ABSTRACT: In this paper, the two-phase (water and air) numerical model which considers the thermal and the dissolved oxygen process has been developed. In order to verify the performance of developed numerical simulator and discuss the progressive failure of the seepage flow, the simple two-dimensional seepage flow experiments along/below a vertical sheet pile have been simulated. In consequent, the simulation results shows the same tendency as the experimental results and the instability due to generated air bubbles can be expressed in our developed.
1. INTRODUCTION
It is necessary for a success of a project on the geotechnical field, such as the nuclear waste disposal, the CO2 geo-sequestration, and the air sparging, to clarify the interaction of geo-material with pore fluids. Pore fluids are strongly affected by not only the flow path depending the geo-material structure (porosity and/or fracture) but also several factors such as temperature, saturated/unsaturated and chemical/ biological reaction. Therefore, the estimation of the behavior of pore fluids must be considered with these several factors. The authors have been developing the simulation technology which could present the injected air flow into the water saturated subsurface [1, 2]. Developed simulator had the performance of both two-phase flow and the mass transport function including the chemical reaction. In consequently, two different air flow patterns, depending on the grain size of porous media: flow through discrete channels and bubble flow could be simulated and the remediation of saturated/unsaturated geo-material contaminated by volatile organic compounds. Several types of geo-disasters, such as slope failures and river dike breaks, have occurred in various areas. These geo-disasters are related to the behavior of pore fluids in geo-materials. The laboratory study by Kodaka and Asaoka [3] was the pioneering work to present the causal relation between the instability of ground and air bubble in the ground water seepage process. They explained that the air bubbles were generated in the seepage process and the ground break was occurred by the generated air bubbles. In order to simulate the Kodaka and Asaoka laboratory works [3], in this paper, the modeling of unsaturated flow in consideration with temperature, Dissolved Oxygen (DO) process and effective stress is developed based on the two-phase numerical model presented by Jacimovic et al. [1]. Then, the relation between the instability of ground and air bubble is discussed using simulation results.
2. GOVERNING EQUATIONS AND NUMERICAL MODEL
2.1. Fluid flow model
As mentioned above, Jacimovic et al. [1] developed twophase numerical simulator which can present two different air flow patterns. Brooks et al. [4] indicated that change in the flow pattern occurs at 1-2 mm grain size with the channel flow below and bubble flow above this size. Several researchers conducted numerical simulations of air flow (Lundegard and Andersen, 1996; McCray and Falta, 1997; van Dijke et al., 1995). However, all these works were applied for the cases where the channel air flow pattern can be expected. On the other hand, Jacimovic et al. [1] performed to analyze the influence of inertia terms in governing equations. Then, dynamically trapped air volume (bubble flow) could be calculated.