ABSTRACT
Studies have reported high fines or high plasticity fill material coupled with lack of drainage in the reinforced zone, as some of the primary reasons for serviceability problems and failure of geosynthetic reinforced structures. Yoo & Jung (2006) reported a case history of geosynthetic reinforced segmental retaining wall failure highlighting the use of a fill with significant percentage of fines as one of the prime factors causing failure. Investigations revealed bad quality backfill coupled with insufficient drainage as one of the key factors for the distress. Hence, when using low permeable soil as a backfill material within the reinforced soil structures, it is imperative to provide sufficient measures to reduce the development of pore water pressure of the reinforced zone by collecting and discharging it away from the reinforced zone for stability of the structure. The use of permeable geosynthetic having good drainage properties along with a reinforcement media, together forming a geocomposite, may be a potential solution to reduce the developed pore water pressures for reinforced soil structures with low-permeable soils (Hiro-oka et al. 2001, Yasuhara et al. 2002, Iryo and Rowe, 2005, Liu et al. 2009, Tolooiyan et al. 2009). To fulfill the requirement of reinforcement coupled with drainage for structures with poor quality backfill, an attempt has been made in the present study to use a geocomposite, with permeable geosynthetic having porous structure as one of the components. Centrifuge modeling offers the advantage of achieving identical stress fields in model and prototype and hence centrifuge modeling technique was chosen for the present study. Geosynthetics with
1 INTRODUCTION
Geosynthetic reinforced structures are being widely used for various geotechnical applications due to the advantage of lower cost and their flexibility. Freely draining soils are highly preferred backfill materials for these structures. The design criteria recommended by various agencies worldwide for backfill material for geosynthetic reinforced soil structures also suggest the use of freely draining soil or soil with less than 15 percent fines to mitigate the build-up of pore water pressures in the backfill soil. However, the need of such granular backfill recommended for its construction negates the economic advantage of geosynthetic reinforced structure with the cost of the fill depending on its availability. Adoption of soils having relatively high percentage fines in place of freely draining soils as backfill materials can lead to additional savings in the range of 20 to 30% of reinforced soil wall costs (Christopher & Stuglis 2005). Hence the need to use the locally available poor backfill for the construction of embankments and retaining walls has arisen and should be explored. However, caution needs to be excersied when using such soils as backfills due to its poor draining properties resulting in build up of pore water pressures and reduction of soil strength. The infiltrating groundwater, rainfall and other sources of water cause pore water pressures to develop within the reinforced fill zone thereby producing a horizontal seepage force and reduction in the shear resistance of the reinforced fill. This affects the stability of reinforced structure.
