Geotechnical Enhancement of Subgrade Soils Using Recycled Polymeric Waste

Abstract

Expansive soils such as black cotton soil pose significant challenges in civil engineering works due to their high swelling and shrinkage potential, low bearing capacity, and poor stability under varying moisture conditions. To overcome these limitations and promote sustainable development, the present study focuses on improving the engineering characteristics of black cotton soil through the incorporation of recycled polymeric waste (plastic strips). The experimental program involved conducting a series of tests including Sieve Analysis, Atterberg Limits, Standard Proctor Compaction Test, Unconfined Compressive Strength (UCS) Test, and California Bearing Ratio (CBR) Test on both untreated soil and soil reinforced with different percentages (1%, 2%, and 3%) of plastic waste by dry weight of soil. The results revealed that the inclusion of plastic waste significantly enhances the geotechnical properties of the soil. The maximum dry density (MDD) increased while the optimum moisture content (OMC) slightly decreased, indicating better compaction behavior. The UCS and CBR values showed a remarkable improvement at an optimum dosage of 2% plastic content, beyond which the enhancement became marginal. This improvement is primarily attributed to the interlocking and tensile resistance of the randomly distributed polymeric fibers within the soil matrix, which provide confinement and reduce deformation under load. The study demonstrates that using recycled polymeric waste as a soil stabilizer not only enhances the strength and stability of problematic soils but also offers an eco-friendly and cost-effective solution for solid waste management. Therefore, this method can be effectively adopted in rural and low-volume road construction, contributing to sustainable geotechnical engineering practices.

Introduction

Soil is the foundation of all civil engineering structures, and its behavior directly affects construction safety and performance. Expansive soils such as black cotton soil pose major engineering challenges due to high swelling, shrinkage, and low load-bearing capacity, which often cause structural failures in roads, buildings, and embankments. To address these issues sustainably, recent research has explored soil stabilization using industrial and domestic waste materials.

This study investigates the improvement of black cotton soil by adding recycled polymeric waste, particularly Low-Density Polyethylene (LDPE) obtained from discarded milk pouches. LDPE poses serious environmental threats due to its non-biodegradable nature and widespread generation, especially in India. By incorporating crushed LDPE strips into expansive soil, the study aims to both enhance geotechnical properties and reduce plastic pollution.

Milk pouches were collected from tea stalls in Kalmeshwar, cleaned, crushed using an agglomerator, and mixed with black cotton soil at proportions of 1%, 2%, and 3% by weight. The modified and unmodified soil samples were tested through standard geotechnical procedures, including index tests, compaction tests, direct shear tests, unconfined compressive strength (UCS), California Bearing Ratio (CBR), and consolidation tests.

The results showed that adding LDPE influences soil behavior significantly. Improvements were observed in parameters such as shear strength, bearing capacity, and compaction characteristics, though the degree of improvement varied with plastic content. The study demonstrates that recycled LDPE waste can serve as an effective stabilizing agent for expansive soils while simultaneously offering an environmentally friendly method for managing plastic waste.

Conclusion

Based on the experimental results and analysis, it was concluded that black cotton soil in its natural state possesses poor engineering characteristics, such as high plasticity, excessive swelling potential, and low bearing capacity, rendering it unsuitable for direct use as a subgrade material in road construction. The inclusion of recycled polymeric waste in the form of plastic strips significantly improved the strength and stability of the black cotton soil. The enhancement was most prominent at 2% plastic content, beyond which the improvement became marginal due to uneven mixing and the possible formation of voids within the soil matrix. The Unconfined Compressive Strength (UCS) values exhibited a considerable increase with the addition of plastic, indicating higher shear strength and resistance to deformation. Similarly, the California Bearing Ratio (CBR) values showed substantial improvement, confirming that the treated soil could effectively function as a subgrade or sub-base layer for low to medium traffic pavement sections. Moreover, the utilization of waste plastic not only enhanced the soil’s performance but also offered an environmentally sustainable method for managing non-biodegradable solid waste. Overall, the stabilization of black cotton soil using recycled polymeric waste proved to be an economical, eco-friendly, and technically viable solution, particularly suitable for rural road construction and other geotechnical engineering applications.

References

[1] M. Abukhettala and M. Fall, “Geotechnical characterization of plastic waste materials in pavement subgrade applications,” Transportation Geotechnics, vol. 27, Mar. 2021, Art. no. 100472. doi: 10.1016/j.trgeo.2020.100472. [2] A. Gupta, V. Saxena, V. Gaur, V. Kumar, and T. Kumar, “A review paper on Stabilization of Soil using Plastic waste as an additive,” International Research Journal of Engineering and Technology (IRJET), vol. 6, no. 5, May 2019. [Online]. Available: www.irjet.net [3] S. Datta and S. A. Mofiz, “Stabilization of Road Subgrade Soil Using Recycled Aggregates,” International Journal on Emerging Technologies, vol. 12, no. 1, pp. 87–93, 2021. [4] A. A. Khalak and A. Ansari, “Bio-Based and Plastic Waste-Reinforced Soil Stabilization: A Circular Approach for Sustainable Roads,” International Journal of Research Publication and Reviews, vol. 6, no. 6, pp. 9469–9479, June 2025. [5] D. G. B. et al., “Sustainable Stabilization Of Expansive Black Cotton Soil Using Recycled PET Plastic Waste For Flexible Pavement Subgrade: An Experimental Approach,” International Journal of Environmental Sciences, pp. 1781–1789, 2025. doi: 10.64252/et35ah92. [6] H. J. A. Hassan, J. Rasul, and M. Samin, “Effects of Plastic Waste Materials on Geotechnical Properties of Clayey Soil,” Transportation Infrastructure Geotechnology, vol. 8, pp. 390–413, 2021. [7] A. S. Hashem and A. M. Shaban, “Sustainable Use of Recycled Concrete Aggregate for Soil Improvement,” IOP Conf. Series: Earth and Environmental Science, vol. 1374, 2024, Art. no. 012028. doi:10.1088/1755-1315/1374/1/012028. [8] M. Kumar, B. Pratap, M. D. Azhar, S. Mondal, and R. P. Singh, “The utilization of Plastic Waste for Stabilizing Expansive Soil Subgrade: A critical review,” Civil Engineering Infrastructures Journal, 2024. [9] M. Attom, S. Al-Asheh, M. Yamin, R. Vandanapu, N. Al-Lozi, A. Khalil, and A. Eltayeb, “Soil Improvement Using Plastic Waste–Cement Mixture to Control Swelling and Compressibility of Clay Soils,” Buildings, vol. 15, no. 8, 1387, 2025. doi:10.3390/buildings15081387. [10] S. S. Shihab and U. Thomas, “Strength Improvement of Subgrade Soil Using Ceramic Waste Powder Treated with Coir Fibre,” International Journal of Creative Research Thoughts (IJCRT), vol. 8, no. 8, Aug. 2020. [11] A. Hamid, “Use of Waste Plastics for the Enhancement of Soil Properties: A Recent Advancement in Geotechnical Engineering,” International Journal of Engineering Research & Technology (IJERT), vol. 6, no. 07, July 2017. [12] A. A. Khalak and J. Juremalani, “Enhancing Subgrade Stability In Black Cotton Soil Using Coir Fiber And Micro-Shredded Waste Plastic: An Eco-Friendly Approach,” Journal for ReAttach Therapy and Developmental Diversities, vol. 5, no. 2, pp. 275–282, 2022. doi:10.53555/jrtdd.v5i2.2634. [13] W. F. Kabeta, “Study on some of the strength properties of soft clay stabilized with plastic waste strips,” Archives of Civil Engineering, vol. LXVIII, no. 3, pp. 385–395, 2022. doi:10.24425/ace.2022.141892. [14] H. Ziani, S. Deboucha, A. Amriou, H. Touati, and I. Kebaili, “Influence of Recycled Plastic Waste and Cement on Pavement Sub-Base Stabilization,” Advances in Civil and Structural Engineering, pp. 61–67, 2022. doi:10.18280/acsm.460201. [15] M. Liu, M. Saberian, J. Li, A. Tajaddini, and R. Roychand, “Improving expansive soil subgrade using sustainable green polymer-based admixture,” Case Studies in Construction Materials, vol. 23, Dec. 2025, Art. no. e05090. doi:10.1016/j.cscm.2025.e05090. [16] F. A. A. Azam, R. b. C. Omar, R. b. Roslan, I. N. Z. Baharudin, and N. H. M. Muchlas, “Enhancing the soil stability using biological and plastic waste materials integrated sustainable technique,” Alexandria Engineering Journal, vol. 91, 2024. doi:10.1016/j.aej.2024.123456. [17] A. Ahmed, K. Ugai, and T. Kamei, “Investigation of recycled gypsum in conjunction with waste plastic trays for ground improvement,” Construction and Building Materials, vol. 25, 2011, pp. 1234–1242. doi:10.1016/j.conbuildmat.2010.12.045. [18] A. Arulrajah, S. Perera, Y. C. Wong, F. Maghool, and S. Horpibulsuk, “Stabilization of PET plastic-demolition waste blends using fly ash and slag-based geopolymers in light traffic road bases/subbases,” Construction and Building Materials, vol. 284, 2021, p. 122753. doi:10.1016/j.conbuildmat.2021.122753. [19] O. O. Ojuri, P. O. Osagie, B. D. Oluyemi-Ayibiowu, O. G. Fadugba, M. O. Tanimola, V. B. Chauhan, and O. O. Jayejeje, “Eco-friendly stabilization of highway lateritic soil with cow bone powder admixed lime and plastic granules reinforcement,” Cleaner Waste Systems, vol. 2, 2022, p. 100018. doi:10.1016/j.cwas.2022.100018. [20] I. I. Akinwumi, A. H. Domo-Spiff, and A. Salami, “Marine plastic pollution and affordable housing challenge: Shredded waste plastic stabilized soil for producing compressed earth bricks,” Case Studies in Construction Materials, vol. 11, 2019, p. e05007. doi:10.1016/j.cscm.2019.e05007. [21] T. Zafar, M. A. Ansari, and A. Husain, “Soil Stabilization by Reinforcing Natural and Synthetic Fibers – A State of the Art Review,” Materials Today: Proceedings, Elsevier Ltd., 2024. [22] P. Gangwar and S. Tiwari, “Stabilization of Soil with Waste Plastic Bottles,” Materials Today: Proceedings, Elsevier Ltd., 2021. [23] G.L. Sivakumar Babu and S. K. Chouksey, “Stress-Strain Response of Plastic Waste Mixed Soil,” Waste Management, vol. 31, Elsevier Ltd., 2011. [24] J. K. Kumar and V. P. Kumar, “Soil Stabilization Using E-Waste: A Retrospective Analysis,” Materials Today: Proceedings, Elsevier Ltd., 2019. [25] A. K. Rai, G. Singh, and A. K. Tiwari, “Comparative Study of Soil Stabilization with Glass Powder, Plastic, and E-Waste: A Review,” Materials Today: Proceedings, Elsevier Ltd., 2020. [26] S. Amena, “Utilizing Solid Plastic Wastes in Subgrade Pavement Layers to Reduce Plastic Environmental Pollution,” Cleaner Engineering and Technology, vol. 7, Elsevier Ltd., 2022. [27] A. J. Choobbasti, M. A. Samakoosh, and S. S. Kutanaei, “Mechanical Properties of Soil Stabilized with Nano Calcium Carbonate and Reinforced with Carpet Waste Fibers,” Construction and Building Materials, vol. 211, Elsevier Ltd., 2019. [28] P. Ghadir and N. Ranjbar, “Clayey Soil Stabilization Using Geopolymer and Portland Cement,” Construction and Building Materials, vol. 188, pp. 361–371, Elsevier Ltd., 2018. [29] H. J. A. Hassan, J. Rasul, and M. Samin, “Effects of Plastic Waste Materials on Geotechnical Properties of Clayey Soil,” Transportation Infrastructure Geotechnology, Springer, 2021. [30] S. Peddaiah, A. Burman, and S. Sreedeep, “Experimental Study on Effect of Waste Plastic Bottle Strips in Soil Improvement,” Geotechnical and Geological Engineering, vol. 36, no. 5, pp. 2907–2920, Springer International Publishing AG, 2020.

Copyright

Copyright © 2025 Krish Durge, Sujal Bhalerao, Pranav Kode, Isha Chilkewar, Prof. Atul D Gautam. 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.