A novel experimental approach for measuring porous flow characteristics using spherical hydro-gel beads and particle image velocimetry (PIV) technique is presented. A transparent porous medium consisting of hydro-gel beads that are made of a super-absorbent polymer, allows using water as the fluid phase while simultaneously having the same refractive index. As a result, a more adaptable and cost effective refractive index matched (RIM) medium is created. The transparent nature of the porous medium allows optical systems to visualize the flow field by using poly-amide seeding particles (PSP). Low risk light emitting diode (LED) based light was used to illuminate the plane in order to track the seeding particles’ path for the characterization of the flow inside the porous medium. The system was calibrated using a manually measured flow by a flow meter. Velocity profiles were obtained and analysed qualitatively and quantitatively in order to characterise the flow. Results show that this adaptable, low risk experimental set-up can be used for flow measurements in porous medium under low Reynolds numbers. The limitations of using hydro-gel beads are also discussed.

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Landfill cover soils have to serve multiple purposes such as operational safety, environmental protection, recultivation and integration of the sites into the landscape. Cover soil properties must therefore be defined with respect to the thickness, bulk density, air permeability and the available field capacity. The primary objective of this study is to examine the cover soil properties of three selected landfill sites (dumpsites) in Sri Lanka in order to propose suitable cover soil properties for similar applications in future dumpsites. Soil samples were obtained from three landfill sites in and around the city of Colombo. Laboratory tests to establish compaction characteristics, air permeability, particle size distribution and Atterberg limits were performed to assess the suitability as landfill cover soils. The study showed that landfill covers with well graded soils comply with the dry density and air permeability values, as per the guidelines. In the absence of proper gas venting facilities, it is essential to study the permeability properties of the cover soil. All three landfill sites tested need to be retrofitted with leachate and gas collecting systems that meet the standards stipulated in the guidelines.

Particle Image Velocimetry (PIV) is a non-invasive optical measurement technique which has been used for many decades to measure fluid velocity. Conventionally, PIV systems are equipped with a laser system for illuminating the flow field. However, laser systems are expensive, and their usage usually creates specific safety precautions. In this work, we used a low cost LED based illumination system in conjunction with the refractive-index matching method to measure flow velocities in porous media. Hydro jelly beads were used as a transparent porous medium which have the same refractive index as water. The movement of tracer particles which were illuminated by the LED pulse was captured by a high-speed double pulsed camera and the resulting images were processed for receiving the pore-scale fluid velocity. Interstitial velocity vectors averaged over a specified region were presented and compared with the vertical velocity component calculated from the volumetric flow rate. In general, our results demonstrated the usability of LED based PIV system for investigating flow conditions in porous media. The future aim of this study is the investigation of micro-scale seepage induced internal erosion of granular structures.

The aim of this paper is to examine the flow characteristics at the initiation of contact erosion. When water flows through fine soil to a coarser soil layer, changes of the flow properties may occur due to transition of the pore structure. A pore scale experiment was developed in order to explore the local flow behaviour which leads to migration of fine particles into a coarse structure. Optical access to the pore structure was obtained by having a transparent soil model consisting of hydrogel beads. This allowed water to be used as the fluid phase and resulted in a more adaptable Particle Image Velocimetry (PIV) system. Upward seeded flow was applied to the test section and illuminated using a low risk Light Emitting Diode (LED) light sheet. After calibrating the set-up with macroscopic flow rate measured by flow meter, images of the contact zone of coarse and fine particles were taken with different flow boundary conditions using a high speed camera. Qualitative and quantitative analysis were carried out to identify spatial variability of the flow conditions which led to initiation of the fine particle movement. Results show that the local reorientation of the flow will lead to local initiation of the contact erosion. Major reasons for this behaviour are discussed in this paper.