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.

성토로 인한 연약지반의 측방유동 거동에 관한 실내모형실험

유승경(You Seung-Kyong),김재홍(Kim Jae-Hong) 한국토목섬유학회 2011 한국지반신소재학회 논문집 Vol.10 No.1

연약 점성토 지반에 성토를 할 경우 과도한 침하와 측방유동으로 인한 피해를 최소화하기 위해 토목섬유/성토지지말뚝공법이 주로 사용되고 있다. 본 공법은 연악지반 층을 관통하여 지지층에 관입시킴으로써 상재하중을 지지하게 하여 상재하중으로 인한 침하와 측방유동 발생을 최소화한다. 본 연구에서는 연약 점성토 지반에 설치된 토목섬유/성토지지말뚝공법의 보강효과를 정량적으로 검토함을 목적으로 하였다. 실내모형실험을 통하여 무보강 및 성토지지말뚝 보강의 경우에 대한 지반 거동을 재현하고 성토지지말뚝에 의한 측방유동 억지효과를 분석하였다. 이때 성토지지말뚝을 설치한 경우에 대해서는 상재하중의 크기를 다르게 설정하여 완속 재하와 급속 재하의 경우에 대한 측방유동의 억지효과를 분석하였다. Pile-supported embankment is one of the reinforcing methods to minimize damage due to the severe subsidence and lateral now when soft clay ground is supported with embankment. pile-supported embankment mainly penetrates soft ground into the bearing stratum in order to support surcharge load which minimizes the subsidence and lateral now due to the surcharge load. The aim of this research is to review quantitatively reinforcing effect of pile-supported embankment which is installed in soft clay ground. From the model test, it reproduced the ground movement with regard to the non-reinforced and reinforcing embankment-pile and also analyzed stabilizing effects of lateral flow due to the pile-supported embankment. With regard to the case of installing pile-supported embankment, its were analyzed stabilizing effects of lateral now in cases of quick-load and slow-load to make different surcharge load.

도로 성토로 인한 연약지반의 측방유동에 관한 연구

김정훈(Kim, Junghoon),홍원표(Hong, Wonpyo),이충민(Lee, Choongmin),이준우(Lee, Junwoo) 한국지반환경공학회 2012 한국지반환경공학회논문집 Vol.13 No.9

각종 연직배수재가 설치된 연약지반의 전단강도, 지반변형의 특성을 조사하기 위해 우리나라 서해안과 남해안 지역에서 계측관리가 실시된 13개 연약지반현장 200개소에서 계측자료를 수집하였다. 먼저 연약지반의 침하량과 측방변위량과의 관계를 성토 초기 단계, 성토 완료 단계 및 성토 완료 후 단계의 세 단계로 구분하여 조사하였다. 다음으로 성토압과 성토고가 연약지반의 비배수전단강도와 어떤 관계에 있는가를 조사하였다. 검토결과, 침하의 증가량에 대한 수평변위의 증가량은 성토 초기 단계에서는 작았으나 점차 증가하여 성토 완료 단계에서 가장 크게 발생되었다. 그러나 성토 완료 후에도 침하량은 계속 증가하고 있었으며 수평변위는 거의 수렴하였으므로 대부분의 측방유동은 성토시공 중에 발생되었다. 침하량증분에 대한 수평변위증분의 비는 성토초기 단계에서 20% 정도로 Tavenas et al.(1979)이 제시한 값과 일치하였으나 성토 완료 단계에서는 Tavenas et al.(1979)이 제시한 값의 절반 정도인 50%밖에 나타나지 않았다. 그리고 성토 완료 후 단계에서는 1%에서 9% 사이로 아주 작게 발생되어 Tavenas et al.(1979)이 제시한 값과 상당한 차이를 보였다. 모든 현장에서 설계성토고가 초기비배수강도 상태에서의 항복성토고보다 높은 상태였으므로, 연약지반 속에 전단변형 내지 전단파괴가 발생될 것이 예상되었다. 그러나 강도가 증가된 후에는 모든 현장에서 설계성토고가 항복성토고보다 낮게 되어 안전한 성토시공이 가능하였던 것으로 판단된다. 도로성토시공을 안전하게 실시하기 위해서는 성토하중이 초기비배수전단강도의 5.14배가 넘지 않도록 하여야 하며 증가된 비배수전단강도의 3.0배 이하가 되도록 설계하여야 한다. 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.

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.

한계평형해석에 의한 연약지반 위의 철도노반 고성토를 위한 직포 보강 효과

김유성(Kim You-Seong),최재선(Choi Jae-Seon) 한국토목섬유학회 2010 한국지반신소재학회 논문집 Vol.9 No.4

직포 보강재는 연약지반 성토시 장비주행성, 지지력 및 활동안정성 개선 등을 목적으로 활발하게 적용되고 있다. 이 논문에서는 연약지반 위에 고강도의 직포를 2층 보강하여 철도제방을 성공적으로 구축한 사례를 소개하였다. 한계평형해석에 근거한 비탈면 활동안정분석결과 연약지반 위에 고강도의 직포를 2층 보강하고 흙쌓기를 수행하였을 때 제체의 활동에 대한 안전율은 0.91에서 l.14로 약 25%증가하고, 2개월 이상의 공기단축효과가 있는 것으로 나타났다. 따라서, 공기가 촉박하거나, 안전율이 다소 부족한 현장의 경우 고강도 직포보강에 의한 연약지반처리공법은 유용한 것으로 판단된다. Woven geotextiles (polyester mats) reinforcement is generally used to improve traffic ability, bearing capacity, and slope stability for embankment construction on soft ground. Cases of two high-strength woven georextiles reinforcement layers are introduced in the present paper, which has been successfully constructed for rail road embankment on soft ground. According to the case results based on the limit equilibrium analyses of slope stability, the two high-strength woven georexriles reinforcement layers on the soft ground can substantially increase the stability of the embankment by about 25%, improve the safety factor from 0.91 to 1.14, and significantly reduce the embankment construction duration at least 2 months. Therefore, the application of high-strength woven geotextiles is found to be useful for in-situ cases having the lack of construction duration and stability, as a soft ground improvement.

연약지반에 시공된 도로용 경량성토체의 재료 및 거동특성

여규권,이용재,김홍연,윤길림,한상현 한국지반신소재학회 2018 한국지반신소재학회 논문집 Vol.17 No.2

The purpose of this study is to fabricate a full scale road embankment using lightweight air foamed soil as a soil material on soft ground and to investigate its material characteristics and behavior in order to promote dredged soil utilization and minimize ground improvement. As a result of the laboratory test of the onsite mixed samples, the total unit weight of the specimens decreased almost linearly until curing 28 days. In particular, the total unit weight after 28 days of curing was reduced to about 81% of the slurry state before curing, which will be useful in the formulation of similar native soil materials in the future. The unconfined compressive strength began to decrease with the 14th day of curing as shown in the previous study. When the cement content is increased, the strength decreases sharply at a small strain change after the occurrence of the maximum compressive strength, and the maximum strength is exhibited in a range of a smaller axial strain than normal range. The settlement at the surface layer of the ground due to the lightweight embankment was about 1 / 2.75 of the soil embankment and was in agreement with the unit weight ratio (1 / 2.7) of the embankment materials. This indicates the cause and effect of the settlement due to the difference in self weight of the embankments. Also, the difference in settlement between soil and lightweight embankment increased with increasing depth. This shows that the difference in the point at which the settlement is terminated is clear. The ground horizontal displacement under the lightweight embankment was about 15~20% smaller than that of the soil embankment and the depth of occurrence was also 4.5~5.0m shallower in the lightweight embankment. 본 연구에서는 준설토 활용을 촉진하고 지반개량을 최소화 하기위한 목적으로 연약지반에서 경량기포혼합토를 토공재료로이용하여 실규모의 도로 성토체를 제작하고 그 재료특성과 거동을 분석하였다. 현장에서 배합된 시료의 실내시험 결과 공시체의 습윤단위중량은 양생 28일까지 거의 선형적으로 감소하였고, 특히 28일 양생 후 습윤단위중량은 양생 전 슬러리 상태의약 81%로 감소되었으므로 향후 유사한 원료토의 배합설계시 활용이 가능하다. 일축압축강도는 기존의 연구와 같이 양생14일을 기준으로 강도증가율이 감소하기 시작하였고, 시멘트 함유량이 많아질 경우 최대 압축강도 발생 후 적은 변형률 변화에서 강도가 급격히 감소하며, 통상보다 작은 축변형률 범위에서 최대강도가 발현되는 현상이 나타났다. 경량성토로 인한 원지반천층부에서의 침하량은 토사성토의 약 1/2.75로서 성토재료의 단위중량 비율(1/2.7)과 일치함으로써 자중의 차이로 인한 침하량의 인과관계가 잘 나타났다. 또한 원지반 하부로 내려갈수록 토사 및 경량성토 사이의 침하량 차이가 크게 나타남으로써침하종료 심도에 차이가 명확하게 나타났다. 경량성토 구간의 지중수평변위량은 토사성토 대비 약 15~20% 정도 작게 나타났고, 그 발생심도 또한 경량성토의 경우가 4.5~5.0m 가량 얕게 나타나 경량기포혼합토가 전단변형의 영향심도를 현저히 감소시키는 효과가 있음을 확인하였다.

성토지지말뚝에 작용하는 연직하중의 이론해석

홍원표,이재호,전성권 한국지반공학회 2000 한국지반공학회논문집 Vol.16 No.1

연약지반속에 말뚝을 설치하고 성토를 실시할 경우 말뚝에 작용하는 연직하중을 산정할 수 있는 이론적 해석법을 개발하였다. 여기서 말뚝은 성토하중지지 효과를 증대시키기 위하여 일정간격의 줄말뚝 형태로 설치하며 각 줄말뚝의 두부는 지중보 형태의 말뚝캡보로 연결시킨 경우를 대상으로 한다. 이론식의 유도과정에서 성토지지말뚝으로 지지된 성토지반의 파괴발생 기구를 말뚝위 성토지반속의 파괴형태에 따라 지반아칭파괴와 펀칭전단파괴의 두 가지로 크게 구분하였다. 여기서 지반아칭은 말뚝캡보 사이의 간격이 좁거나 성토고가 충분히 높을 때 발생된다. 지반아칭파괴는 아치의 파괴부위에 따라 정상파괴와 캡파괴로 나누어 각 파괴형태의 안전성이 검토되었다. 또한, 제안식에 의한 성토지지말뚝의 하중분담효과는 말뚝캡보의 간격과 폭의 크기 및 지반정수에 크게 영향을 받고 있음을 알 수 있다. 즉, 말뚝캡보의 간격이 증가하면 말뚝의 하중분담효과는 감소하며 성토고, 말뚝캡보폭, 내부마찰각 및 점착력의 크기가 증가할수록 하중분담효과가 커지게 된다. 따라서 이러한 말뚝 및 지반에 관한 영향요소를 적절히 결정하면 성토지지말뚝의 성토하중분담 효과를 효과적으로 극대화시킬 수 있을 것이다. Several theoretical analyses are performed to predict the vertical load on embankment piles with cap beams. The piles are installed in a row in soft ground below the embankment and the cap beams are placed perpendicular to the longitudinal axis of the embankment. Two failure mechanisms such as the soil arching failure and the punching shear failure are investigated according to the failure pattern in embankment on soft ground supported by piles with cap beams. The soil arching can be developed when the space between cap beams is narrow and/or the embankment is high enough. In the investigation of the soil arching failure, the stability in the crown of the arch is compared with that above the cap beams. The factors affecting the load transfer in the embankment fill by soil arching are the space between cap beams, the width of cap beams and the soil parameters of the embankment fill. The portion of the embankment load carried by cap beams decreases with increment of the space between cap beams, while it increases with the embankment height, the width of cap beams, the internal friction angle and cohesion of the embankment fill. Thus, the factors affecting load transfer in embankment should be appropriately decided in order to maximize the effect of embankment load transfer by piles.

연약지반에 성토시 발생하는 수평변위 억지를 위한 말뚝보강 효과에 대한 수치해석

김재홍(Kim Jae-Hong) 한국토목섬유학회 2011 한국지반신소재학회 논문집 Vol.10 No.4

측방유동의 발생이 가능한 해안연약지반에 성토를 시행하면 지표면의 하부에는 수평변위가 발생한다. 이러한 수평변위는 인접 지반에 변형을 발생하여 인접 지하에 매설된 각종 기반시설에 영향을 미칠수 있다. 수평변위의 억지대책으로 성토지지말뚝과 억지말뚝을 적용하였고, 억지대책의 효과분석을 위해 무보강지반과 보강지반으로 구분하여 수치해석을 시행하였다. 수치해석 결과는 억지말뚝 보강시가 무보강시보다 1.9배의 효과가 있었다. 성토지지말뚝의 보강은 무보강시보다 2.6배의 효과가 있는 것으로 나타났다. 또한, 두 억지대책중 억지말뚝 보강보다 성토지지말뚝 보강이 1.3~1.6배의 효과가 있는 것으로 나타났다. When an embankment is performed on the soft ground of the coastal with possibilities of lateral flow, lateral displacement occurs to the bottom of the surface of the ground. This lateral displacement can affect existing infra structures that are buried in the adjacent underground by causing a displacement in the nearby base foundation. Soft ground supporting piles and reinforced piles were applied as reinforcement remedies against the lateral displacement. And for the effect analysis, numerical analysis was performed under the classifications of non-reinforcement base and reinforced base. The result of the numerical analysis showed that the reinforced piles had more effects by 1.9 times than non-reinforced piles. Soft ground supporting piles showed better effects by 2.6 times than non-reinforced piles. Additionally, between the two reinforced remedies, soft ground supporting piles showed greater effects by 1.3-1.6 times than the reinforced piles.

Effects of Geosynthetic Reinforcements on Settlement of Embankment on Soft Ground

아리프(Arief Budiman),이광열 대한토목학회 2008 대한토목학회 학술대회 Vol.2008 No.10

Overall stability of geosynthetic-reinforced embankment on soft ground must consider the factor of safety, soilgeosynthetic interface shear stress, reinforcement stiffness and tensile strength of geosynthetic, and the horizontal and vertical displacements of soil. A single layer geosynthetic-reinforced embankment with various heights and reinforcement stiffness was proposed to this study. Moreover, it will be analyzed with numerical model based on the finite element method. This study will compare and analyze the difference in behavior, stiffness, and stress from reinforcement strength gap, with an effort to complement the existing reinforcement (geosynthetic) design on embankment considering the stability of embankment and soilgeosynthetic interaction. As a result, enhancing reinforcement stiffness of geosynthetic can increase the overall stability of embankment. The soil-geosynthetic interface shear stress also gives important role for the stability of embankment. In addition, back calculation is used to compare between actual tensile strength and tensile strength based on geosynthetic strain occurred. Furthermore, it is important to consider the geosynthetic stiffness value for designing the embankment.

성토로 인한 연약지반의 압밀거동 예측 사례

한중근(Jung-Geun Han),김동찬(Dong-Chan Kim),홍기권(Ki-Kwon Hong),유승경(Seung- Kyong You),홍성철(Seong-Cheol Hong) 한국지반신소재학회 2012 한국지반신소재학회 학술발표회 Vol.2012 No.11

This study analyzed to consolidation behavior prediction according to soil properties for soft ground design. Average value and typical value of soil properties based on various behavior result are calculated, because the distribution of soft ground are very different in prediction section. Consolidation settlement and consolidation period had a difference according to prediction result from the selected soil properties for each section. Consolidation settlement distinguished from minimum 6.88cm to maximum 28.77cm. Especially, Case 3 and Case 5 exceed allowable residual settlement(10cm) whereas case 4 and case 6 didn’t exceed allowable residual settlement. consolidation period also had a difference from minimum 3.9 months and maximum 38.9 months. Therefore, the various borehole result should be applied reasonably when soil properties selected for soil behavior prediction of soft ground.