• Journal of the Korean Geotechnical Society
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• v.39 no.5
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• pp.41-50
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• 2023

This study reviewed the liquefaction reinforcement and ground reinforcement methods widely used domestically and abroad through construction method characteristics and analyzed the economic feasibility and reinforcement efficiency of each reinforcement method. The analysis results were used to evaluate the applicability of the appropriate reinforcement method for the liquefaction reinforcement of new and existing structures. As a result of evaluating the applicability of the reinforcement method based on the economic feasibility and reinforcement effect of each reinforcement method, the compaction method, which secures the construct ability by applying large equipment, is advantageous when reinforcing a new structure, and the low-fluidity mortar injection method (C.G.S method) and the high-pressure injection method (J.S.P method) are considered appropriate in the existing structure.

• Nuclear Engineering and Technology
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• v.56 no.3
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• pp.973-979
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• 2024

In the framework of the Generation IV research and development project, in which the French Commission of Alternative and Atomic Energies (CEA) is involved, a main objective for the design of Sodium-cooled Fast Reactor (SFR) is to meet the safety goals for severe accidents. Among the severe ones, the Unprotected Transient OverPower (UTOP) accidents can lead very quickly to a global melting of the core. UTOP accidents can be considered either as slow during a Control Rod Withdrawal (CRW) or as fast. The paper focuses on fast UTOP accidents, which occur in a few milliseconds, and three different scenarios are considered: rupture of the core support plate, uncontrolled passage of a gas bubble inside the core and core mechanical distortion such as a core flowering/compaction during an earthquake. Several levels and rates of reactivity insertions are also considered and the thermal-mechanical behavior of an ASTRID fuel pin from the ASTRID CFV core is simulated with the GERMINAL code. Two types of fuel pins are simulated, inner and outer core pins, and three different burn-up are considered. Moreover, the feedback from the CABRI programs on these type of transients is used in order to evaluate the failure mechanism in terms of kinetics of energy injection and fuel melting. The CABRI experiments complete the analysis made with GERMINAL calculations and have shown that three dominant mechanisms can be considered as responsible for pin failure or onset of pin degradation during ULOF/UTOP accident: molten cavity pressure loading, fuel-cladding mechanical interaction (FCMI) and fuel break-up. The study is one of the first step in fast UTOP accidents modelling with GERMINAL and it has shown that the code can already succeed in modelling these type of scenarios up to the sodium boiling point. The modeling of the radial propagation of the melting front, validated by comparison with CABRI tests, is already very efficient.

• 한국석유지질학회:학술대회논문집
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• autumn
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• pp.63-65
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• 2001

The Chosen Supergroup (Cambro-Ordovician), mid-east Korea consists mainly of shallow marine carbonates and contains a variety of limestone conglomerates. These conglomerates largely comprise oligomictic, rounded lime-mudstone clasts of various size and shape (equant, oval, discoidal, tabular, and irregular) and dolomitic shale matrices. Most clasts are characterized by jigsaw-fit (mosaic), disorganized, or edgewise fabric and autoclastic lithology. Each conglomerate layer is commonly interbedded with limestone-dolomitic shale couplets and occasionally underlain by fractured limestone layer, capped by calcareous shale. According to composition, characteristic sedimentary structures, and fabric, limestone conglomerates in the Hwajol, Tumugol, Makkol, and Mungok formations of Chosen Supergroup can be classified into 4 types: (1) disorganized polymictic conglomerate (Cd), (2) horizontally stratified polymictic conglomerate (Cs), (3) mosaic conglomerate (Cm), and (4) disorganized/edgewise oligomictic conglomerate (Cd/e). These conglomerates are either depositional (Cd and Cs) or diagenetic (Cm and Cd/e) in origin. Depositional conglomerates are interpreted as storm deposits, tidal channel fills, or transgressive lag deposits. On the other hand, diagenetic conglomerates are not deposited by normal sedimentary processes, but formed by post-depositional diagenetic processes. Diagenetic conglomerates in the Chosen Supergroup are characterized by autoclastic and oligomictic lithology of lime-mudstone clasts, jigsaw-fit (mosaic) fabric, edgewise fabric, and a gradual transition from the underlying bed (Table 1). Autoclastic and oligomictic lithologies may be indicative of subsurface brecciation (fragmentation). Consolidation of lime-mudstone clasts pre-requisite for brecciation may result from dissolution and reprecipitation of CaCO3 by degradation of organic matter during burial. Jigsaw-fit fabric has been considered as evidence for in situ fragmentation. The edgewise fabric is most likely formed by expulsion of pore fluid during compaction. The lower boundary of intraformational conglomerates of depositional origin is commonly sharp and erosional. In contrast, diagenetic conglomerate layers mostly show a gradual transition from the underlying unit, which is indicative of progressive fragmentation upward (Fig. 1). The underlying fractured limestone layer also shows evidence for in situ fragmentation such as jigsaw-fit fabric and the same lithology as the overlying conglomerate layer (Fig, 1). Evidence from the conglomerate beds in the Chosen Supergroup suggests that diagenetic conglomerates are formed by in situ subsurface fragmentation of limestone layers and rounding of the fragments. In situ subsurface fragmentation may be primarily due to compaction, dewatering (upward-moving pore fluids), and dissolution, accompanying volume reduction. This process commonly occurs under the conditions of (1) alternating layers of carbonate-rich and carbonate-poor sediments and (B) early differential cementation of carbonate-rich layers. Differential cementation commonly takes place between alternating beds of carbonate-rich and clay-rich layers, because high carbonate content promotes cementation, whereas clay inhibits cementation. After deposition of alternating beds and differential cementation, with progressive burial, upward-moving pore fluid may raise pore-pressure in the upper part of limestone layers, due to commonly overlying impermeable shale layers (or beds). The high pore-pressure may reinforce propagation of fragmentation and cause upward-expulsion of pore fluid which probably produces edgewise fabric of tabular clasts. The fluidized flow then extends laterally, causing reorientation and further rounding of clasts. This process is analogous to that of autobrecciation, which can be analogously termed autoconglomeration. This is a fragmentation and rounding process whereby earlier semiconsolidated portions of limestone are incorporated into still fluid portions. The rounding may be due mainly to immiscibility and surface tension of lime-mud. The progressive rounding of the fragmented clasts probably results from grain attrition by fluidized flow. A synthetic study of limestone conglomerate beds in the Chosen Supergroup suggests that very small percent of the conglomerate layers are of depositional origin, whereas the rest, more than $80\%$, are of diagenetic origin. The common occurrence of diagenetic conglomerates warrants further study on limestone conglomerates elsewhere in the world.

• Journal of the Korean Geosynthetics Society
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• v.18 no.4
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• pp.151-165
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• 2019

In this study, the four types of improvement methods (increase self weight and reducing sliding force etc.) were proposed depending on install location with compaction grouting to improve seismic performance of existing port structure and optimal methods by analyzing the effects of improvement (stability, constructability and economy) by theoretical and numerical methods. From the dynamic time history analysis for artificial seismic waves, the results indicated that the horizontal displacement after improvement decreased compared to before improvement, however the displacement reduction effect among improvement methods was not significantly different. Slope stability based on the strength reduction method and the limit equilibrium analysis method, it is confirmed that the passive pile method is more safe than other methods. It is due to the shear strength at the failure surface is increased. In addition, the analysis of constructability and economy showed that the reduction of earth pressure method (type 02) and the passive pile method (type 03) are excellent. However, in the case of the passive pile method is concerned that there is a shortage of design cases and the efficiency can be reduced depend on various constraints such as ground conditions.

• Journal of the Korean Geosynthetics Society
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• v.15 no.3
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• pp.67-76
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• 2016

The railway bridge abutment subjected to the lateral earth pressure is a sensitive structure that is affected by backfill materials, installation methods, compaction, and drainage system and so on. The several design loads for the bridge abutment design consist of traffic loading on bridges and vertical & lateral force due to surcharge load at backfill. Especially, the lateral earth pressure of design load components is important and considered in the design of geotechnical engineering structure such as bridge abutment wall. The determination of cross section for abutment is finally determined with calculating external stability and member force of abutment wall structures. In this study, the abutment wall height is 12m and the optimal cross section of abutment wall has been determined that satisfies an external stability for abutment structure through friction angles of 35, 40, and 45 degrees of backfill materials. The external stability and member force of abutment wall with friction angle of backfill materials and were calculated and construction cost of each abutment wall structures was compared. It found that the construction cost was reduced from 2.2 to 8.4% with friction angle of backfill materials.

• Earthquakes and Structures
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• v.14 no.4
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• pp.323-336
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• 2018

Machine foundations with impact loads are common powerful sources of industrial vibrations. These foundations are generally transferring vertical dynamic loads to the soil and generate ground vibrations which may harmfully affect the surrounding structures or buildings. Dynamic effects range from severe trouble of working conditions for some sensitive instruments or devices to visible structural damage. This work includes an experimental study on the behavior of dry dense sand under the action of a single impulsive load. The objective of this research is to predict the dry sand response under impact loads. Emphasis will be made on attenuation of waves induced by impact loads through the soil. The research also includes studying the effect of footing embedment, and footing area on the soil behavior and its dynamic response. Different falling masses from different heights were conducted using the falling weight deflectometer (FWD) to provide the single pulse energy. The responses of different soils were evaluated at different locations (vertically below the impact plate and horizontally away from it). These responses include; displacements, velocities, and accelerations that are developed due to the impact acting at top and different depths within the soil using the falling weight deflectometer (FWD) and accelerometers (ARH-500A Waterproof, and Low capacity Acceleration Transducer) that are embedded in the soil in addition to soil pressure gauges. It was concluded that increasing the footing embedment depth results in increase in the amplitude of the force-time history by about 10-30% due to increase in the degree of confinement. This is accompanied by a decrease in the displacement response of the soil by about 40-50% due to increase in the overburden pressure when the embedment depth increased which leads to increasing the stiffness of sandy soil. There is also increase in the natural frequency of the soil-foundation system by about 20-45%. For surface foundation, the foundation is free to oscillate in vertical, horizontal and rocking modes. But, when embedding a footing, the surrounding soil restricts oscillation due to confinement which leads to increasing the natural frequency. Moreover, the soil density increases with depth because of compaction, which makes the soil behave as a solid medium. Increasing the footing embedment depth results in an increase in the damping ratio by about 50-150% due to the increase of soil density as D/B increases, hence the soil tends to behave as a solid medium which activates both viscous and strain damping.

• Restorative Dentistry and Endodontics
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• v.36 no.5
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• pp.377-384
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• 2011

Objectives: The purpose of this study was to observe the change in the viscoelastic properties of thermoplasticized injectable root canal filling materials as a function of temperature and to compare the handling characteristics of these materials. Materials and Methods: Three commercial gutta perchas and Resilon (Pentron Clinical Technologies) in a pellet form were heated in the Obtura-II system (Obtura Spartan) at $140^{\circ}C$ and $200^{\circ}C$, and the extrusion temperature of the thermoplasticized materials was measured. The viscoelastic properties of the materials as a function of temperature were evaluated using a rheometer. The elastic modulus G', viscous modulus G", loss tangent tan${\delta}$, and complex viscosity ${\eta}^*$ were determined. The phase transition temperature was determined by both the rheometer and a differential scanning calorimeter (DSC). The consistency of the materials was compared under compacting pressure at $60^{\circ}C$ and $40^{\circ}C$ by a squeeze test. Results: The three gutta perchas had dissimilar profiles in viscoelastic properties with varying temperature. The phase transition of softened materials into solidification occurred at $40^{\circ}C$ to $50^{\circ}C$, and the onset temperatures obtained by a rheometer and a DSC were similar to each other. The onset temperature of phase transition and the consistency upon compaction pressure were different among the materials (p < 0.05). Resilon had a rheologically similar pattern to the gutta perchas, and was featured between high and low-flow gutta perchas. Conclusions: The rheological characteristics of the thermoplasticized root canal filling materials changed under a cooling process. The dissimilar viscoelastic properties among the materials require different handling characteristics during an injecting and compacting procedure.

• Korean Journal of Agricultural Science
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• v.12 no.1
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• pp.86-100
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• 1985

In order to investigate the strength characteristics of weathered granite soils in unsaturated state, the five physically different weathered granite soils and the common soil (sandy loam) were examined. The disturbed and the undisturbed material were prepared for triaxial compression test. The following conclusions were drawn from the study; 1. Dry density of the undisturbed soil samples was lower than maximum dry density determined from the compaction test and it showed the higher value at the well graded soil. 2. The failure strength of the samples decreased with the increase of moisture content of the soil and these results were highly pronounced at the common soil sample having a good cohesive property. 3. On weathered granite soils, the cohesion was lower measured and the internal friction angle highly, the decrease rate at internal friction angle with increase of moisture content of the soil was more significant than that of cohesion 4. The modulus of deformation of the samples decreased with increase of moisture content of the soil and these phenomena were highly pronounced at the weathered granite soils than common soil. 5. The failure strength of the samples increased with in crease of confining pressure and effect of confining pressure on failure strength was highly significant at the lower moisture content of the soil.

• Magazine of the Korean Society of Agricultural Engineers
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• v.37 no.3_4
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• pp.61-71
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• 1995

Natural ground is a composite consisted of the three phases of water, air and soil paircies. Among the three components, water as a material is weU understood but soil particles are not in foundation engineering. Especially, weathered granite soil generally shows a large volumetric expansion when they freeze. And, the stability and durability of the soil have shown decreased with repetitive freezing and thawing processes. These unique charcteristics may cause various construction and management problems if the soil is used as a construction material and foundation layers. This project was initiated to investigate the soil's physical and engineering characteristics resulting from freezing and freezing-thawing processes. Research results may be used as a basic data in solving various problems related to the soil's unique characteristics. The following conclusions were obtained: The degree of decomposition of weathered granite soil in Kangwon-do was very different between the West and East sides of the divide of the Dae-Kwan Ryung. Soil particles distributed wide from very coarse to fine particles. Consistency could be predicted with a function of P200 as LL=0.8 P200+20. Permeability ranged from 10-2 to 10-4cm/sec, moisture content from 15 to 20% and maximum dry density from 1.55 to 1.73 g /cmΥ$^3$ By compaction, soil particles easily crushed, D50 of soil particles decreased and specific surface significantly increased. Shear characteristics varied wide depending on the disturbance of soil. Strain characteristics influenced the soil's dynamic behviour. Elastic failure mode was observed if strain was less than 1O-4/s and plastic failure mode was observed if strain was more than 10-2/s. The elastic wave velocity in the soil rapidly increased if dry density became larger than 1.5 g /cm$^3$ and these values were Vp=250, Vg= 150, respectively. Frost heave ratio was the highest around 0 $^{\circ}C$ and the maximum frost heave pressure was observed when deformation ratio was less than 10% which was the stability state of soil freezing. The state had no relation with frost depth. Over freezing process was observed when drainage or suction freezing process was undergone. Drainage freezing process was observed if freezing velocity was high under confined pressure and suction frost process was occurred if the velocity was low under the same confined process.

• Journal of the Korean Geotechnical Society
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• v.24 no.5
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• pp.117-127
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• 2008

The volumetric pressure plate extractor (VPPE) was modified for the measurement of shear wave velocity ($V_s$) at various levels of matric suction as well as soil water characteristic curve (SWCC). A non-destructive technique with a pair of bender element (BE) was employed in order to measure the $V_s$ and the corresponding maximum shear modulus ($G_{max}$) of unsaturated soil specimens. Three types of soil were collected from different road construction sites in Korea. For all test soils, the variations in $G_{max}$ with the various levels of water content and matric suction were investigated using the developed apparatus. Compared with the preceding results from the suction-controlled torsional shear (TS) testing system and in-situ seismic tests, the feasibility fur evaluating modulus characteristics of unsaturated compacted soils with the developed VPPE-BE system was assessed. It was confirmed that the newly developed system would be potentially helpful in modeling seasonal variation of modulus.