• Journal of the Korean Geotechnical Society
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• v.22 no.7
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• pp.73-83
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• 2006

The behaviour characteristics of Granular Compaction Pile (GCP) are mainly governed by the lateral confining pressure mobilized in the soft soil matrix to restrain the bulging failure of the granular compaction pile. The GCP method is most effective in soft soil with undrained shear strength ranging $15{\sim}50kPa$. However, the efficiency of this method reduces the more compressible soil conditions, which does not provide sufficient lateral confinement. In the present study, the GCP method reinforced with uniformly graded permeable concrete is suggested for the extension of application to the soft ground. Also, large triaxial compression tests are conducted on composite-reinforced soil samples for verification of availability of the suggested method and the settlement estimation method of the reinforced GCP is proposed. Furthermore, for the verification of the proposed method, predicted settlements by the proposed method are compared with results of 3-dimensional numerical analyses. In addition, parametric studies are performed together with detailed analyses of relevant design parameters.

• Journal of the Korean Geotechnical Society
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• v.26 no.12
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• pp.71-79
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• 2010

The reliable evaluation of the coefficient of variation (COV) of soil properties is required for the determination of adequate design values and the application of a probabilistic method for the design of geotechnical structures. In this paper, the applicability of methods for estimating the standard deviation, such as the. Three-Sigma Rule and a statistical method, is evaluated by using site investigation data of the Songdo area. It is found that the Three-Sigma Rule provides similar results to those of a statistical method when using $N_{\sigma}$=6 for the property with small variability and $N_{\sigma}$=4.2~5.3 for the property with large variability. It is also observed that, for the undrained shear strength that has an increasing trend with depth, a $N_{\sigma}$ value of 4 is adequate for the evaluation of the variability by the Three-Sigma Rule. The COVs of soil properties determined in this paper could be used in the estimation of the confidence interval and characteristic values of soil properties.

• Journal of the Korean Geotechnical Society
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• v.22 no.10
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• pp.93-100
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• 2006

The lateral soil movement in soft grounds undergoing improvement with application of vertical drains is analyzed on the basis of monitoring data at three fields, in which fifty six monitoring sites are located. Based on the investigations, the criterions are suggested to predict the lateral soil movement. In order to predict the lateral soil movement in the improved soft grounds by using the dimensionless parameter R suggested by Marche & Chapuis (1974), it is desirable that the maximum lateral displacement in the soft ground below the toe of embankment should be applied to calculate R instead of the lateral displacement at the toe of embankment. The lateral soil movement may increase rapidly, if the safety factor of slope is less than 1.4 in case of high ratio of H/B (Thickness of soft ground/Embankment width) such as 1.15 or is less than 1.2 in case of low ratio of H/B such as 0.05. Also, the graph suggested by Tschebotarioff (1973), which illustrates the relationship between the maximum height of embankments and the undrained shear strength of soft grounds, can be applied to the evaluation for the possibility of the lateral soil movement due to embankments on soft grounds.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6C
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• pp.321-329
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• 2008

In this study, a series of column test as a way in order to make up for the weakness point of the conventional acceleration method were conducted to both propose the suction board drain method and grapes the specific improvement character of this method as a result of a sort of plastic drain board and a phase of vacuum pressure conditions. On this occasion, the study focused on computing the effective factors of the fittest Suction board drain method affected by each condition through confirming the settlement generated during the test, the water content reduction and stress increase effect occurred arising from the test, and the ratio of consolidation related to the improvement period. In accordance with the shape of core and that whether the core is attached to the filter(pocket or adhesion), the castle type of adhesion and the column type of pocket are more efficient than the others as a consequence of the test to find out the improvement effect depending on each drainage such as a castle type, coil type, harmonica type, column type of pocket and a castle of the adhesion. In case of the step suction pressure, the shorter the period of $-0.8\;kg/cm^2$ as a final step of the suction pressure is, the better the improvement is. In addition, the correlation between degree of consolidation per each suction pressure level and duration of application was drawn as a curve and the point of inflection on this curve was provided to determine the duration period to maximize the consolidation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.251-258
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• 2009

In this study, the optimum design conditions for embankment construction on soft clay layer improved by soil compaction pile (SCP) are discussed by comparing the practical design method to the reliability design which is based on the loss function and advanced first order second moment (AFOSM) method. The results are summarized as follows; 1) the relationship between safety factor and failure probability becomes heavy exponentially, failure probability decreases rapidly till 1% approximately until safety factor is smaller than 1.2 and after then, failure probability decrease gradually along the increase of the safety factor. The design safety factor of 1.2 may be the critical value that has been established on considering both relationships appropriately, 2) the safety factor of 1.15 at the minimum expected total cost is a little smaller than the design safety factor of 1.2 and the failure probability is about 1%, 3) the sensitivities of the ratio of stress share and the internal friction angle of sand is larger than the variables related the undrained shear strength of soft layer. This result means that the distribution characteristic of n and ${\phi}$ influences on the stability analysis considerably and they should be considered necessarily on stability analysis of embankment on soft layer improved by SCP, 4) new failure points of the input variables at the design safety factor of 1.2(below failure probability of 0.1~0.3%) is far 1~2 times of standard deviation from the initial design values of themselves.