Clayey soils are spread over large areas of the world. This soil type has numerous problems
due to its low strength, high compressibility, and high level of volumetric changes. To overcome
these difficulties, many researchers have concentrated their studies on soil improvement techniques.
Recently, soil reinforcement has been considered an effective and reliable technique for improving the
strength and stability of these soils by using different types of reinforcing materials. This paper aims
to investigate the feasibility of using polypropylene fiber as a low-cost and environmentally friendly
reinforcing material for high plasticity clay, and assess the strength and swelling behavioral change
with fiber content to determine the optimum fiber content that meets the effective improvement rate.
A series of laboratory experiments such as a direct shear test, swell test, and unconfined compressive
strength (UCS) test were carried out to evaluate the fiber content effect on the strength and swell
behavior of composite clay (clay mixed with fiber). The fiber content varied from 0% to 1.5% (by
dry weight of the soil). The results show that the inclusion of fiber affects the shear strength (an
average increase of 184% at 1.5% fibers), and unconfined compressive strength (an increase of 86%
at 1.5% fibers). Likewise, the increase in fiber content causes an increase in the strength properties,
cohesion, and friction angle (257% and 62% at 1.5% fibers, respectively). Also, the increase of fiber
content causes a decrease in both swelling potential and swell stress (a decrease of 24% and 46% at
1.5% fibers, respectively) in the studied clayey soil.