• Journal of the Korean GEO-environmental Society
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• v.13 no.9
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• pp.17-29
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• 2012

To investigate the characteristics of shear strength and soil deformation in soft grounds, in which various vertical drains were placed, two hundreds field monitoring data of embankments performed in thirteen road construction sites at west and south coastal areas of the Korean Peninsula were collected. At first, the relationship between settlement and lateral displacement was investigated into three stages, in which embankment construction works were divided into initial filling stage, final filling stage and stage after complete filling. And then, the relationship of surcharge pressures and embankment heights with undrained shear strength of soft grounds were investigated. The investigation on settlement and lateral displacement illustrated that the increment of lateral flow to the increment of settlement was low during initial filling stage, but increased gradually with filling and showed largest during final filling stage. After complete filling, the lateral displacement was converged, even though the settlement was increased continuously. Therefore, most of lateral flow was occurred during embankment filling. The ratio of the lateral displacement increment to the settlement increment was 20% for initial filling stage, which coincided with the one presented by Tavenas et al.(1979), but became 50% for final filling stage, which was half of the one presented by Tavenas et al.(1979). However, the ratio reduced to 1% to 9%, which was quite lower than the one presented by Tavenas et al.(1979). Shear deformations, even shear failures, were predicted in soft grounds under initial undrained shear strength, since the design heights of embankments were higher than the yield height in all the sites. However, embankment construction would be possible since the yield height became higher than the design height due to improvement of shear strength of soft grounds with application of the vertical drains. In order to perform safely embankments for road constructions, the embankment loads should be designed not to be exceed 5.14 times the initial undrained shear strength of soft grounds and to be less than 3.0 times the undrained shear strength improved with application of vertical drains in soft grounds.

• Journal of the Korean GEO-environmental Society
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• v.11 no.6
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• pp.5-20
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• 2010

One-dimensional equivalent linear site response analysis is widely used in practice due to its simplicity, requiring only few input parameters, and low computational cost. The main limitation of the procedure is that it is essentially a linear method, in which the time dependent change in the soil properties cannot be modeled and constant values of shear modulus and damping is used throughout the duration of the analysis. Various forms of modified equivalent linear analyses have been developed to enhance the accuracy of the equivalent linear method by incorporating the dependence of the shear strain with the loading frequency. The methods are identical in that it uses the shear strain Fourier spectrum as the backbone of the analysis, but differ in the method in which the strain Fourier spectrum is smoothed. This study used two domestically measured soil profiles to perform a series of nonlinear, equivalent linear, and modified equivalent linear site response analyses to verify the accuracy of two modified procedures. The results of the analyses indicate that the modified equivalent linear analysis can highly overestimate the amplification of the high frequency components of the ground motion. The degree of overestimation is dependent on the characteristics of the input ground motion. Use of a motion rich in high frequency contents can result in unrealistic response.

• The Journal of Engineering Geology
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• v.22 no.4
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• pp.399-408
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• 2012

To estimate seismic source and soil-structure interaction more reliably, site amplification characteristics should be considered. Among the various estimation methods, we used Nakamura's method (1989) to estimate site amplification. This method was originally applied to background noise; however, it has recently been successfully applied to S-wave and Coda-wave energy, and is applied to S-waves in the present study. We used more than 180 observed ground motions from 23 macro-earthquakes and then analyzed site amplification characteristics at eight seismic stations. Each station showed characteristics of site amplification properties in the low-, high- and resonance-frequency ranges. Comparison of the present results with those of other studies provide successful information regarding the dynamic amplification of domestic site characteristics and site classification.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2007.12a
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• pp.173-175
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• 2007

부산신항 남컨 배후지준설토 투기장은 국제도시 부산의 관문이 될 부산신항만 입구부에 위치한 관계로 아름답고 튼튼한 호안이 될 수 있도록 하고, 입찰안내서에 제시된 호안법선변경 금지, 호안마루높이 DL.(+)7.50m 유지 조건을 준수하면서 최적의 구조물이 되도록 하였다. 본사업지는 지형적 특성상 복잡한 형태의 고파랑 작용으로 수리학적으로 월파, 반사파, 연파를 제어하는 경사호안 구조물을 도입하였고, 초연약지반이 대심도로 분포하는 특성을 고려하여 개선된 S.C.P 연약지반 처리공법을 적용하여 기초굴착 없는 친환경적이고 배수기능을 향상시킨 융기토 유용형 S.C.P공법을 적용하였다. 호안전구간은 친수개념을 도입하였으며, 호남도 주변 해양생태계 보호를 위하여 미티게이션(mitigation) 개념을 도입하여 환경복원 계획 및 생태형 친수호안을 구상하였다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2007.12a
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• pp.176-178
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• 2007

부산신항 북컨테이너터미널 민차부두 1단계 공사에 적용된 안벽기초는 하부 대섬도 연약점토층 개량을 위한 SCP(Sand Compaction Pile) 개량층과 그 상부에 약 6m정도의 사석층으로 구성되어 있다. 안벽은 케이슨식으로 상부의 크레인 풍의 공용하중 작용시에 발생이 예상되는 안벽기초의 과도한 지반침하 방지를 위해 근고블럭에 의한 Preloading 공법이 적용되었다. 따라서, 프리로딩에 의한 하부기초지반의 침하관리가 중요 공사관리 포인트가 된다. 그러나, SCP층이나 사석총에 대한 침하량 예측은 반경험적 방법에 의존하기 때문에 실제와 상당한 차이가 발생하게 된다 본 연구에서는 사석층의 진동다짐에 의한 시공 특성을 반영하기 위해 굴착치환구간의 사석층에 대한 실측값을 이용하여 Terzaghi 변형식의 침하계수 a를 재산정하여 SCP개량구간에 적용함으로써 보다 합리적인 안벽기초의 침하량을 분석하였고 이를 사석층의 여성고 산정에 이용하였다.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.05a
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• pp.118-119
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• 2017

In the S.C.W (soil cement wall) grouting solution, Cement grout ratio of 1 part Portland cement and 1part water is being used. However, Co₂ and harmful heavy metals such as cr6+ are discharged in the process, causing a serious environmental issue. The purpose of the present study is therefore to substitute cement grout to inorganic binder and identify durability properties of ground solidification materials.

• Journal of the Korean Geotechnical Society
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• v.17 no.4
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• pp.15-25
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• 2001

본 고에서는 블록식 보강토 옹벽의 지진시 거동에 관한 유한요소해석 결과를 다루었다. 보강토 옹벽의 지진시 변위거동을 검토한 결과 벽체저부를 지점으로 하는 캔틸레버형태의 변위 거동을 보였으며 따라서 옹벽 상단부에서의 보강재 인장력 증가가 현저하게 나타나 벽체전반에 걸친 분포양상은 균등한 경향을 보였다. 한편, 지진하중으로 인한 증분유발인장력에 관하여 검토한 결과 기존의 보강토 옹벽 내진설계기준과 비교하여 정성.정량적인 측면에서 상당한 차이를 보였으며 내진설계기준이 전반적으로 과소평가 하는 것으로 나타났다. 아울러서, 내진설계측면에서 변위억제 방안에 관한 매개변수 연구결과 임의 조건에 있어서 최대의 보강효과를 나타내는 보강재 임계 강성과 포설길이가 존재하며 최적의 보강효과를 얻기 위해서는 이에 대한 종합적인 검토가 요구되는 것으로 나타났다. 본 고에서는 연구결과를 종합적으로 고찰하여 실무 적용관점에서의 주안점을 언급하였다.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.56-56
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• 2003

계류라인은 해양관측부이 혹은 해양구조물을 일정일치에 계류시키기 위해서 중요한 역할을 수행한다. 본 연구에서는 상부구조물의 거동에 의한 계류라인의 거동특성을 파악하기 위하여, 상부 윗단에서 일정주기와 진폭으르 가진되는 경우에 장력과 변위의 응답을 살펴보았다. 수평으로 가진되는 경우에 규칙적으로 가진됨에도 불구하고 맨윗단에서 장력은 가진 주파수 성분 이외에 고주파수 성분이 함께 응답하였다. 이 때 고주파수 성분은 계류라인의 길이와 장력에 따라서 다른 성분으로 나타났는데, 이 성분은 상부단에서 발생한 에너지가 전달되어 해저고정단에서 다시 반사되어 발생하는 것으로 판단되어 진다. 향후 이 성분에 대한 정량적인 연구가 필요하다. 수직으로 가진되는 경우에는 장력이 충격력 효과로 나타났는데, 이것은 지반과의 상호작용에 의한 것으로 판단된다.

• Tunnel and Underground Space
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• v.16 no.6 s.65
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• pp.486-494
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• 2006

The horizontal to vertical (H/V) ratio technique in spectral domain is a common useful technique to estimate empirical site transfer function. The technique, originally proposed by Nakamura, is proposed to analyse the surface waves in the micrortremor records. The purpose of this paper is to estimate spectral ratio using observed data at the seismic stations distributed within Southern Korean Peninsula from the Fukuoka earthquake including 11 aftershocks. The results show that most of the stations have fairly good amplification characteristics in low frequency band. However, some of the seismic stations show one (resonant frequency specific to the site) or several local peaks of amplification factors with narrow high frequency band. Even though the site amplification characteristics are important information, we should be careful to analyse the observed ground motions from the seismic stations which have several very high amplification peaks for the deconvolution of seismic source and attenuation parameters.

• Journal of the Korean Geotechnical Society
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• v.24 no.3
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• pp.13-23
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• 2008

In a nonlinear site response analysis which is performed in time domain, small strain damping is modeled as viscous damping through use of various forms of Rayleigh damping formulations. Small strain damping of soil is known to be independent of the loading frequency, but the viscous damping is greatly influenced by the loading frequency. The type of Rayleigh damping formulation has a pronounced influence on the dependence. This paper performs a series of nonlinear analyses to evaluate the degree of influence of the viscous damping formulation on Korean soil profiles. Analyses highlight the strong influence of the viscous damping formulation for soil profiles exceeding 30 m in thickness, commonly used in simplified Rayleigh damping formulation overestimating energy dissipation at high frequencies due to artificially introduced damping. When using the full Rayleigh damping formulation and carefully selecting the optimum modes, the artificial damping is greatly reduced. Results are further compared to equivalent linear analyses. The equivalent linear analyses can overestimate the peak ground acceleration even for shallow profiles less than 20 m in thickness.