• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2006년도 추계 학술발표회
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• pp.312-333
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• 2006

This paper presents the results of an analysis of the excess porewater pressure distribution due to piezocone penetration in overconsolidated clays. From piezocone test results for moderately and heavily overconsolidated clays, it was observed that the excess porewater pressure increases monotonically from the piezocone surface to the outer boundary of the shear zone and then decreases logarithmically to the outer boundary of the plastic zone. It was also found that the size of the shear zone decreases from approximately 2.2 to 1.5 times the cone radius with increasing OCR, while the plastic radius is about 11 times the piezocone radius, regardless of the OCR. The equation developed in this study based on the modified Cam clay model and the cylindrical cavity expansion theory, which take into consideration the effects of the strain rate and stress anisotropy, provide a good prediction of the initial porewater pressure at the piezocone location. The method of predicting the spatial distribution of excess porewater pressure proposed in this study is based on a linearly increasing ${\Delta}u_{shear}$. In the shear zone and a logarithmically decreasing ${\Delta}u_{oct}$, and is verified by comparing with the excess porewater pressure measured in overconsolidated specimens at the calibration chamber.

• 한국지반공학회논문집
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• 제30권2호
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• pp.19-32
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• 2014

중동지역 Sabkha층 탄산질 모래는 패각류가 퇴적되어 생성되었으며, 내부간극을 포함한 다공질의 입자로 구성되어 있다. 일반적으로 흙은 항복하중에서 구조가 파괴되어 간극수압 및 침하량이 급격히 증가하게 된다. 그러나 석영질 모래와는 달리 탄산질 모래의 경우 항복하중에 따른 입자파쇄시 내부간극이 외부로 노출되어 간극수압이 감소 될 수 있다. 탄산질 모래에서 발생된 과잉간극 수압은 하중 재하시 상대밀도 증가로 인한 과잉간극수압과 입자파쇄에 따른 내부간극 노출로 인한 과잉간극수압, 파쇄입자의 재배열로 인한 과잉간극 수압의 합에 의해 결정되며, 내부간극의 노출량에 따라 음(-)의 값이 나타날 수 있다. 입자파쇄량이 크면 간극수압이 작게, 입자파쇄량이 작으면 간극수압이 크게 나타난다. 삼축압축시험 결과 음(-)의 간극수압이 나타난 구간은 외부간극 감소에 비해 입자파쇄가 우세한 영역이며, 현장 Sabkha층에서 확인된 입자파쇄 우세 영역의 크기는 1.50~3.46%의 값을 나타내었다.

• 한국지반공학회논문집
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• 제22권11호
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• pp.75-87
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• 2006

본 논문에서는 과압밀된 점토에서 피에조콘 관입으로 인한 과잉간극수압의 공간적인 분포를 알아내기 위한 대형 토조시험을 실시하고 분석결과를 제시하였다. 시험결과에 의하면 콘 주변의 전단영역에서 과잉간극수압은 콘 표면으로부터 전단영역의 경계까지 직선적으로 증가하며, 소성영역에서는 대수적으로 감소하여 소성영역 경계에서 영으로 접근하였다. 또한 전단영역의 크기는 콘 반경의 2.2-1.5배 정도이며 과압밀비 증가 시 전단영역의 크기는 감소하는 반면 소성영역의 크기는 과압밀비에 상관없이 콘 반경의 약 11배로 일정하였다. 본 연구에서는 변형률 속도와 응력이 방성 효과를 고려하여 MCC(Modified Cam Clay) 모델과 공동확장이론으로부터 피에조콘 위치에서의 과잉간극수압을 예측하였으며, 전단영역에서 ${\Delta}u_{shear}$의 선형증가와 전단 및 소성영역에서 ${\Delta}u_{oct}$의 대수적 감소를 가정하여 과잉간극수압의 공간적 분포를 예측하기 위한 방법을 제시하였다. 이러한 방법으로 예측된 간극수압의 분포는 대형 토조시험에서의 콘 관입시험 결과와 비교를 통해 검증되었다.

• 한국지반공학회논문집
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• 제36권6호
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• pp.5-15
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• 2020

본 연구는 필댐에 설치된 간극수압과 댐의 저수위와의 상관관계를 통해 댐의 안정성 평가를 위한 간극수압계의 활용방안에 대해 다루고 있다. 이를 위해 필댐에 설치된 총 8개의 간극수압계에 대해서 주성분 분석을 수행한 결과, 3개의 군집으로 분류되었다. 이는 댐 제체 내에 형성되는 침윤선을 기준으로 내부, 외부, 상단으로 분류된 것으로 나타났다. 침윤선 내부에 위치한 A군집 내 간극수압계와 저수위와의 상관계수는 0.94~1.00로 강한 양의 선형관계를 나타냈다. 즉, 향후 A군집 내에 존재하는 간극수압계에 의해 해당 댐의 유지관리가 필요한 것을 의미한다. 또한, 저수위와 간극수압계에 대한 회귀분석을 수행한 결과, A군집의 결정계수가 0.89~0.99로 선형회귀 모형이 도출되었다. 따라서 저수위가 설명 변수로 고정될 때 간극수압의 예측이 가능하여 현재 계측된 값과의 비교를 통해 댐의 안전성 여부를 판단할 수 있는 것으로 나타났다.

• 한국지하수토양환경학회지:지하수토양환경
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• 제23권1호
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• pp.1-13
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• 2018

A series of experiments using transparent micromodels with an artificial pore network etched on glass plates was performed to investigate the effects of flow rate on the migration and distribution of resident wetting porewater (deionized water) and injecting non-wetting fluid (n-hexane). Multicolored images transformed from real RGB images were used to distinguish n-hexane from porewater and pore structure. Hexane flooding followed by immiscible displacement with porewater, migration through capillary fingering, preferential flow and bypassing were observed during injection experiments. The areal displacement efficiency increases as the injection of n-hexane continues until the equilibrium reaches. Experimental results showed that the areal displacement efficiency at equilibrium increases as the flow rate increases. Close observation reveals that preferential flowpaths through larger pore bodies and throats and clusters of entrapped porewater were frequently created at lower flow rate. At higher flow rate, randomly oriented forward and lateral flowpaths of n-hexane displaces more porewater at an efficiency close to stable displacement. It may resulted from that the pore pressure of n-hexane, at higher flow rate, increases fast enough to overcome capillary pressure acting on smaller pore throats as well larger ones. Experimental results in this study may provide fundamental information on migration and distribution of immiscible fluids in subsurface porous media.

• 한국지하수토양환경학회지:지하수토양환경
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• 제21권3호
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• pp.35-48
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• 2016

A micromodel was applied to estimate the effects of geological conditions and injection methods on displacement of resident porewater by injecting scCO₂ in the pore scale. Binary images from image analysis were used to distinguish scCO₂-filled-pores from other pore structure. CO₂ flooding followed by porewater displacement, fingering migration, preferential flow and bypassing were observed during scCO₂ injection experiments. Effects of pressure, temperature, salinity, flow rate, and injection methods on storage efficiency in micromodels were represented and examined in terms of areal displacement efficiency. The measurements revealed that the areal displacement efficiency at equilibrium decreases as the salinity increases, whereas it increases as the pressure and temperature increases. It may result from that the overburden pressure and porewater salinity can affect the CO₂ solubility in water and the hydrophilicity of silica surfaces, while the neighboring temperature has a significant effect on viscosity of scCO₂. Increased flow rate could create more preferential flow paths and decrease the areal displacement efficiency. Compared to the continuous injection of scCO₂, the pulse-type injection reduced the probability for occurrence of fingering, subsequently preferential flow paths, and recorded higher areal displacement efficiency. More detailed explanation may need further studies based on closer experimental observations.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 봄 학술발표회 논문집
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• pp.463-468
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• 2002

Based on the results obtain from the investigation of Nak-Dong River District, it was classified as very thick, soft soil deposit. Furthermore, during the construction of structures large settlements are expected. Since large settlement affects the structures life, it is very important to accurately determine the consolidation of soil based on the obtained results. In this study piezocone test and laboratory test were performed to determine the consoildtion properties of Nak-Dong River District Pusan, Gyeong-Nam province. Degree of consoildation and the coefficient of consoildation obtained from the data of piezocone test and the results of the Oedometer test were compared and analyzed. Using the results the porewater pressure coefficient($B_q$) was obtained and the relationship with the Plasticity Index was also determined. From the results of this study the effects of the degree of consolidation and consolidation coefficient, and the porewater pressure coefficient and the Plasticity Index was determined.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1998년도 지반조사위원회 봄 학술세미나
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• pp.37-46
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• 1998

Several researchers have developed a number of theoretical time factors to determine the coefficient of consolidation by biezocone excess pore water dissipation test in soft clay deposits. However, depending on the assumptions and analytical techniques, the estimated coefficient of consolidation could be in a considerably wide range even for a specific degree of consolidation. These solutions are obtained from an initial excess porewater pressure distribution which can be determined from. either the cavity expansion theory or the strain path method. The 야ssipation of the initial excess porelvater pressure has been usally simulated by means of linear-uncoupled consolidation analysis and then the dissipation curve is normalized by the initial excess porewater pressure for easy use. However. since there is no guidelines or rules on which method gives the best solution for obtaining the coefficient of consolidation from the dissipation curve, the final selection was only based on engineer's extrience and Judgements. Thus, such an arbitrary selection might be inappropriate for a specific site to characterize the consolidation behavior. In this paper, we reviewed various theoretical time factors and, based on this consideration, we mentioned needs for researches in selecting a specific solution that is compatible for Korean clays. Also we listed some source of errors that can be encountered in the procedure of dissipation analysis.

• 한국지하수토양환경학회지:지하수토양환경
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• 제20권4호
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• pp.73-82
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• 2015

Despite significant effects on macroscopic migration and distribution of CO₂ injected during geological sequestration, only limited information is available on wettability in microscopic scCO₂-brine-mineral systems due to difficulties in pore-scale observation. In this study, a micromodel had been developed to improve our understanding of how scCO₂ flooding and residual characteristics of porewater are affected by the wettability in scCO₂-water-glass bead systems. The micromodel (a transparent pore structure made of glass beads and glass plates) in a pressurized chamber provided the opportunity to visualize scCO₂ spreading and porewater displacement. CO₂ flooding followed by fingering migration and dewatering followed by formation of residual water were observed through an imaging system. Measurement of contact angles of residual porewater in micromodels were conducted to estimate wettability in a scCO₂-water-glass bead system. The measurement revealed that the brine-3M NaCl solution-is a wetting fluid and the surface of glass beads is water-wet. It is also found that the contact angle at equilibrium decreases as the pressure decreases, whereas it increases as the salinity increases. Such changes in wettability may significantly affect the patterns of scCO₂ migration and porewater residence during the process of CO₂ injection into a saline aquifer at high pressures.

• 한국해양학회지:바다
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• 제12권3호
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• pp.244-250
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• 2007

MIMS 시스템은 액체 시료의 용존 가스 농도를 정확하게 측정하는데 이용되어 왔는데, 본 연구에서는 해수와 퇴적물 공극수에 존재하는 용존 메탄 농도를 정량화하는데 사용되었다. 측정의 정밀성을 파악하기 위하여, 여러 분압의 메탄 농도에 대해서 포화된 액체 시료를 준비하였으며 이를 MIMS 시스템으로 측정하였다. 측정된 값은 용존 기체의 포화 상수로부터 계산된 값과 잘 일치하였다. 측정의 표준 오차는 평균값의 $0.13{\sim}0.9%$ 정도였다. 이 시스템을 이용하여 한반도 남해안 인근 해수의 용존 메탄 농도를 측정한 결과, 용존 메탄의 깊이별 분포는 물리적인 요소가 좌우하고 있음을 알 수 있었다. MIMS system을 이용하여, 각 수괴 간의 미세한 용존 메탄 농도의 차이를 구분하여 살펴볼 수 있었다. 또 다른 실험에서는 MIMS 시스템의 inlet 부분을 탐침 형태로 제작하여 퇴적물 깊이에 따른 용존 메탄을 측정할 수 있었다.