점질토와 사질토에서의 지반개량재 혼합에 따른 압축강도반응에 관한 연구

이광준 ( Kwang-joon Lee ) 한국환경기술학회 2009 한국환경기술학회지 Vol.10 No.2

철광석을 제련하면 고로슬래그가 발생하고, 제지류를 소각하면 paper fly ash가 부산물로 발생한다. 이러한 소각잔재물들은 해안점토 구성된 연약지반의 개량에 많이 쓰이게 된다. 본 연구에서는 해안점토 또는 육상의 사질토에 지반개량재를 혼합하였을 때 어떤 강도변화를 보이는지에 관한 연구이다. 따라서, 지반개량의 대상흙을 해안점토와 육상의 사질토 지반으로 구분하여 지반개량재의 반응특성을 검토하였다. 지반개량재를 혼합한 후 함수비, 양생일, 혼합비율 등으로 구분하여 일축압축강도의 변화와 생성물질의 변화를 분석하였다. 실험결과 해안점토는 지반개량재에 대한 효과가 뚜렷한데 반해서, 사질토에서는 작은 효과를 나타내는 것을 확인하였다. 양생 28일의 강도증가 변화를 검토한 결과 해안점토가 사질토보다 11배 정도의 강도증가의 효과를 확인할 수 있었다. 이는 지반개량재의 혼합비율이 증가할수록 ettringite 반응이 증가하기 때문이다. As the blast furnace slag is generated by smelting the iron ore, burning up the paper causes paper fly ash as by-products. These waste residuals by fire are used a lot to improve soft ground. This research reports what the change of strength is, if ground improvement material is added to either coastal clay or silty sandy soil. Therefore, after the target soil for ground improvement was divided coastal soil into silty sandy soil, the characteristics of the reaction of ground improvement was re-examined. First ground improvement material was added to each soil and then it was separated by a function ratio, curing days and a mixed rate and so on. Then the changes of uniaxial compress strength test and the generated substances were analyzed. As a result of experiment, the effect of ground improvement material on the coastal clay was clear. Instead, that on silty sandy soil was little. For 28 curing days, in terms of increase in strength, the effect on coastal clay was eleven times more than that on silty sand soil. It shows that the higher the mixed rate of ground improvement is, the higher ettringite reaction is.

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.

심층혼합공법의 최저 개량 심도 결정에 관한 해석적 연구

박춘식(Choon-Sik Park),송지원(Ji-Won Song) 한국지반신소재학회 2020 한국지반신소재학회 논문집 Vol.19 No.1

연약지반 개량 공법 중 심층혼합공법에 대한 설계 기법으로는 복합지반으로 해석하는 방법과 말뚝지반으로 해석하는 방법이 있다. 그러나 이러한 해석에 대한 비교 연구는 부족한 실정으로 설계 시 해석 기준을 명확하게 정의 내리는 것에 어려움이 있다. 본 연구에서는 2차원 및 3차원 해석을 통해 성토 높이와 연약지반의 심도, 보강구간의 치환율을 변화시키며 각 조건별로 복합지반과 말뚝지반을 가정하여 해석하였다. 그 결과 최저 개량 심도는 3차원 해석에 비해 2차원 해석 결과가 6.85∼9.08% 더 깊은 결과를 도출하였다. 또한 말뚝지반 해석의 경우 복합지반 해석에 비해 개량 심도는 12.22∼14.45% 더 깊은 것을 확인하였다. 이 결과를 통하여 보다 정확한 설계를 위해서는 2차원 해석보다는 3차원 해석을 실시해야 하고, 경제적인 설계를 위해서는 복합지반으로 해석해야 하며, 안정적인 설계를 위해서는 말뚝지반 해석을 실시해야 된다고 판단된다. Design techniques for the deep mixing method, one of the soft ground improvement methods, include two ways to interpret the ground as composite ground and pile ground. However, since comparative studies on these two approaches are insufficient, it is difficult to clearly define the analysis criteria in the design. In this study, two-dimensional and three-dimensional analyses have been performed with different conditions. The three conditions, the embankment height, depth of soft ground, and replacement ratio of reinforcement zones were varied and the analysis was performed on the basis of the assumption of composite ground and pile ground for each condition. As a result, the minimum depth of improvement in the twodimensional analysis was deeper by 6.85∼9.08% than in the three-dimensional analysis. The pile ground analysis showed that the depth of improvement was deeper by 12.22∼ 14.45% than the composite ground analysis. Based on these results, it is concluded that for more accurate design, three-dimensional analysis should be performed rather than two-dimensional analysis. also, it is judged that necessary to analyze the ground as composite ground for economical design, and as the pile ground analysis for stable design.

지반개량을 통한 원지반의 전단파속도 향상에 대한 실험적 연구

정찬유,문재성,조명수,강호덕,양희정 한국구조물진단유지관리공학회 2019 한국구조물진단유지관리공학회 논문집 Vol.23 No.7

In this study, an experimental study was carried out with variables of the shape of the ground soil-binder in order to find out whether the shear wave velocity and the ground grade were improved by the ground improvement. In this study, the shear wave velocity was measured using the crosshole method with variables of the shape of the ground soil-binder. In addition, the prediction formula of the shear wave velocity for suitability of N-Values for the domestic soil conditions are proposed using the result value of this study and the existing results of shear wave velocity . As a result, the shear wave velocity of the ground has increased. In addition, the prediction formula proposed in this study reasonably issued the existing experimental results regardless of the stratum conditions. 이 연구에서는 지반의 개량에 따른 전단파속도 및 지반등급 향상 여부를 알아보기 위하여 지반개량체의 형상을 변수로 실험적 연구를 수행하였다. 실험은 지반개량체의 형상을 변수로 크로스홀(Cross hole) 기법을 이용하여 전단파속도를 측정하였다. 또한, 이 연구에서 측정된 결과 와 기존 전단파속도 측정결과를 이용하여 국내 지반조건에 맞는 N-Value에 대한 전단파속도 예측식을 제안하였다. 실험결과, 지반개량을 수행하는 경우 원지반의 전단파속도는 소폭 상승하였다. 또한, 이 연구에서 제안한 예측식은 지층조건에 관계없이 기존실험결과를 합리적으로 예측하였다.

연직 매트로 보강된 연약지반의 지지력 특성

신은철(Eun-Chul Shin),이길호(Gil-Ho Lee) 한국지반환경공학회 2012 한국지반환경공학회논문집 Vol.13 No.6

일반적으로 심층혼합공법에 의한 점토지반의 개량효과는 물리적 개량효과에 비해서 훨씬 크며 조기에 큰 개량 강도를 얻을 수 있으나, 국내 시공실적이 부족하고 시멘트-점토의 혼합방법에 따른 품질관리에 문제점이 있는 것으로 알려져 있다. 본 연구에서는 시멘트, 모래, 점토의 배합비에 따른 강도특성과 연직MAT의 형태에 따른 연약지반의 개량특성을 파악하기 위해 해성점토를 이용하여 일축압축 강도시험과 모형토조시험을 수행하였다. 일축압축강도 시험을 위한 공시체는 시멘트와 물의 중량비를 기준으로하여 모래를 일정 비율로 혼합하였고, 시멘트는 점토중량대비 각각 10%, 20%, 30%, 40%를 혼합하였고 대상지반토의 함수비는 40%, 60%, 80%로 조정하여 제작하였다. 공시체는 습윤방법을 이용하여 7일, 14일, 28일간 양생하여 양생기간에 따른 일축압축강도 시험을 수행하였다. 지지력시험은 모형토조를 제작하고 Mat식으로 개량한 지반을 형성한 다음 개량률에 따른 지지력을 비교하고 연직MAT 장벽 상호간의 간섭효과를 분석하였다. Generally, the effect of the cement deep mixing method on the improvement of clay ground is far greater than the effect of physical improvement. Although it leads to great improvement strength in the initial stage, there are not many constructional precedents in Korea and it is hard to manage quality according to the cement-clay mixing method. In order to figure out the strength characteristics according to the mixing ratio of cement, sand, and clay and the improvement characteristics of weak ground according to the forms of the specimens to be improved, marine clay was used in this study to conduct the uniaxial compression test and soil bin model test. The test piece specimens for the uniaxial compression test were mixed with sand in a fixed ratio with the criterion of the water cement ratio. The cement was mixed with clay in the ratios of 10%, 20%, 30%, and 40% to the clay weight. The moisture content of the soil ground was made in the ratios of 40%, 60%, and 80%. The test piece specimens went through curing by moistening for 7, 14, and 28 days and underwent the uniaxial compression test according to the curing period. For the bearing test, the soil bin models were made and the ground improved in the Mat type was formed. After that, the bearing strength was compared in this study according to the improvement ratio and analyzed the intervening effect between the walls of the improved specimens.

Influence of Ground Improvement on liquefaction Induced Settlement Observations from Case Histories and Centrifuge Experiments

Ni Cholas Sitar,Eliza Beth Hausle 한국지반공학회 2012 international journal of geo-engineering Vol.4 No.2

Over 100 case histories for sites with ground improvement has been compiled in order to provide an overview of the actual field performance of improved sites under strong seismic loading. The data show that improved sites generally performed well. Improved ground sites experience less deformation than their unimproved neighbors. Unacceptable performance, when it occurs, can be explained most commonly by excessive ground displacements due to laterally flowing soils or inadequate remediation zone depth or lateral extent. The case history data is supported by results of dynamic centrifuge experiments which show that for low levels of shaking, typically 0.2 g or less, the amount of settlement of the foundation element decreases with increasing improved zone depth. Moreover, the amount of differential settlement of the foundation decreases significantly with increasing level of ground improvement. For high levels of shaking (peak ground acceleration in excess of 0.7 g) and very loose soil the settlements are significantly greater for all depths of improvement. The experimental results also show that leaving a thin layer of unimproved soil below a thick improved zone can lead to large concentrations of strains and liquefaction and produce excessive settlements.

CGS공법의 지반개량 효과에 관한 연구

도종남 ( Do Jong-nam ),유준희 ( Yoo Jun-hee ),천병식 ( Chun Byung-sik ) 한국구조물진단유지관리공학회 2007 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.11 No.1

CGS (Compaction Grouting System) is widely used in reinforcement of structural foundation and ground improvement in soft ground. But the effects of ground improvement depending on the type of soil must be studied in order to adopt in various soils (granular soil and cohesive soil). In this study, characteristics of ground improvement(the increase of N value, increase in unit weight, vertical displacement on the ground surface) by CGS method was compared through two cases that were performed in granular and cohesive soil. The results were showed that the closer to the grout hole, the more increase in N value and this trend appear distinctly in far from it independently of the soil type. The vertical displacement on the ground surface appeared in smaller area in case of granular soil than chesive soil.

CGS공법의 지반개량 효과에 관한 연구

도종남(Do Jong-Nam),유준희(Yoo Jun-Hee),천병식(Chun Byung-Sik) 한국구조물진단유지관리학회 2007 한국구조물진단학회 학술발표회논문집 Vol.11 No.1

CGS(Compaction Grouting System) is widely used in reinforcement of structural foundation and ground improvement in soft ground. But the effects of ground improvement depending on the type of soil must be studied in order to adopt in various soils(granular soil and cohesive soil). In this study, characteristics of ground improvement(the increase of N value, increase in unit weight, vertical displacement on the ground surface) by CGS method was compared through two cases that were performed in granular and cohesive soil. The results were showed that the closer to the grout hole, the more increase in N value and this trend appear distinctly in far from it independently of the soil type. The vertical displacement on the ground surface appeared in smaller area in case of granular soil than chesive soil.

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.

나노섬유를 이용한 동전기 지반개량에 관한 특성

안광국(Ahn Kwangkuk),정구식(Jeong Kusic),이준대(Lee JunDae) 한국지반환경공학회 2009 한국지반환경공학회논문집 Vol.10 No.4

본 연구는 지반개량공법에 사용되는 동전기 공법에서 나노섬유를 전극재로 사용하여 지반개량효과 및 나노섬유에 대한 전극재로서의 대체가능성을 확인하였다. 이를 위해 Electrokinetic cell을 제작하여 나노섬유를 PBD에 삽입 후 교반된 Kaolin clay에 전기삼투를 적용한 후 실험전후의 침하량, 함수비, 압밀배수량, 전단강도에 대한 지반개량효과를 비교 분석하였다. 또한 전기삼투실험은 전극거리와 전압경사를 변화시키면서 실험을 수행하였으며, 그 결과로 전압경사증가 및 전극거리가 감소할수록 침하량, 전단강도, 압밀배수량은 증가하였고 함수비는 감소하는 것으로 나타났다. 이는 지반개량을 위한 동전기 적용시 사용되는 전극재의 소재로 나노섬유가 충분한 가능성이 있는 것으로 판단된다. In this study, Nano-geosynthetics with electroosmosis method was used and tried to verify the possibility of usage for soft ground improvement. Electroosmosis tests were performed with increasing the voltage level and changing distance between electrodes. The electrokinetic cell was assembled and a Nano-geosynthetics was inserted into the plastic drain board. And electroosmosis was applied to the disturbed kaolin clay. In order to study the effects of ground improvement, ground settlement, water content, collected pore water and shear strength were compared and analyzed with non-applied kaolin clay. Also, the electroosmosis tests were performed with changing the distance between electrodes and the voltage size. As a results of changing the distance and voltage between electrodes, the more voltage size was increased, the more the settlement of ground, shear strength and collected pore water were increased. As the distance between electrodes were increased, the settlement of ground, shear strength, water content and collected pore water were decreased. Finally, Nano-geosynthetics as a material of electrode have the sufficient potential to improve soft ground.