• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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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.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.14 no.4
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• pp.286-294
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• 2002

This study investigated the effects of stress and time history of overconsolidated clayey soils on pore pressure parameter, A. Laboratory tests were carried out under the conditions of both varying stress and time history. The stress history is classified into (i) rotation angle of stress path, (ii) overconsolidation ratio, and (iii) magnitude of length of recent stress path. The time history is divided into (i) loading rate of recent stress path and (ii) rest time. Pore pressure parameters are different both in the magnitude and trend with the rotation angle, depending on the magnitude of overconsolidation ratio but not in a trend. In addition, the pore pressure parameters have no effects on the magnitude of length of recent stress path except the level of initially small strain, while loading rates of recent stress path have effects on it. Finally, the pore pressure parameters of overconsolidated clays increase with the existence of the rest time, until either the deviator stress exceeds 70 kPa or the strain up to 0.1%.

• Journal of The Korean Society of Agricultural Engineers
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• v.47 no.2
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• pp.87-96
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• 2005

In this research, an attempt is made to derive the practical estimation of the degree of consolidation in soft clay from field measurements under embankments. For the practical estimation of pore water pressure in soft clay, the elasto-viscous rheological model was proposed, with a transform of parameters and a field geotechnical measurements in southern Korea. By using the rheological properties of soft clays and the dissipation of excess pore water pressure behaviour during step loading, a degree of consolidation or pore water pressure estimation in the future can be performed, and are shown to be generally close to the field measurements of pore water pressure. Finally, a pore water pressure behaviour in soft clay can be explained through measured data in field and the excess pore water pressure data can also be used to estimate settlement.

• Magazine of the Korean Society of Agricultural Engineers
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• v.36 no.3
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• pp.90-99
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• 1994

To investigate the undrained shear strength characteristics of marine soils with high water content, high compressibility and weak bearing capacity, a series of undrained triaxial tests with pore pressure measurements on undisturbed and disturbed Banwol marine clay in normally consolidated and overconsolidated states is carried out. The results and main conclusions of this study are summarized as follows : 1 . When the consolidation pressure is increased, the maximum deviator stress of disturbed and undistubed clay in normally consolidated state is increased. Pore pressure parameters and internal friction angle of undisturbed clay are greater than those of disturbed clay. 2. The relationship between pore pressure and axial strain of undisturbed clay in normally consolidated state can be expressed as a hyperbolic function like stress-strain relation proposed by Kondner. 3. In the pore pressure-axial strain relation of disturbed clay in normally consolidated state, failure ratio R'f is greatly deviated in the range of 0.7~0.9 proposed by Christian and Desai. 4. For overconsolided clay, when overconsolidation ratio (OCR) is increased, normalized maximum deviator stress is increased and maximum pore pressure is decreased gradually. 5. Cohesion of overconsolidated clay is greater than that of nomally consolidated clay and internal friction angle slightly is decreased. 6. Pore pressure parameter at failure (Af) of overconsolidated clay is varied with OCR, Af becomes negative values with increment in OCR

• 한국방재학회:학술대회논문집
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• 2007.02a
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• pp.546-550
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• 2007

High excess pore water pressure may develop when loose saturated sand is subjected to earthquake excitation, resulting in reduction in the shear strength and stiffness, and ultimately can result in liquefaction. It is very important to accurately assess the level of the pore pressure generation for seismic design and to perform effective stress analysis. A simple numerical 모형 is developed for estimating the development of pore water pressure due to seismic loading. The method only uses two parameters and the length of the accumulated shear strain. The accuracy of the proposed 모형 is verified through a series of laboratory test data. Comparisons show that the modified 모형 is an improvement over existing 모형s.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.201-208
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• 2000

In this study, the behavior of saturated sandy soils under dynamic loads - pore water pressure and effective stress - was investigated using Disturbed State Concept(DSC) model. The model parameters are evaluated from laboratory test data. During the process of loading and reverse loading, DSC model is utilized to trace strain-hardening and cyclic softening behavior. The procedure of back prediction proposed in this study are verified by comparing with laboratory test results. From the back prediction of pore water pressure and effective mean pressure under cyclic loading, excess pore water pressure increases up to initial effective confining pressure and effective mean pressure decrease close to zero in good greement with laboratory test results. Those results represent the liquefaction of saturated sandy soils under dynamic loads. The number of cycles at initial liquefaction using the model prediction is in good agreement with laboratory test results. Therefore, the results of this study state that the liquefaction of saturated sandy soils can be explained by the effective tress analysis.

• Journal of Korean Society on Water Environment
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• v.24 no.6
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• pp.793-800
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• 2008

Recently domestic drinking water industry has recognized membrane-based technology as a promising alternative for water treatment. To ensure successful application of membrane processes, the integrity of membrane systems should be maintained. According to US EPA guidance, the pressure decay test based on the bubble point theory is recommended to detect any membrane defection of which size is close to the smallest diameter of Cryptosporidium oocysts, $3{\mu}m$. Proper implementation of the pressure decay test is greatly affected by initial test pressure, and the interpretation of the test results is associated with upper control limit. This study is conducted to investigate various factors affecting determination of initial test prtessure and upper control limit, including membrane-based parameters such as pore shape correction factor, surface tension and contact angle, and system-based parameters, such as volumetric concentration factor and total volume of system. In this paper, three different hollow fibers were used to perform the pressure decay test. With identical initial test pressure applied, their pressure decay tendency were different from each other. This finding can be explained by the micro-structure disparity of those membranes which is verified by FESEM images of those membranes. More specifically, FESEM images revealed that three hollow fibers have asymmetry, deep finger, shallow finger pore shape, respectively. In addition, sensitivity analysis was conducted on five parameters mentioned above to elucidate their relation to determination of initial test pressure and upper control limit. In case of initial pressure calculation, the pore shape correction factor has the highest value of sensitivity. For upper control limit determination, system factors have greater impact compared to membrane-based parameters.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2007.11a
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• pp.179-186
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• 2007

The best way to understand paper properties is to study paper structure. Paper is composed solid materials (pulp and other additives) and air three-dimensionally, it's important to understand pore structure of the paper. There are several method to analysis pore structure of the paper. Mercury intrusion technique is frequently used for the characterization of the porous paper, giving access to parameters such as pore size and pore distribution. But some researchers indicated mercury intrusion distorts the structure due to application of high pressure. So this paper suggest new analysis technique to pore structure of the paper. New pore analysis technique with SEM does not require high pressure, gives good resolution and measures pore structure.

• 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.

• Geomechanics and Engineering
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• v.6 no.5
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• pp.503-515
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• 2014

On the basis of Hoek-Brown failure criterion, a numerical solution for the shape of collapsing block in the rectangular cavity subjected to seepage forces is obtained by upper bound theorem of limit analysis. The seepage forces obtained from the gradient of excess pore pressure distribution are taken as external loadings in the limit analysis, and the pore pressure is easily calculated with pore pressure coefficient. Thus the seepage force is incorporated into the upper bound analysis as a work rate of external force. The upper solution of the shape of collapsing block is derived by virtue of variational calculation. In order to verify the validity of the method proposed in the paper, the result when the pore pressure coefficient equals zero, and only hydrostatic pressure is taken into consideration, is compared with that of previous work. The results show good effectiveness in calculating the collapsing block shape subjected to seepage forces. The influence of parameters on the failure mechanisms is investigated.