Evaluation of strength and stiffness response of coir-fibre-reinforced soil

Coir, a natural biodegradable material, is abundantly available in most parts of south-west India, Sri Lanka, and other Asian countries, and is cheap. The use of coir in geotechnical construction started in the early 1990s, and it is found in many applications, such as drainage and filtration, erosion control, and the improvement of surficial stability of embankments in the form of sheets and mats in some of these areas. A few attempts are also made to use coir as random reinforcing material, in which some percentage of fibre is added to obtain an improvement in performance, and laboratory tests indicate that the strength increases considerably with the inclusion of coir fibres. However, there is a lack of a proper methodology for quantifying the strength and stiffness of soil due to the inclusion of fibres. This paper discusses a few experimental results, different methods for evaluating the strength of fibre-reinforced soil, and the application of these methods to predict the strength response of coir-fibre-reinforced soil. The paper suggests a simple analytical approach to predict the stiffness modulus of fibre-reinforced soil.