• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2001년도 춘계학술대회 논문집
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• pp.108-119
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• 2001

The Spectral Analysis of surface Waves(SASW) Method has a great has a great potential for rapid determination of shear wave velocity profile of ground. However, it has an inherent limitation in the interpretation of test results due to the assumption that the ground is layered horizontally. The reason of the assumption is that difficulties exist in obtaining analytical solutions of wave equation when a soil system is composed of inclined soil layer. In this study, a finite-element method has been employed to assess the effects of dip angle and stiffness contrast of inclined soil layers and the testing direction on the dispersion curve. The propagation of wave front in the inclined soil layer was also investigated. The results indicated that the influence of dip angle on the dispersion curve is getting obvious as the dip angle increases and the propagation of wave front in the inclined layer also entirely different compared with the case of the horizontal layer.

• 한국토양비료학회지
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• 제49권6호
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• pp.807-812
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• 2016

Soil amendment, especially addition of clay minerals, has been widely conducted to improve the physical and chemical properties of cultivated soils. However, there are no systematic studies on the effects of the structural type of clay minerals added. This study was conducted to investigate the effects of structural type of clay minerals on physical properties of soils. Two experimental soils, layer-dominant and granule-dominant ones, were mixed with either a layer-type smectite or a granule-type zeolite at a level of 2.0 wt%. It was observed that water permeability of soils was decreased by smectite whereas not significantly changed by zeolite. This effect was much greater in layered clay-dominant soil than in granular clay-dominant soil. Our results clearly indicated that the relationship of structural type between a soil and an amendment plays a decisive role in the soil properties. Therefore, it is highly recommended that the structural types of both soil and amendment be taken into consideration for soil amendment by clay minerals.

• The Korean Journal of Ecology
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• 제13권1호
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• pp.25-32
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• 1990

The vertical distribution and seasonal fluctuation of soil microarthropods in the forests with different flora were investigated in this study. soil micrarthropods were concentrated as much as 71.8% in the first layer subsoil (0-5cm), 22.3% in the second layer subsoil (5-10cm), and 5.9% in the third layer subsoil (10-15cm) in the decreasing order. The population density in the first layer decreased slightly in winter while that of the second layer increased. However, the density in the first layer bounced back in the following spring. Seasonal fluctuations of population density were revealed "Two peak-Two valley type", that is, the densities were high in fall and spring, and low in winter and summer.nd summer.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1999년도 토목섬유 학술발표회 논문집
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• pp.129-141
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• 1999

This paper presents the results of plate load test and dynamic load test performed to evaluate the performance of geocell where it is used to reinforce soft subgrade for high-speed railroad. Efficacy of geocell was observed in increase in bearing capacity of subgrade and reduction of thickness of reinforced sub-ballast. Plate load tests were carried out at four different places with varying foundation soil strength as a function of number of geocell layer, type of filler material, thickness of cover soil, and the presence of non-woven geotextile. Dynamic load tests were performed in a laboratory. The test soil chamber consists of, from the bottom, 50 cm thick clayey soil, one layer of geocell filled with crushed stone, 10 cm thick crushed stone cover, reinforced sub-ballast of varying thickness, 35 cm thick ballast. This configuration was determined based on the results of numerical analysis and plate load tests. For each set of the dynamic load tests, loads were applied more than 80,000 times. One layer of geocell underlying a 10 cm thick cover soil led to an increase in bearing capacity three to four times compared to a crushed stone layer of the same thickness substituted for the geocell and cover soil layer. Given the test conditions, the thickness of reinforced sub-ballast can be reduced by approximately 35 cm with the presence of geocell.

• 한국환경복원기술학회지
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• 제4권3호
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• pp.49-54
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• 2001

It is common that the soil layer is a few meters below the earth's surface and the rock mass is below the soil layer in the view of geological characteristics in Korea. And the boundary between rock and soil is clearly divided. When dealing with the stability of rock masses, as in the case of rock slopes or dam foundations, the majority of the collapses is not within the soil layer, but within the soil-rock boundary. Therefore it is important to identify the shear strength characteristics between soil-rock boundary. And then in the method of reinforcement on landslide this chose a cut slope near Daemo elementary school in Seoul, surveyed shear strength between soil-rock contacts and considered a large scale collapse using a limit equilibrium method.

• 한국지진공학회논문집
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• 제21권1호
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• pp.69-76
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• 2017

Seismic analyses of a pile under a large rigid basement foundation embedded in the homogeneous soil layer were performed practically by a response displacement method assuming a sinusoidal wave form. However, it is hard to take into account the characteristics of a large mat foundation and a heterogeneous soil layer with the response displacement method. The response displacement method is relevant to the 2D problems for longitudinal structures such as tunnel, underground cave structure, etc., but might not be relevant with isolated foundations for building structures. In this study, seismic pile analysis by a pseudo 3D finite element method was carried out to compare numerical results with results of the response displacement method considering 3D characteristics of a foundation-soil system which is important for the building foundation analyses. Study results show that seismic analyses results of a response displacement method are similar to those of a pseudo 3D numerical method for stiff and dense soil layers, but they are too conservative for a soft soil layer inducing large soil pressures on the foundation wall and large pile displacements due to ignored foundation rigidity and resistance.

• 한국수자원학회논문집
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• 제40권3호
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• pp.215-221
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• 2007

본 연구에서는 침투정 설치 시 침투정 토양표면의 막힘 현상에 따른 침투능 저하를 감소시키기 위한 빙안을 강구 하고자 하였다. 또한 각기 다른 토양특성에 따른 침투능의 변화를 알아보기 위하여 여러 다른 실험조건에서 침투능의 변화를 관찰하였다. 실험결과에 의하면 침투정 설치 시 침투정의 하부토양은 자갈이나 가급적 입경이 큰 토양을 설치함으로써 침투정으로부터 우수를 빠른 시간 내에 배수시킬 수 있을 것으로 사료된다. 하지만 장기적으로 시간이 경과함에 따라서 침투능이 감소하는 경향을 보이는 것을 고려할 때 토양 내부에 부유토사의 침투에 따른 막힘 현상이 발생되고 있는 것으로 사료된다. 하부 자연 토양의 다짐을 방지하기 위하여 자연토양 상부에 가급적 얕은 깊이로 모래를 설치하고 가급적 굵은 자갈을 상부에 설치하여 저류능과 수두를 높여 침투능을 향상시키는 것이 바람직하다. 또한 정기적으로 침투정에 발생하는 crust(경화 토피층)를 제거하고 침투정내 모래를 수시로 교체하여 원래의 침투능을 유지하도록 하는 것이 필요하다.

• 한국농공학회지
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• 제31권4호
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• pp.90-95
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• 1989

The purpose of this study is to seek out the harrow water requirement applicable for the irrigation plan of paddy field and to find out the factors influenced on a variation in the requirement. The plots of experiment were arranged with randomized block design which was compo- sed of three kinds of soil texture (sandy loam, loam and silty loam) and ploughing depth (12cm, 17cm, and 22cm). The results obtained from this experimental study are summarized as follows. 1. Harrow water reguirement is not only changed by soil texture, but influenced by soil water content just before irrigating 2. Magnitude of total harrow water reguirement appli(able for the irrigation plan, when surface water depth and the water content just before irrigating is fixed on the basis of 30 mm and a shrinkage limit respectively, generally becomes to be 177.5mm, 116.3mm and 113. 8mm in the sandy loam, loam amd silty loam block, respectively. 3. The more a percolation of soil layer occurs, the more the harrow water requirement increases, but it is not much influenced by the increase in ploughing depth. 4. The larger a porosity of soil layer is, the more a net harrow requirement increases 5. The factors that influence on a variation in the harrow water requirement are appea- red to be percolation of soil layer, soil water content just before irrigating, porosity of soil layer, ploughing depth and designed surface water depth etc.

• Geomechanics and Engineering
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• 제5권1호
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• pp.1-15
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• 2013

Pressure transducers are increasingly used within soil mass or at soil-structure interface for appraisal of stresses acting at point of installation. Calibration of pressure transducers provides a unique relationship between applied pressure and voltage or strain sensed by transducer during various loading conditions and is crucial for proper interpretation of results obtained from pressure transducers. In the present study an in-house calibration device is used to calibrate pressure transducers and the study is divided into two parts: 1) demonstration of developed calibration device for fluid and in-soil calibration of pressure transducers; 2) effect of soil layer thickness on the earth pressure cell (EPC) output. Results obtained from the present study revealed successful performance of the developed calibration device, and significant effect of sand layer thickness on the calibration results. The optimum sand layer thickness is obtained as 1.5 times the diameter of EPC.

• 한국작물학회:학술대회논문집
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• 한국작물학회 2017년도 9th Asian Crop Science Association conference
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• pp.321-321
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• 2017

Water availability in rainfed lowlands (RFL) is strongly affected by climate change. In RFL, rice plants are exposed to soil moisture fluctuations (SMF) but rarely to simple progressive drought as widely believed. Typical RFL field is characterized by a about 5-cm thick high bulk density hardpan layer underneath the cultivated layer at about 20 cm depth that impedes deep root development. Root system has the ability to develop in response to changes in SMF, known as phenotypic plasticity. We hypothesized that genotypes that can adapt to RFL have root plasticity. The roots can sharply respond to re-wetting after drought period and thus penetrate the hardpan layer when the hardpan is wet and so becomes relatively soft, and thus access water under the hardpan. This study aimed to identify CSSLs derived from a cross between Sasanishiki and Habataki which adapted to such RFL conditions. We used 39 CSSLs together with the parent Sasanishiki, which were grown in hydroponics and pot under transient soil moisture stresses (drought and then rewatering), and compared with continuously well-watered (WW) (control) up to 14 days after sowing (DAS), and 20 DAS, respectively. Based on the results of hydroponics and pot experiments, we selected a few lines, which were grown in the soil-filled rootbox with artificial hardpan layer and without artificial hardpan. For the rootbox without artificial hardpan, plants were grown under WW and transient soil moisture stresses for 49 DAS. While the rootbox with artificial hardpan, the plants were grown under WW (control) and SMF (WW up to 21 DAS, 1st drought (22-36 DAS), rewatering (37-44 DAS), and followed by 2nd drought (45-58 DAS)). Among the 39 CSSLs, only CSSL439 (SL39) consistently showed significantly higher shoot dry weight (SDW) than Sasanishiki under transient soil moisture stress conditions as well as SMF conditions in all the experiments. Furthermore, under WW, SL39 consistently showed no significant differences from Sasanishiki in shoot and root growth in most of traits examined. SL39 showed significantly greater total root length (TRL) than Sasanishiki under transient soil moisture stress, which is considered as phenotypic plasticity in response to rewatering after drought period. Such plastic root development was the key trait that effectively contributed to root elongation and branching during the rewatering period and consequently enhanced the root to penetrate hardpan layer when the soil penetration resistance at hardpan layer reduced. In addition, using the rootbox with artificial hardpan layer ($1.7g\;cm^{-3}$, heavily compacted), SL39 showed greater root system development than Sasanishiki under SMF, which was expressed in its significantly higher TRL, total nodal RL, and total lateral RL at hardpan layer as well as at below the hardpan layer. These results prove that SL39 has plasticity that enables its root systems to penetrate hardpan layer in response to rewatering. Under SMF, such root plasticity contributed to its higher gs and Pn.