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<p>This study evaluates the performance and design optimisation of flexible pavements reinforced with alkali-treated Pine needle (PNs) geotextiles over weak clayey subgrades in the Himalayan region of India. Subgrade soils in Bidholi, Dehradun, exhibit critically low California Bearing Ratio (CBR) values (unsoaked: 1.25%, soaked: 0.75%) and are classified as CH under IS 1498. Locally sourced materials, including granular sub-base (GSB), water-bound macadam (WBM), and Pine needles, were systematically characterised. Cellulosic fibres extracted from Pinus roxburghii were treated with 5% NaOH to enhance mechanical properties, resulting in a tensile strength of 19–22 kN/m and strain at failure of 150–180%. Laboratory experiments revealed significant CBR improvements due to the inclusion of PNs’ geotextile, up to 128% (unsoaked) and 185% (soaked), with optimal performance at a depth of 1&#xa0;cm and a D/d ratio of 2–3. Direct shear tests validated higher angles of internal friction from 22° to 35° for reinforced soil, and up to 48° along the WBM-soil interface. Pavement design modelling according to Burmister’s theory showed a reduction in WBM thickness by 47.6% for target rutting requirements. The results establish the structural and sustainability advantages of using biodegradable, locally available PNs geotextiles in flexible pavements. The research is useful in sustainable infrastructure development by minimising reliance on manufactured materials and foreign aggregates, which supports global sustainability goals.</p> Graphical Abstract <p></p>

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Geotechnical Performance and Design Optimisation of Flexible Pavements Reinforced with Alkali-Treated Pine Needle Geotextiles Over Weak Subgrades

  • 期刊论文

  • 发表日期：

    2026年3月8日

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  • Vimal Mohan,
  • Abhishek Nandan

摘要

This study evaluates the performance and design optimisation of flexible pavements reinforced with alkali-treated Pine needle (PNs) geotextiles over weak clayey subgrades in the Himalayan region of India. Subgrade soils in Bidholi, Dehradun, exhibit critically low California Bearing Ratio (CBR) values (unsoaked: 1.25%, soaked: 0.75%) and are classified as CH under IS 1498. Locally sourced materials, including granular sub-base (GSB), water-bound macadam (WBM), and Pine needles, were systematically characterised. Cellulosic fibres extracted from Pinus roxburghii were treated with 5% NaOH to enhance mechanical properties, resulting in a tensile strength of 19–22 kN/m and strain at failure of 150–180%. Laboratory experiments revealed significant CBR improvements due to the inclusion of PNs’ geotextile, up to 128% (unsoaked) and 185% (soaked), with optimal performance at a depth of 1 cm and a D/d ratio of 2–3. Direct shear tests validated higher angles of internal friction from 22° to 35° for reinforced soil, and up to 48° along the WBM-soil interface. Pavement design modelling according to Burmister’s theory showed a reduction in WBM thickness by 47.6% for target rutting requirements. The results establish the structural and sustainability advantages of using biodegradable, locally available PNs geotextiles in flexible pavements. The research is useful in sustainable infrastructure development by minimising reliance on manufactured materials and foreign aggregates, which supports global sustainability goals.

Graphical Abstract