• Journal of the Korean Geotechnical Society
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• v.15 no.3
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• pp.151-160
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• 1999

The settlement limit concept is generally adopted as design criteria of rock-socketed pile foundations, therefore, the load-displacement$(\sigma-\sigma)$ behavior of the rock-socketed piles should be well understood at the design stage, which, however, is hard to achieve due to its complexity. To help this out, field pile load tests are executed on cast-in-situ concrete piles, first, to figure out the $\sigma$-$\delta$ behavior of rock-socketed piles. Next, the $\sigma-\sigma$ relations of the piles are simulated numerically using commercial package program(ELAC) varying a couple of input data which are sensitive in shaping the $\sigma$-$\delta$ curves. Finally, the relation between the best input data for the numerical simulations and the geotechnical field data are cultivated to generalize the numerical simulation procedures, which enables geotechnical engineers to predict the $\sigma$-$\delta$ behavior at the design stage, if appropriate geotechnical field data are provided.

• Journal of the Korean Geotechnical Society
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• v.23 no.5
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• pp.131-141
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• 2007

Because pile behavior is governed by geotechnical characteristics of surrounding soils, it is therefore necessary to monitor ground responses during pile driving and analyze the relation between the behaviors of pile and ground. In this research, the 57 m long PHC pile was driven into deep soft clay in the Nakdong River estuary area. During and after the pile driving, the ground responses and the residual load of pile have been monitored for about a year, by using piezometers, inclinometers, level posts for surface settlement, and strain gauges in piles etc. As the results, the residual load by the negative skin friction along the pile increased with the dissipation of the excess pore pressure, which was developed by pile driving and reclamation. About 30% of the maximum residual load developed due to the dissipation of the increased excess pore pressure during the driving. It is thus emphasized that most piles driven in clay deposits need to be designed by considering negative skin friction along the pile.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.4
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• pp.705-713
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• 2016

For the soft ground construction, the factors not considered in the design stage occurs in the construction stage so that they cause the increase of the construction cost due to the structural stability and the design change. The subject of the study is the construction section of the industrial complex access road made in the Ochang region of Chungcheongbuk-do. The study is concerned with selecting the soft ground handling method such as the replacement method using rock debris and the surcharge reflecting the service load as the soft ground handling measure and analyzing the effect of reducing the construction cost with the stability of structures and the reduction of the construction period. The soft ground in the study section consists of sandy and cohesive soil and is 2.4m to 5.5m deep. It is distributed unevenly between the 1.5m to 5.9m stratums under the ground surface. Settlement is not serious, but the future uneven settlement and difference are expected so that the future settlement behavior is estimated by analyzing the site measurement results after the soft ground treatment. Moreover, in consideration of the regional characteristics and economic efficiency, soil with good quality is replaced with rock debris as the replacement material so that 29% of the construction cost is reduced due to the increase of stability and the reduction of duration. If the estimation of the dispersion of the pore water pressure within the dam body and the change of the underground water level and the relation of the actually measured soft ground with consolidation is studied further on the basis of the study, it is expected that the behavior of the soft ground will be correctly estimated in various site conditions.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.3
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• pp.255-264
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• 2009

This paper concerns the behavior of 2-Arch tunnel constructed under various conditions. A 2-Arch tunnel section adopted in a subway tunnel construction site is considered in this study. A calibrated 3D finite element model was adopted to conduct parametric studies on a variety of construction scenarios including lagged distance between left and right tunnels, overburden, and geological condition. The results of analyses were examined in terms of crown settlement, shotcrete lining stress, and load on center column in relation to the lagged distance, cover depth, and the ground condition. The results indicate that the shotcrete lining stress and the center pillar load are more influenced by the second tunnel excavation than the tunnel deformation. Also shown is that a greater lagged distance is required to minimize the interaction between two tunnels when the ground condition becomes weaker. Fundamental mechanisms of 2-arch tunnel were also discussed based on the results.

• Journal of the Korean Geotechnical Society
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• v.27 no.6
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• pp.39-48
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• 2011

In this paper the method of estimating the bearing capacity of shallow foundation on a finite layer of sandy ground underlain by a rigid base was proposed by assessing results of the model test and the numerical analyses. For model experiments, the centrifuge tests under 1g and 20 g of gravitational levels were performed with sandy soils sampled from the field, changing the relative density of sandy soil and the ratio of thickness of sand layer (H) to the width of strip footing (B). As results of tests, bearing capacity tends to increase with the value of H/B while settlement for a given load intensity decreases. Bearing capacity also increases with relative density of the soil. In order to propose the method of estimating the bearing capacity of thin sandy layer underlain by a rigid base, values of bearing capacity factors from test results were compared with the values of modified bearing capacity factor by Mandel & Salencon (1972) considering the effect of H/B value on bearing capacity. The relation of bearing capacity factor ratio, normalizing friction angle of sandy soil, with the value of H/B was suggested so that this relation could be applied to design in the safe side. The results of numerical analyses obrained by changing the layout of footing, relative density of sandy soil and the value of H/B, were in good agreements with the suggested relation.

• Journal of the Korean GEO-environmental Society
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• v.5 no.2
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• pp.51-62
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• 2004

Granular compaction piles have the load bearing capacity of the soft ground increase and have the settlement of foundation built on the reinforced soil reduce. The granular compaction group piles also have the consolidation of the soft ground accelerate and have the liquefaction caused by earthquake prevent using the granular materials such as sand, gravel, stone etc. However, this method is one of unuseful methods in Korea. The Granular compaction piles are constructed by grouping it with a raft system. The confining pressure at the center of bulging failure depth is a major variable in relation to estimate for the ultimate bearing capacity of the granular compaction piles. Therefore, a share of loading is determined considering the effect of load concentration ratio between the granular compaction piles and surrounding soils, and varies the magnitude of the confining pressure. In this study, method for the determination of the ultimate bearing capacity is proposed to apply a change of the horizontal pressure considering bulging failure depth, surcharge and loaded area. Also, the ultimate bearing capacity of the granular compaction piles is evaluated on the basis of previous study on the estimation of the ultimate bearing capacity and compared with the results obtained from laboratory scale model tests. And using the result from laboratory model tests, it is studied increase effect of the bearing capacity on the granular compaction piles and variance of coefficient of consolidation for the ground.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1115-1123
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• 2008

When constructing projects such as road embankments, bridge approaches, dikes or buildings on soft, compressible soils, significant settlements may occur due to the consolidation of these soils under the superimposed loads. The compressibility of the soil skeleton of a soft clay is influenced by such factors as structure and fabric, stress path, temperature and loading rate. Although it is possible to determine appropriate relations and the corresponding material parameters in the laboratory, it is well known that sample disturbance due to stress release, temperature change and moisture content change can have a profound effect on the compressibility of a clay. The early research of Tezaghi and Casagrande has had a lasting influence on our interpretation of consolidation data. The 24 hour, incremental load, oedometer test has become, more or less, the standard procedure for determining the one-dimensional, stress-strain behavior of clays. An important notion relates to the interpretation of the data is the ore-consolidation pressure ${\sigma}_p$, which is located approximately at the break in the slope on the curve. From a practical point of view, this pressure is usually viewed as corresponding to the maximum past effective stress supported by the soil. Researchers have shown, however, that the value of ${\sigma}_p$ depends on the test procedure. furthermore, owing to sampling disturbance, the results of the laboratory consolidation test must be corrected to better capture the in-situ compressibility characteristics. The corrections apply, strictly speaking, to soils where the relation between strain and effective stress is time independent. An important assumption in Terzaghi's one-dimensional theory of consolidation is that the soil skeleton behaves elastically. On the other hand, Buisman recognized that creep deformations in settlement analysis can be important. this has led to extensions to Terzaghi's theory by various investigators, including the applicant and coworkers. The main object of this study is to suggestion the modified compression index value to predict settlements by back calculating the $C_c$ from different numerical models, which are giving best prediction settlements for multi layers including very thick soft clay.