Water Content Effect on Shear Strength Parameters in Coir Fiber Reinforced Pilani Soil: Recent Observations

Recently, much work has been done on strength deformation behaviour of fiber reinforced soil and it
has been established beyond doubt that addition of fiber in soil improves the overall engineering
performance of soil. Fiber reinforced soil is effective in all types of soils (i.e. sand, silt and clay). Use
of natural fibers in civil engineering construction practice is often advantageous as they are cheap,
locally available, biodegradable, and ecofriendly. Among the available natural fibers (jute, coir,
bamboo, etc.), coir is produced in large quantities in South Asian countries, such as India, Ceylon,
Indonesia, Philippines, etc. and has better mechanical properties, such as tensile strength. In this
paper, results on the cohesion and angle of internal friction behavior (obtained from direct shear
testing) of local soil reinforced with coir fibers are presented at varied water contents. Soil sample
reinforced with randomly distributed coir fibers of 2.5 cm length and 2.85 mm to 0.64 mm average
diameter range (measured using screw gauge) were made for direct shear testing at 0.5% fiber
content. Testing was done at four different water contents. The results show that cohesion increased
and angle of internal friction decreased with increase in water content. Unreinforced in-situ local soil
has negligible cohesion and angle of internal friction around 280 under similar direct shear testing
conditions. Practical significance of the study has also been discussed.