• Geomechanics and Engineering
• /
• v.33 no.2
• /
• pp.167-174
• /
• 2023

This study evaluated slope stability through a case study to determine the disaster risks associated with increased deforestation in structures, including schools and apartments, located in urban areas adjacent to slopes. The slope behind the ○○ High School in Gwangju, Korea, collapsed owing to heavy rain in August 2018. Historically, rainwater drained well around the slope during the rainy season. However, during the collapse, a large amount of seepage water flowed out of the slope surface and a shallow failure occurred along the saturated soil layer. To analyze the cause of the collapse, the images of the upper area of the slope, which could not be directly identified, were captured using unmanned aerial vehicles (UAVs). A digital elevation model of the slope was constructed through image analysis, making it possible to calculate the rainfall flow direction and the area, width, and length of logging areas. The change in the instability of the slope over time owing to rainfall lasting ten days before the collapse was analyzed through numerical analysis. Imaging techniques based on the UAV images were found to be effective in analyzing ground disaster risk maps in urban areas. Furthermore, the analysis was found to predict the failure before its actual occurrence.

• Geomechanics and Engineering
• /
• v.33 no.4
• /
• pp.369-380
• /
• 2023

The aim of this paper is to investigate stress analysis of semi-infinite soils consisting of two layers with twin rectangular tunnels under static loads. The region close to the ground surface and tunnel modelled within finite elements. In order to use a more realistic model, the far region is modelled within infinite elements. The material model of the layered soil is considered as elastic and isotropic. In the finite element solution of the problem, two dimensional (2D) plane solid elements are used with sixteen-nodes rectangular finite and eight-nodes infinite shapes. Finite and infinite elements are ordered to be suitable for the tunnel and the soils. The governing equations of the problem are obtained by using the virtual work principle. In the numerical process, the five-point Gauss rule is used for the calculation of the integrations. In order to validate using methods, comparison studies are performed. In the numerical results, the stress distributions of the two layered soils containing twin rectangular tunnels presented. In the presented results, effects of the location of the tunnels on the stress distributions along soil depth are obtained and discussed in detail. The obtained results show that the locations of the tunnels are very effective on the stress distribution on the soils.

• Geomechanics and Engineering
• /
• v.33 no.4
• /
• pp.341-352
• /
• 2023

Long-short pile composite foundations bear both vertical and horizontal loads in many engineering applications. This study used indoor model tests to determine the horizontal bearing mechanism of a composite foundation with long and short piles under horizontal loads. A custom experimental device was developed to prevent excessive eccentricity of the vertical loading device caused by the horizontal displacement. ABAQUS software was used to analyze the influence of the load size and cushion thickness on the horizontal bearing mechanism. The results reveal that a large vertical load leads to soil densification and increases the horizontal bearing capacity of the composite foundation. The magnitude of the horizontal displacement of the pile and the horizontal load borne by the pile are related to the piles' positions. Due to different pile lengths, the long piles exhibit long pile effects and experience bending deformation, whereas the short piles rotate around a point (0.2 L from the pile bottom) as the horizontal load increases. Selecting a larger cushion thickness significantly improves the horizontal load sharing capacity of the soil and reduces the horizontal displacement of the pile top.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.26 no.1C
• /
• pp.19-24
• /
• 2006

In this study, centrifugal model tests were performed to evaluate the stress sharing between SCP and surrounding clayey soil at composite ground improved by sand compaction pile with the low area replacement ratio. The SCPs were formed by the "frozen pile" method and pressure cells were installed on pile and surrounding clayey soil to observe stress sharing characteristics. As a result of centrifugal tests, it is shown that the value of stress concentration ratio is mainly affected by area replacement ratio, loading condition and elapsed time.

• Proceedings of the Korean Society of Crop Science Conference
• /
• 2022.10a
• /
• pp.58-58
• /
• 2022

With the development of advanced technology, automation of agricultural work is spreading. In association with the 4th industrial revolution-based technology, research on field smart farm technology is being actively conducted. A state-of-the-art unmanned automated agricultural production demonstration complex was established in Naju-si, Jeollanam-do. For the operation of the demonstration area platform, it is necessary to build a sophisticated, advanced, and intelligent field smart farming model. For the operation of the unmanned automated agricultural production demonstration area platform, we are building data on the growth of soybean for smart cultivated crops and conducting research to determine the optimal time for agricultural work. In order to operate an unmanned automation platform, data is collected to discover digital factors for water management immediately after planting, water management during the growing season, and determination of harvest time. A subsurface drip irrigation system was established for smart water management. Irrigation was carried out when the soil moisture was less than 20%. For effective water management, soil moisture was measured at the surface, 15cm, and 30cm depth. Vegetation indices were collected using drones to find key factors in soybean production prediction. In addition, major growth characteristics such as stem length, number of branches, number of nodes on the main stem, leaf area index, and dry weight were investigated. By discovering digital factors for effective decision-making through data construction, it is expected to greatly enhance the efficiency of the operation of the unmanned automated agricultural production demonstration area.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.28 no.4
• /
• pp.205-213
• /
• 2024

In the seismic evaluation of underground utility tunnels, selecting an analytical method is critical to estimating reasonable seismic responses. In simplified pseudo-static analysis methods widely applied to typical seismic design and evaluation of underground tunnels in practice, it is essential to check whether the methods provide valid results for cut-and-cover tunnels buried in shallow to medium depth. The differences between the two simplified pseudo-static methods are discussed in this study, and the analysis results are compared to those obtained from FLAC models. In addition to the analysis methods, seismic site classification, overburden soil depth, and sectional configuration are considered variables to examine their effects on the seismic response of underground utility tunnels. Based on the analysis results, the characteristics derived from the concepts and details of each simplified model are discussed. Also, general observations are made for the application of simplified analysis methods.

• Journal of the Korean Geographical Society
• /
• v.44 no.2
• /
• pp.122-145
• /
• 2009

Terrain parameters calculated from digital elevation models (DEM) have become increasingly important in current spatially distributed models of earth surface processes. This paper investigated how the ability of upslope area for predicting the spatial distribution of soil properties varies depending on the selection of spatial resolutions of DEM and algorithms. Four soil attributes from eight soil-terrain data sets collected from different environments were used. Five different methods of calculating upslope area were first compared for their dependency on different grid sizes of DEM. Multiple flow algorithms produced the highest correlation coefficients for most soil attributes and the lowest variations amongst different DEM resolutions and soil attributes. The high correlation coefficient remained unchanged at resolutions from 15 m to 50 m. Considering decreasing topographical details with increasing grid size, we suggest that the size of 15-30 m may be most suitable for soil-landscape analysis purposes in our study areas.

• Korean Journal of Soil Science and Fertilizer
• /
• v.18 no.1
• /
• pp.94-98
• /
• 1985

A laboratory experiment was conducted to find out the denitrification rate upon the different levels of nitrogen fertilizer in submerged sandy soil. The results obtained were summarized as follows: 1. The highest denitrification rate was observed at 25 days after incubation. The amount was reached at 1830 ug/100g soil for 20mg nitrogen was applied in 100g soil. 2. Increases of fertilizer nitrogen was enhanced the rate of ammonification and nitrification during the incubation time. 3. Deep correlation was observed between the denitrification capacities which was determined as nitrous oxide and Mitchaelis-Menten kinetic with relation to nitrate concentration. More higher denitrification rates were observed in Mitchaelis-Menten kinetic than dentrification rate with determined as nitrous oxide. 4. A Zero order (with relation to nitrate concentration) kinetic model for denitrification was presented in this experiment condition to illustrate the variability of nitrous oxide concentrations in the submerged soil atmosphere.

• Microbiology and Biotechnology Letters
• /
• v.26 no.5
• /
• pp.465-469
• /
• 1998

The quantitative and rapid method for measuring the biodegradation of polymer materials in soil was developed. In this study, cellophane film was used as a model biodegradable polymer and the biodegradation was assayed by measuring the amount of glucose which was produced by a hydrolysis reaction using HCl after collecting the film from soil. Cellophane film was degraded 41.2% in 4 months during winter while it was degraded 76.5% in 2 months during summer. It means that biodegradation in soil is affected by environmental conditions. The biodegradation was also measured in an incubator (30$^{\circ}C$, humidity 50-55%) to exclude the environmental variations. Cellophane film was degraded 94% in that condition in 40 days. The biodegradation showed the first order kinetics and the rate constant was 0.067 (1/day). Acceleration of the biodegradation in soil was also studied. We added cultured soil microorganisms or nutrients such as N, P, and S into the soil. While the addition of microorganisms showed the temporary increase of rate constant, the addition of nutrients not only showed the increase of rate constant from 0.096 (1/day) to 0.21 (1/day) but also maintained the effect continuously.

• Korean Journal of Ecology and Environment
• /
• v.46 no.2
• /
• pp.310-318
• /
• 2013

In territorial ecosystem, soil has stored considerable amount of carbon, and it is vulnerable to weakness release much of the carbon to atmosphere. In this study, we have been effort realization and discussion to the error between inter-instruments and measurement methods, time and special variations, gap filling and separation from each source included in soil respiration, used to collect soil respiration data in various ecosystems in Korea. In conclusion, it have to collect calibration data throughout comparison test between methods and instruments because accumulated data from past and accumulating data in present did not calibrated. In predicting change of soil carbon dynamic using the model method, it needs important data such as longterm and short-term data, artificial handling data of major factor, data from various ecosystem, soil texture, soil depth etc. In company with, we should collect highly qualified data through deep consideration of present problems.