• The Journal of Engineering Geology
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• v.24 no.1
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• pp.23-38
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• 2014

The composition of carbonate sands from a sabkha at Ruwais in the UAE differs from that of silica sand, and these sands are crushed easily under low compression pressures. Accordingly, particle crushing of carbonate sand occurs under high pressure, which results in additional settlement and reduces the shear strength. In this study, consolidation and triaxial tests were conducted to analyze the characteristics of carbonate sands following particle crushing. The unusual shear strength graphs of the carbonate sands result from the degree of particle pre-crushing. For the range at p' > p in the p (p')-q diagram, negative (-) excess porewater pressures occur if the axial pressure causes particle crushing that induces exposure of the inner voids. In addition, the q value decreased after particle crushing. In conclusion, the unusual characteristics of the carbonate sands were induced by particle crushing. The triaxial tests revealed that the degree of particle pre-crushing influenced the excess porewater pressure.

• Journal of the Korean GEO-environmental Society
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• v.14 no.9
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• pp.57-65
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• 2013

Carbonate sands can be crushed under low confining pressure to achieve high compressibility. So particle crushing has significant influence on characteristics of strength and deformation. Trial embankment and hydrotest are conducted on Sabkha layer, consisting of carbonate sand to build tank structure. In this paper the settlement behavior was analyzed from each test. Particle crushing happened from 80 to 170kPa stress under compression test, and calcium was detected from chemical test. The test result came out Sabkha soil was very weak and easy to be crushing. About trial embankment test, particle crushing was not happen, and then extinction of pore water pressure and settlements were finished just during 2 days. On the other hand, the long-term settlement was happened in hydrotest. So the two test results did not correspond to each other. If loading stress is higher than yielding stress, instant settlement and secondary compression settlement are happened as a result of the particle crushing.

• Journal of the Korean Geotechnical Society
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• v.30 no.2
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• pp.19-32
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• 2014

Carbonate sand of Sabkha layer in the middle east was made of deposition of shell fragments and it consisted of porous particles containing inner void. Generally, at yield stress the soil structure begins to break down, so the porewater pressure and the settlement are increased rapidly. In carbonate sand, unlike quartz sand if particle crushing happens, the inner voids are exposed and porewater pressure can be decreased under yield stress. Porewater pressure can be determined as the sum of excess porewater pressure due to increase of relative density, inner void expose of particle under particle crushing stress and rearrangement of crushed particle fragments. The porewater pressure can be negative value in case of greater amount of inner void expose, so if particle crushing is bigger, the porewater pressure value is smaller. The negative value zone of porewater pressure from triaxial test result means particle crushing effect is bigger than outer void decrease effect and the particle crushing effect dominant zone size was 1.50∼3.46% from triaxial test result of Sabkha layer.

• The Journal of Engineering Geology
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• v.23 no.3
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• pp.247-256
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• 2013

The carbonate sands of the Sabkha layer in the Middle East have very low shear strength. Therefore, instant settlement and time-dependent secondary settlement occur when inner voids are exposed, as in the case of particle crushing. We analyzed settlement of the Sabkha layer under a large-scale foundation by hydrotesting, and compared the field test results with the results of laboratory tests. With ongoing particle crushing, we observed the following stress-strain behaviors: strain-hardening (Sabkha GL-1.5 m), strain-perfect (Sabkha GL-7.0 m), and strain-softening (Sabkha GL-7.5 m). General shear failure occurred most frequently in dense sand and firm ground. Although the stress-strain behavior of Sabkha layer carbonate sand that of strain-softening, the particle crushing strength was low compared with the strain-hardening and strain-perfect behaviors. The stress-strain behaviors differ between carbonate sand and quartz sand. If the relative density of quartz sand is increased, the shear strength is also increased. Continuous secondary compression settlement occurred during the hydrotests, after the dissipation of porewater pressure. Particle crushing strength is relatively low in the Sabkha layer and its stress-strain behavior is strain-softening or strain-perfect. The particle crushing effect is dominant factor affecting foundation settlement in the Sabkha layer.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.16 no.4
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• pp.169-179
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• 2011

To investigate the controlling factor and accumulation of trace metal concentrations in Chun-su Bay sediments, grain-size, specific surface area, organic carbon content, calcium carbonate content, and concentration of Al, Fe, Na, K, Mg, Ca, Ti, Mn, P, S, Ba, Sr, Li, Co, Cr, Ni, Cu, Zn, As, Cd, Cs, Sc, V, Sn were analyzed. Controlling factors of metals were quartz-dilution, calcium carbonate and coarse sand or K-feldspar. Although the distribution of V, Co, Cr, Ni, Cu, Zn, Sn, and Cd concentration was explained by grain-size effiect, Mn and As showed the similar importance of grain-size effect and coarse sand or K-feldspar factors. By virtue of enrichment factor and 1 M HCl experiment, there were little enrichment in all the trace metals in bay sediments, which were explained well by geochemical properties of sediments. Since the concentration levels of As in coarse sand were high as much as those in fine-grained sediments and it was combined with Mn oxide (1 M HCl leached) and K-feldspar (residual), it was suggested that when the enrichment of As in sediments would be assessed, it is necessary to separate the coarse sand from bulk sediments or to use only sediments with higher than 10% in < $16{\mu}m$ fraction.

• Proceedings of the Korean Quaternary Association Conference
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• 2004.11a
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• pp.4-13
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• 2004

제주도 북제주군 한림읍 협재리에는 대부분 탄산염퇴적물로 이루어진 해안사구가 분포하고 있다. 사구를 이루는 탄산염퇴적물은 연체동물과 홍조류의 조각이 약 80% 이상을 차지하며 그 외에 저서성 유공충, 성게류와 태선동물의 조각, 그리고 화산암편으로 이루어져 있어, 제주도에 분포하는 여러 탄산염 해빈퇴적물의 입자조성과 매우 유사한 경향을 나타낸다. 이러한 탄산염 입자들은 천해에 서식하던 해양생물들에 의해 생성되며, 그 각질이 해빈으로 운반되고 바람에 의해 재동되어 사구를 형성하였다. 특히 이 연구지역의 사구가 분포하는 지점에서 북쪽으로 약 1km 떨어져 있는 협재 해수욕장에는 현재에도 천해에서 생성된 많은 양의 탄산염 해빈퇴적물이 퇴적되어 있으며, 제주도의 타 지역에 비해 매우 빠른 북동${\sim}$북서방향의 바람이 불고 있어, 퇴적물을 해빈에서부터 사구형성지점으로 운반시키는 데 효과적인 역할을 했을 것으로 판단된다. 사구를 절개하여 그 단면을 관찰한 결과, 전반적으로 희미한 수평층리와 사층리가 발달하고 있으며, 그 외의 다른 뚜렷한 퇴적구조는 관찰되지 않는다. 퇴적물의 입자들은 주로 직경이 $0.27{\sim}0.40mm$로 중립질 모래에 해당한다. 이 크기의 입자들은 가장 침식이 잘 될 수 있는 입자크기에 해당하는 것으로 알려져 있으며, 따라서 해빈으로부터 퇴적물이 운반될 때에 특히 이 크기의 입자들이 차별적으로 더 많이 운반되었을 것이라고 생각된다. 또한 퇴적물 입자의 크기와 구성성분의 함량은 각 사구의 전 층준에서 크게 변화하지 않는 것으로 나타나며, 이는 사구가 형성되는 기간 동안 탄산염퇴적물을 운반한 바람의 세기가 어느 정도 일정하였음을 지시한다. 해안사구의 형성시기를 알아보기 위하여 사구의 기반을 이루는 고토양층과 사구 최하부와 최상부의 탄산염퇴적물에 대해 방사성탄소연대측정을 실시하였다. 그 결과, 사구의 형성시기를 지시하는 고토양의 연령은 $680{\sim}720\;BP\;(1,200{\sim}1,300\;AD)$로 측정되었으며, 사구를 이루는 탄산염퇴적물의 연령은 전 층준에서 모두 약 3,500 BP로 측정되었다. 따라서 약 3,500 BP에 천해에서 생성된 탄산염퇴적물이 해빈에 분포하다가 $1,200{\sim}1,300\;AD$에 바람에 의해 재동되고 현재의 위치에 쌓여 사구를 형성한 것이라고 해석할 수 있다. 사구가 형성되기 시작하던 시기는 전세계적으로 춥고 바람이 세었던 Little Ice Age ($1,300{\sim}1,820\;AD$)에 해당하며, 따라서 해빈에 분포하던 많은 양의 탄산염퇴적물이 이 시기에 집중적으로 운반된 것으로 사료된다.

• Journal of the Korean Geotechnical Society
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• v.29 no.11
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• pp.61-72
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• 2013

The consolidation tests are conducted to investigate the soil particle crushing stress for understanding the secondary compression characteristics of carbonate sandy sabkha soil caused by particle crushing under a high confining stress. The rate of secondary crushing compression ($C_{{\alpha}{\epsilon}}{^*}$) is introduced instead of the rate of secondary compression to define the characteristic of the particle crushing compression settlement ($S_s{^*}$). Void ratio ($e_p{^*}$) and settlement ($H_p{^*}$) in particle crushing are used as a reference point of secondary behavior, and the ratio of primary compression index ($C_c$) to secondary crushing compression ($C_{{\alpha}{\epsilon}}{^*}$), $C_{{\alpha}{\epsilon}}{^*}/C_c$ value was changed from 0.0105 to 0.0187. When comparing with quartz sands, secondary compression settlement of sabkha is very large due to particle crushing which is not usually observed in quartz sand. It is observed that as the depth of sabkha layer becomes deep, the $S_s{^*}$ and $C_{{\alpha}{\epsilon}}{^*}$ increase under the same stress level.

• Asian Journal of Turfgrass Science
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• v.20 no.2
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• pp.223-235
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• 2006

Soil testing laboratories unfamiliar with turfgrasses will often overestimate the plant's need for phosphorus and underestimate the need for potassium. This is partly due to differences in rooting between grasses and many garden plants and crops. The grasses are generally more efficient in extracting phosphorus from the soil, reducing their need for phosphorus fertilizer. The fact that crop yield is often the primary objective in field crop production, and is usually of little interest in turfgrass management, may affect soil test interpretation for potassium. Potassium levels above those required for maximum tissue yield of grasses may improve stress tolerance and turfgrasses will usually benefit from higher applications of this element. There are also diffrrences in soil testing philosophies. Some laboratories use the sufficiency level of available nutrients(SLAN) approach, whereas others prefer the basic cation saturation ratio(BCSR) approach. Some will use a combination of the two methods. The use of the BCSR theory easily lends itself to abuse and questionable fertilizer applications and products are sometimes recommended citing imbalances in cation ratios. The usefulness of the BCSR ratio theory of soil testing varies with soil texture and interpretations on tests performed on sand-based media are particularly a problem. Other soil testing problems occur when sand-based media used on sports fields and golf greens contain free calcium carbonate. The ammonium acetate extractant at pH 7.0 dissolves excessive amounts of calcium that can bias cation exchange capacity measurements and measurements of cation ratios. Adjusting the pH of the extractant to 8.1 can improve the accuracy of the testing procedure for calcareous media.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.6 no.3
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• pp.126-134
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• 2001

Several angular sandstone fragments (about 7 cm in longest diameter) occur in two piston cores, obtained from the submarine trough in the northeastern part of Korea Strait. The origin of the sandstone fragments and the paleoenvironment of trough sediment could be suggested from sedimentary facies analysis of cores and identification of ostracod within sandstone fragments. Echo characteristics around two core sites in submarine trough represent the prolonged bottom echoes with diffuse or no subbottom reflectors. The cores consist of a lower bioturbated mud and an upper gravelly sand sediments with sandstone/shell fragments. The bioturbated mud sediments show low water contents (27-44%) and high shear strength (19.2->37 kPa) compared with those of Holocene sediments (60-219% and 1.0-2.7 kPa, respectively) in the inner shelf and continental slope. However, clay contents (48-56%) of the bioturbated mud sediments are similar to those of fluviatile Holocene sediments in the inner shelf. The mean grain size of gravelly sand sediments ranges from 2.3 to 3.0 ${\phi}$ and shows coarsening upward with sandstone/shell fragments. The Holocene palimpsest in the continental shelf are composed of muddy sand sediments or sandy mud sediments (mean grain size: 4.6-7.6 ${\phi}$). Those suggest that two core sediments might be formed from Paleofluvial and paleocoastal deposits during sea-level lowstand. However, sandstone fragments mainly consist of quartz grains and bioclasts, with carbonate matrix, hollow pore, and glauconite. Two extinct ostracod species, Normanicythere sp. and Kotoracythere sp., are recovered in the sand-stone fragments of core EP-7, and they continued to exist from late Pliocene to early Pleistocene in cold water environment of this area. Thus, the sandstone fragments are interpreted to be formed at the paleocoastal environment derived from the Plio-Pleistocene outcrops exposed around the submarine trough during the LGM (Last Glacial Maximum) period.