• Earthquakes and Structures
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• v.20 no.1
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• pp.87-96
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• 2021

Ground motions recorded in near-fault sites, where the rupture propagates toward the site, are significantly different from those observed in far-fault regions. In this research, finite element modeling is used to investigate the effect of pile cap stiffness on the seismic response of soil-pile-structure systems under near-fault ground motions. The Von Wolffersdorff hypoplastic model with the intergranular strain concept is applied for modeling of granular soil (sand) and the behavior of structure is considered to be non-linear. Eight fault-normal near-field ground motion records, recorded on rock, are applied to the model. The numerical method developed is verified by comparing the results with an experimental test (shaking table test) for a soil-pile-structure system. The results, obtained from finite element modeling under near-fault ground motions, show that when the value of cap stiffness increases, the drift ratio of the structure decreases, whereas the pile relative displacement increases. Also, the residual deformations in the piles are due to the non-linear behavior of soil around the piles.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.03a
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• pp.69-76
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• 2003

Near-field ground motions exhibit special characteristics that are different from ordinary far-field ground motions. This paper first briefly examines the characteristics of near-field ground motions associated with fault directivity and fling-step effects. Then evaluation of near-field ground motions by inelatstic response spectrum analysis is performed and analyzed. As a result, ductility demand in near-field ground motions is larger in hanging wall than in foot wall in long period regions. Also in long period regions ductility demand in soil site is larger than that in rock site.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.285-289
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• 2005

The Cenozoic Era consists of two period , the Tertiary and the Quaternary Period. Weak rock types may include areas containing: 1) poorly cemented or uncemented sediments, 2) highly weathered rock, or 3) fault lines. Especially this paper deal with poorly cemented or uncemented sedimentary rocks in slope. Mechanical weathering is caused by physical processes such as absorption and release of water, and changes in temperature and stress at or near the exposed rock surface. It results in the opening of discontinuities, the formation of new discontinuities by rock fracture, the opening of grain boundaries, and the fracture or cleavage of individual mineral grains. Decomposition causes some silicate minerals such as feldspars to change to clay minerals. There was a strong negative correlation between water absorption and important engineering properties such as strength and durability.

• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2003.04a
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• pp.219-222
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• 2003

Even through hundreds of meters high steep slope is stable, only several ten meters high dull slope could be collapsed. This means that stability of slope is depend on the slope of a surface of discontinuity like faults existing in rock floor. The existence and nonexistence of a discontinuity surface have a very important effect to the stability of a rock floor slope, and examination for geologic peculiarity is one of the most important pant for investigation of stabilities. Accordingly, in the study, we extracted three dimension coordinates of slope with close photogrammetry, and through interpretations of three dimensions' position of fault within rock floor slope, we expect this will be use as a important sauces when evaluate stabilities of rock floor slope.

• Journal of the Korean Geophysical Society
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• v.2 no.1
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• pp.45-56
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• 1999

Seismic refracrion and reflection surveys were conducted along an E-W trending track of 482 m long in Ilwall-dong, Pohang. End-on spread was employed as source-receiver configuration with 2 m for both geophone interval and offset. Seismic data were acquired using 24 channels at every shot fired every 2 m along the track. Refraction data were interpreted using equations for multi-horizontal layers. Reflection data were processed in the sequence of trace edit, gain control, CMP sorting, NMO correction, mute, common offset gathering, and filtering to produce a single fold seismic section. There are two layers in shallow subsurface of the study area. Upper layer has the P-wave velocities ranging from 267 to 566 m/s and is interpreted as a layer of unconsolidated sediments. Lower layer has P-wave velocities of 1096-3108 m/s and is interpreted as weathered rock to hard rock. Most of the lower layer classified as soft rock. Upper layer has lateral variations in both P-wave velocity and thickness. The upper layer in the eastern part of the seismic line is 3-5 m thick and has P-wave velocity of 400 m/s in average. The upper layer in the western part is 8-10 m thick and has P-wave velocity of 340 m/s in average. The eastern part is interpreted as unconsolidated beach sand, while the western part is interpreted as infilled soil to develop a construction site. Three fault systems of high angle are imaged in seismic reflection section. It is interpreted that the area between these fault systems are relatively safe. Large buildings should be located in the safe ground condition of no fault and footings should be designed to be in the basement rock of 3-10 m deep below the surface.

• Journal of the Korean Geosynthetics Society
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• v.18 no.3
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• pp.11-22
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• 2019

This study was conducted to identify the causes of the unusually high number of rock slope failures during an expressway construction in Yangsan fault system. The shear strength (cohesion and internal friction angle) of 128 slopes of discontinuities including bedding, joint, and fault planes were re-evaluated through the examination of face mapping and back analysis. The re-evaluated values were analyzed and then compared with the existing data and values used in the design. As a result, the re-evaluated cohesion and friction angles were very low compared to the existing data and the values applied in the design. This incongruity was pointed as the primary reason for the rock slopes failures during the construction. This may be related to the inherent features of clastic sedimentary rocks in the study area, and the discontinuities in the sedimentary rocks in this region played a significant role. Especially, bedding discontinuity showed a big difference compared to the existing data. The shear strength depended on the type of discontinuity in case of clay filled in discontinuity. However, shear strength was independent on the type of discontinuity in case of shattered materials filled in discontinuity.

• Proceedings of the Korean Geotechical Society Conference
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• 2007.09a
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• pp.160-169
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• 2007

In this study, Analyzed stress history, state of stress, ratio of stress/strength to use FEM. Fault Zone depth is 3m, 6m, 9m, 12m and 15m for study, and also Distance is 3m, 6m, 9m, 12m and 15m at center of tunnel with thickness 3m fault zone. It is not appeared that Arching in stress state and stress history by FEM. On the other hand, excessive shear stress and high compressive stress happened. Therefore, Tunnel design is desirable that do it so that state of stress that is the imbalance may be uplemented. it is important that examine each state of stress and stress history in detail tunnel design.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.121-128
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• 2001

This is a case study of stability analysis and reinforcement design for the tunnel where the collapse of the entrance slops occured along the fault zone developed in the bed rock. According to the site investigation, the main factor of sliding is the influence of fault gouge and heavy rainfall. Considering the in-situ condition, the versatile reinforcement methods is needed, and so the close investigation on the site area was accompanied with the stability analysis of tunnel and slops. The FRP(Fiberglass reinforced plastic) grouting method improved the defect of Steel Umbrella Arch Method, such as oxidation, low work efficiency, the material's heavy weight, is adapted as the reinforcement methods.

• Tunnel and Underground Space
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• v.28 no.5
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• pp.400-425
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• 2018

This study presents the research results and current status of the DECOVALEX-2019 project Task B. Task B named 'Fault slip modelling' is aiming at developing a numerical method to simulate the coupled hydro-mechanical behavior of fault, including slip or reactivation, induced by water injection. The first research step of Task B is a benchmark simulation which is designed for the modelling teams to familiarize themselves with the problem and to set up their own codes to reproduce the hydro-mechanical coupling between the fault hydraulic transmissivity and the mechanically-induced displacement. We reproduced the coupled hydro-mechanical process of fault slip using TOUGH-FLAC simulator. The fluid flow along a fault was modelled with solid elements and governed by Darcy's law with the cubic law in TOUGH2, whereas the mechanical behavior of a single fault was represented by creating interface elements between two separating rock blocks in FLAC3D. A methodology to formulate the hydro-mechanical coupling relations of two different hydraulic aperture models and link the solid element of TOUGH2 and the interface element of FLAC3D was suggested. In addition, we developed a coupling module to update the changes in geometric features (mesh) and hydrological properties of fault caused by water injection at every calculation step for TOUGH-FLAC simulator. Then, the transient responses of the fault, including elastic deformation, reactivation, progressive evolutions of pathway, pressure distribution and water injection rate, to stepwise pressurization were examined during the simulations. The results of the simulations suggest that the developed model can provide a reasonable prediction of the hydro-mechanical behavior related to fault reactivation. The numerical model will be enhanced by continuing collaboration and interaction with other research teams of DECOLVAEX-2019 Task B and validated using the field data from fault activation experiments in a further study.

• Geotechnical Engineering
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• v.12 no.6
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• pp.37-50
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• 1996

In this study, we collected data through the investigation of rock slopes of highway. By analyzing the collected data, the main factors of rock slope failure were studied. We studied on the failure types and scales according to rock types and geological structures in many rock slopes of highway. As a result, it was shown that many failed slopes were distributed in the areas of Cretaceous sedimentary rocks of south-eastern part in the Korean Peninsula and the Gneiss Complex in both Kyonggi-Do and Kangwon-Do. According to rock types, the following slope failure types were shown : that igneous rocks had the types of rock fall, plane failure, soil erosion and circular failure but had low failure frequency, and sedimentary rocks had predominantly the type of plane failure. Metamorphic rock showed the types of circular failure, wedge failure and plane failure due to poor rock qualities . According to geological structures, the following slope failure types were shown slope failure in igneous rocks was caused by joints, and in sedimentary rocks by bedding plane, and in metamorphic rocks by faults and poor rock qualities.