DCM으로 개량된 연약점토지반의 지반융기에 관한 고찰

유승경(Seung-Kyong You),홍기권(Gigwon Hong) 한국지반신소재학회 2020 한국지반신소재학회 논문집 Vol.19 No.4

본 연구에서는 DCM으로 개량된 연약점토지반에 관한 실내모형실험 결과를 바탕으로, DCM 개량 형식에 따른 연약점토지반의 융기량을 분석하였다. 즉, 무보강 및 3종류의 DCM 개량 형식에 대한 하중 재하에 따른 연약지반의 융기 특성을 평가하였다. DCM이 적용되지 않은 경우에는 4단계 하중조건에서부터 연약점토지반의 측방변형이 크게 증가하면서 미성토구간의 융기가 급격하게 발생하였다. 그리고 최종 하중단계에서의 융기량은 지표면의 인장파괴가 발생되었다. DCM 개량 형식에 따른 지반의 최대 융기량은 최종 하중단계에서 발생하였으며, 융기량의 크기는 말뚝식, 벽식 및 격자식 순으로 감소하였다. 특히, 격자식 개량체가 적용된 경우에는 최종 하중단계에서 재하부 지반의 극단적 파괴에도 불구하고, 지반 융기에 대한 억지효과가 매우 크게 나타났다. 또한 계측위치별 최대 융기량을 분석한 결과, LVDT-1의 위치에서 격자식은 말뚝식과 벽식에 비하여 각각 3.1% 및 1.6% 수준의 융기량을 보였고, LVDT-2의 위치에서는 각각 1.0% 및 2.1%의 융기가 발생하였다. This paper described the analysis result on heaving of soft ground with DCM column type, based on the results of laboratory model tests on the soft ground with DCM column. The heave characteristics of the soft ground were evaluated according to the application of DCM column in soft ground. The results showed that the heaving of soft ground without DCM column occurred rapidly when the lateral deformation of soft ground increased significantly under the 4th load step condition. In addition, the heaving of soft ground in final load step caused tensile failure of the ground surface. The maximum heaving of the soft ground with the DCM column occurred in the final load step, and the heaving quantity decreased in the order of pile, wall, and grid type. Especially, the soft ground with DCM of grid type effectively resisted ground heaving, even if it was extremely failure in the bottom ground of embankment. The results of the maximum heaving according to the measurement point showed that the heaving of the soft ground with DCM of grid type was 3.1% and 1.6% compared to that of the pile and wall type at the location of LVDT-1, and the heaving of the LVDT-2 position was 1.0% and 2.1%, respectively.

스파이럴 볼트 변형률계를 이용한 연약지반기초 및 암반사면 거동 계측

강성승(Seong-Seung Kang),히라타 아츠오(Atsuo Hirata),정승회(Seong-Hoi Jeong),이우람(Woo-Ram Lee),제동광(Dong-Kwang Je),김대현(Dae-Hyeon Kim) 한국암반공학회 2010 터널과지하공간 Vol.20 No.2

본 연구에서는 연약지반기초 및 암반사면 거동 계측 도구로서 스파이럴 볼트 변형률계의 적용 가능성을 살펴보고자 한다. 이 변형률계가 지중에 설치되었을 때, 지반에 대한 인발 저항성이 높아 지반 보강용으로 적용될 수 있을 뿐만 아니라, 유연성의 특징을 가지고 있기 때문에 지반의 거동 상태를 파악하는데 유용하게 이용될 수 있다. 연약지반기초에 대한 스파이럴 볼트의 변형률 계측결과, 변형률 측정 초기에는 안정한 상태를 보이다가 400일이 경과한 시점에서는 스파이럴 볼트 변형률계의 윗부분과 중간부분에서 큰 변화가 관찰되었다. 이러한 변화는 동일한 시기에 강수량 증가와 함께 빈번하게 발생한 진도 1∼2의 지진에 의한 영향으로 지반이 이완되어 야기한 것으로 분석된다. 암반사면에 대한 스파이럴 볼트의 변형률 계측결과, 측정시작일로부터 50일 동안에 안정한 상태를 보였으며 50∼160일 기간에는 매설길이 4.2 m 지점(P6)의 변형률 게이지에서 가장 큰 변형률을 보였다. 그러나 P6 변형률 게이지를 제외한 나머지 게이지는 특이한 변화를 보이지 않았다. 스파이럴 볼트 변형률계의 측정결과를 종합적으로 살펴보면 측정대상인 연약지반기초와 암반사면은 안정적인 것으로 판단된다. 본 연구에서 소개하는 스파이럴 볼트 변형률계는 연약지반기초 및 암반사면 거동의 모니터링과 동시에 대상지반의 보강에 적용될 수 있을 것으로 사료된다. This study is to consider applicability of spiral bolt strain gauge as an instrument measuring behavior of soft ground foundation and rock slope. When the instrument was installed on the ground, it can be useful to identify the state of ground behavior because it has the characteristics of flexibility, as well as to apply the ground reinforcement because it has higher pull-out resistance to the ground. From the measurement of behavior to soft ground foundation, the strain shows a stable state in the beginning, then was observed significant change in the upper and the middle of spiral bolt strain gauge after 400 days. This is analyzed that ground loosening, which is due to occurred frequent earthquake of magnitude 1∼2 with increased rainfall, lead to the instability of the ground. From the measurement of behavior to rock slope, the strain shows a stable state with very little change in a period of 0∼50 days and the biggest strain at 4.2 m (P6) in a period of 50∼100 days, then other places except P6 was maintained at a stable state in a period of 100∼160 days. The reason is analyzed because that blasting for excavated limestone surrounding was affected to the largest at P6. However, based on the size of strain change by behavior of the soft ground foundation and rock slope, it is considered that the present condition are not effected on stability of retaining structure and rock slope. In conclusion, the proposed spiral bolt strain gauge can be useful to measure behavior of soft ground foundation and rock slope, and also to be measured behavior as well as reinforcement of the target ground.

연약지반에 적용된 변단면 연약지반보강기초의 거동분석

김기웅(Khi-Woong Kim),김동욱(Dong-Wook Kim),조명수(Myoung-Su Jo) 한국지반신소재학회 2016 한국지반신소재학회 논문집 Vol.15 No.4

인천 ○○지역의 연약지반에 시공된 변단면 연약지반보강기초(Variable cross-section soft ground reinforced foundation)의 연직압축거동을 분석하였다. 변단면 연약지반보강기초는 원지반과 고화재를 혼합교반하여 형성되는 고형체의 높은 강성과 강도를 이용하여 상부구조물로부터 유발되는 연약하중을 효과적으로 저항하기 위하여 시공된다. 변단면 연약지반보강기초는 군말뚝 형식으로 시공이 되는데, 정확한 연직거동을 알기 위하여 1 개소의 기초에 대한 연직재하시험을 수행하였다. 변단면 연약지반보강기초의 거동을 일반적인 깊은 기초의 거동과 비교하기 위하여 유사한 천층지반조건에 시공된 PHC 파일의 재하시험 결과와 비교하여 재하하중에 따른 침하량 및 하중전이 거동특성을 분석하였다. 연직재하시험결과를 비교분석하였다. 변단면 연약지반보강기초는 제한된 범위의 연직하중에 대하여 천층에서도 효율적으로 저항하는 것으로 분석되었다. Compressive axial behavior of the variable cross-section soft ground reinforced foundation is investigated from the field load test results at ○○ construction site in Incheon city. Variable cross-section soft ground reinforced foundation is a type of partial-displacement pile formed by mixing bidding material with in situ soils to obtain a rigid and strong variable cross-section column in a relatively soft ground. The foundations are usually constructed as a group; however in this study, only single foundation was installed and tested under compressive axial load on foundation head. For the comparison of the variable cross-section soft ground reinforced foundation axial behavior, behavior of typical Pretensioned spun high strength concrete (PHC) pile constructed on a relatively soft ground near the surface was analyzed. It was concluded that variable cross-section soft ground reinforced foundation efficiently resists against axial load with sufficient stiffness and strength within a considerable range of axial load magnitude.

연직배수공법이 적용된 연약지반 상에 도로성토로 인한 측방유동의 특성

홍원표,김정훈 한국지반공학회 2012 한국지반공학회논문집 Vol.28 No.9

Field monitoring data for embankments in thirteen road construction sites at coastal area of the Korean Peninsula were analyzed to investigate the characteristics of lateral flow in soft grounds, in which vertical drain methods were applied. First of all, the effect of the embankment scale on the lateral flow was investigated. The thicker soft soils and the lager relative embankment scale produced the more horizontal displacements in soft grounds. Especially, if thick soft grounds were placed, the relative embankment scale, which was given by the ratio of thickness of soft ground to the bottom width of embankments, became larger and in turn large horizontal displacement was produced. And also the higher filling velocity of embankments induced the more horizontal displacements in soft grounds. The other major factors effected on the lateral flow in soft ground were the thickness and undrained shear strength of soft grounds,the soil modulus and the stability number. The more maximum horizontal displacement was induced by the less undrained shear strength and soil modulus of soft grounds. Also the more stability number produced the more maximum horizontal displacement. When the shear deformation was not developed, the stability number was less than 3.0 and the safety factor of bearing was more than 1.7. However, if the stability number was more than 5.14 and the safety factor of bearing was less than 1.0, the unstable shear failure was developed in soft ground. 50mm can be recommended as a criterion of the allowable maximum horizontal displacement to prevent the shear deformation in soft ground, while 100mm can be recommended as a criterion of the allowable maximum horizontal displacement to prevent the shear failure in soft ground.

유한요소해석에 의한 측방이동 방지효과에 대한 연구

박춘식,노태경 한국지반공학회 2018 한국지반공학회논문집 Vol.34 No.12

This study presents a reasonable and economical DCM reinforcement length for the various factors (the embankment height, the distance from the embankment to the underground structure, the depth of the soft ground, and the compression index and the swelling index of the soft ground) that affect the stability of the structure due to lateral movement. Based on these results, we analyzed each factor’s degree of influence and figured out which factor influenced the lateral movement most. The cross section of the embankment on the soft ground was modeled by using the Finite Element Program and reinforced with DCM. The results show that the increase rate of the reinforcement length with the increase of the embankment height is about 9~50%, the increase rate of the reinforcement length with the depth of soft ground is about 13~30%, and the increase rate of the reinforcement length with increasing compression index is about 3~25%. In addition, the influence of each factor on each other was analyzed. As a result, among the separation distance, the compressive index and the maximum to minimum slope ratio of the reinforcement length of the embankment height, the separation distance was the largest for the depth of soft ground. As the depth of the soft ground increases, the ratio of the maximum to minimum slope of the reinforcement length according to the embankment height is 3.75, the ratio of the maximum to minimum slope of the reinforcement length according to the spacing distance is 4.3, and the ratio of maximum to minimum slope according to compression index is 2.5. From these results, it is confirmed that the three factors are greatly affected by the depth of soft ground.

표층처리공법으로 개량된 초연약지반의 침하거동에 미치는 영향인자 분석

유승경,이종선,함태규,양기석,조삼덕,최항석,You, Seung-Kyong,Lee, Jong-Sun,Ham, Tae-Gew,Yang, Kee-Suk,Cho, Sam-Deok,Choi, Hang-Seok 한국지반공학회 2008 한국지반공학회논문집 Vol.24 No.12

It is necessary to develop a rational design method for surface reinforcement of very soft ground because most current design works rely on merely crude empirical correlations. In this paper, the mechanical behavior of very soft ground that is surficially reinforced was investigated with the aid of a series of numerical analyses. Several material properties of each dredged soft ground, reinforcement and backfill sand mat have been exercised in the numerical analysis. The result of numerical analysis was compared with those of the laboratory model test. Through the matching process between the numerical and experimental result, it is possible to determine representative material properties of the dredged soft ground, reinforcements and backfill sand mat. These verified material properties permit to evaluate the effect of the stiffness of reinforcement and the thickness of sand mat on the overall deformation of the reinforced soft ground.

전극간 거리에 따른 연약지반의 지반개량 효과와 전기적 특성

변인성(Inseong Byeon),강홍식(Hongsig Kang),선석윤(Seokyoun Sun),한정훈(Jeonghoon Han),안광국(Kwangkuk Ahn) 한국지반환경공학회 2016 한국지반환경공학회논문집 Vol.17 No.1

연약한 점토지반에 대규모 토목시설을 건설하기 위해서는 연약지반 안정화 처리가 불가피하다. 일반적으로 연약지반 안정화 처리를 위해 압밀촉진공법으로 선행재하공법이 사용되고 있으나 선행재하공법은 공사기간이 매우 길고, 재하용 성토재료를 확보해야 하는 단점이 있기 때문에 이를 해결하기 위한 방법으로 전기삼투공법 등이 사용되고 있다. 전기삼투공법은 금속성 전극재가 사용되기 때문에 시공 및 경제적 측면에서 불리하다. 따라서 금속성 전극재를 대신하기 위해 기존 플라스틱 드레인 보드(PBD)에 전기를 공급할 수 있도록 나노기술을 이용한 플라스틱 전극재가 개발되었다. 이에 본 연구에서는 플라스틱 전극재의 간격에 따른 연약지반의 개량 효과와 전기적 특성을 확인하기 위한 모형실험을 수행하였으며, 그 결과 지반개량 효과는 전극간 거리가 길수록 최대 49% 감소하였고 전기적 특성은 전극간 거리에 따른 압밀침하에 영향을 받는 것으로 나타났다. Soft ground stabilization is needed to construct large civil facilities on the soft clay ground. Pre-loading method, which is accelerating consolidation method, is generally used to stabilize the soft ground. However, pre-loading method is required long construction period and quantities of fill material. Therefore, electro-osmosis method is used to replace pre-loading method for stabilizing the soft ground. Electro-osmosis method is disadvantageous in constructive and economic aspects because it is needed a metallic electrode. So, in order to solve the those disadvantages, plastic electrode was developed to replace metallic electrode. Plastic electrode, which is made by using nano-technology on existing Plastic Drain Board (PDB), was used to supply the electric power. In this study, therefore, the model test was conducted to confirm the effect of improvement and electrical characteristics of soft ground by spacing of plastic electrode. The result shows that the effect of improvement of soft ground was decreased up to 45% by increasing electrode spacing and electrical characteristics on the soft ground were influenced by consolidation settlement with electrode spacing.

성토하부 연약지반의 측방유동 평가

홍원표,이광우,조삼덕,이재호 한국지반공학회 2006 한국지반공학회논문집 Vol.22 No.10

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.

구성모델에 따른 연약지반 영역에서의 철도 노반 침하 특성

김규화,오동욱,짠하미,최봉혁,정혁상 한국철도학회 2024 한국철도학회논문집 Vol.27 No.2

This study, using the constitutive model of numerical analysis, quantitatively analyzed the settlement characteristics of railway roadbeds constructed on soft ground and presented the most appropriate constitutive model for clay conditions . The M.C. Model is a representative ground configuration model derived from the L.E. Model and can be used for carbon materials; the S.S.C. Model can simulate the creep compaction of materials and is suitable for soft ground. Soft ground settlement is caused by a combination of factors, including ground properties, grade, and groundwater level. Although each cause of subsidence has been studied through a single numerical model, there is still a lack of comparative analysis research for these numerical models under identical conditions. Therefore, this study analyzed the effects of the numerical model on the residual and instantaneous settlement characteristics of soft ground. As a result of the analysis, both the M.C. and S.S.C. models showed cases that exceeded the allowable residual settlement standard, but the M.C. model showed a tendency in which residual settlement did not increase even when train load was repeated. Therefore, the M.C. Model was used to analyze the behavior of sandy soil, and it is judged to be an inappropriate model for predicting soft ground.

수치해석을 통한 연약지반을 고려한 철도노반 침하 특성에 대한 고찰

오동욱,김규화,윤환희,정혁상 한국철도학회 2023 한국철도학회논문집 Vol.26 No.2

This paper presents quantitative numerical analysis results of effects of underground water level and train load on subsidence of rail trackbed in soft ground. Although the railway subgrade strictly limits the allowable residual settlement to 30mm through the railroad design standards and specifications, it is reported that subsidence occurs continuously in some sections of the Honam high-speed rail and Gyeongbu high-speed rail 2nd phase. The causes of subsidence of the rail trackbed include the groundwater level, height of embankment, and soft ground, and although studies on causes of each type of subsidence have been conducted, research on the complex causes of subsidence have been insufficient. Therefore, in this study, the effects of soft ground conditions, groundwater level, fill height, and train load, the main causes of subsidence of railway subgrade, on residual subsidence of soft ground were analyzed. Secondary compaction was considered to simulate soft ground. Soil Soft Creep Model was used. As a result of the analysis, it was confirmed that the rate of residual settlement increased significantly as the liquid limit of the silt layer increased. In addition, the factors of greatest influence on increase of residual settlement were found to be, in order, liquidity of soft ground, thickness of soft ground, and location of groundwater level were determined.