Migration of aqueous and non-aqueous phase liquids in deformable double-porosity subsurface under vibration
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Date
2019
Authors
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Publisher
Universiti Teknologi Malaysia
Abstract
Aqueous Phase Liquids (APL) and Light Non-Aqueous Phase Liquids (LNAPL) chemicals that contain different type of minerals, miscible phase and immiscible phase respectively. The issue of leakage and spillage of APL and LNAPL contribute to groundwater contamination, resulting in groundwater pollution and reducing the quality of groundwater unsafe for drinking and agriculture activities. Higher infiltration of these chemicals into groundwater might be observed for soil with double-porosity. It is well established that double-porosity soil has two distinct scales of porosity, the surrounding intra-aggregate pores and inter-aggregate pores. Therefore, this research investigates characteristic of APL and LNAPL migrations in double-porosity soil under fractured and unfractured (intact) condition considering different moisture content. Also, it identifies suitable engineering simulation model for fractured and intact double-porosity soil features. A series of experiment model was simulated using kaolin soil type S300 which used to model double-porosity soil. Vibration was imposed on the double-porosity soil using a vibration table along with several accelerometers. The characteristics of APL and LNAPL migration in double-porosity soil were monitored using digital image processing technique (DIPT). The recorded images were analyzed through plots of the hue saturation intensity (HSI) for the APL and LNAPL migration characteristics and the LNAPL saturation calibration curve was developed. These curves help to verify the hue values of the image to the actual LNAPL saturation in fractured double-porosity soil. A series of computer simulations for modelling APL and LNAPL migration behaviours in the soil were modelled using COMSOL Multiphysics software, which implements the Richards Equation to simulate unsaturated flow (i.e., with retention of the pore estimated using van Genuchten formulation). The COMSOL models were verified after comparing the numerical outputs with the results obtained from the experimental work. The experiments show that the simulated results were reasonably concise with the visual observations. The gradual increase in vibration table excitation frequency yielded different vibration responses from the respective soils. Faster migration occurred at the cracked soil surface condition compared to the soil surface that was not cracked. Comparison between soils with 25% and 30% moisture contents showed that the downward migration of LNAPL is faster when the soil moisture content is higher. The main reason behind this difference is that for soil with higher moisture content a greater capillary pressure was exerted by the liquids and inter-aggregates pores. The significant finding was that the LNAPL fully migrated to the bottom of the soil sample, but the APL migration was not fully migrated due to the physical bonding and Van der Waals forces. In conclusion, this research has successfully simulated APL and LNAPL migration as well as proper verification of the experimental outputs using the COMSOL software. This research will help facilitate researchers to understand the liquids’ migration pattern better and to ensure the sustainability of groundwater resources.
Description
Thesis (PhD. (Civil Engineering))
Keywords
Water quality management, Water quality, Groundwater—Pollution, Groundwater—Research
Citation
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