An Experimental Study on Soil Spring Stiffness of Vibrating Bases on Polypropylene Fibre-Reinforced Fine Sand

The scarcity of conventional backfill materials has necessitated exploring marginal soils for use by stabilization. Efforts of researchers have indicated significant improvement in engineering properties of fine sand stabilized with the addition of synthetic fibres. Industrial establishments in coastal areas at sites comprised of fine sand or filled up ground are preferring the use of fibre-reinforced fine sand cushions to support the foundations due to good frictional characteristics and better drainage. As the design of vibrating bases requires the soil spring stiffness, it is essential to study the coefficient of elastic uniform compression (Cu) of fibre-reinforced fine sand for supporting vibrating bases. Hence, in the present study, the effect of polypropylene fibre addition in fine sand is studied through small-scale cyclic load tests. The effect of the addition of polypropylene fibres of 6 mm and 12 mm length at optimum fibre content (1% based on improved shear strength parameters) on Cu is evaluated to quantify the reduction in amplitude of vibration for damping ratios of 0–0.15. At optimum fibre content, the values of Cu of 6 mm and 12 mm fibre-reinforced fine sand decreased by about 40% and 58%, respectively. The study indicated a reduction in amplitude of vibration of about 25% for square and circular vibrating bases in fine sand with the addition of 1% of randomly distributed polypropylene fibre of 12 mm length due to improved elastic response and increased frequency ratio (r) from 1.5 in unreinforced to 2 in reinforced case.