• Journal of the Society of Disaster Information
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• v.13 no.4
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• pp.483-490
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• 2017

Recently, the demand for industrial and residental land are increasing with economic growth, but it is difficult to obtain the area for development with good ground condition. Various kinds of vertical drain technologies such as sand drain, sand compaction pile, packed drain, PVD are commercially available to improve the soft ground. Discharge capacity is the important factor of vertical drains. However, under field conditions, discharge capacity is changed with various reasons, such as soil condition, overburden pressure, and so on. In this paper, the experimental study was carried out to estimate the discharge capacity of four different types of PBD, PBD for double core PBD, deep type PBD, X type PBD, general type PBD. Characteristics of the discharge capacity for the surcharge load and hydraulic gradient were analysed. The double core PBD was excellent for discharge capacity in this study.

• Journal of the Society of Disaster Information
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• v.14 no.3
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• pp.305-314
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• 2018

Purpose: Dynamic Replacement Method currently lacks of sufficient research, implementation cases, and case histories, compared with other comparable methods, such as Dynamic Compaction Method. Method: In this study, for Dynamic Replacement Method, the effective improvement depth and improved strength were analyzed for silty clayey soils. Results: Testbed test was performed to verify the effectiveness of Dynamic Replacement Method followed by the main dynamic replacement implementation on real construction site. Conclusion: A The effects of changes of soft ground depth, dynamic replacements' diameter, depth, spacing, and applied energy on dynamic replacement efficiency in silty clays were assessed and the followings were found: Empirical coefficient for soil $n_R$ of Dynamic Replacement Method was within the range of 0.14~0.32 and its ${\sqrt{WH}}$ is recommended to be 1.25~2.5 times of those from Dynamic Compaction Method.

• The Korean Journal of Mycology
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• v.46 no.2
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• pp.200-204
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• 2018

Sclerotinia rot symptoms were frequently found on the stems of Aster yomena in the Gurye region of Korea in April 2016. The symptom, watery soft rot, mainly appeared on the stems, and severely infected plants blighted. White mycelia spread over the stems of the infected plants and the soil surface. Small black sclerotia formed on the plant lesions and inside the diseased stems. Incidence of the disease was as high as 20~80% in the A. yomena fields. Based on the morphological and molecular characteristics of the isolates, the fungi were identified as Sclerotinia minor. This is the first report of Sclerotinia rot caused by Sclerotinia minor on A. yomena in Korea.

• The Journal of Engineering Geology
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• v.31 no.3
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• pp.269-281
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• 2021

Land creeping is the imperceptibly slow, steady, downward movement o f slope-forming soil or rock. Because creep-related failures occur frequently on a large scale without notice, they can be hazardous to both property and human life. Korea Forest Service has operated the prevention and response system from land creeping which has been on the rise since 2018. We categorized and proposed three survey steps (e.g., preliminary, regional, detailed) for investigation of creeping susceptibility site with a focus on geophysical mapping of a selected test site, Yongheung-dong, Pohang, Korea. The combination of geophysical (dipole-dipole electrical resistivity tomography and reciprocal seismic refraction technique, well-logging), geotechnical studies (standard penetrating test, laboratory tests), field mapping (tension cracks, uplift, fault), and comprehensive interpretation of their results provided the reliable information of the subsurface structures including the failure surface. To further investigate the subsurface structure including the sliding zone, we performed high-resolution geophysical mapping in addition to the regional survey. High-resolution seismic velocity structures are employed for stability analysis because they provided more simplified layers of weathering rock, soft rock, and hard rock. Curved slip plane of the land creeping is effectively delineated with a shape of downslope sliding and upward pushing at the apex of high resistive bedrock in high-resolution electrical resistivity model with clay-mineral contents taken into account. Proposed survey steps and comprehensive interpretation schemes of the results from geological, geophysical, and geotechnical data should be effective for data sets collected in a similar environment to land-creeping susceptibility area.

• Journal of the Korean Geotechnical Society
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• v.34 no.11
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• pp.71-80
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• 2018

In this study, the seismic response of cut-and-cover box tunnels is evaluated from pseudo-static analyses and the fragility curves are derived. A series of site profiles were used to evaluate the effect of soil conditions. A total of 20 ground motions were used. The fragility curves were developed as functions of peak ground acceleration for three damage states, which are minor, moderate, and extensive states. The damage indices, defined as the ratio of the elastic moment to the yield moment, correlated to three damage states, were used. The curves are shown to greatly depend on the site profile. The curves are further compared to those derived in previous studies. The widely used empirically derived curves are shown not to account for the site effects, and therefore underestimate the response for soft sites.

• Journal of the Korean Geotechnical Society
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• v.34 no.12
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• pp.59-69
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• 2018

In order to use the limit equilibrium theory, it is necessary to find a slip line under the ultimate failure condition. The strength reduction method using the Lagrangian finite element method defines the ultimate failure state at a time when the numerical solution cannot converge within the certain number of the iteration. When the coupled Eulerian-Lagrangian (CEL) method is used, however, such definition is inappropriate because the numerical solution of the CEL method can converge even under the ultimate failure condition. In this study, an objective condition designating the ultimate failure state in the finite element analysis adopting the CEL method was proposed. In the problem of the bearing capacity of the undrained soft ground subjected to the strip footing loading, we found that the rate of the plastic dissipated energy is highly sensitive at the load of the theoretical limit of the ultimate failure state.

• The Journal of Engineering Geology
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• v.31 no.1
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• pp.83-101
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• 2021

The high-density polyurethane method uses the instantaneous expansion pressure of injected material to stabilize soft ground, allowing reinforcement, restoration, and construction to be carried out in suboptimal ground conditions. Under normal and, even poor conditions, the method is easily applied because the working time is very short. The method is environmentally friendly and results have excellent durability. The purpose of this study was to verify the physical and mechanical properties of high-density polyurethane in the ground. Initial testing of strength, direct shear, and soil environment stability was followed by testing for permeability in order to address environmental concerns. The results of the experiments showed that the internal friction angle was about twice as high and the adhesion was about 2.5 to 3.5 times higher than for dense and hard clay, and that the permeability factor was significantly lower compared with the existing grouting method, within the range of 1.0 × 10-5.

• International conference on construction engineering and project management
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• 2009.05a
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• pp.432-439
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• 2009

This research project was carried out to develop the technique to assess quantitatively and rapidly the stability of a tunnel by using the measured displacement at the tunnel construction site under excavation. To achieve this purpose, a critical strain concept was introduced and applied to an assessment of a tunnel under construction. The new technique calculates numerically the strains of the surrounding ground by using the measured displacements during excavation. A numerical practical system was developed based on the proposed analysis technique in this study. The feasibility of the developed analysis module was verified by incorporating the analysis results obtained by commercial programs into the developed analysis module. To verify the feasibility of the developed analysis module, analysis results of models both elastic and elasto-plastic grounds were investigated for the circular tunnel design. Then the measured displacements obtained in the field are utilized practically to assess the safety of tunnels using critical strain concept. It was verified that stress conditions of in-situ ground and ground material properties were accurately assessed by inputting the calculated displacement obtained by commercial program into this module for the elastic ground. However for the elasto-plastic ground, analysis module can reproduce the initial conditions more closely for the soft rock ground than for the weathered soil ground. The stability of tunnels evaluated with two types of strains, that is, the strains obtained by dividing the crown displacement into a tunnel size and the strains obtained by using the analysis module. From this study, it is confirmed that the critical strain concept can be fully adopted within the engineering judgment in practical tunnel problems and the developed module can be used as a reasonable tool for the assessment of the tunnel stability in the field.

• Journal of the Korean Geotechnical Society
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• v.25 no.11
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• pp.117-130
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• 2009

In this paper, a series of laboratory chamber tests were carried out to evaluate the applicability of a porous concrete pile fabricated with recycled aggregates (RAPP) for the soft ground improvement. While performing the laboratory chamber tests for the RAPP, the surface settlement, excess pore pressure and vertical stress distribution with time were compared with those of SCP provided by You (2003) under the same experimental condition. In addition, the experimental results were compared with the numerical simulation using ABAQUS in this study. The results show that the settlement reduction is significantly enhanced due to the stress-sharing mechanism between the RAPP and soil formation by stress concentration on the RAPP. Furthermore, the comparison of consolidation rate shows that the RAPP can accelerate consolidation as well, which behaves as a vertical drain.

• Journal of the Korean Geotechnical Society
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• v.23 no.6
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• pp.115-126
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• 2007

The tilting-train is very attractive to the railroad users in the world because it runs with high speed in curved track using pre-existing infrastructure. The tilting-train has a unique allowable speed and mechanism expecially in curved track. Therefore, it should be evaluated in terms of the stability of the train operation and roadbed. In this study, when the tilting-train is being operated with the allowable speed, the behavior of the roadbed is evaluated by examining the settlement and bearing capacity of the roadbed. Additionally, the stability of the roadbed is estimated in the condition of soft roadbed influenced by the weather effects and cyclic train loading. The numerical results show that the roadbed settlements satisfy the allowable settlement when Young's moduli of the upper roadbed and in-situ soil are more than $2,300t/m^2\;and\;3,300t/m^2$, respectively, in the continuous welded rail (CWR) and $3,800t/m^2\;and\;4,600t/m^2$, respectively, in the rail joint.