• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 봄 학술발표회 논문집
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• pp.49-54
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• 2002

This paper describes a systematic way of simultaneously identifying the ambient pore pressure and the rigidity index (=G/s$\_$u/) of soil by applying an optimization technique to the piezocone dissipation test result. An ambient pore pressure and optimal rigidity index were determined by minimizing the differences between theoretical excess pore pressures developed by Randolph ＆ Wroth(1979) and measured excess pore pressures from piezocone using optimization technique. The effectiveness of the proposed back-analysis method was examined against the well-documented performance of piezocone dissipation tests (Tanaka ＆ Sakagami, 1989), from the viewpoints of proper determination of selected target parameters and saving of test duration. It is shown that the proposed back-analysis method can evaluate properly the ambient pore pressure and the rigidity index by using only the early phase of the dissipation test data. Also, it is shown that with the optimized rigidity index and ambient pore pressure the proposed back-analysis method permits the horizontal coefficient of consolidation to be identified rationally.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2004년도 춘계학술발표회
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• pp.714-721
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• 2004

The purpose of this study is to find out the similitude laws for dissipation velocity of excess pore pressure after liquefaction according to magnitude of input accelerations and height of model soils from the results of impulse load tests. In impulse load tests, model soils were constructed to the height of 25cm, 50cm, and 100cm in acrylic tubes whose inside diameters were 19cm and 38cm respectively, and impulse loads were applied at the bottom of each model soil to liquefy the entire model soil. Excess pore pressure distribution by depth and settlement of soil surface were measured in each test. Dissipation curves of excess pore pressure measured in each tests were simulated by solidification theory, and dissipation velocities of excess pore pressure were determined from the slope of simulated dissipation curves. From the results of impulse load tests, dissipation velocity of excess pore pressure was not affected by magnitude of input acceleration, and from this fact, dissipation process was proved to be different from dynamic phenomenon. However, dissipation velocity of excess pore pressure increased as height of model soil increased and showed little difference as diameter of model soil increased. Therefore, the similitude law for dissipation velocity could be expressed by the similitude law for model height to 0.2 without regard to the diameter of model soil.

• 한국지반공학회지:지반
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• 제13권6호
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• pp.25-36
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• 1997

피에조콘을 이용하면 연약지반 개량후 임의의 시점에서 지반의 압밀도를 파악할 수가 있다. 이 경우 임의의 심도에서 피에조콘의 관입을 멈추고 간극수압이 일정한 값에 이를 때까지 간극 수압 소산시험을 실시하는데, 연약지반의 투수계수가 작기 때문에 대체적으로 상당히 오랜 시간 동안 소산시험을 하게 된다. 본 논문에서는 침하 분석기법 가운데 일반적으로 널리 알려져 있는 쌍곡선법, 아사오카법, 호시노법을 이용하여 간극수압 소산시험시의 평형간극수압을 각각 추정한 후 장시간에 걸친 실제 시험결과와 비교함으로써 간극수압 소산시험에 소요되는 시간을 단축할 수 있는 방법을 연구하였다. 그 결과, 호시노법을 이용한 추정방법이 가장 적합한 방법임을 알 수 있었으며 이를 이용한 효율적인 간극수압 소산시험 방법을 제시하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.1204-1211
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• 2008

Compression index is one of the important characteristic numbers in soft soil engineering. Since 1940's, many researchers have suggested various practical solutions to define the compression index of clay using other soil properties. But, these results are only can give us an outline of soft soil behavior. In this study, the relationships between pore water pressure dissipation test results and compression index were suggested using comparison results of both tests. This relationships are based on basic concept of consolidation phenomena, essential difference between pore water pressure dissipation test and consolidation test, and disagreements between theoretical time factor and real time factor. To identify proportional factor of proposed equation, Geotechnical investigation results of Kwang-Yang(KY) site and Busan New Port(BN) site were used. The proportional factor was 0.0031 from 20 to 50% of consolidation rate where correlation parameter($R^2$) is 0.9051.

• 한국지반공학회논문집
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• 제23권10호
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• pp.13-22
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• 2007

최근 액상화 이후의 구조물 거동에 관심이 높아지면서, 액상화 지반의 과잉간극수압 소산에 대한 연구가 활발히 이루어지고 있다. 본 연구에서는 포화된 수평모래지반에 대한 원심모형실험을 수행하여 액상화 이후의 과잉간극수압 소산거동을 계측하고 계측결과를 바탕으로 견고화층의 비선형적인 두께 변화에 대한 예측모델을 제안하였다. 기존의 침강이론과 압밀이론에 이 예측모델을 결합함으로써 과잉간극수압 소산을 모델링하는 새로운 소산 예측모델을 개발하였다. 개발된 소산모델은 원심모형실험 결과와 비교하여 견고층 두께 증가와 과잉간극수압 소산양상을 잘 모사하는 것으로 나타났다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.1328-1339
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• 2008

For a commonly used piezocone with a shoulder filter element, dilatory dissipation behavior, which shows an initial temporary increase in pore pressure, has been observed in overconsolidated cohesive soils. However, there is no appropriate way to estimate a consolidation parameter from a dilatory dissipation curve because currently available interpretation methods were developed based on the monotonic decrease of the excess pore pressure. In this study, the interpretation method for evaluation of coefficient of consolidation from a dilatory dissipation result of piezocone test was developed by performing the finite difference analysis on the dissipation after cone penetration. The distribution of the initial excess pore pressure induced by cone penetration, which is the core of the analysis, was estimated from the empirical modification of a solution proposed by cavity expansion theory and critical state concept. And the proposed interpretation method was applied to the field piezocone data and the results were compared to those obtained from laboratory tests. Its reliability was confirmed by the insignificant difference between the values of coefficient of consolidation from piezocone tests and laboratory consolidation tests.

• 한국지반공학회논문집
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• 제18권2호
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• pp.161-170
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• 2002

본 논문은 최적화기법을 이용하여 현장에서 수행된 피에조콘 소산시험의 초기 경향으로부터 평형간극수압과 지반의 강성지수$(=G/s_u)$를 역해석하는 기법에 관하여 기술하였다. 피에조콘 관입으로 인해 콘 주변에 발생된 초기 과잉간극 수압의 크기 및 분포, 그리고 연속된 간극수압 소산과정은 Randolph & Wroth(1979)가 제안한 해석적 해를 이용하여 지반의 강성지수의 함수로 표현되었다. 제안된 기법에서는 주어진 강성지수에 대해 정규화 된 이론 소산곡선과 평형간극수압으로 정규화 된 피에조콘 관측 소산곡선이 가장 일치하도록 하는 평형간극수압과 지반의 강성지수가 최적화기법을 이용하여 결정되었다. 제안된 기법을 압밀이 진행중인 지반에서 관측된 피에조콘 소산시험 결과(Tanaka & Sakagami, 1989) 해석에 적용하였고 역해석된 평형간극수압과 현장에서 관측된 평형간극수압의 크기를 비교하였다. 또한 제안된 기법으로 얻어진 지반의 강성지수와 평형간극수압을 바탕으로 수평압밀계수를 추정하였으며 일차원 압밀실험 결과와 비교하였다. 그 결과 제안된 기법이 지반에 잔류하는 평형간극수압의 크기를 매우 정확하게 예측함을 알 수 있었고 역해석 된 강성지수를 이용한 압밀계수의 추정이 타당함을 알 수 있었다. 또한 얻어진 강성지수의 변형 률수준에 관한 검토결과 피에조콘 해석을 위한 강성지수는 중간 또는 대변형 상태의 변형상태에 해당하는 값을 사용하는 것이 타당할 것으로 판단되었다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2006년도 학술발표회 논문집
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• pp.97-104
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• 2006

The centrifuge and 1-g shaking table tests were performed simultaneously to compare the dynamic behaviors of loose sands of same geotechnical properties. The prototype soils were 10 m thick liquefiable loose sands. The geometric scaling factors were 20 for 1-g and 40 for centrifuge tests. The excess pore pressure, surface settlement, and acceleration in the soil were measured at the same locations in the 1-g and centrifuge tests. The total excess pore pressure from development to dissipation was measured. In the centrifuge test, viscous fluid was used as the pore water to eliminate the time scaling difference between dynamic time and dissipation time. In the 1-g tests, the steady state concept was applied to determine the unit weight of the model soil, and two different time scaling factors were applied for the dynamic time and the dissipationtime. It is concluded that the 1-g tests can simulate the excess pore pressure of the prototype soil if the permeability of the model soil is small enough to prevent dissipation of excess pore pressure during shaking and the dissipation time scaling factor is properly determined.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2001년도 봄 학술발표회 논문집
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• pp.485-492
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• 2001

Weathered soil is one of the most representative soils in Korea. In this study, a series of cyclic triaxial tests was carried out to predict the post-cyclic deformation behavior of weathered soils in case of non-liquefaction. Excess pore pressure response during cyclic loading and volumetric strain during the dissipation of excess pore pressure were measured varying the confining pressure, relative density and cyclic stress ratio. Based on the test results, it Is found that the modified excess pore pressure ratio, excess pore pressure ratio normalized by cyclic stress ratio, is uniquely correlated with the number of cycles irrespective of confining pressure and cyclic stress ratio. Using the newly proposed MEPPR(modified excess pore pressure ratio) concept, it is possible to easily evaluate the excess pore pressure and the settlement of weathered soils due to cyclic loading by greatly reduced number of tests. It is also verified that the reconsolidation volumetric strain is independent of the way how the excess pore pressure was generated.

• 한국지반공학회논문집
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• 제19권6호
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• pp.363-369
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• 2003

액상화후 과잉간극수압 소산양상을 파악하고 액상화를 겪는 지반의 침하량을 예측하는데 필요한 진동하중이 작용하는 동안의 포화된 모래지반의 투수계수 변화를 추정하기 위하여, 액상화 가능성이 큰 5종류의 모래에 대해 1-g 진동대시험을 수행하였다. 시험과정중에 깊이별 과잉간극수압과 지표면 침하량을 계측하였다. 액상화후 계측된 과잉간극수압 소산곡선을 침강이론으로 선형모사하였고 선형모사된 소산곡선의 기울기를 분석함으로써 소산속도와 입도특성치와의 상관관계를 얻었다. 이러한 상관관계와 계측된 침하량을 침강이론에서 제안한 소산속도식에 대입하여 소산과정중 투수계수를 역산하였고 산정된 소산과정중 투수계수를 이용하여 진동하중이 작용하는 동안의 투수계수 변화를 추정하였다. 액상화후 과잉간극수압의 소산속도는 유효입경을 균등계수로 나눈 값에 선형적 상관관계를 갖는 것으로 나타났으며, 이러한 상관관계를 이용하여 구한 소산과정과 액상화동안의 투수계수는 원지반의 초기투수계수에 비해 각각 1.1∼2.8배, 1.4∼5배 증가하였다 그리고 이러한 증가 정도는 시험모래의 유효입경이 클수록 균등계수가 작을수록 더 커짐을 알 수 있었다.