Laboratory Study on Shear Strength Behaviour of Reinforced Sandy Soil: Effect of Glass-Fibre Content and Other Parameters

The areas near Chlef Valley (Algeria) and the Constructions built on show many phenomena during the last earthquake (El Asnam 1980). A significant decrease in shear strength of Chlef sandy soil, especially in the presence of water, has been reported in numerous researches. Several methods and techniques of soil stability and capacity are available. However, including geosynthetic material, the use of fibres as reinforcement showed some efficiency due to friction between the synthetic material and the soil particles, which increases the bonding between the grains. In this paper, the influence of the glass-fibres content for medium and high densities on the shear strength behaviour of Chlef sandy soil was studied, highlighting the percentage of fibre content (0.1, 0.3 and 0.5% as a fibre volumetric content), and this will be investigated by a series of direct shear tests. The results will be compared with those of unreinforced sand. Before this work, a further set of direct shear tests will be performed to study the effect of water content on shear strength behaviour (water content of 0, 1.5, 2.3 and 3 %). The experimental results show that the mechanical characteristics are improved with the addition of glass-fibres, especially for wet specimens. It has been showed also that 0.3% of fibre content is a critical value for fibre contribution to improve the mechanical characteristics. The addition of fibres not only improves the shear strength of soil, but also provides diversity in the resistance against the deformations imposed load, which can be established by a decrease in the soil dilatancy observed by a minimization of the vertical displacement. For the dry case, the reinforcement with fibre has a negative effect on the residual strength especially for average dense samples which may explain probably by the low specific weight of geosynthetics materials.