challenges with Black Cotton Soil

• Structures built on BCS face issues like:

  • Cracks during wet seasons due to swelling

  • Settlement in dry seasons due to shrinkage

  • Structural instability without proper treatment

3. Literature Review Highlights

• Polypropylene fibers (PP fibers) are gaining popularity for soil stabilization due to their:

  • Durability

  • Water resistance

  • Cost-effectiveness

• Prior studies have explored:

  • PP fiber with lime, silica fume, cement, and nanosilica

  • Improved unconfined compressive strength (UCS) and California Bearing Ratio (CBR)

  • Reduced swelling pressure and liquid limits

4. Objectives of the Present Study

The experimental study aimed to:

1. Evaluate plasticity (LL, PL, PI) changes with lime and PP fibers.

2. Study swelling behavior of treated BCS.

3. Perform UCS tests on treated soils.

4. Analyze and compare results across different compositions.

5. Materials Used

• Black Cotton Soil from Jabalpur (M.P.), oven-dried and sieved.

• Polypropylene fibers cut from waste plastic files (12 mm).

• Quicklime, crushed into powder.

6. Tests Conducted (IS Codes Followed)

1. Atterberg Limits – LL, PL, PI

2. Proctor Test – OMC & MDD

3. Free Swell Index

4. UCS Test

5. Swelling Pressure Test

7. Results Summary

• Key findings based on 13 combinations of lime and PP fiber proportions:

• Improvements Observed:

  • UCS increased by over 50% with lime + PP fiber.

  • Swelling pressure dropped significantly from 67.21 kPa to 9.1 kPa.

  • Plasticity Index reduced from 26 to 3, indicating better stability.

  • MDD increased, and OMC decreased, indicating denser and more stable soil.

8. Key Takeaways

• Adding lime improves strength and reduces swelling, while polypropylene fibers enhance durability and reduce plasticity.

• Optimal performance was seen at 9% lime + 0.75% PP fibers.

• The method is cost-effective, uses recycled materials, and significantly improves soil for construction purposes.

Conclusion

The experimental study clearly demonstrates that the addition of lime and polypropylene fibers significantly improves the mechanical and swelling behaviour of clayey soil. The incorporation of lime (3%, 6%, 9%) reduces the plasticity index and swelling pressure of the clayey soil, while increasing the plastic limit and lowering engineering properties such as the liquid limit. The addition of polypropylene fibers (0.25%, 0.5%, and 0.25%) to lime-treated clayey soil enhances its strength. The optimal combination of 6% lime and 0.5% polypropylene fiber results in a reduction of swelling pressure and an increase in soil strength. These proportions were found to improve soil strength, reduce swelling, and enhance stability under varying moisture conditions. Overall, it can be concluded that lime treated fiber-reinforced soil is an effective ground improvement technique, particularly in engineering projects involving weak soils, as it enhances strength and reduces swelling behavior.

References

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Copyright

Copyright © 2025 Neeti Dwivedi, RK Yadav. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.