• Journal of Korean Society of Coastal and Ocean Engineers
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• v.3 no.1
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• pp.38-44
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• 1991

A simple box model was applied to the sedimentation of fine-grained sediments in a rectangular basin. Using the model explanation of the net depositional process of One-grained sediments in a small tide-dominated rocky embayment was possible by a careful evaluation of coefficients for erosion and deposition. For a basin with an inlet through which the exchange of suspended sediments occurs between open sea. the model shows that the time-averaged concentration of suspended sediments for a tidal cycle reaches a steady state initial abrupt change in concentration. During a tidal cycle deposition of sediments seems to occur when the magnitude of tidal currents is substantially low near the slack waters. Resuspension and erosion of bottom sediments take place near the peak of tidal currents. For a depositional basin. Gamagyang Bay, the duration and the maximum rate of deposition appear to be longer and higher than those of erosion. which accounts for the net deposition of fine-grained sediments. The time-averaged concentration of suspended sediment in the basin is slightly lower than that of the open water due to the net deposition. The instantaneous concentration of suspended sediments showed the maximum value about an hour before high water and the minimum about an hour after low water.

• Journal of the Korean Geotechnical Society
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• v.15 no.1
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• pp.99-112
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• 1999

By using 92 values of lateral earth pressure coefficient(K) measured in Korea, the tendency of K with varying depth is analyzed and compared with the range of K defined by Hoek and Brown. The horizontal stress is generally larger than the vertical stress in Korea : About 84 % of K values are above 1. In this study, the theory of elasto-plasticity is applied to analyze the variation of K values, and the results are compared with those of numerical analysis. This reveals that the erosion, sedimentation and weathering of earth crust are important factors in the determination of K values. Surface erosion, large lateral pressure and good rock mass increase the K values, but sedimentation decreases the K values. This study enable us to analyze the effects of geological processes on the K values, especially at shallow depth where underground excavation takes place. A neural network expert system using multi-layer back-propagation algorithm is developed to predict the K values. The neural network model has a correlation coefficient above 0.996 when it is compared with measured data. The comparison with 9 measured data which are not included in the back-propagation learning has shown an average inference error of 20% and the correlation coefficient above 0.95. The expert system developed in this study can be used for reliable determination of K values.

• Resources Recycling
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• v.15 no.4 s.72
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• pp.52-59
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• 2006

The purpose of this study was to evaluate the effects of ground granulated blast-furnace slag on strength development and durability of ordinary portland cement concrete (OPC) with steam curing types. Main experimental variables were slag contents(0%, 10%, 30%, 50%, 70%) and curing types (standard, accelerated curing). It were performed to check the basic properties of concretes that compressive strength, rapid chloride ion permeability and chemical resistance. From the result, we have found that increasing the amount of blast-furnace slag produced concrete with increased compressive strength and permeability resistance. Rapid freezing-thawing test showed that they were good enough to protect the concrete structures and to carry out cyclic freezing and thawing. The freeze-thaw resistance of blast-furnace slag produced concretes maintained above 90% of relative dynamic modulus after 300 freezing-thawing cycles. Increasing the amount of blast-furnace slag produced concretes with increased chemical resistance.

• Journal of Korea Water Resources Association
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• v.46 no.5
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• pp.531-545
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• 2013

This paper was considered on the applicability of EFDC KUNSAN_SEDTRAN MODEL (2012) to calculate Gunsan Port sediment deposition height efficiently and to use for grasping its aspects quantitatively and providing its prevention measures reasonably based on well-known 3-dimensional EFDC sediment transport module. This model was calibrated and verified with various measured field data of A Report of Hydrological Variation on Kum River Estuary (2004). Due to the model calibration and relevant literature investigation for cohesive sediment parameters, settling velocity (WS), critical deposition stress (TD), reference surface erosion rate (RSE), critical erosion stress (TE) were identified as 2.2E-04m/s, 0.20 $N/m^2$, 0.003 $g/s{\cdot}m^2$, 0.40 $N/m^2$ respectivly on this model. In order to examine the applicability and precision of the model computation, the calculated model data of sediment deposition height at 13 stations for 71 days and suspended-sediment concentration at 2 stations, inner port and outer port for 15 days were compared and analyzed with the measured field data. As a result, the model applicability for sediment deposition height simulation was evaluated as NSE coefficient 0.86 and the precision for suspended-sediment concentration computation was evaluated as time averaged relative error (RE) 23%.

• Journal of Korean Society of Forest Science
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• v.101 no.3
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• pp.538-545
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• 2012

This study addressed soil disturbances following harvesting as well as soil physical and hydrological properties within three first-order headwater catchments characterized by ephemeral-intermittent streams. Four treatments representing a range of potential Best Management Practices(BMPs) for ephemeral-intermittent streams were used; BMP1, BMP2, clearcut and reference. This study includes 1 year of pre- and post-harvest observations. Results showed that post-harvest disturbances were closely related with harvesting intensity and generally tended to reflect changes in soil physical and hydrological properties following harvest with the except of bulk density and porosity. Forest clearcutting decreased macroporosity and saturated hydraulic conductivity, and increased soil resistence as a result of severe soil disturbances thereby increasing soil erosion. These impacts were reduced by implementing two BMP treatments during harvesting activities. The finding support the use of either BMP treatments for ephemeral-intermittent streams, however, the additional measure of leaving logging debris in BMP2 did not cover enough soil surface to reduce erosion.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.117-124
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• 1991

Based on the momentum equation for the flow in a stream bend, the force per unit area which the flow exerts on the outer of a bend is directly proportional to a certain curvature coefficient, $C{\alpha}$. This coefficient is dependent on the ratio of bend radius(R) to flow width(W), as well as on the coefficient of dynamic bedload friction, $tan{\alpha}$. According to the results of the data analysis for the downstrream at the Han river, the range of R/w values is between 2.0 and 4.0. Exploring the variations of $C{\alpha}$ with R/w values a functional relationship which, for the known values of $tan{\alpha}$, shows maximum values of $C{\alpha}$ for R/w values between 2.21 and 4.42 in 1963, while in 1981 its values lied between 1.93 and 3.54.

• Journal of the Korean Association of Geographic Information Studies
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• v.21 no.3
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• pp.48-62
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• 2018

In this study, landslide of debris flow occurred at 51 sites around Daeryounsan located in between Chuncheon-si and Hongcheon-gun during July in 2013 were investigated in field and behavior characteristics of debris flow were analyzed on the basis of records of rainfall and site investigation. According to debris flow types of channelized and hill slope, location and slope angle of initiation and deposit zone, and width and depth of erosion were investigated along entire runout of debris flow. DEM(Digital Elevation Model) of Daeryounsan was constructed with digital map of 1:5,000 scale. Land slide hazard was estimated using SINMAP(Stability INdex MAPping) and the predicted results were compared with field sites where debris flow occurred. As analyzed results, for hill slope type of debris flow, predicted sites were quite comparable to actual sites. On the other hand, for channelized type of debris flow, debris flow occurrence sites were predicted by using stability index associated with topographic wetness index. As analyzed results of 4 different conditions with the parameter T/R, Hydraulic transmissivity/Effective recharge rate, proposed by NRCS (Natual Resources Conservation Service), predicted results showed more or less different actual sites and the degree of hazard tended to increase with decrease of T/R value.

• Journal of Korea Water Resources Association
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• v.46 no.5
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• pp.559-568
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• 2013

Surface compaction significantly impacts runoff and soil erosion under rainfall since it leads to changes of soil physical characteristics such as increase of bulk density and shear stress, change of microporosity, and decrease of hydraulic conductivity. This study addressed surface compaction effects on runoff and soil loss from bare and disturbed soils that are commonly distributed on construction sites. Thirty-six rainfall simulations from three replicates of each involving rainfall intensities (68.5 mm/hr, 95.6 mm/hr) and plot gradients ($5^{\circ}$, $12.5^{\circ}$, $20^{\circ}$) were conducted to measure runoff and soil loss for two different soil surface treatments (compacted surface, non-compacted surface). Compacted surface increased significantly soil bulk density and soil strength. However, the effect of surface treatments on runoff changed with rainfall intensity and plot gradient. Rainfall intensity and plot gradient had a positive effect on mean soil loss. In addition, the effect of surface treatments on soil loss responded differently with rainfall intensity and plot gradient. Compacted surfaces increased soil loss at gentle slope ($5^{\circ}$) while they decreased soil loss at steep slope ($20^{\circ}$). These results indicate that there exists transitional slope range ($10{\sim}15^{\circ}$) between gentle and steep slope by surface compaction effects on soil loss under disturbed bare soils and simulated rainfalls.