• Journal of the Korean Geosynthetics Society
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• v.13 no.4
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• pp.33-43
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• 2014

Recently, the case to construct the structure on the soft clayey ground has increased and in order to the reduction of the cost of construction and maintenance on the social infrastructure facilities we have been trying to improve the soft clayey ground using the existing methods such as the pre-loading method and the vertical drain method. Like this, when various ground improvement methods are applied on the soft clayey ground, a long-term consolidation settlement will be key issue due to low permeability coefficient of cohesive soil. According to existing research results that relate to the consolidation settlement, the loading periods for existing the standard consolidation test (Oedometer test) to obtain the consolidation parameters are needed for minimum ten days or more. Therefore, in this study, the standard consolidation test (24 hours step-loading) and constant strain rate consolidation test changed by strain rate was performed using the remolded marine clay on Gwangyang bay composed of a soft clayey ground of the south-west coast. From the laboratory test results, the characteristics of compression, strain-effective stress relations by constant strain rate and the variation characteristic of the pore water pressure by different of loading speed and the relation between consolidation parameters and constant strain rate are compared and analyzed.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.922-929
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• 2004

In some port construction, a case of reclamation with dredged soil for land use can be found. Even though this is not a new technology, there are some problems on the test method and analysis. The design parameters are still remained to be solved to get accurate prediction. Sedimentation of particle and self-weight consolidation are the most important design parameters in reclamation by dredged soils. The design parameters are influenced by properties of the physical and sedimentation of dredged soils. This influencing factors can be determined depend on the history of long term sedimentation and particle characteristics. Thus, properties of the sedimentation and consolidation are varies depend on the regional geologic formation. In this paper, three different sites with different regional soil properties will be compared in design parameters of sedimentation and self-weight consolidation.

• Science of Emotion and Sensibility
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• v.15 no.4
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• pp.527-540
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• 2012

We examined the effect of delayed and immediate rewards on short- and long-term memory performance depending on the level of stress. It has been demonstrated that delaying feedback during memory tasks could lead to better retention than presenting it immediately (a.k.a., feedback delay benefit or delay-retention effect). In this study, we manipulated stress level(high-stress or low-stress), reward-timing(delayed or immediate reward), reward-existence(500 or 0 won) and retrieval-timing(delayed or immediate memory test). On the high-stress learning condition, one week later, the number of correct answers with delayed-rewards were significantly more than that of delayed-no-rewards but there was not any difference between immediate-rewards and immediate-no-rewards. On the other hand, in the high-stressful immediate memory test, immediate-rewards only had a positive effect on memory performance. The results indicated that delayed rewards improved long-term memory performance by promoting memory consolidation and the sensitivity to rewards was higher under the high-stress condition.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.10a
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• pp.133-145
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• 2001

This paper presents quality and measure controls of Plastic Board Drains(PBD) for improvement of soft ground. Laboratory and field tests has been carried out to evaluate the quality of PBD focussing on : discharge capacity of flow area; permeability of filter sleeve; migration of fine particles; deformed shape of PBD; consolidation of clay in the close vicinity of PBD; tensile strength of PBD; long-term consolidation behavior of clay-PBD. Test results show that the quality of PBD is sufficient to perform the improvement of soft silty and clayey ground. But, geotechnical engineer must make efforts minimizings of PBD damage and ground disturbance, continuity of drainage system during construction. Adequate monitoring system should apply at ground focussing on number, location, and accuracy of geotechnical instrumentation, measurement and evaluation of data for ground behaviour.

• Journal of the Korean GEO-environmental Society
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• v.19 no.9
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• pp.21-28
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• 2018

In this study, a standard consolidation test (Oedometer) was performed on the relative density of sand in the south coast to evaluate long-term creep settlement characteristics. Experimental results show that the cumulative settlement at the final loading stage decreases as the relative density increases and the variation of the void ratio decreases. As a result of analyzing the settlement rate of long-term creep of sand, creep settlement of 4.7~11.0% occurred depending on relative density with respect to total settlement. The creep parameter, Beta, of Schmertmann et al. (1978) was estimated to be 0.17~0.40 (average 0.21), and it tended to converge to a certain value when the load step becomes more than a certain level. It was found that there is no significant difference in the creep parameter depending on the layer thickness, and it was confirmed that the creep parameter could be applied regardless of the field layer thickness.

• Geotechnical Engineering
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• v.10 no.4
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• pp.167-180
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• 1994

A series of long term consolidation tests were conducted under loading -unloading and loading(pc) -unloading(p.) -reloading(p,) conditions using reconstituted clay in order to investigate the effect of stress history on secondary consolidation characteristics and the applicability of the secondary consolidation model suggested by Bjerrum to overconsolidated clays. According to the test results, the secondary compression settlement affected by the stress history in the first half of experimental period and the coefficient of secondary compression, C‥‥ is dependent on overconsolidation ratio, OCR(p,1 p.), maBium OCR (p./p.), and unloading duration time. Moreover the coefficient of secondary consolidation in the latter half of experimental period Cn is mainly affected by OCR and it gradually reduces with OCR increment. Finally the comparison of the experimental results with the Bjerrum model indicates that the Bjerrum model can be applied beyond certain range of stress history in the overconsolidated clay.

• Journal of the Korean GEO-environmental Society
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• v.1 no.1
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• pp.35-42
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• 2000

The settlement characteristics of waste landfill site must be considered in the design of sanitary landfill as well as in the course of the rehabilitation of the landfill site. Among prediction methods for settlement of landfill site, especially Gibson and Lo model and Power Creep Law have been successfully applied to the landfill site where the amount of settlement was large and the secondary settlement was obvious. Therefore, the effects of organic content on the model parameter values utilized in both Gibson Lo model and Power Creep Law were studied by using a large consolidation testing apparatus. The organic content is each 20%, 40%, 60% of total volume and consolidation load is $0.1{\sim}1.6kg/cm^2$. The main results can be summarized as follows: (1) The reference compressibility of Power Creep Law is decreased according to the increments of consolidation load: (2) The field measurement is more similar to the Power Creep Law than the Gibson and Lo model.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.127-135
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• 2002

The accurate evaluation of settlement is important to every steps in the constructions involving soft soils. Relating with those constructions, especially, it has been emphasized recently that the influnce of secondary settlement is important. The ratio of $C_a/C_c$ and the surcharging tests can be applied collaboratively to predicting and reducing secondary consolidation. A series of incremental loading consolidation test and surcharging tests for undisturbed samples of Kunsan clay were performed in this study. As a result of the tests, the ratio of $C_a/C_c$ for the clay was found to be 0.0329. Also, the relationship between void ratio and $t/t_p$ was shown to be linear. Accordingly, the secondary compression index, $C_a for a long term loading had a constant value regardless of time. When the total surcharge ratio was 0.4 and the dissipation ratio of excessive porewater pressure was in the range from 80% to 100%, secondary settlement was effectively reduced for Kunsan clay.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.3
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• pp.75-84
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• 1991

When we construct the earth structures such as embankments, on soft ground which are consisted of thick marine silty clay, the foundations deform due to consolidation and creep. For the stabilization of the earth structures constructed on soft foundations, we usually uses the mattress and they play an important role in increasing an ultimate bearing capacity by the dispersion of load of embankment. The purpose of this paper was to predict rationally a long term deformation of earth structures and to contribute to embankment design and maintenance. We determined a rheological model of marine clay from experimental data, and developed a computer program using the chosen model and found out the long term behavior of embankment. The results of this paper are as follows: 1. The developed program can analyze simultaneously consolidation and creep. 2. From the results of creep test, the rheological model of marine silty clay can be represented by the Vyalov model. 3. The displacement of embankment on reinforced foundation were smaller than those of the unreinforced foundation in showing the effects of geotextiles on foundation deformations.

• Journal of The Korean Society of Agricultural Engineers
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• v.55 no.5
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• pp.9-16
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• 2013

This study finds the characteristics of long-term settlement of Bottom Ash and to review the application of Singh-Mitchell creep equation and Burgers Model to the creep behavior of Bottom Ash. In the undrained state, it was confirmed that creep behavior appeared in the range to 30-80 % of the maximum deviator stress by applying condition in other three stresses through triaxial compression test after isotropically consolidation. By using sieve analysis, it was compared to each sample that was passed through 9.5 mm, 2 mm, 0.25 mm sieves. Also, using Singh-Mitchell creep equation and Burgers Model, it was compared between the theoretical behavior and the observed behavior for each sample. In the result, it is found that creep behavior of Bottom Ash is similar to the theoretical behavior of Singh-Mitchell creep equation and Burgers Model in early stage and it is possible to predict creep behavior of Bottom Ash by these models.