Kwang Yeom Kim

Effect of hydrate nucleation mechanisms and capillarity on permeability reduction in granular media

A model for water permeability reduction in hydrate-bearing sediments is presented by considering capillary effect in hydrate nucleation. Both grain-coating and pore-filling cases are considered. The model is developed from a series of lattice Boltzmann flow simulations. Results show that the permeability decreases quasi-linearly with increasing hydrate saturation during grain-coating nucleation and that the permeability tends to be higher than predicted by previous analytical models in which capillarity is not taken into account. The permeability follows unique reduction curve and is not so sensitive to initial sediment bulk density and grain size distribution. Simulations further show that there is a transition zone at Shydu2009=u20090.3u2009~u20090.4 where permeability reduction trend switches from grain-coating model to pore-filling model. Analyses of tortuosity and surface area confirm that the permeability reduction mechanisms result from pore-channel blocking in grain-coating case and pore-size reduction in pore-filling case.

Effect of particle shape on the shear strength of fault gouge

The shear strength of fault gouge plays an important role in the dynamic behavior of faults, ranging from small-scale displacements to severe earthquakes. The characteristics and interactions of constituent materials in fault gouge are the main determinants of shear strength. Assessing the shear strength of fault gouge by means of experiments, however, requires time-consuming procedures, including sampling, shear testing, and reliability checking; consequently, simple and indirect methods to assess shear strength in terms of the characteristics of fault gouge fragments have been investigated. This study focuses on the influence of the shape of fault gouge particles on the shear strength of gouge. We introduce a novel technique to obtain shape parameters of particles using Xray computed tomography (CT), and then show the effects of particle shape on the friction angle of the fault gouge. Samples collected from fault zones developed in various parent rock materials were tested in laboratory experiments to characterize their shear strengths. After shear testing, the particles in the fault gouge were collected, scanned by X-ray CT, and then analyzed for shape characterization. We successfully determined the shape parameters (sphericity, elongation, flatness, and slenderness) of the fault gouge fragments, and found that the parameters are well correlated with the friction angle of the gouge.

Time-Dependent Drainage Capacity and Runoff of Pervious Block Subjected to Repeated Rainfall Simulation

AbstractTo mitigate flood damage in cities, pervious concrete has been developed as a viable and sustainable alternative to traditional concrete to facilitate drainage. Previous studies have tended to evaluate the drainage capacity of pervious blocks through permeability and drainage tests in simplified conditions, giving little consideration to multiple environmental factors such as rainfall rate and temporal changes in the blocks’ drainage capacity. This study presents experimental results of the runoff and drainage capacity of pervious blocks subjected to time-dependent evaporation and corresponding changes in their degree of saturation. Different levels of repeated water charging at designated time intervals simulated the urban environment, and both runoff and drainage were continuously monitored. The results highlight that runoff can take place after certain time intervals despite the same water charge because of evaporation and prewetting-induced changes in water-retention capacity. The effects of t...