• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.472-481
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• 2009

Cementation phenomenon has a huge influence on geotechnical stiffness and strength under low confining pressure. The goal of this study is to evaluate the characteristics of stiffness according to the depth. The piezo disk elements are installed at each layer of the cell for the detection of the compressional waves. The change of compressional wave velocity is classified by three stages. The compressional wave velocities are shown different according to the depth. The compressional wave velocity is especially influenced by cementation, effective stress, and coordinate number. Furthermore, the electrical conductivity and cone tip resistance are measured according to the depth. The electrical conductivity and the cone tip resistance show the similar trend with the compressional wave velocity. This study shows that the cementation by salt is affected by the depth on the granular materials.

• Journal of the Korean Geotechnical Society
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• v.37 no.4
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• pp.39-47
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• 2021

Recently, the enzyme-induced carbonate precipitation (EICP) technique has been considered as one of the alternatives to the cement-based soil reinforcing method. However, the problem with the emission of ammonium ion has not been solved. In this study, an experimental study on the EICP without releasing an environmental contaminant (Ze-EICP) is performed using calcium-exchanged zeolite. The results show that the Ze-EICP using calcium-exchanged zeolite reduced the amount of ammonium ions by 96.96% and precipitated almost the same amount of calcium carbonate, compared to the EICP using calcium chloride. In addition, the Ze-EICP shows higher strength improvement rate than the EICP due to densification of zeolite and cementation of calcium carbonate.

• Journal of the Korean Ceramic Society
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• v.36 no.3
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• pp.274-283
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• 1999

1.1-nm tobermorite의 수열합성에 SiO2원으로 zeolite광물을 출발물질로하여 소석회와 Ca(Si+Al)의 몰비 0.8~1.0로 150$^{\circ}$~23$0^{\circ}C$,8~48시간 동ㅇㄴ 포화증기압하에서 수열반응을 시킨 결과, 반응초기단계에서 tobermorite가 생성되었고, 고결정성 1.1-nm tobermorite의 최적합성조건은 0.8몰, 23$0^{\circ}C$, 48시간이었다. 출발물질중 Al의 존재로 tobermorite는 Ca/(Si+Al)몰비 0.8이 1.0보다 결정화가 급속히 이루어지고 있으나 Al를 함유치 않은 석영의 경우에는 Ca/Si 몰비 1.0이 0.8에서 보다 결정화가 빠르게 진행되었다 1.1-nm tobermorite는 $700^{\circ}C$에서 일주일간 가열처리하여도 저면간격이 변화하지 않는 열적거동이 이상형임을 보여주었다. 특히 출발물질중 Al의 존재는 1.1-nm tobermorite의 결정화와 안정화를 촉진시켜주며 Al이온이 tobermorite구조중의 Si이온과 동형치환을 한다.

• Journal of the Korean Geotechnical Society
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• v.22 no.8
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• pp.43-54
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• 2006

The scope of this paper covers the applications of bender element tests in consolidation, tomography, and liquefaction. Loading and unloading time during consolidation are evaluated based on shear wave velocity. As S-wave velocity is dependent on effective stress, the loading step may be determined. However, cautions are required due to the different mechanism between the settlement and effective stress criteria. The stress history may be evaluated because the S-wave shows the cement controlled regime and stress controlled regimes. A fixed frame complemented with bender elements permits S-wave tomography The tomography system is tested at low confinement within a true triaxial cell. Results show that shear wave velocity tomography permits monitoring changes in the velocity field which is related to the average effective stress. To monitor the liquefaction phenomenon, S-wave trans-illumination is implemented with a high repetition rate to provide detailed information on the evolution of shear stiffness during liquefaction. The evolution of shear wave propagation velocity and attenuation parallel the time-history of excess pore pressure during liquefaction. Applications discussed in this paper show that bender elements can be a very effective tool for the detection of shear waves in the laboratory.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.121.2-121.2
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• 2010

제주도는 지질학적으로 제4기에 형성된 화산섬으로 지금까지 고온의 지열징후는 보고된 바 없으나, 남한에서 가장 최근까지 화산활동이 있었던 것으로 기록되어 있어 화산활동과 관련된 심부 지열자원 부존 가능성은 아직 열려있다고 할 수 있다. 본 연구에서는 제주도에서 지열부존 가능성을 타진하고 제주도 심부 지질구조 파악을 목적으로 2차원 및 3차원 자기지전류 (MT) 탐사를 수행하였다. 탐사는 중산간지역에서 한라산을 중심으로 동, 서, 남, 북의 4방향 4측선과 제주 서부지역에 남북방향의 1측선을의 총 5개 측선에 대해 수행하였으며, 이에 대한 MT 탐사자료의 2차원 및 3차원 역산을 통하여 한라산 하부 및 주변의 심부 지질구조를 파악하고자 하였다. 역산 해석 결과는 천부 구조는 기존 시추조사 결과 밝혀진 층서구조의 형태를 잘 나타내어 획득된 자료의 신뢰도가 높음을 지시하였다. 즉, 제주도 최 상부를 피복하고 있는 현무암 등의 화산암류는 고비저항(수백 ohm-m)으로, 그 하부의 해성 미고결퇴적층(U층 및 서귀포층)은 저비저항으로, 그리고 최하부의 응회암이나 화강암으로 구성된 기반암은 1,000 ohm-m 이상의 고비저항 층으로 잘 구분되어 나타났다. 특히, 제주도에서 특징적으로 해수면 하부 수십 ~ 수백 m에 존재하는 것으로 알려진 미고결퇴적층이 10 ohm-m 내외로 측선 전반에 걸쳐 나타났다. 이는 기존의 시추결과에서 미고결 퇴적층이 제주도 전역에 걸쳐 해수면 하부 100 m 내외의 심도에서 관찰되는 것과 일치하는 결과이다. 기반암 하부에서는 특징적으로 모든 측선의 중앙부에서 저비저항 이상대가 영상화되었으며 이는 2차원 역산과 3차원 역산해석에서 공통적으로 나타났다. 특히, 3차원 해석에서는 이러한 저비저항 이상대가 한라산 정상에서 서북쪽 부근에 나타나는데 이는 과거의 화산활동과 관련된 지질학적인 구조에 의한 영향일 가능성과 측선의 양단과 중앙에서 주변 바다의 영향이 다르게 나타나기 때문일 가능성으로 볼 수 있다. 즉, 전자는 심부에 발단된 각각의 파쇄대가 모든 측선의 중앙부에서 교차하거나 이를 통한 한라산의 생성과정과 연관된 지질학적인 구조일 가능성을 의미한다. 만약 한라산을 형성한 화성활동의 영향이 아직 지하 심부에 남아있다면 지열수의 부존 혹은 마그마의 통로가 되었을 단층의 영향으로 한라산 하부에 저비저항 이상대로 나타날 가능성이 높다. 그러나 후자에 의한 가능성도 배제할 수는 없으므로 향후 주변바다에 대한 영향을 고려한 3차원 역산해석이나 심부시추 등을 통한 상세한 지질조사 등 추가적인 연구가 이루어져야 할 것으로 판단된다.

• Journal of the Korean Geotechnical Society
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• v.28 no.6
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• pp.71-79
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• 2012

Sand compaction pile and stone column replacement methods have been commonly used for improving soft ground in the nearshore. Recently, DCM (Deep cement mixing) method, which can harden soft clays by mixing with cement, is more popularly used in such soft ground improvement. Sandy soils also exist in the seashore. Therefore, in this study, the effect of salinity in sea water and curing methods on the strength of cemented sand was evaluated in terms of unconfined compressive strength (UCS). The sand was mixed with five different cement ratios and distilled water or sea water, and then compacted into a cylindrical specimen. They were cured for 3 days under sea water for DCM construction condition and air cured for onshore curing condition. When a specimen was cured under sea water without confinement, it was easily collapsed due to initiation of cracks. When the cement ratio and curing method were the same, the UCS of the specimen without sea water was at maximum 3.5 times higher than those with sea water. The sea water used for mixing sand had more influence on strength reduction than the sea water used for curing. When the cement ratio was the same, the UCS of air-cured specimen was at average 2 times higher than those of water-cured specimen, regardless of water used.

• Journal of the Korean Geotechnical Society
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• v.27 no.9
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• pp.47-53
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• 2011

Marine dredged soils taken from navigation channels or construction sites of coastal area usually have a lot of salt in pores of clayey soils. This paper investigates effect of salt on mechanical characteristics of non-salt and salt-rich stabilized dredged soil. The stabilized dredged soil (SDS) consisted of dredged soil and cement. Several pairs of SDS with non-salt and salt-rich dredged soils, noted as N-SDS and S-SDS, respectively, were prepared to compare their strengths and compressibility characteristics. The microstructures, strength and compressibility characteristics of N-SDS and S-SDS specimens at 7 and 28 days of curing time were evaluated using scanning electronic microscope (SEM), unconfined compression test, and oedometer test. It was found that salt concentration of clayey soil affected not only the formation of soil structure but also the strength development of mixture. The compression index and swelling index of S-SDS were also greater than those of N-SDS, which indicated that the compressibility of mixture increased due to salt concentration. Salinity in clayey soil had a negative effect on the strength development and compressibility characteristics of stabilized dredged soils.

• Applied Chemistry for Engineering
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• v.25 no.4
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• pp.414-417
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• 2014

LED scraps consisting of highly crystalline GaN and their leaching behavior are comprehensively investigated for hydro-metallurgical recovery of rare metals. Highly stable GaN renders the leaching of the LED scraps extremely difficult in ordinary acidic and basic media. More favorable state can be obtained by way of high temperature solid-gas reaction of GaN-$Na_2CO_3$ powder mixture, ball-milled thoroughly at room temperature and subsequently oxidized under ambient air environment at $1000-1200^{\circ}C$ in a horizontal tube furnace, where GaN was effectively oxidized into gallium oxides. Stoichiometry analysis reveals that GaN is completely transformed into gallium oxides with Ga contents of ~73 wt%. Accordingly, the oxidized powder can be suitably leached to ~96% efficiency in a boiling 4 M HCl solution, experimentally confirming the feasibility of Ga recycling system development.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.255-264
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• 2009

Soils containing vanishing materials lead changes in the microstructure of particulate media due to water inflow. Thus, dissolution renders some local unstability. As the moisture contents decease, the component of the vanished materials may affects on the cementation of paniculate materials. This cementation phenomenon has a huge influence on the stiffness, strength and stability under lower stress level. The goal of this study is to introduce the cementation effects on a compressional wave velocity, a shear wave velocity, and the resonant frequency of shear waves. The glass bead and salt water with different mole contents are used. Test results show that the changes of shear and compressional wave velocities consist of three stages. In the first region, compressional wave velocities increase and shear wave velocities decrease with a decreases in reducing water contents from 100% to 90~95%. In the second region, shear and compressional wave velocities become stable at 90~95% to 10% of the water contents. In the third region, shear and compressional wave velocities increases dramatically with a decrease in the water content due to the capillary force and cementation of salt. Furthermore, the resonant frequency of the shear waves shows similar phenomenon. Specimens prepared by glass beads and salt water are proved to be able to provide a meaningful insight in under structural behaviors of the cementation.

• Journal of the Korean Geotechnical Society
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• v.29 no.2
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• pp.23-34
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• 2013

An organic acid material, which can be manufactured by plants extraction, encourages microbe proliferation over time. Microbial activity, which is affected by organic acid, encourages accelerating consolidation with biochemical penetration; soil particles are compacted by microbes and pore water is dissipated quickly. Additionally, $CaCO_3$ for cementation was made by proliferating microbes. Accordingly, tests were conducted to investigate the unconfined compressive strength and permeability of soil samples aged with and without an organic acid. In the 96 days of aging, the strength was generally 1.5~2.5 times greater than those without an organic acid material and permeability was definitely decreased to 74.2~93.1%. SEM analysis showed the change of pore structure and the change of the total bacteria counts revealed the activity of microbes reflecting the engineering characteristics and this material would be an environment-friendly for soil improvement.