SHEAR CHARACTERISTICS OF RANDOMLY DISTRIBUTED FIBRE REINFORCED SOIL UNDER CYCLIC LOADING

Abstract

Fibre reinforced soil termed as "Plysoil" is a composite material obtained by mixing randomly distributed discrete fibres to soil (RDFS). The main advantages of RDFS are the 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 utilised as a soil improvement technique with respect to embankment, subgrade/sub-base and in similar other problems. Most of the experimental investigations reported in the literature have been carried out on soils reinforced with discrete fibres under monotonic static loading. A very limited effort has been made to study the behaviour of fibre reinforced soil under cyclic loading. The present study is aimed to bring out the influence of fibre parameters and confining pressure on the strength of RDFS under cyclic loading. An exhaustive and well planned cyclic triaxial test programme has been carried out to study the behaviour of RDFS. A computer controlled "GDS Triaxial Testing System" was used. The effect of fibre content has been studied by varying it between 0.5 % to 3% (by weight of soil). The confining pressure used in the present investigation are 100, 200, 300 and 400 kPa.The aspect ratio (ratio of length to diameter of fibre) has been varied between 50 to 125. Analysis of the cyclic triaxial tests data reveals that the peak axial strain in compression increases slightly with increase in number of cycles. At the end of 40 cycles the peak axial strain of RDFS decreases with increase in fibre content but has practically no influence of fibre aspect ratio. Bulging failure mode was observed for RDFS under cyclic loading. Shear strength in terms of stress ratio of RDFS increases with increase in fibre content and aspect ratio.Shear strength decreases with increase in cell pressure. The findings of the present study are .'useful in understanding the behaviour of RDFS under cyclic loading. They have practical significance as a ground improvement technique with respect to subgrade/sub-base in the road pavement and other such problems.