3223 Utilisation of polyethylene (plastic) shopping bags waste for soil improvement in sandy soils Utilisation des déchets de sacs en polyéthylène (plastiques) pour l'amélioration des sols sableux Kalumba D., Chebet F.C. University of Cape Town, South Africa ABSTRACT: This study investigated the possibility of utilising polytheylene shopping bags waste to reinforce soils to pave way for its use in civil engineering projects such as in road bases, embankments and slope stabilisation. A series of direct shear tests was undertaken on soil-plastic composites of two selected sandy soils: Klipheuwel and Cape Flats sands. Strips of shredded plastic material were used as reinforcement inclusions at concentrations of up to 0.3% by weight. The effect of varying dimensions of the strips was investigated by using strip lengths from 15 mm to 45 mm and strip widths from 6 mm to 18 mm. Shear strength parameters were obtained for composite specimen from which analyses were done to identify the extent of soil improvement. The testing programme involved addition of solid strips as well as perforated strips with varied diameter of perforations to examine the effect of the openings on the strips. Laboratory results obtained favourably suggest that inclusion of this material in sandy soils would be effective for ground improvement in geotechnical engineering. RÉSUMÉ : Cette étude a examiné la possibilité de l’utilisation des déchets des sacs d’épicerie en polyéthylène pour renforcer les sols afin de promouvoir son intégration dans les projets de génie civil tels que les couches d’assise des routes, les remblais et la stabilité des pentes. Une série d’essais de cisaillement direct a été réalisée sur des composites plastique-sols sur deux sols sableux sélectionnés : sable de Klipheuwel et de Cape Flats. Des lamelles de matériau plastique déchiqueté ont été utilisées comme intrants de renforcement à des concentrations allant jusqu’à 0,3% du poids. L’effet de la variation des dimensions des lamelles a été apprécié en modifiant leurs longueurs de 15 à 45 mm et leurs largeurs de 6 à 18 mm. Les paramètres de la résistance au cisaillement obtenus pour les spécimens de composites ont servi à faire des analyses pour l’estimation du degré d’amélioration des sols. Le procédé scientifique a été fait avec des lamelles pleines et des lamelles perforées à divers diamètres afin d’observer l’effet des interstices dans les lamelles perforées. Les résultats de laboratoire obtenus confirment favorablement que l’ajout de ce matériau dans les sols sableux serait efficace pour l’amélioration des sols dans les applications d’ingénierie géotechnique. KEYWORDS: Plastic bags, Polyethylene, Waste minimisation, Soil reinforcement, Ground improvement, Shear strength 1 INTRODUCTION Increased use of plastics in day to day consumer applications has resulted in municipal solid waste containing an ever growing fraction of plastic material used for a short time and discarded. Ever since their invention over 60 years ago, plastics have taken centre stage in daily life due to favourable attributes such as low weight, durability and lower cost as compared to other material types (Thompson et al. 2009, Andrady and Neal 2009). These attributes make plastics convenient and therefore highly demanded by consumers with production increasing substantially from about 0.5 million tonnes in 1950 to over 260 million tonnes by 2008 with higher projections expected in the future (Thompson et al. 2009). A large percentage of plastics produced are used for disposable applications like packaging and therefore reach the waste stream more quickly since their usage life is shorter than that of plastics used in the construction or automotive industry (Azapagic et al. 2003). Consequently about 10% by weight and 20% by volume of the municipal waste stream is composed of plastics destined for landfills (Barnes et al. 2009, Azapagic et al., 2003). Of the plastic material discarded, 50% is from packaging, a third of which consists of plastic shopping bags (Nhamo 2008). Plastic shopping bags are water resistant materials mostly made of polyethylene, a non-biodegradable polymer produced from non-renewable petroleum and natural gas resources. The linear consumption patterns of plastic bags involving single usage and then disposal has led to environmental challenges such as diminishing landfill space, marine and urban littering. There is therefore a growing need to find alternative uses of reclaimed plastic bag waste to lengthen the usage time of the plastic material. This is so as to tap into the abundant plastic resource that possesses a great extent of versatility and yet in the same vein poses a danger to the environment if not well managed in terms of responsible disposal that involves resource recovery vital in contributing to sustainable development. Chen et al. (2011) maintain that new approaches on the reuse of plastic waste in cities as alternative materials for urban developmental programs, referred to as urban symbiosis, could help reduce green house gas emissions and fossil fuel consumption. This study explored the possibility of utilising reclaimed plastic material from polyethylene bags as tensile inclusions to reinforce soil for ground improvement schemes in geotechnical engineering applications such as retaining walls, road bases, embankments and slope stabilisation. Research into random inclusion of discrete polypropylene fibres in soil as reinforcement material have reported increases in peak shear strengths and reductions of post peak losses in soils (Zornberg 2002, Consoli et al., 2007, Falorca and Pinto 2011). Furthermore, these fibres have been found to improve compressive strength and ductility of soils (Maher and Ho 1994, Santoni et al., 2001, Miller and Rifai 2004). As a result, fibre reinforced soil consisting of polypropylene fibres have been successfully used on embankment slopes in the US (Gregory and Chill 1998) and in applications such as foundations for sport pitches, horse racing tracks and access for secondary roadways (Ibraim and Fourmont 2006). The main objective of this study was therefore to investigate the effect of including plastic strips from polyethylene shopping