Improvement in Soil Subgrade Using Natural Fibre (Kenaf and Coir Fibre)

India has one of the largest road networks in the world. Around 20% land area of India is covered with soils having low California bearing ratio (CBR) and shear strength values. Pavements laid over such type of soil lead to continuous deformation as a result of which cracks are developed. It increases the maintenance cost and disrupts traffic services. From past decades, various researchers have tried to overcome such type of problems either by using traditional techniques like lime, cement, mechanical stabilization or by using modern techniques like geosynthetics or natural fibres, etc. The present paper deals with the use of natural fibres (kenaf and coir) as a reinforcing material to assess the improvement in strength characteristics of unreinforced soil. The soaked CBR and maximum dry density (MDD) of virgin soil were 2.11% and 1.823 gm/cc, respectively. Kenaf and coir fibre were cut in length of 15 mm and randomly mixed with the unreinforced soil in different percentages (i.e., 0.25, 0.50, 0.75, 1.0, 1.25 and 1.5%) by weight of dry soil. The results obtained indicate that MDD value decreases with increase in fibre content with maximum value of 2.01 g/cc at 0.25% fibre content. The soaked CBR value increases up to 1% fibre content and then decreases. Increase in CBR value indicates that the bearing capacity of mixture (soil + fibre) increased due to the three-dimensional bonding between them. It can be concluded that natural fibres like coir and kenaf can be effectively used as soil reinforcement material.