Physical model experiments were conducted to observe the migration of light non-aqueous phase liquids (LNAPL) in a double-porosity soil medium. The double-porosity characteristics of the soil were simulated through aggregation of kaolin which resulted in well-defined intra-aggregate and inter-aggregate pores. Digital images were collected to monitor LNAPL (modeled by toluene) migration. A special experimental setup was developed to enable the instantaneous capture of the LNAPL migration around the whole soil column using a single digital camera. An image processing module was applied to the captured images and the results plotted using a surface mapping programme. Events observed during the duration of the experiments were discussed. It was found that the LNAPL flowed much faster in the aggregated soil as compared to a single-porosity soil. The wettability of the fluid and the capillary pressure characteristics were demonstrated to be influential factors in immiscible fluids migration when the soil fabric showed highly contrasting porosity values.
A numerical model describing the flow of multiphase, immiscible fluids in a deformable, double-porosity featured soil has been developed. The model is focused on the modelling of the secondary porosity features in soil, which is more relevant to groundwater contamination problems. The non-linear saturation and relative permeabilities were expressed as functions of the capillary pressures. The governing partial differential equations in terms of soil displacement and fluid pressures were solved numerically. Galerkin's weightedresidual finite element method was employed to obtain the spatial discretization whereas temporal discretization was achieved using a fully implicit scheme. The model was verified against established, peer-reviewed works, and the assumption that the immiscible fluids (non-aqueous phase liquids) will flow preferentially through the secondary porosity features in soil was validated.
In recent years, research on natural fiber composites increased owing to their lightweight, easy availability and improved mechanical characteristics. Natural fiber is also an environmentally friendly material, which produces less pollutant during its production. Therefore, extensive research has been carried out on natural fibers as they constitute an interesting alternative to traditional synthetic fibers, especially for composite materials. This paper presents a comprehensive review on the physical, mechanical and thermal properties as well as chemical composition of natural fibers. Comparison between different natural fibers regarding the aforementioned properties and composition are presented and discussed. This review will provide a useful guide on the performance of natural fibers in natural fiber reinforced composites for other applications such as structural strengthening.
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