Stress-Strain Characteristics of Polypropylene Fibre Reinforced Soil Tara Leander M Tech. Student: Dept. of Civil Engineering Marian Engineering College Trivandrum, India Neeraja V.S. Asst. Professor: Dept. of Civil Engineering Marian Engineering College Trivandrum, India Abstract - The study provides an approach for the use of polypropylene fibre as reinforcement material in clayey soil, which can be used for ground improvement. Fibre is being added to the soil in four different percentages of fibre content, i.e. 0.25, 0.50, 0.75 and 1.0% by weight of raw soil. The change in properties like optimum moisture content, maximum dry density and unconfined compressive strength has been recorded. Through the results obtained, it was observed that on addition of polypropylene fibre the optimum moisture content of soil increased while maximum dry density decreased and UCC strength increased. A series of triaxial tests at different confining pressures were performed to determine stress-strain response of the soil. The results show a significant improvement in the failure deviator stress on the addition of fibre. Keywords— Fibre reinforcement; cohesive soil; polypropylene fibre; stress strain behaviour; triaxial test I. INTRODUCTION With urbanization and modernisation at its peak, less amount of land is available for construction. Owing to this, structures these days are being designed on land having weak or soft soil. Stability of any structure depends on the properties of soil. Most of the soils available are such that they have good compressive strength and adequate shear strength but are weak in tension or have poor tensile strength. Using land having soft soil for construction necessitates various ground improvement or soil stabilization techniques. Earth reinforcement is an effective and reliable technique for increasing the strength and stability of soils. The concept and principle was first developed by Henri Vidal in 1969 by which he demonstrated that the introduction of reinforcing elements in a soil mass increases the shear resistance of the medium. Reinforced soil is a construction material that consists of soil fill strengthened by a variety of tensile inclusions ranging from low-modulus, polymeric materials to relatively stiff, high-strength metallic inclusions. These tensile inclusions come in many forms ranging from strips and grids to discrete fibres and woven and non-woven fabrics. Reinforcement can vary greatly; either in form (strips, sheets, grids, bars, or fibres), texture (rough or smooth), and relative stiffness (high such as steel or low such as polymeric fabrics). Earth reinforcement has become routine in geotechnical engineering to enhance the bearing capacity of geostructures such as airfields, foundations, embankments, and pavement roads built on soft soils, and to stabilize engineered soil slopes and loosely filled retaining walls. Fibre reinforced soil exhibits greater extensibility and small losses of post peak strength i.e., greater ductility in the composite material as compared to unreinforced soil or soil reinforced with high modulus inclusions. A number of factors such as the fibre characteristics (content, length, thickness, modulus, tensile strength, and failure strain) and the soil characteristics (grain size distribution and mean particle size) influence the behaviour of the soil–fibre composite. Randomly distributed fibre reinforcement technique has successfully been used in a variety of applications such as slope stabilization, road subgrade and sub base etc. This is a relatively simple technique for ground improvement and has tremendous potential as a cost effective solution to many geotechnical problems. One of the main advantages of randomly distributed fibres is the maintenance of strength isotropy and absence of potential failure plane that can develop parallel to oriented reinforcement. The soil and reinforcing element will interact by means of frictional resistance. Appropriate selection of the type and location of the reinforcement material is necessary in order to achieve optimum improvement. Using fibres ranging from steel bars, polypropylene, polyester, glass fibres, and biodegradable fibres such as coir and jute, has been proven to be particularly effective for soil reinforcement. Due to access of cheap polypropylene fibre material, short discrete polypropylene fibre is employed to prepare the fibre reinforced soil samples in this investigation. A series of tests were carried out to analyze the variation of engineering properties of soil reinforced by polypropylene fibre and some significant findings are presented here. Polypropylene fibre is the most widely used inclusion in the laboratory testing of soil reinforcement. Polypropylene fibre has the following unique advantages: (i) it is of high intensity; (ii) like lime and cement, it can be dispersed easily into soil and the reinforced soil samples take on isotropic strength characteristics; and (iii) the presence of short discrete polypropylene fibre in soil can prevent the occurrence of potential weak structural planes which usually form due to the laying direction of geotextile and laying distance of geogrid. II. MATERIALS The soil (naturally occurring kaolin clay) was collected from Thonakkal region, obtained through quarrying from English India Clays Ltd. The physical properties of the soils are presented in Table1. International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 Published by, www.ijert.org NCRACE-2015 Conference Proceedings Volume 3, Issue 29 Special Issue - 2015