LABORATORY EVALUATION OF FIBRE REINFORCED SOIL

Abstract

We all know that the soil is good in compression, but very weak in tension. This weakness of the soil restricts its use in certain civil engineering applications such as steep slopes in which generally shear failure occurs. Thus arises the need for the modification of soil strength parameters for its improved performance in desired areas. This deficiency of soil can be eradicated by reinforcing the soil; i.e. the introduction of an external material into the soil. The main aim is the creation of such a material/system that will hold under the design use conditions and for the designed life of the engineering project. The concept of earth reinforcement with the help of fibrous materials is an ancient technique and has been demonstrated abundantly in nature by animals, birds and the action of tree roots. This fibrous reinforcement resists tensile stress developed within the soil mass thereby restricting shear failure. In this investigation, Recron 3S polypropylene fibre manufactured by Reliance India Ltd., has been used. Polypropylene Fibres are engineered micro fibers with a unique “Triangular” Cross-section shape and are widely used in construction, mining, agricultural, textile and automotive industry. An experimental investigation was undertaken to study the effect of polypropylene fibre inclusion on the interface shear strength of soil. Test specimens were prepared with varying percentages of 6 mm PP fibre (non-reinforced, 0.25%and 0.50%) by the weight of dry soil. A series of Direct Shear Tests & Unconsolidated-Undrained Triaxial tests were conducted on randomly distributed fibre reinforced soil and the effect of various proportions of polypropylene fibre on the properties of soil were noted. The soil was obtained from a proposed Nuclear Power plant site in Gorakhpur, Haryana. The shear strength parameters were measured using a standard size (60 mm*60 mm) Direct Shear box test. The tests were conducted on three different normal stress i.e. 0.1, 0.2 & 0.3 N/mm2 and the angle of internal friction and cohesion intercept values were obtained by plotting a straight line through the plot of shear stress versus the normal stress. Also the Mohr failure envelope was plotted by conducting UU Triaxial tests at three different confining pressures; i.e. 0.1, 0.2 & 0.3 N/mm2. The variation in the cohesion & angle of internal friction of the unreinforced soil and fibre reinforced soil were compared. There was increase in the compressive strength & shear strength value of the soil on the addition of fibre. Also the cohesion intercept of the reinforced soil increased slightly. But the angle of internal friction reduced for the fiber reinforced soil. Scanning Electron Micrographs indicated that the obtained results were due to the special cross-section of the polypropylene fibre.