Strength and Permeability Characteristics of Fibre-Reinforced Liner Material

Abstract

Sand–bentonite mixture is a widely used liner material. After optimisation, it is observed that sand–bentonite mix with bentonite content 15% satisfies the criteria of compacted clay liner (CCL) material stipulated by the United States Environmental Protection Agency (USEPA). Bentonite, one of the primary elements of the mixture, is an expensive material. So, the focus of this study is to reduce the bentonite content with reinforcing the mix by random inclusion of polypropylene fibres. In this study, sand–bentonite mixture with 10, 15 and 20% bentonite content is used and 0, 0.2, 0.5 and 1% polypropylene fibre by weight of the mixture is added. Unconfined compressive strength (UCS) test is done to observe the strength characteristics of the mix. The UCS specimens are statically compacted to their respective maximum dry densities (MDD) at optimum moisture content (OMC). UCS values are determined at this moulded water content as well as in fully saturated conditions. It is observed that the failure strength and ductility of a sample with a given bentonite content increases with increasing fibre content. It is also noticeable that normalised strain energy is improved and reduction of post-peak strength is minimised with increasing fibre content. However, at a particular fibre content, the strength initially increases up to 15% bentonite content and after that it reduces. This trend is observed for all the samples. The UCS value of sand–bentonite specimens, containing 15% bentonite and compacted at OMC with compaction effort of 595 kJ/m3, increases from 60.92 to 483.46 kPa when the fibre content is increased from zero to 1% which is 694% increment of strength. Permeability test is done with distilled water under pressure head of 4 kg/cm2 to find out the effect of fibre content on hydraulic conductivity of the mixtures. It is noticed that inclusion of fibres increases the hydraulic conductivity of the compacted sand–bentonite mixes. Scanning electronic microscopy (SEM) is performed to observe the distribution of fibres in the sand–bentonite mixture.