The migration of fine particles in porous media has been studied for different applications, including gas production from hydrate-bearing sediments. The clogging behavior of fine particles is affected by fine particle-pore throat size ratio, fine particle concentration, ionic concentration of fluids, and single/multiphase fluid flow. While previous studies presented valuable results, the data are not enough to cover a broad range of particle types and sizes and pore throat size in natural hydrate-bearing sediments. This paper presents a novel micromodel to investigate the effects of fine particle-pore throat size ratio, fine concentration, ionic concentration of fluid, and single/multiphase fluid flow on clogging or bridging in porous media. The results show that (1) the concentration of fine particles required to form clogging and/or bridging in pores decreased with the decrease in fine particle-pore throat size ratio, (2) the effects of ionic concentration of fluid on clogging behaviors depend on the types of fine particles, and (3) fine particles prefer to accumulate along the deionized water- (DW-) CO2 interface and migrate together, which in turn easily causes clogging in pores. As a result, multiphase fluid flow during gas production from hydrate-bearing sediments could easily develop clogging in pore throats, where the relative permeability of DW-CO2 in porous media decreases. Accordingly, the relatively permeability of porous media should be evaluated by considering the clogging behavior of fines.

Accidents involving vehicles crashing into reinforced retaining walls are increasing because of the increased construction of reinforced retaining walls on roads. Unlike a normal retaining wall, a reinforced retaining wall is not one united body but is made up of blocks. Hence, a reinforced wall can break down when a vehicle crashes into it. The behavior of such a wall during vehicle collision depends upon the reinforcement material used for its construction, its design, and the method of the construction. In this study, the behavior of a reinforced retaining wall was analyzed while changing the reinforcement spacing using LS-DYNA, a general finite-element program. Eight tons of truck weight was used for the numerical analysis model. The behavior of a reinforced retaining wall under variable reinforcement spacing and positioning was analyzed. The results indicated that the reinforcement material was an important resistance factor against external collision load.

Soft ground stabilization is needed to construct large civil facilities on the soft clay ground. Pre-loading method, which is accelerating consolidation method, is generally used to stabilize the soft ground. However, pre-loading method is required long construction period and quantities of fill material. Therefore, electro-osmosis method is used to replace pre-loading method for stabilizing the soft ground. Electro-osmosis method is disadvantageous in constructive and economic aspects because it is needed a metallic electrode. So, in order to solve the those disadvantages, plastic electrode was developed to replace metallic electrode. Plastic electrode, which is made by using nano-technology on existing Plastic Drain Board (PDB), was used to supply the electric power. In this study, therefore, the model test was conducted to confirm the effect of improvement and electrical characteristics of soft ground by spacing of plastic electrode. The result shows that the effect of improvement of soft ground was decreased up to 45% by increasing electrode spacing and electrical characteristics on the soft ground were influenced by consolidation settlement with electrode spacing.

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