• Geomechanics and Engineering
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• v.32 no.1
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• pp.111-123
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• 2023

The slope of an open cut tunnel is located above the exit of the Leijia tunnel on the Changgan high-speed railway. During the excavation of the open cut tunnel foundation pit, the slope slipped twice, a large landslide of 92500 m³ formed. The landslide body and unstable slope body not only caused the foundation pit of the open cut tunnel to be buried and the anchor piles to be damaged but also directly threatened the operational safety of the later high-speed railway. Therefore, to study the stability change in the slope of the open cut tunnel under heavy rain and excavation conditions, a 3D numerical calculation model of the slope is carried out by Midas GTS software, the deformation mechanism is analyzed, anti-sliding measures are proposed, and the effectiveness of the anti-sliding measures is analyzed according to the field monitoring results. The results show that when rainfall occurs, rainwater collects in the open cut tunnel area, resulting in a transient saturation zone on the slope on the right side of the open cut tunnel, which reduces the shear strength of the slope soil; the excavation at the slope toe reduces the anti-sliding capacity of the slope toe. Under the combined action of excavation and rainfall, when the soil above the top of the anchor pile is excavated, two potential sliding surfaces are bounded by the top of the excavation area, and the shear outlet is located at the top of the anchor pile. After the excavation of the open cut tunnel, the potential sliding surface is mainly concentrated at the lower part of the downhill area, and the shear outlet moves down to the bottom of the open cut tunnel. Based on the deformation characteristics and the failure mechanism of the landslides, comprehensive control measures, including interim emergency mitigation measures and long-term mitigation measures, are proposed. The field monitoring results further verify the accuracy of the anti-sliding mechanism analysis and the effectiveness of anti-sliding measures.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2020.12a
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• pp.62-62
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• 2020

Ginseng is a shade-plant cultivated using shading facilities. However, at too low light levels, root growth is poor, and at high light levels, the destruction of chlorophyll reduces the photosynthesis efficiency due to leaf burn and early fall leaves. The ginseng has a lightsaturation point of 12,000~15,000 lux when grown at 15 to 20℃ and 9,500 lux at 25℃. This study was conducted to select the optimal light intensity of 3-year-old ginseng grown in blue-white film plastic house. The seeds were planted in the blue-white film plastic house with different light receiving rate (March 17, 2020). Between April and September, the average air temperature in the house was 20.4-20.7℃. Average soil temperature was 18.3℃-18.5℃. The chemical properties of the test soil was as follows. The pH level was 7.0-7.4, EC was 0.5-0.6 dS/m, OM was at the levels of 33.6-37.7 g/kg, P₂O₅ was 513.0-590.8 mg/kg, slightly higher than the allowable 400 mg/kg. The amount of light intensity, illuminance, and solar radiation in the blue-white film house was increased as the light-receiving rate increased and the amount of light intensity was found to be 9-14% compared to the open field, 8-13% illuminance and 9-14% solar irradiation respectively. The photosynthesis rate was the lowest at 3.1 µmolCO²/m²/s in the 9% light blue-white plastic house and 4.2 and 4.0 µmolCO²/m²/s in the 12% and 14% light blue-white plastic house, respectively. These results generally indicate that the photosynthesis of plants increases with the amount of light, but the ginseng has a lower light saturation point at high temperatures, and the higher the amount of light, the lower the photosynthetic efficiency. The SPAD (chlorophyll content) value decreased as the increase of light-receiving rate, and was the highest at 32.7 in 9% light blue-white plastic house. Ginseng germination started on April 11 and took 13-15 days to germinate. The overall germination rate was 82.9-85.8%. The plant height and length of stem were long in the 9% light-receiving plastic house. The diameter of stem was thick in the 12-14% light-receiving plastic house. In the 12% and 14% light-receiving plastic house, the length and diameter of taproot was long and thick, so the fresh weight of root per plant was 20 g or more, which was heavier than 16.9 g of the 9% light-receiving plastic house. The disease incidence (Alternaria blight, Gray mold and Damping-off etc.) rate were 0.9-2.7%. The incidence of Sclerotinia rot disease was 7.5-8.4%, and root rot was 0-20.0%. The incidence ratio of rusty root ginseng was 34.4-38.7% level, which was an increase from the previous year's 15% level.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.44 no.5
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• pp.695-705
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• 2024

As a result of Typhoon Hinnamnoh, several slope failures occurred in the Pohang region, it is necessary to perform infiltration and slope stability analyses due to the actual rainfall. In the failed sites, samples were collected, and the hydro-mechanical properties of unsaturated soil were examined. Modeling the actual behavior using a single-mode function characteristic curve was found to be inadequate, leading to the adoption of a dual-mode function characteristic curve. The dual-mode function showed better agreement with the water retention test data. We calculated the unsaturated hydraulic conductivity for single and dual modes and performed rainfall-induced infiltration analysis. The variations in saturation and pore water pressure were calculated due to rainfall for three landslide-prone areas, Stability analysis based on effective stress of unsaturated soil was conducted, and safety factors were computed over time steps. The dual-mode model successfully reproduced landslides triggered by Typhoon Hinnamnoh, while the single-mode model exhibited a minimum safety factor of 1.2-1.3, making slope failure unpredictable. The dual-mode model accurately predicted instability in the slope by appropriately accounting for pore water pressure variations during Typhoon.

• The Journal of Engineering Geology
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• v.24 no.1
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• pp.111-122
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• 2014

For accurate laboratory evaluations of soil deposits, it is essential that the samples are undisturbed. An artificial ground-freezing system is the one of the most effective methods for obtaining undisturbed samples from sand deposits. The objective of this study is to estimate the shear strengths and the characteristics of elastic waves of frozen-thawed and unfrozen specimens through the undrained triaxial compression test. For the experiments, Jumunjin standard sands are used to prepare frozen and unfrozen specimens with similar relative densities (60% and 80%). The water pluviation method is used to simulate the fully saturated condition under the groundwater table. When thawing the frozen specimens, the temperature is measured every minute. After the specimens are completely thawed, undrained triaxial compression tests are conducted using the same procedures as for the unfrozen specimens. During the triaxial tests (saturation, consolidation, and shear phase), compressional and shear waves are measured. The results show that the freeze-thaw process has minor effects on the peak deviatoric stress and shear strength values, and that the process does not affect the internal friction angle. The compressional wave velocity increases with increasing B-value to 1800 m/s in the saturation phase, but tends to remain constant in the process of consolidation and shearing. The shear wave velocity decreases with increasing B-value in the process of saturation, but changes velocity in accordance with the change in effective stress in the processes of consolidation and shearing. The compressional wave velocity has similar values regardless of the freeze-thaw process, but values of shear wave velocity are slighly lower in frozen-thawed specimens than in unfrozen specimens. This study is a preliminary experiment for estimating the shear strength and characteristics of elastic wave velocity in undisturbed frozen specimens that have been obtained using the artificial ground-freezing method.

• Journal of Korea Soil Environment Society
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• v.3 no.3
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• pp.93-107
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• 1998

Because of its stable quantity and quality, groundwater has long been a reliable source of drinking water for domestic users. Rapid economic growth and rising standards of living have in recent years put severe demands on drinking water supplies in Korea. Groundwaters that are currently being used for natural mineral water were hydrochemically evaluated and investigated in order to maintain their quality to satisfy strict health standards. There exist 15 natural mineral water plants in the Okcheon metamorphic belt. Characteristics of groundwaters are different from those of other areas in that electrical conductivity, hardness, contents of Ca, Mg and $HCO_3$are relatively high. The content of major cations is in the order of Ca>Mg, Na>K, whereas that of major anions shows the order of $HCO_3$>$SO_4$>Cl>F. The fact that the Ca-Mg-HCO$_3$type is mostly predominant among water types reflects that dissolution of carbonates that are abundantly present in the metamorphic rocks plays an important part in groundwater chemistry. Representative correlation coefficients between chemical species show Mg-$HCO_3$(0.92), Ca-$HCO_3$(0.88), Ca-Mg(0.80), Ca-Cl(0.78), Mg-$SO_4$(0.78), Ca-$SO_4$(0.71), possibly due to the effect by dissolution of carbonates, gypsum or anhydrite. Determinative coefficients between some chemical species represent a good relationship, especially for EC-(K+Na+Ca), Ca-$HCO_3$, Ca-Mg, indiacting that they are similar in chemical behaviors. According to saturation index, most chemical species are undersaturated with respect to major minerals, except for some silica phases. Groundwater is slightly undersaturated with respect to calcite and dolomite, whereas it is still greatly undersaturated with respect to gypsum, anhydrite and fluorite, Based on the Phase equilibrium in the systems $NA_2$O-$Al_2$$O_3$-$SiO_2$-$H_2$O and $K_2$O-$Al_2$$O_3$-$SiO_2$-$H_2$O, it is clear that groundwater is in equilibrium with kaolinite, evolved from the stability area of gibbsite during water-rock interaction. It is expected that chemical evolution of groundwater continue to proceed with increasing pH by reaction of feldspars, with calcite much less reactive.

• The Journal of Engineering Geology
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• v.22 no.2
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• pp.145-155
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• 2012

The matric suction and volumetric water content of Jumunin standard sand with a relative density of 60% were measured using an Automated Soil-Water Characteristic Curve (SWCC) apparatus during both drying and wetting processes. The test time for the drying process was longer than that for the wetting process, because the flow of water is likely to be protected by air trapped in voids within the soils during the drying process. Based on the matric suction and volumetric water content, the SWCC was estimated using the model proposed by van Genuchten (1980). For the drying process, the unsaturated fitting parameters ${\alpha}$, n, and m were 0.399, 8.586, and 0.884, respectively; for the wetting process, the values were 0.548, 5.625, and 8.220, respectively. The hysteresis phenomenon occurred in the SWCCs, which means the SWCC of the drying process is not matched with the SWCC of the wetting process. Using these unsaturated parameters, we estimated the Suction Stress Characteristic Curve (SSCC), based on the relationship between suction stress and the effective degree of saturation. The suction stress showed a rapid decrease when the matric suction exceeds the Air Entry Value (AEV). Therefore, the effective stress of unsaturated soils is different from that of saturated soils when the matric suction exceeds the AEV. The suction stress of the drying process exceeds that of the wetting process for a given effective degree of saturation. The hysteresis phenomenon was also recognized in SSCCs. The hysteresis phenomenon of SSCCs arises from that of SWCCs, which is induced by the ink bottle effect and the contact angle effect. In the case of a sandy slope, the suction stress is positive and acts to enhance the slope stability as the water infiltrates the ground, but is negative when the suction stress exceeds the AEV. The results obtained for the wetting process should be applied in analyses of slope stability, because the process of water infiltration into ground is similar to the wetting process.

• Korean Journal of Soil Science and Fertilizer
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• v.18 no.3
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• pp.289-296
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• 1985

To clarify the soil characteristics and genesis of the clayey terrace soils distributed in Yeongcheon (inland region) and Yeongil (coastal region), 9 typifying pedons including a recent local deposits were studied. The physico-chemical properties found were summarized as follows; 1. The contents of available water of the terrace soils were ranged from 12.0 to 20.3%. They were increased with increaseing clay content up to 35%, and then decreased at clay content of 35 to 55%, but were maintained about 12 to 13% when the clay content exceeds 55%. 2. The amount of water stable aggregates in the surface soils were ranged from 55.0 to 81.1%, and were low in cultivated upland where water erosion were accelerated while high in the paddy where the double cropping were practiced. The index of aggregate in cultivated upland were higher in the surface soils but the paddy soils were higher in subsoils. 3. The colloidal reactions checked by the differences between pH in $0.01N-Na_2SO_4$ and $H_2O$ indicate exchangeable acidity to exchangeable neutrality, which means a sort of Red-yellow soil forming process had been prevailed during genesis of the terrace soils. 4. Cation exchange capacity of the clayey terrace soils were averaged about 15.8-20.2me/100g of fine earth and 35.6-52.6me/100g of clay. The rates of base saturation were 32.7 to 57.6% and the rates decreased with increasing the elevations of terraces. 5. The activities of free iron oxides were 0.061 to 0.739 and the values decreased with increasing elevation while the crystallinity index of iron oxides positively correlated with elevations the values ranged from 0.067 to 0.537.

• Journal of the Korean GEO-environmental Society
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• v.15 no.5
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• pp.47-56
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• 2014

In winter season, the pore water inside the ground freezes and thaws repetitively due to the cold air temperature. When the freezing-thawing processes are repeated on the ground, the change in soil particle structure occurs and thus the damage of the infrastructure may be following. This study was performed in order to investigate the stiffness change of soils due to the freeze-thaw by using elastic waves. Sand-silt mixtures are prepared with in the silt fraction of 40 %, 60 % and 80 % in weight and in the degree of saturation of 40 %. The specimens are placed into the square freezing-thawing cell by the temping method. For the measurement of the elastic waves, a pair of the bender elements and a pair of piezo disk elements are installed on the cell, and a thermocouple is inserted into soils for the measurement of the temperature. The temperature of the mixtures is decreased from $20^{\circ}C$ to $-10^{\circ}C$ during freezing, is maintained at $-20^{\circ}C$ for 18 hours, is gradually increased up to the room temperature of $20^{\circ}C$ to thaw the specimens. The shear waves, the compressional waves and the temperature are measured during the freeze-thaw process. The experimental result indicates that the shear and the compressional wave velocities after thawing are smaller than those of before freezing. The velocity ratio of after thawing to before freezing of shear wave is smaller than that of the compressional wave. As silt fraction increases from 40 % to 80 %, the shear and compressional wave velocities are gradually increased. This study suggests that the freezing-thawing process in unsaturated soil loosens the soil particle structure, and the shear wave velocity reflects the effect of freezing-thawing more sensitively than the compressional wave velocity.

• Korean Journal of Soil Science and Fertilizer
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• v.6 no.2
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• pp.75-81
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• 1973

The morphological, physical, and chemical properties of Sonjeong series derived from acidic crystalline rocks are presented. Also it deals with the genesis and classification of the Songjeong series. Morphologically these soils have brown to dark brown loam A horizons and yellowish red to red clay loam Bt horizons with moderate, medium subangular blocky structure and thin patchy clay cutans on the ped faces. C horizons are very deep, yellowish red to yellowish brown fine sandy loam or sandy loam with original rock structure. Physically distribution of particle size indicates that clay increases with depth up to argillic horizons but below the argillic horizons clay content decrease. The moisture holding capacity is fairly good in Songjeong soils. Chemically soil reaction is strongly to very strongly acid throughout the profile and content of organic matter is less than 1 per cent except A horizons. Cation exchange capacity ranges from 5 to 9 me/100g of soils and base saturation is less than 35 per cent throughout the profile. The natural fertility of Songjeong soils are usually low. It needs lime, organic matter, and heavy application of fertilizer for the crop land. These soils occur temperate and humid climate under coniferous, deciduous, and mixed forest vegetation. Songjeong soils are classified as Red-Yellow Soils. Characteristically Songjeong soils are similar to Red-Yellow Podzolic soils in the United States but lack of A2 horizons and are quite liket Red-Yellow Soils of the Japan. According to new classification system which is 7th approximation of USDA Songjeong soils can be classified as fine loamy, mesic family of Typic Hapludults and in the FAO/UNESCO project World Soil Map as Orthic Acrisols.

• The Journal of Engineering Geology
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• v.27 no.4
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• pp.475-487
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• 2017

We performed landslide flume tests to analyze characteristics of landslide occurrence and change in the ground materials due to rainfall infiltration. The test apparatus is composed of flume, rainfall simulator, and measurement sensors and landslides were triggered by heavy rainfall (Intensity=200 mm/hr) sprinkled at the above of an artificial slope. The measurement sensors for matric suction and volumetric water content were installed with 3 sets at shallow (GL-0.2 m), middle (GL-0.4 m), and deep depth (GL-0.6 m) in the slope and the tests were performed with in-situ, loose, and dense condition of each weathered soils of granite, gneiss, and mudstone. The analyses show that surface erosion was dominant in initial time of the test due to heavy rainfall and then landslides occur following locally happened transverse tension cracks. The characteristics of landslide were both shallow failure because of a spread of wetting front induced by the rainfall infiltration and retrogressive failure. While the matric suction was decreased rapidly without any precursor in the soil saturation, the volumetric water content was increased gradually, reached its maximum value, and then decreased rapidly with landslide.