Yong-k Seo

Marinoscillum luteum sp. nov., isolated from marine sediment.

A novel strain, designated SJP7(T), was isolated from sediment of the Tofua Arc of the Tonga Trench. The 16S rRNA gene sequence of the isolate showed the highest similarity to that of Marinoscillum pacificum KCCM 42325(T) (95.9%). Phylogenetic analysis revealed that the isolate formed a distinct phyletic line with Marinoscillum pacificum KCCM 42325(T) and Marinoscillum furvescens LMG 13023(T) within the family Cytophagaceae. Cells of strain SJP7(T) were Gram-stain-negative and appeared as long rods that were motile by gliding. Growth was observed at 15-40 °C (optimum, 30 °C), at pH 5.5-9.0 (optimum, pH 7.5-8.0) and in the presence of 0.5-7.0% (w/v) NaCl (optimum, 2.5-3%). The major respiratory quinone was MK-7. The dominant fatty acids were summed feature 3 (comprising C(16:1)ω7c and/or C(16:1)ω6c), iso-C(15:0) and C(16:1)ω5c. The DNA G+C content was 43.5 mol%. These properties support the affiliation of strain SJP7(T) with the genus Marinoscillum. Further phenotypic differentiation of strain SJP7(T) from other species of the genus Marinoscillum was indicated by the results of physiological and biochemical tests. On the basis of evidence from our polyphasic taxonomic study, strain SJP7(T) represents a novel species of the genus Marinoscillum, for which the name Marinoscillum luteum sp. nov. is proposed. The type strain of Marinoscillum luteum is SJP7(T) ( =KCTC 23939(T) =NCAIM B02491(T)).

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.

Suggestion of a Landslide Early Warning Method Using a Gradient of Volumetric Water Content

This study involved the installation of a real-time monitoring system to observe physical property changes in soils in a slope during rainfall events. This monitoring included the measurement of volumetric water content, which was compared with the results of laboratory flume tests to identify landslide indicators in the soils. The response of volumetric water content to rainfall events is more immediate than that of pore-water pressure, and volumetric water content retains its maximum value for some time before a slope failure. Therefore, an alternative method for landslide monitoring can be based on the observation of volumetric water content and its changes over a time at shallow soil depths. Although no landslide occurred, the field monitoring results showed a directly proportional relationship between the effective cumulative rainfall and the gradient of volumetric water content per unit time (t/t max ). This preliminary study thus related slope failure to the volumetric water content gradient as a function of rainfall. Laboratory results showed that a high amount of rainfall and a high gradient of volumetric water content can induce slope failure. Based on these results, it is possible to suggest a threshold value of the volumetric water content gradient demarcating the conditions for slope stability and slope failure. This threshold can thus serve as the basis of an early warning system for landslides considering both rainfall and soil properties.

Prediction of fault zone ahead of tunnel face using x-Rs control chart analysis for crown settlement

A measurement of tunnel displacement plays an important role for stability analysis and prediction of possible fault zone ahead of tunnel face. In this study, we evaluated characteristics of tunnel behaviour due to the existence and orientation of fault zone based on 3-dimensional finite element numerical analysis. The crown settlement representing tunnel behaviour is acquired at 5 m away from tunnel face in combination with x-Rs control chart analysis based on statistics for trend line and L/C (longitudinal/crown displacement) ratio in order to propose risk management method for fault zone. As a result, x-Rs control chart analysis can enable to predict fault zone in terms of existence and orientation in tunnelling.

A STUDY OF THE PRESSURE SOLUTION AND DEFORMATION OF QUARTZ CRYSTALS AT HIGH pH AND UNDER HIGH STRESS

Bentonite is generally used as a buffer material in high-level radioactive waste disposal facilities and consists of 50% quartz by weight. Quartz strongly affects the behavior of bentonite over very long periods. For this reason, quartz dissolution experiment was performed under high-pressure and high-alkalinity conditions based on the conditions found in a high-level radioactive waste disposal facility located deep underground. In this study, two quartz dissolution experiments were conducted on 1) quartz beads under low-pressure and high-alkalinity conditions and 2) a single quartz crystal under high-pressure and high-alkalinity conditions. Following the experiments, a confocal laser scanning microscope (CLSM) was used to observe the surfaces of experimental samples. Numerical analyses using the finite element method (FEM) were also performed to quantify the deformation of contact area. Quartz dissolution was observed in both experiments. This deformation was due to a concentrated compressive stress field, as indicated by the quartz deformation of the contact area through the FEM analysis. According to the numerical results, a high compressive stress field acted upon the neighboring contact area, which showed a rapid dissolution rate compared to other areas of the sample.

Determination of representative elementary volume of fault core materials by particle distribution analysis

Fault core materials (fault breccia and fault gouge) exhibit heterogeneous particle size distributions due to many factors, including the type of cataclasis, the degree of weathering, and the scale and mechanism of the fault system. When studying particle size distributions in fault core materials, there is no clear standard of the sample size that should typically be used for testing and analysis. In this study, we present a method to establish the ideal sample size by statistically assessing a suite of laboratory tests on 451 fault-core samples from 21 locations in South Korea. These samples were divided into five different classes according to grain size. Weight ratios of gravel, sand, and silt/clay were calculated from laboratory tests on each sample, and the means and standard deviations were subsequently assessed via analysis of variance and multiple comparison analysis. The results of the analysis of variance suggested that classes 1–5 are different from each other in at least one factor. Tukey’s HSD tests and Duncan’s LSR tests were also applied to identify groups within the classes that might be statistically similar to each other. In this manner, it was found that classes 1 and 2 could be grouped together (group A), as could classes 3, 4, and 5 (group B). Standard deviation means and distribution ranges within groups were used to deduce that group B, rather than group A, contained the sample sizes that best represented the site. Furthermore, class 3 (which had the smallest weight among the different classes in group B) was determined as being the representative elementary volume (REV). This deduction is consistent with the recommendation for reference sample size used in soil particle size analysis (as defined by the American Society for Testing and Materials).

Classification of geological and engineering properties in weak rock: a case study of a tunnel in a fault zone in southeastern Korea

Given that the rock mass classifications of weak rocks observed in tunnels are evaluated only as ‘poor rock mass’ or grades IV–V using existing rock mass classification methods, a new scheme is needed that would better distinguish the various geological properties of weak rocks. In this study, geological and engineering properties of weak rocks were classified based on the analysis results of a total of 55 faces in a tunnel that passes through a fault zone in southeastern South Korea. Geological observations, point load tests, and Schmidt hammer tests were conducted to analyze the properties of the weak rocks. Through this analysis, the weak rocks were classified into two weathering types: ‘disintegrated rocks’ and ‘decomposed rocks’. This division is based on the tectonic mechanisms and parameters necessary to determine the engineering geological properties of individual rock-weathering types according to their geological properties. The ‘disintegrated rocks’ have been physically weathered by brittle deformation and are classified into three subtypes using the rock quality designation (RQD) and joint set number (Jn), which can characterize the discontinuity properties of the rocks. Point load tests were conducted on these individual subtypes to calculate the point load index (Is(50)). The resultant values are clearly related to the assigned three subtypes. The ‘decomposed rocks’ have been chemically weathered by ductile deformation and are classified into five subtypes based on the results of Schmidt hammer tests conducted on faces and Is(50) values calculated using the average of the Schmidt hammer values. The geological properties of the individual subtypes of the ‘disintegrated rocks’ and ‘decomposed rocks’ are clearly related to their engineering properties. Based on these results, rock mass classification diagrams are proposed that can be simply and easily applied to weak rocks.

Interaction between an Eco-Spiral Bolt and Crushed Rock in a Borehole Evaluated by Pull-Out Testing

The interactions between an eco-spiral bolt and crushed rocks in a borehole were evaluated by pull-out testing in a laboratory and numerical analysis. The porosity of the crushed rock surrounding the bolt depended on the size of the eco-spiral bolt and affected the eco-spiral bolt’s axial resistance force. The axial resistance force and the porosity of the crushed rocks in the borehole showed an inverse relationship. The porosity was also related to the size of the eco-spiral bolt. The maximum principal stress between the bolt and the rock was related to the porosity of the crushed rock and the size difference between the eco-spiral bolt and the borehole. At low porosity the experimental and numerical analyses show similar relationships between the axial resistance force and the displacement. However, at high porosity, the numerical results deviated greatly from the experimental observation. The initial agreement is attributed to the state of residual resistance after the maximum axial resistance force, and the latter divergence was due to the decreasing axial resistance force owing to slippage.

Database Construction for Tunnel Management in Korea

In the present study, we introduce the database constructed for tunnel maintenance. The item of database is standardized by selecting elements necessary for maintenance of approximately 400 tunnels on general national roads in South Korea. The forms and items for database standardization were derived by analyzing various data of tunnel such as design documents, specifications, maintenance data, calculation reports, drawings, and panoramic photographs. We analyzed statistically geological and geotechnical factors of 202 tunnel cases based on support patterns. The database system can be used for optimum performance, accident prevention, quick selection of deformation repair and reinforcement methods and efficient management of deteriorated facilities during tunnel operation.

Effect of geological characteristics on differential weathering of low-graded metasedimentary rock slopes

This study evaluates correlation between petrographic characteristics and weathering grade of low-graded metasedimentary rocks mainly consisting of phyllite. Weathering grade of rock material was determined based on the results of geological survey. The Schmidt hammer test was carried out to obtain estimates of strength of rock materials. Point counting and microscopic observation were also conducted to analyze mineral composition and to measure spacing of foliation for 9 rock specimens. As a result of microscopic analysis, as the weathering grade was lower, the quartz was found more in quantity, consequently making rock stronger against weathering process. On the other side, lower weathering grade of rock resulted in less content of mica which is weak against weathering process. In addition, the rock materials with closer foliation spacing are found to be weaker in strength and have higher weathering grade.