The permeability of natural fibre drains, capturing their micro-features

Natural fibres such as jute and coir are emerging as distinct alternatives to synthetic geomaterials, and in recent years they have been used increasingly for drainage and filtration in field applications. However, these naturally occurring materials are extremely variable in micro-characteristics such as the size, uniformity and shape of their fibres, while there is a lack of studies addressing how these differences can affect the hydraulic behaviour of fibrous media. This paper offers a laboratory study of the influence of micro-features on the hydraulic conductivity of fibre drain. Non-twisted and twisted fibre drains made from jute and coir were subjected to hydraulic conductivity testing and micro-analyses. Experimental results show a considerable contribution of the size characteristics of fibre to the hydraulic behaviour of the drain. A less-rounded shape of fibre and a larger twisting angle of the drain can increase the fluid-fibre contact area and the corresponding tortuosity of flow, which significantly reduces the drain permeability. The way in which the Kozeny-Carmen analytical approach can be adopted to predict the permeability of a fibre drain is discussed based on the experimental results, considering various micro-factors including the size of fibre, uniformity and the associated porosity.