ABSTRACT
The feasibility of using Limited Life Geotextiles (LLGs) has been demonstrated by the construction and testing of reinforced soil retaining walls reinforced with Vegetable Fibre ropes (Ali 1992). Investigators such as Mwasha (2005) and (Sarsby et al. 2006) have demonstrated analytically that vegetable fibres can be used to reinforce an embankment on soft soil. It is now necessary to consider how the tensile strength of the vegetable fibres will change with time once they have been surrounded by different types of foundation and fill materials. Unfortunately this problem of durability of natural fibres is complex, and contradictory examples of both very fast decay and remarkable stability are cited. In the 1920s and 1930s, an extensive investigation was undertaken by the then Imperial Institute of Tropical Agriculture into the suitability of Sisal for the manufacture of marine ropes. Numerous samples of Sisal rope were subjected to cyclic wetting (with sea-water) and drying over a period of 12 months (Imperial Institute 1927). The data collected showed concerns with regard to the use of this type of material as basal reinforcement for an embankment built on soft soil. It was found that the ropes exhibited much higher rates of tensile strength loss with immersion time than that permitted if any of the backcalculated design Time-Strength Envelopes were to be satisfied economically (Sarsby et al. 2006). The receding requirement for geotextiles for the
embankment (Fowler et al. 1983). Based on these assumptions, a new tensile/strain gauging method is proposed, which is intended to minimize or eliminate the limitations of the present tensilestrain measurement methods. This new method makes use of the idea of attaching gauges “externally” to a high strength steel wire connected via a proving ring to the geotextile via T-shaped rods. The geotextiles held by the T-rod support the loading from an embankment as well as the outward directed lateral force caused by the horizontal stress in the fill acting on the foundation surface. The advantages of this method over the traditional method are the role for the reinforcement to support the outward shear stress, which relieves the foundation of critical loading, is represented by the process of the diminishing need of tensile strength from geotextiles. The properties of interaction between Vegetable Fibre Geotextiles and soil are needed for the proper design of these types of geotextiles in any specific environment. Pullout tests were conducted in order to explain the interaction between Sisal geotextiles and Caroni soil. Different granular soils of various grain sizes were spread on the geotextiles to simulate a free draining embankment. The results of this experiment showed that the local rounded Guanapo gravel had a higher coefficient of adhesion compared to much angular limestone gravel. The opening size of mesh relative to the soil grain size could have influenced the pullout interaction between soil and geotextile. It was also found that the coefficient of adhesion increased during the consolidation process. Since the strain in the soil is considered to be negligible and the coefficient of adhesion is almost 1 (Pritchard 1999), the strain deformation of geotextiles will not be considered in this paper.
