A STUDY ON PERMEABILITY OF SOILS REINFORCED WITH RANDOMLY DISTRIBUTED FIBRES

Abstract

Fibre reinforced soil known as "pe~yo.& " is a composite material obtained by mixing randomly distributed discrete fibres to soil. The technique of fibre reinforcement is in much way similar to soil stabilization by cement, lime and other additives. The main advantages of RDFS are the simplicity in mixing, maintenance of strength isotropy and absence of potential planes of weakness which may develop parallel to the oriented reinforcement. RDFS having got numerous advantages, it has been considered as an alternative to granular material in stone/granular piles. Various studies have been reported on load-deformation behaviour of clay treated with sand-fibre columns. However, only a few studies have been reported on the compressibility characteristics of clay treated with sand-fibre columns. The present study is aimed to study the compressibility characteristics of clay treated with sand-fibre columns. A well planned consolidation test programme, to study the influence of various parameters viz., relative core area (defined as the ratio of area of sand-fibre column to the area of clay sample) and fibre characteristics (fibre type and fibre content), have been carried out on locally available clay treated with sand-fibre columns. The relative core areas have been varied from 0.00 to 0.44. Two types, namely synthetic (polypropylene) and natural (coir), of fibre have been used to study the influence -- of type of fibre. The effect of fibre content has been studied with 1 % and 2 % fibre contents. An exhaustive and well planned permeability test programme has been carried out to study the permeability characteristics of RDFS. The influence of various parameters viz., soil type, dry density and fibre characteristics (fibre type, fibre content and aspect ratio) has been investigated. Two types of soils namely sand and silt have been used to study the permeability of fibre reinforced soil. The effect of dry density iii has been investigated through three different densities (1.00 '"dmax' 0.95 7dmax & 0.90 a'dmax). The effect of type of fibre has been brought out by considering two types of fibres namely synthetic (polypropylene) and natural (coir). Also, the effect of fibre content has been investigated by varying it from 0.5 to 4%. Analysis of consolidation test results indicates that there is decrease in the compressibility of clay with the introduction of sand-fibre columns and further, compressibility of composite clay decreases with increase in relative core area. A significant decrease in the volume compressibility coefficient as well as compression index of composite clay has also been observed. Whereas consolidation of clay expedites with the introduction of sand-fibre column. The permeability tests indicate that randomly distributed fibre reinforced sand is isotropic as far as coefficient of permeability is concerned. The results of permeability tests ; indicate that the permeability of soil decreases initially with the addition of synthetic fibres and later increases with the further addition of synthetic fibres. This trend is identical to synthetic and natural fibers tested. Further the aspect ratio of fibre has practically no influence on the permeability of 'RDFS .