ORIGINAL PAPER Mechanical Behavior of a Clay Soil Reinforced with Nylon Fibers A. R. Estabragh • A. T. Bordbar • A. A. Javadi Received: 27 April 2011 / Accepted: 1 July 2011 / Published online: 5 August 2011 Ó Springer Science+Business Media B.V. 2011 Abstract Soft soils are well known for their low strength and high compressibility. Several tech- niques, including reinforcement, are commonly used to increase the strength and decrease the deformation of this kind of soil. This paper presents the results of an investigation into the effects of fiber on the consolidation and shear strength behavior of a clay soil reinforced with nylon fibers. A series of one dimensional consolidation and triaxial tests were conducted on samples of unreinforced and reinforced clay with different percentages of randomly distrib- uted nylon fibers. The results show that the precon- solidation pressure decreases and the coefficient of swelling and compression generally increase with increasing the fiber content. Furthermore, the addition of the fiber leads to a significant increase in shear strength and friction angle of the natural soil. Keywords Fiber  Random reinforcement  Consolidation  Triaxial test 1 Introduction It is generally accepted that there is a distinction between oriented and aligned and randomly distrib- uted reinforcing elements in reinforced soils. In the former case, the inclusions are placed in the soil at strategic locations, whereas in the latter, reinforce- ment elements, usually fibers, are mixed with the soil and may be placed within the problematic shear zone. In comparison with oriented or systematically rein- forced soils, fiber reinforced soils with random distribution of fibers exhibit some advantages. One of the main advantages of using randomly distributed fibers is the maintenance of strength isotropy and the absence of potential planes of weakness that can develop in soils with oriented reinforcement (Gray and Maher 1982; Maher 1988). Although the concept of randomly reinforced soil is relatively new in geotechnical engineering but the reinforcement of clay soils with natural fibers has been practiced from the time of Pharaohs. Recently soil reinforcement with short, discrete, randomly oriented fibers is getting more attention from many researchers around the world. Many investigators have used fiber to improve various properties of sandy soil (e.g., Gray and Ohashi 1983; Maher and Gray 1990; Al-Rafeai 1991; Consoli et al. 2009; Yetimoglu and Salbas A. R. Estabragh (&)  A. T. Bordbar Faculty of Soil and Water Engineering, University of Tehran, PO BOX 4411, 31587-77871 Karaj, Iran e-mail: raeesi@ut.ac.ir A. T. Bordbar e-mail: Alitabe@ut.ac.ir A. A. Javadi Computational Geomechanics Group, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Devon EX4 4QF, UK e-mail: a.a.javadi@exeter.ac.uk 123 Geotech Geol Eng (2011) 29:899–908 DOI 10.1007/s10706-011-9427-8