• Journal of the Korean GEO-environmental Society
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• v.11 no.9
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• pp.55-60
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• 2010

This study are carried out to an lab model tests to develop a construction method that solidifies high-water content cohesive soil by using filter type drain and vacuum pressure, and that stabilizes the ground by accelerating horizontal drain at incline or in tunnel. The calibration chamber was designed within length of 1.5m and height of 50cm, and a drainage hole for preconsolidation, a switchgear and a piezometer were installed at the bottom part of the chamber. Also, a settlement gage was installed at the top part so that it can measure the settlement by time. The calibration ground basis was made in a form of thin layer from kaolinite and bentonite in 9:1 ratio stirred at 130% water content condition. A filter type drain was installed at chamber center and a vacuum pressure of 0.8MPa was applied through a hose linked to the cap at the top part, then, the settlement was measured in every 1 hour interval. After experiment, the moisture contents were measured by position, then, verified the increase of solidity of the ground through a triaxial compression test on undisturbed profile. After 11 days from the effective date, it was observed that the settlement decreased by maximum 35mm and the water content ratio was reduced by 38% at most while the solidity of the ground increased by 5~8 times greater than before preconsolidation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.6
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• pp.68-79
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• 2018

An examination of the characteristics of the ground material in is very important in a ground investigation. Casagrande classified soil using the material properties of soils. The liquid-plastic limit test is useful for obtaining basic information of soil, and is an effective method for classifying silt and clay, as well as the material properties, such as shear strength, shrinkage, and expansion. Unlike the liquid limit test, the plasticity limit test is due to the ambiguity of the test procedure. Many geotechnical engineers and scholars have questioned the test results. In this study, a new plasticity limit method was used to compare with the thread rolling method with kaolinite, ilite and bentonite at a certain ratio, and samples were collected from the west coast of Korea. As a result of the comparison, the test value of the new test method showed high reproducibility because the error range of the test value of the conventional thread rolling test was only 10% but the error range of the new test values decreased to 2%. The difference in the slope of the existing plasticity test values was 0.1519 ~ 0.1925, and the results of the test were similar or coincided with each other. Aone - point method was proposed to make it easier to apply the new test method.

• Journal of Soil and Groundwater Environment
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• v.7 no.1
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• pp.33-40
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• 2002

The study was performed to evaluate the effect of landfill leachate on the hydraulic conductivity of Geosynthetic Clay Liner (GCL) with two types of leachate. GCL used in waste landfills have a significant ability as a barrier material, however, they also have a potential danger when exposed to some organic and inorganic leachate as well as humic materials. In this study, swelling tests and hydraulic conductivity tests were performed to evaluate the effect of humic materials and landfill leachate on the hydraulic characteristics of the GCL. The result of swelling tests showed that the amount of humic materials and high electronic conductivity caused a decrease of the swelling of bentonite. This is expected to increase the hydraulic conductivity of GCL. The increasing of hydraulic conductivity observed for GCL permeated with 0-leachate was significantly higher than that of Y-leachate. This result shows that humic materials are obviously affecting with the increasing of hydraulic conductivity of GCL.

• Korean Journal of Environment and Ecology
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• v.20 no.4
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• pp.436-447
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• 2006

Recently, there is increasing demand on enhancing the efficiency of hydro-seed spraying in afforestation for damaged or degraded land including forest road slopes. In this study, we focus on how seed coating and molding may affect seed germination and seedling growth. Plant species used in the study are Lespedeza cyrtobotrya, Indigofera pseudotinctoria, Arudineila hirta, Poa pratensis, and Lolium perenne. The results of seed germination and seedling growth with and without seed coating and molding are analyzed as follows: 1. For all the species and in both seeding with molding covered with soil and seeding without molding in which seeds were over sown, the increment of germination ratio by seed coating method is greater than by non·coating one. Seed coating increases average germination ratios observed in seeding with molding and without molding by 11.2% and 21.4%, respectively. Germination force may decrease from 0.8 to 3.7 days depending on the plant species and the treatments. The $LD_{50}$ decreased by $0.8{\sim}2.6$ days. However, seed coating delays the start of germination by approximate 1 day for all of the observed plants. 2. Seed coating may have the effect of accelerating the growth of stem and leaf and root. The experimental result shows that seed coating leads to 21.7% and 34.8% increment of average stem and leaf growth by seeding with molding and without molding, respectively. In terms of root growth, seeding with molding results in 22.0% increment while seeding without molding produces 26.2% increased root growth. 3: Compared to seeding without molding, germination starts on an average of 1.3 days later in seeding coated seeds with molding. However. the germination ratio is increased by 5%, and germination force and $LD_{50}$ are observed to shorten by 1.0 day and 1.4 days, respectively. Meanwhile, whether seeds are coated or not may be more related with germination and seedling growth in seeding without molding than with those in seeding with molding. 4. In this study, coating materials are examined to look at which ones are better in each treatment. Coating with Vermiculite+Talcum is the most effective in germination and seedling growth for overall plants. Seed coating using Bentonite, Calcium Carbonate, and Calcium Hydroxide shows better results than non-coating does. 5. When seeds are coated, the greatest enhancement of seed germinations was observed in Indigofera pseudotinctoria and, in the case of seedling growth, Lespedeza cyrtobotrya has the most increasing observation value among the 5 examined species. These results may indicate that woody plant seeds, having greater sizes of seeds than ones of grass seeds, may have greater relation with seed coating than grass plant seeds may have. 6. Therefore, if seeds cannot be molded up after hydro-seeding on forest road slopes, it is recommended that seeds for restoration be pre-coated with Vermiculite+Talcum and then be sowed, in order to quickly stabilize the damaged slope and achieve successful afforestation.

• Journal of the Korean Geotechnical Society
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• v.30 no.2
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• pp.65-76
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• 2014

For soil improvement, sand mats or sand compaction piles are often constructed on soft marine clays. In such cases, some amounts of sand and clay are inevitably mixed. Sand or gravel often exists in the weathered soils near the slope surface. This research investigates the effect of mixing sand content on consistency limits and shear strength of clays. Firstly, sand was mixed with kaolinite or bentonite at 0, 9, 17, 23, 29, 33, 50% and then liquid and plastic limits were measured. Both plastic and liquid limits decreased as a sand content increased. The water content of clay-sand mixtures with different sand content increased by 10% or 20% step by step and then their undrained shear strength was measured using a portable vane shear device called Torvane. For all cases, undrained shear strength of clay-sand mixtures decreased rapidly until reaching a certain value. Their state changed from undrained to drained state gradually as the sand content increased, which caused their undrained shear strength to decrease. On the other hand, a series of direct shear tests were also conducted on such clay-sand mixtures to investigate the effect of sand content on cohesion and angle of internal friction. It was found from clay-sand mixtures that their cohesion decreased but angle of internal friction increased as the sand content increased.

• Water for future
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• v.24 no.3
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• pp.49-60
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• 1991

As a second part of the study entitled "Field Measurement and Analysis of Fluvial Sediment in the Cheongmi-Strea", this study concerns mineralogical and contaminative characteristics of sediment particles collected at Wonbu-Gyo and Hanpyeong-Gyo in the Cheongmi-Stream. The mineralogical analysis of the bed sediment collected reveals that, in general , quarz is the most abundant mineral found in sands with feldspars and rock fragments in the next, which confirms what is known in the literature. The shape factor of sand particles is about 0.7, which also agrees to what is known in the foreign literature. The analysis also reveals that the clay particles collected are composed mainly of illite, kaolinate, and chlorite. The analysis of contamination reveals that there is no substantial difference between the contents of organic material and heavy metals in the surface water and those in the pore water beneath the river bed. It is because the sampling for this analysis was conducted right after the September flood during which the fresh top soil from the upstream watershed replaced the old bed sediment and pore water that would probably be more contaminated. The contents of geavy metals in the bed sediment of sand particles do not exceed those in the soils adjacent to the river. For fine sediment such as clays, however, the contents of heavy metals, especially of mercury and zinc, far exceed those in the soils adjacent to the river. These fine sediments are transported downstream in the form of wash load and deposited in part on flood plains, which could be a new source of contaminants.taminants.

• Journal of the Mineralogical Society of Korea
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• v.23 no.4
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• pp.377-393
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• 2010

Pumiceous tuffs occurring in the Beomgockri Group are examined applied-mineralogical characteristics and their controling factors to evaluate their potentials as the adsorption-functional mineral resources. The pumiceous tuffs are diagenetically altered to low-grade zeolitcs and bentonites in the Janggi area. Compositional specialty due to the presence of pumice fragments induces the altered tuffs to exhibit the characteristic adsorption property combined with cation exchange capacity, specific surface area, and acidic pH. Unusual lower pH in the adsorption-functional mineral substances is turned out to be originated from the presence of H-smectite having $H^+$ in the interlayer site of the sheet structure. On account of disordered crystallinity resulting from the exchanged $H^+$ in the interlayer site, the smectite commonly forms crenulated edges in the planar crystal form and exhibits characteristic X-ray diffraction patterns showing comparatively lower intensities of basal spacings including (001) peak than conventional Ca-smectite. Based on the interpretation of paragenetic relations and precursor of the H-smectite, a genetic model of the peculiar clay mineral was proposed. The smectite formation may be facilitated resulting from the precipitation of opal-CT at decreasing pH condition caused by the release of H+ during diagenetic alteration of pumice fragments. Because of the acidic smectite, the low-grade mineral resources from the Beomgockri Group may be applicable to the adsorption industry as the raw materials of acid clays and bed-soil.

• Journal of the Korean Geotechnical Society
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• v.24 no.11
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• pp.121-131
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• 2008

In constructing a slurry trench cutoff wall, bentonite-water slurry is used to secure the stability of sidewalls during excavation before the wall is completed by backfilling. Unexpectedly, a thin but relatively impermeable layer called filter cake can be formed on the excavation surface, which significantly influences the result of slug test analysis in the cutoff wall if not considered. This study is to examine the effect of filter cake on evaluating hydraulic conductivity of the vertical cutoff wall through slug test analysis with the aid of the verified numerical program Slug_3D. The no-flux boundary conditions were adopted in Slug_3D to simulate the filter cake on the interface between the wall and the natural soil. A new set of type curves were built for applying the type curve method. New modification factors were obtained for using the modified line-fitting method. With consideration of filter cake, the type curve method and the modified line-fitting method were adopted to reanalyze the case study taken from EMCON (1995). The previous results achieved by Choi and Daniel (2006) without consideration of filter cake were compared with the present results obtained in this paper. The comparison emphasizes the necessity of considering filter cake when analyzing slug test results in vertical cutoff walls.

• Journal of the Korean Geotechnical Society
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• v.24 no.8
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• pp.99-109
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• 2008

The standard consolidation tests using the incremental loading technique test (IL) were performed on remolded normal consolidation and undisturbed clay samples to find out the effects of plastic index and loading period on consolidation in this study. The remolded samples used were prepared by mixing Gunsan-Samangum clay with bentonite so that they may have plasticity indexes of 15, 30, 45, and 60%, respectively. The undisturbed clay samples were collected from Inchon, Kwangyang, and Uoolsan. The samples were tested at the condition of 4 different loading periods (1, 2, 4, and 8 days). Settlement, coefficient of consolidation, compression index, secondary compression index, and pore water pressure characteristics were investigated from the plastic index and loading period aspects, and the compression index, coefficient of consolidation, and secondary compression index were formulated in terms of the plastic index and loading. To verify the applicability of proposed equations, the settlements obtained from Terzaghi's theory, modified Cam-Clay model (elasto-plastic model), and the Sekiguchi model (elasto-viscoplastic mode) were compared with the test results. The comparison indicates that the Sekiguchi model incorporating the secondary consolidation characteristic well predicts the results.