• Journal of the Korean Geotechnical Society
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• v.16 no.6
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• pp.141-151
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• 2000

본 연구에서는 토사나 사석을 이용하여 자체를 축조하는 과정에서 발생하는 연약지반의 강제치환거동을 연구하기 위하여 다양한 시험조건에 대한 원심모셩을 수행하였다. 제체축조에 따른 연약지반의 강제치환거동은 제체의 성토시공방법, 성토재의 입경, 연약지반의 종류와 강도 등에 따라 맣은 차이를 보였는데, 특히 성토과정 중에 발생하는 과잉간극수압의 크기와 밀접한 상관관계를 보였다. 급속시공인 경우에 연약지반의 파괴영역은 회적으로 확대되고 성토사면의 기울기는 완만해졌으며, 성토재의 입경이 클수록 치환깊이가 증가하고 성토사면의 기울기가 급하게 형성되었다. 그리고 동일점토에서는 지반의 강도가 클수록 치환량이 적었지만, 점토의 종류가 다른 경우에는 지반내 발생하는 과잉간극수압의 크기와 소산성조에따라 치환거동이 많은 영향을 받는 것으로 나타났다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.11a
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• pp.32-32
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• 1997

복합재 연소관의 구조적 건전성 평가 방법을 개발하기 위하여 표준 평가용 시편의 수압 시험 중, 연소관으로부터 방출되는 음향방출(acoustic emission: AE) 신호를 측정 장비를 이용하여 신호 처리함으로써 시편이 파괴되기 전, 대략적인 시편의 파열 위치 및 일정 압력 유지상태에서 hit rate 양상에 의한 건전성 평가 방법을 제시하였다. 데이터의 분석 기법 향상을 위하여 음향방출 데이터를 시간 및 센서별로 분류하는 프로그램을 개발하였다. 수압 시험을 낮은 압력 단계부터 높은 압력 단계까지 일정 압력 유지 상태(load-hold)에서 발생한 hit 수와 1분간 유지한 후 발생되는 hit rate(hit/sec)의 값의 크고 작음이 복합재 압력 용기의 결함수의 증감으로 나타났으며, 이로부터 복합재 압력 용기의 파열 압력과의 상관관계 및 건전성을 예측할 수 있었다. 복합재 압력 용기의 파열 위치는 energy rate(energy/sec) 측정값을 분석하여 예측하였으며, 파열 압력의 30∼50%에서 가능하였다.

• Journal of the Korean Geotechnical Society
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• v.19 no.1
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• pp.151-161
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• 2003

In this study, an interpretation method is proposed to evaluate the stress conditions, including individual excess pore pressure components ($\Delta{u}_{oct}$/ and $\Delta{u}_{shear}$), of normally consolidated clay elements adjacent to the cone face. It is assumed that the stress path of triaxial compression is representative f3r that of the soil element and the soil is elastic-perfectly plastic material. The proposed method is applied to the results of miniature piezocone tests conducted at Louisiana State University calibration chamber system. Based on the results of interpretation, it was found that the ratio of $\Delta{u}_{oct}$/ $\Delta{u}$and $\Delta{u}_{shear}$/$\Delta{u}$ estimated by the proposed method is affected only by the pore pressure parameter. The proposed method gives consistent and reliable values of $\Delta{u}_{oct}$/ $\Delta{u}$and $\Delta{u}_{shear}$/$\Delta{u}$ compared with early works, whereas those obtained by other solutions are significantly dependent on the accuracy in estimating soil properties such as undrained shear strength and rigidity index.

• Geotechnical Engineering
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• v.13 no.4
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• pp.95-108
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• 1997

For normally consolidated clay, several researchers have developed a number of theoretical time factors to determine the coefficient of consolidation However, depending on the assumptions and analytical techniques, it could considerably vary even for a specific degree of consolidation. In this paper, a method is proposed to determine a consistent coefficient of consolidation over all ranges of degree of consolidation by applying the concept of the Optimum Design Technique. The initial excess pore pressure distribution is assumed to be obtainable by the successive spherical cavity expansion theory. The dissipation of pore pressure is simulated by means of two dimensional linear-uncoupled axisymmetric consolidation analysis. The minimization of the differences between the measured and the predicted excess pore pressures was carried by BFGS unconstrained optimum design algorithm with one dimensional golden section search technique. By analyzing numerical and real field examples, it can be found that the adopted optimum technique gives a consistent and convergent results.

• Journal of the Korean Geotechnical Society
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• v.22 no.3
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• pp.13-21
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• 2006

Geosynthetic damage has attracted a major attention since the introduction of geotextiles for civil engineering applications. In this study 3 pilot trial embankments were carried out to investigate the behaviours of reinforced embankments over soft cohesive soils and to find the optimum methodology of embankments over soft soils. As the seamed part of polyester mat (PET, tensile strength 15 ton) used in the first full-scale field test was ruptured under progressing rotational slope failure because of unexpectedly rapid construction of embankments, the excessive pore water pressures were measured. On the soil behavior where tension explosion of mat was continued, pore pressure larger than the one caused by embankment height was measured. Especially, at the depth of 5.0 m under the ground pore pressure increased over long term. It was discussed with respect to the height of embankment and heaving behavior of soft soils.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.311-320
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• 2003

The coefficient of consolidation of clay deposit is one of the most important properties in the design of ground improvement. The in-situ value of $c_h$ is generally estimated by pore pressure dissipation using piezocone. Many researchers have suggested theoretical formula for its estimation. This study attempts to find out the validity of the existing theoretical formula in Korea and to find out the characteristics of $c_h$ related to the mechanical properties of clay. Piezocone tests and laboratory tests were performed at the site of pilot project of ground improvement at Yangsan-Mulgeum, Gyeongnam. Comparison of the estimated values of $c_h$using piezocone tests results and those from laboratory consolidation tests are carried out. Results show that Torstensson(cylindrical cavity theory) and Teh & Houlsby solutions derive similar values of $c_h$. And $c_h$ from oedometer test shows values similar to the above two methods. The value from either of the above two methods[Torstensson(cylindrical) or Teh & Houlsby] is recommended to be used as $c_h$.

• Tunnel and Underground Space
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• v.28 no.3
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• pp.258-276
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• 2018

The accurate and quantitative ground information on the hydraulic conductivity characteristics of rock mass is one of the key factors for evaluation of the hydro-geological behaviour of rock mass around an excavated opening under high water pressure. For tunnel and rock structures in seabed, where the sea acts as an infinite source of water, its importance become greater with increasing construction depth below sea level. In this study, to improve the problems related with poor system configuration and incorrect data acquisition of previous hydraulic packer testing equipment, we newly developed an integrated main frame and 30 bar level waterproof downhole sonde apparatus, which were optimized for deep hydraulic packer test in seabed rock mass. Integration of individual test equipment into one frame allows safe and efficient field testing work on a narrow offshore drilling platform. For the integrated type main frame, it is possible to make precise stepwise control of downhole net injection pressure at intervals of $2.0kg_f/cm^2$ or less with dual hydraulic oil volume controller. To ensure the system performance and the operational stability of the prototype mainframe and downhole sonde apparatus, the field feasibility tests were completed in two research boreholes, and using the developed apparatus, the REV(Representative Elementary Volume) scale deep hydraulic packer tests were successfully carried out at a borehole located in the basalt region, Jeju. In this paper, the characteristics of the new testing apparatus are briefly introduced and also some results from the laboratory and in-situ performance tests are shown.

• 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.

• Journal of the Korean Geotechnical Society
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• v.15 no.4
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• pp.185-205
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• 1999

Hydraulic fracturing tests were performed in two inclined boreholes for the design of underground oil storages in Korea. Extensions of their application limits were expected through a precise comparison between the interpretation techniques for the vertical and the inclined boreholes. Especially, it was verified that the magnitude of in-situ stress can be varied even in the same rock mass with a variety of geographic/geotechnical characteristics. It was also demonstrated that its orientation can be changed even in the same borehole with the existence of explicit discontinuities.

• Journal of the Korean Geotechnical Society
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• v.28 no.5
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• pp.95-107
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• 2012

Even though the importance of predicting build-up of pore pressure under cyclic loading is recognized, effective stress analysis is rarely performed due to difficulties in selecting the parameters for the pore pressure model. In this paper, a new stress based numerical model for predicting pore pressure under cyclic loading is developed. The main strength of the model is that it is easy-to-use, requiring only the CSR-N curve in selecting the parameters. Another advantage of the model is that it can be used for any loading pattern and therefore can be implemented in an effective stress time-domain dynamic analysis code. The accuracy of the model is validated through its comparisons with measurements in literature and laboratory test data collected in Korea. Further comparisons with another stress based pore pressure model highlighted the superiority of the proposed model.