Han-Saem Kim

Geo-spatial data integration for subsurface stratification of dam site with outlier analyses

A geo-spatial data integration method for three-dimensional subsurface stratification is proposed in this study. The proposed method integrates the boring data modified with the cross-validation based outlier detection method and the geophysical testing results using indicator kriging to offer the appropriate criteria of P-wave velocity, which are derived site specifically to classify the local geomaterials for dam site. Cross-validation for the outlier analysis of boring data is a test to evaluate the susceptibility of variogram models or kriging models and to reduce the statistical uncertainty of the boring data, and indicator kriging, the integration method, is characterized by geostatistical non-linear procedures to model the variability of spatial attributes. Using the integration method, the site-specific criteria of geomaterials are determined. The computer software is developed for the proposed method with ArcGIS developer tool and GSLIB. The results show that this proposed method presents more reliable stratification results than the conventional classification criteria.

Geostatistical assessment for the regional zonation of seismic site effects in a coastal urban area using a GIS framework

Earthquake-induced hazards are profoundly affected by site effects related to the amplification of ground motions, which are strongly influenced by local geologic conditions such as soil thickness, bedrock depth, and soil stiffness. Seismic disasters are often more severe over soft soils than over stiff soils or rocks due to differences in local site effects. In this study, on the basis of a geotechnical information system (GTIS) framework, we developed an advanced geostatistical assessment for the regional zonation of seismic site effects. In particular, to reliably predict spatial geotechnical information, we developed a procedural methodology for building an advanced GTIS within a geographic information system framework and applied it to the Busan area in Korea. The systemized GTIS comprised four functional components: database, geostatistical analysis, geotechnical analysis, and visualization. First, to build the GTIS, we collected pre-existing geotechnical data in and around the study area, and then conducted a walk-over site survey to acquire surface geo-knowledge data. Second, we determined the optimum geostatistical estimation method using a cross-validation-based verification test, considering site conditions. The advanced GTIS was used in a practical application to estimate the site effects in the study area. We created seismic zoning maps of geotechnical earthquake parameters, such as the depth to bedrock and the site period, and present them as part of a regional synthetic strategy for earthquake risk assessment.

Application of statistical geo-spatial information technology to soil stratification in the Seoul metropolitan area

Typical geotechnical testing results reflect the level of soil uncertainty, which requires statistical corrections of the data for an appropriate engineering decision. This study proposes frameworks to detect outlying data points using statistical analyses, the cross-validation-based method and the generalised extreme value distribution-based method. The borehole data regarding soil depth distribution in a central area of Seoul, South Korea are assessed to validate the aforementioned methods for comparison with the distribution-based method and the Moran scatterplot method. The results show that the proposed methods enable more reliable spatial distributions to be achieved with a quantitative evaluation of local reliability.

Geospatial Big Data-Based Geostatistical Zonation of Seismic Site Effects in Seoul Metropolitan Area

Seismic site effects are influenced mainly by geospatial uncertainties corresponding to geological or geotechnical spatial variance. Therefore, the development of a geospatial database is essential to characterize site-specific geotechnical information in multiscale areas and to optimize geospatial zonation methods with potentially high degrees of spatial variability based on trial-and-error geostatistical assessments. In this study, a multi-source geospatial information framework, which included the construction of a big data platform, estimation of geostatistical density, optimization of the geostatistical interpolation method, assessment of seismic site effects, and determination of geospatial zonation for decision making, was established. Then, this framework was applied to the Seoul metropolitan area, South Korea. The GIS-based framework was established to develop the geospatial zonation of site-specific seismic site effects before considering the local characteristics of site effects dependent on topographic or geological conditions, based on a geospatial big-data platform in Seoul. The zonal conditions were composed of geo-layers, site effect parameters, and other multi-source geospatial maps for each administrative area, and infrastructure was determined based on the integration of the optimized geoprocessing framework.

GIS-based regional assessment of seismic site effects considering the spatial uncertainty of site-specific geotechnical characteristics in coastal and inland urban areas

ABSTRACT Earthquake-induced hazards are profoundly affected by site effects related to the amplification of ground motions, which are strongly influenced by site-specific geologic conditions such as soil thickness, bedrock depth and soil stiffness. Seismic disasters are often more severe in coastal or riverside locations than over stiff soils or rocks due to differences in local site effects. In this study, a recently developed geographic information system-based framework was applied in coastal and inland urban areas in Korea, and its applicability for regional assessments was evaluated using appropriate geostatistical zonation of site-specific seismic site effects. The proposed framework was composed of four functional components: multivariable statistical clustering, geostatistical optimization, geotechnical analysis, and local visualization. The framework was applied in the Seoul and Busan areas of Korea for consideration of site effects in inland and coastal urban areas. Such zones of thick soil, or with a deep depth to bedrock, are susceptible to ground motion amplification due to site effects during earthquakes. The earthquake losses associated with possible building damage can be estimated based on spatial zoning maps considering geological and topographical characteristics and by a comparison of the spatial correlations of seismic site classes between inland and coastal areas of Korea.

Integrated system for site-specific earthquake hazard assessment with geotechnical spatial grid information based on GIS

An integrated earthquake hazard assessment system with geotechnical spatial grid information was developed based on a geographic information system (GIS). The developed system, built, within the frame of GIS, consists of a database (DB) containing all available site information and processed data in the standard formats, and system software that performs various functions to manage and utilize the data in the DB. The system software is divided functionally into an input module, a geostatistical three-dimensional integration module, a real-time earthquake hazard assessment module, and an output or visualization module. A systematic framework for construction of a geotechnical spatial grid was developed to consider local site response characteristics for target areas. According to the framework, three interrelated assessment procedures were incorporated into the DB on a real-time basis: real-time seismic load determination, real-time liquefaction hazard estimation, and real-time structure fragility evaluation. The DB and these sub-modules of the system software were combined and integrated into a single system to provide a familiar and user-friendly working environment with a standard interface. In addition, the integrated system was imbedded into the Korea Integrated Seismic System server to be linked with real-time seismic accelerations, and a simulation of the system was specifically conducted at Incheon Port, Korea, using two actual earthquake events (the 2013 Baengnyeong and 2014 Taean earthquakes) and one virtual earthquake scenario. The simulation results were visualized as a geotechnical earthquake hazard map to verify the computer-aided real-time assessment framework at the times, when the three notable earthquake events occurred at the nearby Incheon Port.

A GIS-Based Framework for Real-Time Debris-Flow Hazard Assessment for Expressways in Korea

Debris flows caused by heavy rainfall in mountain areas near expressways lead to severe social and economic losses and sometimes result in casualties. Therefore, the development of a real-time system for debris-flow hazard assessment is necessary to provide preliminary information for rapid decision making about evacuations or restoration measures, as well as to prevent secondary disasters caused by debris flows. Recently, various map-based approaches have been proposed using multi-attribute criteria and assessment methods for debris-flow susceptibilities. For the macrozonation of debris-flow hazard at a national scale, a simplified method such as the Korea Expressway Corporation (KEC) debris-flow hazard assessment method can be applied for systematic analysis based on geographic information systems (GIS) and monitoring networks. In this study, a GIS-based framework of real-time debris-flow hazard assessment for expressway sections is proposed based on the KEC debris-flow hazard assessment method. First, the KEC-based method was standardized in a systematic fashion using ArcGIS, enabling the objective and quantitative acquisition of various attribute datasets. The quantification of rainfall criteria also was considered. A safety management system for debris-flow hazard was developed based on the GIS platform. Finally, the method was applied and verified on three expressway sections in Korea. The grading standard for each individual influencing attribute was subsequently modified to more accurately assess the debris-flow hazards.

Visible Assessment of Earthquake-induced Geotechnical Hazards by Adopting Integrated Geospatial Database in Coastal Facility Areas

Earthquake event keeps increasing every year, and the recent cases of earthquake hazards invoke the necessity of seismic study in Korea, as geotechnical earthquake hazards, such as strong ground motion, liquefaction and landslides, are a significant threat to structures in industrial hub areas including coastal facilities. In this study, systemized framework of integrated assessment of earthquake-induced geotechnical hazard was established using advanced geospatial database. And a visible simulation of the framework was specifically conducted at two coastal facility areas in Incheon. First, the geospatial-grid information in the 3D domain were constructed with geostatistical interpolation method composed of multiple geospatial coverage mapping and 3D integration of geo-layer construction considering spatial outliers and geotechnical uncertainty. Second, the behavior of site-specific seismic responses were assessed by incorporating the depth to bedrock, mean shear wave velocity of the upper 30 m, and characteristic site period based on the geospatial-grid. Third, the normalized correlations between rock-outcrop accelerations and the maximum accelerations of each grid were determined considering the site-specific seismic response characteristics. Fourth, the potential damage due to liquefaction was estimated by combining the geospatial-grid and accelerations correlation grid based on the simplified liquefaction potential index evaluation method.

Three-dimensional geostatistical integration of borehole and geophysical datasets in developing geological unit boundaries for geotechnical investigations

Borehole data are more commonly used than other geotechnical methods for determining the 3D geospatial information of a given site. However, the inadequate acquisition of continuous geotechnical information over an entire site limits the usefulness of this technique. In contrast, 2D continuous geophysical tomography over a large area reveals geophysical characteristics that can be transformed into geotechnical information. It is therefore possible to obtain more reliable stratal information by combining borehole datasets and geophysical measurements using geostatistical methods. In this study, a 3D geostatistical integration method incorporating site-specific geotechnical variability was proposed to construct a 3D geospatial database for developing geological unit boundaries for engineering projects. First, borehole datasets, reviewed by a geologist, were modified to fit a geostatistical trend of geological strata using a cross-validation-based outlier detection method. Then, site-specific geological layer criteria were determined based on proper statistical comparisons to convert geophysical values into boundary criteria for each geological layer. Finally, 3D geospatial information incorporating site-specific geomaterial characteristics was determined using indicator kriging. The proposed framework was established as functional modules in a geographic information system (GIS) platform and applied to three testbeds in Korea, incorporating a variety of site conditions such as spatial variability of coastal and mountainous areas, to validate its applicability depending on various geophysical characteristics. Application of the proposed framework indicates increases in estimation accuracy of 3D subsurfaces using geophysical and borehole information. However, the geostatistical integration of the two datasets has limited application in areas of geological complexity, such as areas with faults or anisotropic geological strata.

Geospatial Assessment of the Post-Earthquake Hazard of the 2017 Pohang Earthquake Considering Seismic Site Effects

The 2017 Pohang earthquake (moment magnitude scale: 5.4) was South Korea’s second strongest earthquake in decades, and caused the maximum amount of damage in terms of infrastructure and human injuries. As the epicenters were located in regions with Quaternary sediments, which involve distributions of thick fill and alluvial geo-layers, the induced damages were more severe owing to seismic amplification and liquefaction. Thus, to identify the influence of site-specific seismic effects, a post-earthquake survey framework for rapid earthquake damage estimation, correlated with seismic site effects, was proposed and applied in the region of the Pohang earthquake epicenter. Seismic zones were determined on the basis of ground motion by classifying sites using the multivariate site classification system. Low-rise structures with slight and moderate earthquake damage were noted to be concentrated in softer sites owing to the low focal depth of the site, topographical effects, and high frequency range of the mainshocks.