A number of studies have been conducted recently to investigate the influence of randomly oriented fibers on the geotechnical behavior of grained soils. However, very few studies have been carried out on fiber-reinforced clayey soils. Therefore, this experimental work has been performed to investigate the influence of randomly oriented fiber inclusion on the geotechnical behavior of clayey soils. This research evaluates the use of waste fiber materials such as scrap tire rubber, polyethylene, and polypropylene fiber for the modification of clayey soils. This investigation focuses on the strength and dynamic behavior of the reinforced soils with randomly included waste fiber materials. The unreinforced and reinforced samples were subjected to unconfined compression, shear box, and resonant frequency tests to determine their strength and dynamic properties. These waste fibers improve the strength properties and dynamic behavior of clayey soils. The scrap tire rubber, polyethylene, and polypropylene fibers can be successfully used as reinforcement materials for the modification of clayey soils. (c) 2007 Elsevier B.V. All rights reserved.