Excessive Settlement Back-Analysis of Railway Embankment on Soft Soils during Service

안태봉 한국지반환경공학회 2019 한국지반환경공학회논문집 Vol.20 No.1

This paper presents case history of railway embankment excess settlement on soft clay during service in southern region of Korea. A lot of field observations show that the measured settlements are a lot larger than settlements actually calculated in this area. Back analysis is carried out to verify the soil parameters which are intended to investigate in the subsurface exploration phase and later in a laboratory test program. Recommendations and causes for the engineering practice are suggested to review the determination of excess settlements and, consequently, to improve the settlement prediction. This enormous discrepancy is due to the passing over secondary consolidation, and the design filling did not meet to real construction filling. Immediate settlement could be subsidiary factor of excess settlement.

Excessive Settlement Back-Analysis of Railway Embankment on Soft Soils during Service

Ahn, Taebong Korean Geo-Environmental Society 2019 한국지반환경공학회논문집 Vol.20 No.1

This paper presents case history of railway embankment excess settlement on soft clay during service in southern region of Korea. A lot of field observations show that the measured settlements are a lot larger than settlements actually calculated in this area. Back analysis is carried out to verify the soil parameters which are intended to investigate in the subsurface exploration phase and later in a laboratory test program. Recommendations and causes for the engineering practice are suggested to review the determination of excess settlements and, consequently, to improve the settlement prediction. This enormous discrepancy is due to the passing over secondary consolidation, and the design filling did not meet to real construction filling. Immediate settlement could be subsidiary factor of excess settlement.

Excessive Settlement Back-Analysis of Railway Embankment on Soft Soils during Service

Taebong Ahn 한국지반환경공학회 2019 한국지반환경공학회논문집 Vol.20 No.1

This paper presents case history of railway embankment excess settlement on soft clay during service in southern region of Korea. A lot of field observations show that the measured settlements are a lot larger than settlements actually calculated in this area. Back analysis is carried out to verify the soil parameters which are intended to investigate in the subsurface exploration phase and later in a laboratory test program. Recommendations and causes for the engineering practice are suggested to review the determination of excess settlements and, consequently, to improve the settlement prediction. This enormous discrepancy is due to the passing over secondary consolidation, and the design filling did not meet to real construction filling. Immediate settlement could be subsidiary factor of excess settlement.

유효응력해석과 등가선형해석을 이용한 매립지반의 액상화 평가

박성식(Park Sung-Sik) 대한토목학회 2008 대한토목학회논문집 C Vol.28 No.2

본 연구에서는 흙의 미소변형에서 대변형까지 고려할 수 있는 유효응력해석을 이용하여 매립지반에 대한 액상화 및 진동으로 발생하는 침하량을 예측하였다. 유효응력모델은 진동 중에 발생하는 과잉간극수압을 계산하여 이에 따른 흙의 강성저하와 수반되는 지반의 변위를 모델링하였다. 진동으로 인한 지반의 변형률 수준이 작은 경우에 적합한 등가선형해석을 이용한 액상화 평가를 실시하여 유효응력모델을 이용한 예측법과 비교하였다. 등가선형해석에서 계산된 전단응력비에 해당하는 표준관입시험치를 국내에서 발생 가능한 지진규모와 실트질 함유량에 따라 콘관입저항치로 환산한 값과 현장에서 계측된 콘관입저항치를 서로 비교하여 액상화 가능성을 예측하였다. 두 곳의 인천지역 매립지에 대한 액상화 해석을 위하여 매립지에서 계측된 콘관입저항치와 전단파 속도를 이용하여 입력 물성값을 결정하였다. 인천 매립지에 대한 두 액상화 해석 방법의 결과는 액상화 발생 여부에서 유사하였으며 깊이에 따른 연속적인 액상화 판정과 얇은 층의 액상화 예측이 가능하여 액상화 예측의 정밀도를 높였다. 유효응력모델을 이용한 액상화 해석 결과는 지표면 아래 20m 이내에서 초기 유효수직응력의 40%~70% 정도의 과잉간극수압이 발생하였으며 이로 인하여 지표면에서 10㎝ 미만의 침하가 발생하였다. In this study an effective stress analysis was performed to evaluate liquefaction potential and ground settlement for reclaimed sites. The effective stress model can simulate the stiffness degradation due to excess pore pressure and resulting ground deformation. It is applicable to a wide range of strain. An equivalent linear analysis suitable for low strain levels was also carried out to compare the effective stress analysis. Shear stress ratio calculated from an equivalent linear analysis was used to determine SPT blow count to prevent liquefaction. Depending on the magnitude of potential earthquake and fine contents, the SPT blow count was converted into an equivalent cone tip resistance. It was compared with the measured cone tip resistance. The measured elastic shear wave velocity and cone tip resistance from two reclaimed sites in Incheon were used to perform liquefaction analyses. Two liquefaction evaluation methods showed similar liquefaction potential which was evaluated continuously. The predicted excess pore pressure ratio of upper 20 m was between 40% and 70%. The calculated post-shaking settlement caused by excess pore pressure dissipation was less than 10 ㎝.

차수그라우팅 적용에 따른 터널주변 수리학적 거동 분석과 그라우팅 적용범위 산정방법의 제안

문준식 사단법인 한국터널지하공간학회 2024 한국터널지하공간학회논문집 Vol.26 No.1

Excessive inflow of groundwater during tunnel excavation not only affects the stability and constructability of the tunnel, but is also one of the main causes of ground settlement due to groundwater level drawdown. The most commonly applied measure against excessive groundwater inflow during tunnel excavation in soil or fractured zone is to reduce the ground permeability coefficient by injecting grout material. Generally, the grouting area is assumed to be same as the plastic zone that occurs during tunnel excavation, but injecting grout material in the area of plastic zone is appropriate only for reinforcement grouting. In order to determine the thickness of cutoff grouting, the amount of reduction in the water permeability coefficient due to the application of cutoff grouting must be considered. In this study, a method for estimating the range of cutoff grouting considering the reduction in permeability coefficient was mathematically derived and evaluated through computer numerical analysis.

연직천연섬유배수재를 이용한 연약지반 개량

김주형(Kim Ju-Hyong),조삼덕(Cho Sam-Deok) 한국토목섬유학회 2008 한국지반신소재학회 논문집 Vol.7 No.4

친환경배수재에 대한 현장 적용성을 평가하기 위해 연직배수재와 수평배수재 설치 조합으로 현장시험시공을 수행하였다. 본 시험시공에서는 기존의 천연섬유배수재(FDB)와 새로 개발한 볏짚배수재(SDB) 그리고 플라스틱배수재(PDB)를 연직배수재로 설치하였으며, 화이버매트와 샌드매트를 수평배수재로 사용하였다. 볏짚배수재(SDB) 설치지역을 제외하고는 플라스틱배수재(PDB)와 천연섬유배수재(FDB) 설치 지역에서 측정한 지표침하발생속도와 과잉간극수압 발생/소산 양상은 거의 유사한 것으로 나타났으며, 1차 압밀방치기간동안 측정된 상부 연약층의 콘관입저항력도 설치된 연직배수재 종류와 상관없이 일정하게 증가한 것으로 나타나 천연섬유배수재가 기존의 플라스틱이나 모래재료를 대체할 수 있을 것으로 판단된다. A pilot test using environmentally friendly drains, was carried out to evaluate their applicability potential in the field. The pilot test site was divided into 5 different areas, with several combinations of vertical and horizontal drains installed for evaluation. Conventional natural fiber drains (FDB), new developed straw drain board (SDB) and plastic drain board (PDB) were used as vertical drains, while sand and fiber mats were used as horizontal drains. Surface settlement rates and excess pore pressure generation/dissipation tendency of PDB and FDB are almost identical except those of SDB. Cone tip resistance obtained from cone penetration test measured at the end of 1st consolidation stage for upper soft layer definitely increased irrespective of types of vertical drains. The monitoring and site investigation test data obtained at the pilot test site prove the vertical natural fiber drains can be used as substitutes of conventional plastic and sand material.

파압에 의한 해안구조물-해저지반의 침하거동에 대한 수치해석

강기천(Kang, Gi-Chun),윤성규(Yun, Seong-Kyu),김태형(Kim, Tae-Hyung),김도삼(Kim, Dosam) 한국해안해양공학회 2013 한국해안해양공학회 논문집 Vol.25 No.1

태풍에 의해 발생된 파랑하중에 의해 방파제, 안벽 등과 같은 해안구조물 하부의 해저지반 침하가 발생될 수 있다. 만약 해저지반이 모래인 경우, 잔류과잉간극수압발생과 반복적인 파랑하중에 의해 해저지반의 침하현상이 더 발생될 확률이 높아질 것이다. 그러나 대부분의 해안구조물은 설계에서 파랑하중을 정적상태의 등분포하중으로 구조물에만 작용하는 것으로 가정하고 있지만 실제로는 동적인 파랑하중이 구조물과 해저지반에 동시에 작용한다. 따라서 본 연구에서는 시간에 따른 실제파압을 고려하고, 구조물뿐만 아니라 해저지반에도 작용하는 것으로 고려하였다. 수치해석 결과 파랑하중이 구조물과 해저지반에 큰 영향을 미친 것으로 나타났다. 시간에 따른 해저지반의 변형거동이 해석되었으며 해저지반에서 유효응력의 변화와 유효응력경로의 변화를 분명하게 확인할 수 있었다. Seabed settlement underneath a coastal structure may occur due to wave loading generated by storm surge. If the foundation seabed consists of sandy soil, the possibility of the seabed settlement may be more susceptible because of generation of residual excess pore-water pressure and cyclic mobility. However, most coastal structures, such as breakwater, quay wall, etc., are designed by considering wave load assumed to be static condition as an uniform load and the wave load only acts on the structure. In real conditions, however, the wave load is dynamically applied to seabed as well as the coastal structure. In this study, therefore, a real-time wave load is considered and which is assumed acting on both the structure and seabed. Based on a numerical analysis, it was found that there exists a significant effect of wave load on the structure and seabed. The deformation behavior of the seabed according to time was simulated, and other related factors such as the variation of effective stress and the change of effective stress path in the seabed were clearly observed.

미국 회사임원배상책임보험의 새로운 유형 및 주요계약조건

육태우 한국경영법률학회 2010 經營法律 Vol.20 No.3

The primary purpose of D&O liability insurance is to protect the individual directors and officers from personal financial loss arising from claims against them for alleged wrongful acts undertaken in their capacity as directors and officers. It has been developed since securities market fell down in 1929 in the United States. Especially, since July 2002 when the Sarbanes-Oxley Act was signed into law, the necessity of D&O liability insurance for private companies and not-for-profit companies has increased so much in the United States. The interests to the D&O liability insurance and its volume of sales has increased recently in Korea. However, it is difficult to say that D&O liability insurance has made satisfactory progress, because many CEOs do not realize the necessity of D&O liability insurance, policies' coverage is so narrow, and insurance companies do not sell D&O liability insurance policy or otherwise sell it very expensively to the small corporations which need this insurance so much. In addition, the severability clause of Korean D&O liability insurance policy is not so general as those of many countries advanced in the field of insurance industry. In order to solve these problems, Korean insurers should strengthen their promotion of D&O liability insurance policies and improve their D&O liability insurance systems from various angles. In this respect, American D&O liability insurance policies could be a good model and the developing process of academic theories and courts' precedents in the United States concerning D&O liability insurance could be referred to.

시험시공을 통한 연직배수재 종류별 압밀 효과 평가 (1)

김주형,조삼덕 한국토목섬유학회 2006 한국토목섬유학회 학술발표회 Vol.2006 No.12

1) 천연섬유배수재의 현장 적용성을 분석하기 위해 동일현장에 PDB, SDB 그리고 FDB를 시공하고, 이 지역의 침하량 및 간극수압에 대한 계측이 진행 중에 있다. 현재까지 세 종류의 연직배수재 설치 지역에서 측정된 지표면 침하양상은 유사하게 나타나, 각각의 연직배수재는 유사한 현장적용성을 나타내고 있는 것으로 판단된다. 2) 시험시공 현장에서 측정한 간극수압 양상을 분석한 결과 PDB와 FDB가 설치된 지역에서 측정된 과잉간극수압은 비슷한 거동을 나타내고 있으나, 새로 제작한 SDB의 경우에는 지표면 침하양상과는 달리 상대적으로 높은 과잉간극수압 발생양상을 나타내고 있음을 확인하였다. 3) 본 연구에서는 장기간의 지표 침하와 간극수압 양상을 분석하여 각 연직배수재의 현장적용성을 지속적으로 분석할 예정이다. The advantages of geosynthetic-reinforcing technology to construct new soil structures including; a) a relatively short construction period; b) small construction machines necessary; and c) a higher stability of completed structures, all contributing to a higher cost-effectiveness, are addressed. Several typical cases in which embankments having a gentle slope and conventional type soil retaining walls that were seriously damaged or failed were reconstructed to geosynthetic-reinforced steepened slopes or geosynthetic-reinforced soil retaining walls are reported. It is shown that the reconstruction of damaged or failed conventional soil structures to geosynthetic-reinforced soil structures is also highly cost-effective. Rehabilitation of an old earth-fill dam in Tokyo to increase its seismic stability by constructing a counter-balance fill reinforced with geosynthetic reinforcement is described.A pilot test using environmentally friendly drains, is being carried out to prove their effective discharge capacity in the field. The pilot test site was divided into 5 different areas, with various combinations of vertical and horizontal drains installed for evaluation. Conventional natural fiber drains (FDB), new developed straw drain board (SDB) and plastic drain board (PDB) used as vertical drains, while sand and fiber mats were used as horizontal drains. Pore pressure ratio (B) obtained at PDB and FDB installation field is in the range of 0.09~0.37 except that of SDB installation fields. However, surface settlement rates of installation of three types of vertical drains are identical.

압밀촉진 케이슨 기초공법에 관한 연구

박정순,조남준 한국지반공학회 2001 한국지반공학회논문집 Vol.17 No.2

연약한 점토 지반에 안벽을 축조하고 매립하는 경우, 안벽의 기초로서 케이슨 기초공법이 종종 쓰이고 있다. 케이슨 기초는 안벽의 연직 하중을 지지층에 전달할 뿐만 아니라, 매립하중에 의한 연약 점토의 횡방향 소성 유동에 대하여는 매우 효과적인 공법으로 호안공사에서 그 사용 빈도가 증가하고 있는 추세이다. 반면 매립하중에 의해 점토지반에서 장기간에 걸쳐 발생하는 압밀침하에 대해서는 아무런 역할을 하지 못하는 단점이 있다. 따라서 본 연구에서는 기존 케이슨 기초의 배면에 다수의 강관 배수공을 설치함으로써 과잉간극수압의 횡방향 소산을 촉진시켜 압밀 시간을 단축시키는 \"매립측 연약점토 압밀촉진 케이슨 기초공법\"을 제안하였다. 이 새로운 케이슨 공법의 압밀촉진 효과를 분석하기 위하여 2차원 압밀방정식의 해석해를 유도하였다. 연구결과, 등방성 점토에서 압밀촉진 케이슨 사용시 ξ=0.1인 단면에서 평균압밀도 50%, 90%에 이르는 시간이 기존 케이슨을 사용한 것에 비해 각각 약 7배, 3.5배 단축되는 것으로 나타났다. 것으로 나타났다.