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This paper presents the effect of short, discrete, randomly oriented fibres (natural and synthetic) on the mechanical properties of clayey soils. The mechanical properties investigated include peak unconfined compressive strength, stiffness and ductility. Three types of clayey soil were obtained from the eastern part of Irbid city in northern Jordan. Two types of fibre were used in this study: nylon and palmyra fibres, with aspect ratios () equal to 75. The clayey soils were mixed with fibres at five different percentages by volume of solid soil particles: 1%, 2%, 3%, 4% and 5%. The results showed that the peak unconfined compressive strength, stiffness and ductility of the clay-fibre mixture increased with fibre content. The post-peak softening in compression resistance decreased with increasing fibre content. The relative unconfined compressive strength increased with fibre content. Palmyra fibre showed a higher increase in the relative unconfined compressive strength than nylon fibre when mixed with clayey soil, for all fibre contents. Furthermore, the clayey soil with a high activity index showed greater improvement when mixed with fibres than that with a low activity index. [ABSTRACT FROM AUTHOR]

This study investigates the anisotropic behaviour of the shear strength of overconsolidated clayey soils. The results of the study will help engineers and scientists to predict the lateral shear strength of clayey soils from the ordinary vertical shear strength. The main objective of this paper is to investigate experimentally the effect of anisotropy on the shear strength properties of clayey soil. Fifteen types of clayey soil were obtained from various locations in the Irbid area, Jordan, and from different depths. Three undisturbed samples were obtained from each location at three different inclinations (horizontal, vertical, and inclined at 458 to the vertical). Unconfined compression tests were conducted on all soil samples. It was found that the unconfined compressive strength values were greater in the vertical direction than in the inclined and horizontal directions, and increased as the overconsolidated ratio increased. It was also noticed that the failure strain in the horizontal samples was smaller than in the vertical samples. The anisotropic behaviour of clayey soils almost disappeared at greater depth for both unconfined compressive strength and failure stain. [ABSTRACT FROM AUTHOR]