Reinforcement of clay soils using waste carpet fibres.

It is reported that about 500,000 tonnes (i.e. 2% of the total waste) of waste carpet fibres are plunged into landfills annually in the UK. Municipalities and environmental authorities are increasingly concerned about the growing amount of carpet waste produced by household, commercial and industrial sectors. The notion of reusing such waste in industry has therefore attracted substantial attention in recent years by researchers and environmentalists. There have been a large number of studies in utilisation of virgin fibres in soils and other civil engineering applications. However, by contrast there have been relatively few studies of waste fibres especially waste carpet fibres in this context and in particular in cohesionless soils. In this study, the mechanical behaviour of composite cohesive soils (i.e. clay soils) with proportionate concentration of two types of waste carpet fibre is investigated. A series of consolidated undrained triaxial shear tests, Oedometer tests, swelling pressure tests and unconfined compression tests have been carried out to evaluate the effectiveness of the waste carpet fibres in improving the mechanical properties of cohesive clay soils including; shear strength and compression strength as well as reducing swelling pressure and consolidation settlement of such soils. The results have shown that waste carpet fibres do increase the shear strength and unconfined compression strength of clay soils proportional to fibre content. It was found that relative increase in unconfined compression strength or reduction in swelling pressure of the fibre reinforced clay soils is dependent on the initial dry unit weight and moisture content of the clay. A neural network analysis was conducted on the results of the triaxial shear tests to construct a predictive model for estimating the maximum deviator stress in consolidated undrained triaxial tests as a function of fibre type, fibre content, dry unit weight and consolidation pressure. The modelled behaviour was shown to be a perfect fit with the experimental data. Model slope tests were also carried out using a large scale laboratory test tank (L:800mm x W:300mm x H:500mm) to investigate the load bearing pressure of the slope made of fibre reinforced clay soil under strip footing load. The results confirmed that bearing pressure of the model slopes increased significantly with increased fibre content. Particle image velocimetry (PIV) method was used to track the displacement of the soil particles in the exposed front view of the model slope and contours of displacement and slip surfaces of the model slopes were determined and compared