This document discusses research into reinforcing soils with polypropylene fibers. Direct shear tests were conducted on two soil samples, river sand and sea sand, with varying amounts of polypropylene fibers added. The tests showed that adding fibers up to an optimum content of around 10% increased the angle of shearing resistance and cohesion of both soils. Maximum dry density decreased slightly with fiber addition while optimum moisture content increased. The study concluded that fiber reinforcement improved the mechanical properties and strength of the soils, making them more suitable for geotechnical applications.