BEHAVIOUR OF FIBRE REINFORCED SAND

Abstract

Fibre reinforced soil termed as "Plysoil" is a composite material obtained by mixing randomly distributed fibres to soil (RDFS). The main advantages of RDFS are simplicity in mixing, maintenance of stress isotropy and absence of potential planes of weakness which may develop parallel to the oriented reinforcement. RDFS can be advantageously utilized as a soil improvement technique with respect to embankment/sub-base and in similar other problems. An experimental study on the behaviour of dry sand reinforced with randomly distributed fibres of polypropylene has been undertaken in the present investigation. The effect of fibre reinforcement has been studied with the change of fibre content (FC) and length of fibre through direct shear test and triaxial tests. Firstly, direct shear test on the specimens of dry sand and fibre reinforced sand (fibre length -= 24 mm, fibre content = 0%, 0.05%, 0.1%, 0.2%, 0.3%) on relative densities 50% and 70% have been carried out at five different normal stresses (50, 100, 150, 200, and 250 IcN/m2). Then triaxial tests have been carried out by varying Length of fibre (24 mm, 30 mm, 36 mm and 48 mm) and Fibre content (0%, 0.05%, 0.1%, 0.2% and 0.3%) with different relative densities (50% and 70%) at Confining stresses of 50 kN/m2, 100 kN/m2, 150 kN/m2 and 200 Ici\l/m2. Further, plate load tests have been conducted to study the pressure settlement behaviour of square footing of size 150 mm X 150 mm resting on randomly distributed fibre reinforced sand (RDFS) in a tank of size 1.0 m X 1.0 m X 0.45 m depth . The tests have been performed on dry sand with 30 mrn length of fibre and with 0.0%, 0.05%, 0.1% and 0.2% fibre content. Analysis of direct shear tests and triaxial tests reveal that the $-value of the RDFS is more than that of the unreinforced sand but increase in the fibre content does not have significant effect on the 4-value. The effect of fibre inclusion at 50% relative density is more than at 70% relative density. From the plate load tests it has been found that the bearing capacity of the RDFS increases with increase in Fibre Content. The percentage increase in the bearing capacity with the increase in the fibre content shows almost a linear trend.