Evaluation of the Effect of Penetration Ratios on Composite Grounds Improved with Sand Compaction Piles     

Youl Heo  Geun Chae Jeong 《Marine Georesources & Geotechnology》2013,31(3):253-263

In this paper, centrifuge model tests were conducted in order to understand the deformation characteristics and behavior of sand compaction piles (SCPs) reinforced grounds in relation to area replacement ratios and penetration ratios. To simulate ground stress conditions, preliminary compaction was conducted to form grounds that maintained a certain level of strength. SCPs were installed in the grounds using compaction methods, and the relationship between loads and settlement as well as stress under rigid loading conditions were compared and analyzed. In addition, finite element analyses were conducted in order to verify the results of the centrifuge model tests and assess the effects of penetration ratios and depths on variations in stress. According to the results of the analyses, stress concentration ratios gradually decreased as depths increased, and the decreasing rate increased as penetration ratios decreased. However, in regions close to the surface layer in depth in which SCPs were installed, stress concentration ratios showed almost the same range regardless of penetration ratios. Stress concentration ratios showed proportional relations with penetration ratios. However, they showed similar values in regions close in depth to the surface of the ground. In particular, they showed very close ranges at penetration ratios of 100% and 80%.  相似文献   

Response of Single Piles in Marine Deposits to Negative Skin Friction from Long-term Field Monitoring     

Sangseom Jeong  Junyoung Ko  Junghwan Kim 《Marine Georesources & Geotechnology》2013,31(3):239-263

The behavior of single piles subjected to negative skin friction in soft soil was conducted by analyzing the results from full-scale long-term field measurements and three-dimensional (3D) numerical analyses. A skin friction coefficient (α and β coefficients) of the instrumented piles is back-calculated at different degrees of consolidation (U) of soft marine clay. Back-calculated β-values ranged from 0.15 to 0.35 for clay, and from 0.30 to 0.55 for sand, respectively. In addition, back-calculated α-values ranged from 0.1 to 0.3 for coated pile, and from 0.2 to 0.8 for uncoated pile when undrained shear strength of the soft clay was about 30–60 kPa, respectively. Moreover, this study describes behavior of a pile based on full-coupled 3D finite element (FE) analysis. The appropriate parametric studies needed for verifying the pile-soil interaction with consolidation are presented in this paper. Compared to the results from the measurements, it is shown that the computed results are capable of predicting the pile-soil behavior under consolidation. The major parameters that influence the pile behavior are discussed for different soil-pile conditions.  相似文献   

Right-lateral strike-slip movement of the South Korea Plateau associated with the opening of the East Sea (Sea of Japan)     

Dong-Lim Choi  Han-Joon Kim  Hyeong-Tae Jou  Seom-Kyu Jeong  Yong-Kuk Lee  Tae-Hee Lee 《Ocean Science Journal》2013,48(1):59-66

Multi-channel seismic profiles and swath bathymetric data were used to investigate the tectonic evolution of the South Korea Plateau (SKP) associated with the opening of the East Sea (Japan Sea). The SKP is a deformed fragment of continental crust with numerous horsts and sediment-filled grabens. Three sedimentary units in the plateau were identified, which consist of the lower sequence (Unit I) interpreted as syn-rifting deposition during the early to middle Miocene, and the middle and upper sequences (Units II and III) considered as post-rifting deposition since the late Miocene. The fault system in the SKP includes the South Korea Plateau Fault (SKPF) trending NNW-SSE and smaller en echelon normal faults oriented NE-SW. We interpreted the information to postulate that the formation of the SKPF is the result of divergent right-lateral strike-slip movement in the SKP. This study suggests that the dextral movement of the SKP was induced by WSW-ward propagation of the spreading center located in the Japan Basin from the early to middle Miocene times.  相似文献   

Growth dynamics of eelgrass, Zostera marina, in the intertidal zone of Seomjin Estuary, Korea     

Jeong Bae Kim  Won-Chan Lee  Kun-Seop Lee  Jung-Im Park 《Ocean Science Journal》2013,48(3):239-250

To examine the growth dynamics of eelgrass, Zostera marina, in the intertidal zone of Seomjin Estuary, Korea, we surveyed environmental factors such as water temperature, underwater irradiance, tidal exposure, and nutrient concentrations in the water column and sediment pore water in relation to the shoot density, biomass, morphological characteristics, and growth of Z. marina inhabiting the upper and lower intertidal zones. The survey was conducted monthly from January 2003 to December 2004. The water temperature of the two areas displayed seasonal fluctuations. Underwater irradiance was significantly higher in the upper intertidal zone than in the lower intertidal zone. Tidal exposure was also markedly longer in the upper intertidal zone than in the lower intertidal zone, whereas tidal exposure was highest in the spring and lowest in the summer in both areas. Water column NH₄ ⁺ and sediment pore water NO₃ ^?+NO₂ ^? concentrations were significantly higher in the upper intertidal zone than the lower intertidal zone. The eelgrass shoot density, biomass, morphology, and leaf productivity were significantly higher in the lower intertidal zone than in the upper intertidal zone. Both areas displayed a clear seasonal variation depending on changes in water temperature. However, leaf turnover time was significantly shorter in the upper intertidal zone than in the lower intertidal zone, with a higher turnover rate in the upper intertidal zone. Compared to the seagrasses in the lower intertidal zone, those in the upper intertidal zone showed more effective adaptations to the stress of long tidal exposure through downsizing and increased turnover time. These results suggest that tidal exposure, coupled with desiccation stress, can be a limiting factor for seagrass growth in the intertidal zone, along with underwater irradiance, water temperature, and nutrient availability.  相似文献   

Determining uraniferous host rocks and minerals as a source of dissolved uranium in granite aquifers near the central Ogcheon metamorphic belt,Korea     

Jeong Hwang  Sang-Ho Moon  Edward M. Ripley  Yang Ho Kim 《Environmental Earth Sciences》2014,72(10):4035-4046

Korea has suffered from high U concentrations in some groundwater, especially in Daejeon near the central Ogcheon metamorphic belt. However, clear explanation has not been yet reported for the uranium sources in groundwater. This study is focused on identifying the potential uraniferous host rocks and finding the exact U-minerals serving as uranium sources in groundwater near Daejeon, Korea. For this work, we performed an in situ gamma ray spectrometer survey and a laboratory microscopic study with electron micro-probe analysis. The measurements for radioactive element content did not show any prominent K- and Th-anomaly spots, but they did result in several observations of considerable U-anomalies in pegmatite and hydrothermally altered granite, in which uraninite, coffinite and uranophane were found by electron micro-probe analysis. The occurrences of U-minerals are the first such discovery except in the low-grade U deposits of the Ogcheon metamorphic belt in Korea. All observed U-minerals were intimately associated with hydrothermal alteration. The remarkably low Th/U ratios in the studied uraniferous rocks also suggest that the U enrichment was genetically related to a post-magmatic hydrothermal process. However, many of the uraniferous parts were controlled by a reducing environment and occurred near the border between graphite-rich mica-schist and Jurassic leucocratic granite. The findings on these uraniferous rocks can be used in elucidating the source of highly enriched U groundwater in granite aquifers as well as in understanding the occurrence of igneous U-minerals, which has not been previously reported in Korea.  相似文献   

Correlation of unsaturated soil and dielectric property for monitoring of subsurface characteristics: development of unsaturated dielectric mixing models and its application     

Man-Il Kim  Byung-Gon Chae  Gyo-Cheol Jeong 《Environmental Geology》2009,57(1):49-58

The behavior due to rainfall infiltrating the ground plays a role in landslides, groundwater recharge and various other ground responses. Most of these geotechnical behaviors have a correlation between soil pore space and soil volumetric water content in the unsaturated and saturated soil porous media. Therefore, the soil porosity associated with soil pores and the distribution of volumetric water content are significantly important hydrological characteristics. In the case of shallow slope failure such as landslide, the infiltration activity due to the connectivity of soil pore spaces in a porous media is induced. Slope failure may be attributed to the effect of a wetting front with the slope due to liquid infiltration, which changes the volumetric water content, soil matric suction and shear strength of the slope. This study was performed with an unsaturated injection test using a frequency domain reflectometry (FDR) dielectric device which measures the dielectric constant of unsaturated soil and the study then proposed the unsaturated dielectric mixing models to calculate soil porosity and effective porosity of unsaturated soils. From the experimental results the ratio of effective porosity to porosity of soils are measured in a range of 70–85%. These experimental results show a decrease of about 5–10% for unsaturated soil compared to the ratio of effective porosity to porosity of saturated soil. The infiltration passages of tracer material are restricted within the pore connectivity in the unsaturated soil which is caused by dead-pores in the soil. Using the FDR device and the unsaturated dielectric mixing models, we can consider the acquisition of physical properties to detect the infiltration activity, the response of the dielectric constant along with the injected tracer and hydrological parameters for the unsaturated soil porous media.  相似文献   

Experimental assessment of the infiltration properties of a coarse soil medium in a dielectric infiltration test     

Man-Il Kim  Gyo-Cheol Jeong  Il-Moon Chung  Nam-Won Kim 《Environmental Geology》2009,57(3):591-600

An accurate determination of the hydrological characteristics of porous media, such as the values of the porosity and effective porosity, are essential. This is important to understand the transport processes of infiltration and the movement of water and contaminants in the porous media. In this study, a laboratory soil column experiment to estimate the porosity and effective porosity of Toyoura standard sand samples, using a dielectric method termed the frequency domain reflectometry with vector network analyzer (FDR-V), was performed. The FDR-V device uses high-frequency microwaves, ranging from 0.1 to 3 GHz, to measure the complex dielectric constants of the sample. From the measured complex dielectric constant, the two parameters of the soil samples then were derived, using a proposed dielectric mixture model and tracer concentration model. The effective porosity of the soil sample is measured at 0.311 with the FDR-V dielectric method and 0.345 by the soil tracer column test. Comparing this with the calculated porosities of the soil sample, the ratio of effective porosity is approximately 78% for the dielectric method, and approximately 86% for the tracer concentration method. These different values can be explained to be within the measurement range with regard to the measurement volume for the soil column. These results indicate that measurement by the dielectric method using an FDR-V device is an efficient and useful tool for estimating the hydrological parameters of porous media because of the dielectric response of earth materials.  相似文献   

Enhanced Benthic Nutrient Flux During Monsoon Periods in a Coastal Lake Formed by Tideland Reclamation     

Seok-Hwi Kim  Kangjoo Kim  Minhyung Lee  Hwa-Jin Jeong  Won-Jang Kim  Jong-Gyu Park  Jae-sam Yang 《Estuaries and Coasts》2009,32(6):1165-1175

Sediment and water quality were investigated in an artificial coastal lake (Saemangeum Lake, Korea) that was formed by constructing a 33-km long sea-dyke offshore from the mouths of two adjacent rivers, which discharge into the Yellow Sea. Sediment showed drastic increases in fine fraction (silt and clay) after the dyke construction. TN, TP, and OC contents in the sediment showed the similar spatial variation to that of fine fraction. A mixing model indicated benthic fluxes of nutrients such as PO₄, NH₄, and SiO₂, which were considerably elevated during the summer monsoon season. It is revealed that this phenomenon was associated with the development of strong salinity stratification, elevated water temperature, and increased groundwater discharge. However, a change in the sedimentation environment due to dyke construction is suggested as the primary reason for the enhanced benthic fluxes.  相似文献   

Validity evaluation of a groundwater dam in Oshipcheon River,eastern Korea using a SWAT–MODFLOW model     

Jong-Tae Kim  Chang-Oh Choo  Man-Il Kim  Gyo-Cheol Jeong 《Environmental Earth Sciences》2017,76(22):769

It is assumed that the groundwater dam under consideration is located in the lower Oshipcheon River along Yeongdeok-gun County, Gyeongsangbuk-do Province, eastern Korea. In this study, changes in groundwater level and construction effects of the groundwater dam were analyzed using a SWAT–MODFLOW model designed for integration of surface water and groundwater, and validity analysis before and after construction of the groundwater dam was evaluated. There are an average increase of 0.46 m and a maximum increase of 1.16 m, respectively, at the upstream region due to the groundwater dam. Groundwater levels at the upstream region show an average increase of 0.42 m by the groundwater dam when the water quantity of demand (10,080 m³/day) is pumped. The groundwater dam has potential as an alternative for the surface water dam to secure water resources in the study area.  相似文献   

A Fast Approximation for Seismic Inverse Modeling: Adaptive Spatial Resampling     

Cheolkyun Jeong  Tapan Mukerji  Gregoire Mariethoz 《Mathematical Geosciences》2017,49(7):845-869

Seismic inverse modeling, which transforms appropriately processed geophysical data into the physical properties of the Earth, is an essential process for reservoir characterization. This paper proposes a work flow based on a Markov chain Monte Carlo method consistent with geology, well-logs, seismic data, and rock-physics information. It uses direct sampling as a multiple-point geostatistical method for generating realizations from the prior distribution, and Metropolis sampling with adaptive spatial resampling to perform an approximate sampling from the posterior distribution, conditioned to the geophysical data. Because it can assess important uncertainties, sampling is a more general approach than just finding the most likely model. However, since rejection sampling requires a large number of evaluations for generating the posterior distribution, it is inefficient and not suitable for reservoir modeling. Metropolis sampling is able to perform an equivalent sampling by forming a Markov chain. The iterative spatial resampling algorithm perturbs realizations of a spatially dependent variable, while preserving its spatial structure by conditioning to subset points. However, in most practical applications, when the subset conditioning points are selected at random, it can get stuck for a very long time in a non-optimal local minimum. In this paper it is demonstrated that adaptive subset sampling improves the efficiency of iterative spatial resampling. Depending on the acceptance/rejection criteria, it is possible to obtain a chain of geostatistical realizations aimed at characterizing the posterior distribution with Metropolis sampling. The validity and applicability of the proposed method are illustrated by results for seismic lithofacies inversion on the Stanford VI synthetic test sets.  相似文献