1. Introduction. The concept of soil reinforcement is an ancient technique and is demonstrated abundantly in nature by animals, birds, and the action of tree roots. Constructions using these techniques are known to have existed in the fifth and fourth millennia B.C. (Jones, 1985). This concept is used for the improve- ment of certain desired properties of soil such as bearing capacity, shear strength (c and ϕ), permeabil- ity, etc. This concept and principle was first developed by Vidal (1969), in which he demonstrated that the introduction of reinforcing elements in a soil mass increases the shear resistance of the medium. At present, the soil reinforcement technique is well established and is used in various applications such as improving bearing capacity, filter, and drainage control. Conventional reinforcement methods comprise continuous inclusions of strips, fabrics, and grids into the soil mass. Also the random inclusion of vari- ous types of fibers is considered to be a modification of the same technique. These fibers act to inter- lock particles and aggregates in a unitary coherent matrix. This work investigates the use of papyrus fiber for similar purposes. Mostly, the discrete fibers are simply added and mixed with the soil much the same as cement, lime, or any other additives. One of the main advantages of randomly distributed fibers is the maintenance of strength isotropy and absence of potential failure planes, which can develop parallel to the oriented reinforcement (Chakraborty and Dasgupta, 1996). Soil Mechanics and Foundation Engineering, Vol. 48, No. 6, January, 2012 (Russian Original No. 6, November-December, 2011) Construction of building and other civil engineering structures on weak or soft soil is highly risky because such soil is susceptible to differential settlements, poor shear strength, and high compressibility. Various soil improvement techniques have been used to enhance the engi- neering properties of soil. Soil reinforcement by fiber material is considered an effective ground improvement method because of its cost effectiveness, easy adaptability, and repro- ducibility. Hence, in the present investigation, papyrus fiber has been chosen as the rein- forcement material, and it was randomly included into the soil at four different percentages of fiber content, i.e., 5, 10, 15, 25% by volume of raw soil. The main objective of this research is to focus on the strength behavior of soil reinforced with randomly included papyrus fiber. Direct shear, consolidation, and displacement tests were performed on papyrus- reinforced specimens with various fiber contents. The results of these tests have clearly shown a significant improvement in the failure deviator stress and shear strength parameters (c and ϕ) of the studied soil with a percent addition of 10% (the preferred percent). Moreover, this addition ratio reduced the displacement of the soil under loading. It can be concluded that papyrus fiber can be considered an appropriate soil reinforcement material. STRENGTH OF SOIL REINFORCED WITH FIBER MATERIALS (PAPYRUS) Aqeel Al Adili University of Technology, Building and Construction Engineering Department, Baghdad, Iraq (Email: aqeel64aladili@yahoo.com); Rafig Azzam, Giovanni Spagnoli, and Joerg Schrader Dept. of Engineering Geology and Hydrogeology, RWTH Aachen University, Germany Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, p. 15, November-December, 2011. 0038-0741/12/4806-0241 © 2012 Springer Science+Business Media, Inc. 241