• Proceedings of the Korean Geotechical Society Conference
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• 2010.09b
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• pp.53-60
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• 2010

The natural soils are classified in saturated soils and unsaturated soils according to level of ground water but the research for only saturated soils has been conducted by this time. However, there are many proble.ms which are not solved by using the concept and principle of saturated soils on the natural soils. In fact, it is known that unsaturated soils represent the behavior characteristic unlike completely saturated soils because of the adhesion under the influence of negative pore water pressure, the high angle of friction and the low water permeability by the air entry. So it needs to conduct the various researches on insufficient unsaturated soils. In this paper, unsaturated triaxial compressive tests are conducted in order to do research on shear strength characteristic on sands and silty sands of Nakdong river. As a result of the tests, the cohesion is increased in non-linear type according to the change of the matric suction, but the angle of internal friction is not changed much.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.205-210
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• 2002

As the deposits of natural sands have slowly been depleted, it has resulted in an increase in manufactured fine aggregate (MFA). Standard specifications for fine aggregate for concrete contained in KS F 2558 permit a maximum of 7 percent finer than the No. 200 sieve (75${\mu}{\textrm}{m}$). Since the production process for MFA normally generates 10 to 20 percent of micro fines-which is defined as aggregates passing the No. 200 sieve (75${\mu}{\textrm}{m}$)-more than permitted by specifications, Excess fines must be removed by screening and/or washing operations. The amount of by-products will continue to grow as production increases with environmental discharge restrictions. This fundamental study focuses on experimental research for the adequacy of use of micro fines included in crushed aggregate using methylene blue test. Total of 63 types of sands from seven different rocks were tested. Based on the test results, the methylene blue test was turned out to be a good indicator of the quality of micro fines for concrete and a supplementary article and an amendment of the KS standard were recommended.

• Journal of Industrial Technology
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• v.22 no.A
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• pp.119-125
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• 2002

In Kwangjin industrial company, mill is operating for the foundry sand production at the rate of 25t/hr from quartzite. Foundry sands fall into four distinct categories: silica sand, lake sand, bank sand, and natural molding sand. Silica sand is a general term used to describe crushed, washed, graded, dried, and cooled clay-free sands. This study was conducted for the investigation of the foundry sand productivity and the life span of the hammer according to the material quality. The life time of hammer from several manufacturer were compared in order to find out the grinding efficiency of the various hammer material. In the result of tests, the life time of high-Mn hammer was 10.5 hours while that of high-Cr was 19.5 hours. The life time in case of typical worn shape hammers was about 12 hours and the average time of a blowhole hammer was about 6.5 hours.

• Geomechanics and Engineering
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• v.3 no.4
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• pp.323-337
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• 2011

Israel's coastal region consists, mainly, of Pleistocene and Holocene sands with varying degrees of calcareous cementation, known locally as "kurkar". Previous studies of these materials emphasized the difficulty in their geotechnical characterization, due to their extreme variability. Consequently, it is difficult to estimate construction stability, displacements and deformations on, or within these soils. It is suggested that SPT and Menard pressuremeter tests may be used to characterize the properties of these materials. Values of elastic modulus obtained from pressuremeter tests may be used for displacement analyses at different strain levels, while accounting for the geometric dimensions (length/diameter ratio) of the test probe. A relationship was obtained between pressuremeter modulus and SPT blow count, consistent with published data for footing settlements on granular soils. Cohesion values, for a known friction angle, are estimated, by comparing field pressuremeter curves to curves from numerical (finite element or finite difference) analyses. The material analyzed in the paper is shown to be strain-softening, with the initial cohesion degrading to zero on development of plastic shear strains.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.703-710
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• 2003

In the sub-surface environments, detection of the movement of contaminant substances and recharge of groundwater by rainfall are very important factors which contain porosity and effective porosity of porous media. In this paper, the applicability of permittivity methods and proposed dielectric mixing models (DDMs) are discussed. This study showed that the ratio of effective porosity to porosity of Toyoura and River sands were 0.856 and 0.843. From the relationships between the relative porosity and effective porosity, all measured values can be confirmed to outside the range to about 0.800 for Toyoura and River sands under all experiments by FDR and FDR-V systems. In the study, this permittivity equipment can be considered to be good enough to measure determining the physical parameters of saturated soils. Consequently, this permittivity method can be contributed to estimate a porosity and effective porosity of saturated porous media because it is easy and instantaneous than previous in-situ methods.

• Journal of the Korean GEO-environmental Society
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• v.14 no.1
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• pp.33-42
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• 2013

In this paper, a series of monotonic undrained shear tests were carried out on four kinds of sand-fine mixtures with various fines content. Two kinds of sands (Silica sand V3, V6) and fines (Iwakuni natural clay, Tottori silt) were mixed together in various proportions, while paying attention to the void ratio expressed in terms of sand structure $(F_c{\leq}F_{cth})$. The undrained shear strength of mixtures below the threshold fines content was observed so that as the plastic fines content increases, maximum deviator stress ratio decrease for dense samples while an increase is noted for loose samples. For non-plastic fines, the increase in the amount of fines leads to an increase in density of the soil, which results in an increase in strength. Then, the monotonic shear strength of the mixtures was estimated using the concept of granular void ratio. It was found that the shear strength of mixtures is greatly dependent on the skeleton structure of sand particles.

• Journal of Korean Port Research
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• v.12 no.2
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• pp.329-336
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• 1998

Sandmats are used to dissipate trapped water rapidly from the embankment built on marine soft ground. At present, however, it becomes difficult to obtain qualified sands since natural resources such as river sand are to exhausted. Also, low permeability of sand may cause low degree of consolidation and instability of embankment. In this study, design and construction methods was discussed. Drainage capacities of prefabricated horizontal drains which were installed in highway construction site are investigated in order to find possible substitution for river sands as drainage materials. On the basis of measurement data at the construction site, it was concluded that use of the prefabricated horizontal drains shows satisfactory drainage capacity without instability of embankment.

• Geomechanics and Engineering
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• v.19 no.3
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• pp.229-240
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• 2019

The physical models are useful to understand the soil behaviour. Hence, these tools allow validating analytical theories and numerical data. This paper addresses the design, construction and implementation of a physical model able to simulate the soil liquefaction under different cyclic actions. The model was instrumented with a piezoelectric actuator and a set of transducers to measure the porewater pressures, displacements and accelerations of the system. The soil liquefaction was assessed in three different grain size particles of a natural sand by applying a sinusoidal signal, which incorporated three amplitudes and the fundamental frequencies of three different earthquakes occurred in Colombia. In addition, such frequencies were scaled in a micro shaking table device for 1, 50 and 80 g. Tests allowed identifying the liquefaction susceptibility at various frequency and displacement amplitude combinations. Experimental evidence validated that the liquefaction susceptibility is higher in the fine-grained sands than coarse-grained sands, and showed that the acceleration of the actuator controls the phenomena trigging in the model instead of the displacement amplitude.

• Journal of Species Research
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• v.12 no.1
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• pp.38-47
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• 2023

Seven new species of genus Dysidea (Demospongiae: Dictyoceratida: Dysideidae) are described from Jejudo Island and Geomundo Island, Korea. These new species are compared with other reported species in fibre structure and arrangement, and cored detritus. Dysidea reticulum n. sp. is similar to D. glavea in skeletal structure but differ in sponge shape. Dysidea simplex n. sp. is close to D. glavea with loosely arranged skeletal structure but fibres in this new species are not cored with large sands. Dysidea pyeongdaensis n. sp. is characterized by tube-like surface oscules open toward the sandy bottom. Dysidea capillus n. sp. is similar to D. dokdoensis in skeletal structure, but differs in long surface conules. Dysidea mukriensis n. sp. is close to D. corallina in distinct dense surface conules, but differs in sponge shape and skeletal structure. Dysidea membrana n. sp. is similar to D. sabulum in primary fibres cored with numerous large sands, but differs in sponge surface conules and secondary fibres. Dysidea chujaensis n. sp. is unique in the sponge shape and skeletal structure.

• Journal of Environmental Health Sciences
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• v.28 no.4
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• pp.23-26
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• 2002

This study was conducted to investigate water quality after construction of straightened concrete block at Tongbok stream and difference of water quality between natural stream and municipal stream artificially straightened. In Tongbok upstream which was natural block having a variety of sand, there was ability to purify pollutants by microorganism and filtration. There was ability to purify pollutants in natural section of the natural midstream which have a diversity and a plenty of sands. In Tongbok upstream BOD concentration was lower than that of reservoir, but in midstream which was straightened concrete block without sand, BOD and NH$_3$-N concentration was higher than that of upstream and deteriorated water quality.