• Title, Summary, Keyword: 초연약지반

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Reclamation and Soil Improvement on Ultra Soft Soil (II) - Soil Improvement (초연약지반의 매립 및 지반개량 사례 연구 (II) - 지반개량)

  • Na, Yung-Mook;Kim, Hee-Hong;Kwon, Duk-Woo
    • Journal of the Korean Geoenvironmental Society
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    • v.6 no.1
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    • pp.33-44
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    • 2005
  • The 'Silt Pond' is 180 hectares in size and contained ultra soft slurry-like soil varying between 3 to 20 meters in thickness. Soil improvement work in the Silt Pond commenced by installing vertical drains in the mid of 1996, following completion of sand spreading up to +4.0m CD. Prior to soil improvement work in the main area of Silt Pond, experimental tests including laboratory tests with a large diameter consolidation cell and pilot tests were carried out to investigate the deformation behavior of an extremely soft soil. Due to its high compressibility, large strain usually occurred in the initial stage of deformation does not comply with Terzaghi's one dimensional consolidation theory. Taking into consideration experimental test results, the soil improvement works were carried out in main area of Silt Pond containing ultra soft soil. This paper presents the case study on improvement of ultra-soft soil.

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Numerical Analysis on Behaviors of Very Soft Ground Improved by Geotextile (토목섬유로 개량된 초연약지반의 거동에 관한 수치해석)

  • Ahn, Dong-Han;You, Seung-Kyong
    • Journal of the Korean Geosynthetics Society
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    • v.8 no.3
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    • pp.9-16
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    • 2009
  • In generally, ground surface strengthening such as using geotextile is needed to secure trafficability of construction equipment. Several calculation methods for bearing capacity for very soft ground improved by geotextile have been proposed already but they are not established yet. In this paper, elastoplastic finite element analysis is carried out to estimate bearing capacity improvement for very soft ground reinforced by geotextile. In conclusion, by reinforcing with geotextile the bearing capacity improvement of very soft ground is increased with the increase of the settlement after yielding. And it is enough that the length of geotextile is about 3~4 times of the loaded width for the effect to the bearing capacity improvement. Finally, the biggest tensile force of geotextile occurs at an edge of the uniform load.

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An Analytical Study on Bearing Mechanism of Very Soft Ground Covered with Geotextile by Effects of Friction between Ground and Geotextile (토목섬유로 표층 처리된 초연약지반의 지지 메커니즘에 미치는 토목섬유와 지반의 마찰 영향)

  • Ahn, Dong-Han;You, Seung-Kyong
    • Journal of the Korean Geosynthetics Society
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    • v.9 no.4
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    • pp.47-55
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    • 2010
  • In general, ground surface strengthening such as using geotextile is needed to secure trafficability of construction equipment. There are many researches for mechanical beha-vior of very soft ground covered with geotextile, however, most of them are under the condition to fix geotextile completely. In this study, numerical analyses were carried out to figure out the effects of restricting conditions of geotextile on bearing mechanism of very soft ground covered with geotextile. In numerical analyses, joint elements were used to figure out the friction properties between ground and geotextile. The results of numerical analyses were compared with the results of model test. In conclusion, the effects of restricting conditions of geotextile on bearing mechanism of very soft ground covered with geotextile became clear.

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Evaluation of Influencing Factors on Settlement Behavior of Very Soft Ground with Reinforced Surface (표층처리공법으로 개량된 초연약지반의 침하거동에 미치는 영향인자 분석)

  • You, Seung-Kyong;Lee, Jong-Sun;Ham, Tae-Gew;Yang, Kee-Suk;Cho, Sam-Deok;Choi, Hang-Seok
    • Journal of the Korean Geotechnical Society
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    • v.24 no.12
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    • pp.85-92
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    • 2008
  • 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.

Characteristics of Undrained Shear Strength and Development of Modified SPT on Very Soft Ground in Korea (국내 초연약지반의 비배수전단강도 특성 및 개량표준관입시험기 개발)

  • Jung, Hyuksang;Cho, Changkoo;Chun, Byungsik
    • Journal of the Korean Geoenvironmental Society
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    • v.10 no.6
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    • pp.105-115
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    • 2009
  • In this study, SPT, FV, and CPT tests were performed at five very soft grounds in southern coast of Korea to characterize the $S_u$ of very soft ground. In addition, a new modified SPT that is applicable to very soft ground was developed. Tests results showed that in very soft ground (N<2), the $S_u$ was lower than 12.5 kPa using the empirical N-Su correlation, and lower than 50 kPa and 65 kPa using vane shear test and CPT, respectively. It was shown that the results of in-situ tests were higher than those estimated from the N-Su correlation, and it was also demonstrated that the range of estimated $S_u$ was quite wide. New correlations that relate the modified SPT $N_m$ with Su from FV and CPT were developed, which are $S_u=1.76N_m-10.47$ and $S_u=1.82N_m-9.71$, respectively.

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Reclamation and Soil Improvement on Ultra Soft Soil (I) - Reclamation (초연약지반의 매립 및 지반개량 사례 연구 (I) - 매립)

  • Na, Yung-Mook;Hong, Eui;Han, Jung-Soo
    • Journal of the Korean Geoenvironmental Society
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    • v.6 no.1
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    • pp.23-31
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    • 2005
  • The "Silt Pond" is 180 hectares in size and contained ultra soft slurry-like soil varying between 3 to 20 meters in thickness. Reclamation works in the Silt Pond commenced in the mid of 1990s. A considerable amount of subsurface investigation inclusive of sampling, field vane and density logging tests were carried out prior to the reclamation of the Silt Pond. Since material in the Silt Pond is extremely soft, filling was done by spreading sand with high water content in thin and equal thickness lifts, allowing the stability of the slurry-like foundation. Despite the extreme care taken, failures occurred during the sand spreading phase. A large piece of high strength geotextile measuring $900m{\times}700m$ was placed to strengthen the slurry like soil foundation at locations where the ultra-soft soil was found to be exposed. Following the remedial works, the Silt Pond was again reclaimed by sand spreading up to +4.0m CD. The success of the reclamation was confirmed by marine CPT profiling.

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A Study on Bearing Capacity Evaluation Method of Surface Reinforcement Method for Soft Ground in Consideration of Stiffness (강성도를 고려한 연약지반 표층처리공법 지지력산정방법에 관한 연구)

  • Ham, Tae-Gew;Seo, Se-Gwan;Cho, Sam-Deok;Yang, Kee-Sok;You, Seung-Kyong
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.1118-1125
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    • 2009
  • This study, as basic research which was intended to develope the surface reinforcement method using reinforcement material which is applicable to very soft ground in Korea, was aimed at proposing Bearing Capacity Evaluation method for the surface ground improvement method. To that end, a wide width tensile test using geotextile, geogrid and steel bar (substitute for bamboo) and 21 kinds of the laboratory model tests with the end restraint conditions of the reinforcement that comprises the constrained and partially constrained (3 types) conditions were conducted. According to result of tests, Terzaghi's bearing capacity method is adequate to calculate bearing capacity in non-stiff material(geotextile, geogrid). But, It can't adequate to stiff material(bamboo net). So, New bearing capacity method suggest surface reinforcement method of very soft ground which Terzaghi's bearing capacity method modify for effect of stiffness.

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Research on the Surface Improvement of High Soft Ground Using Calibration Chamber Test (모형토조실험에 의한 초연약지반의 표층개량에 관한 연구)

  • Bang, Seongtaek;Yeon, Yongheum
    • Journal of the Korean Geoenvironmental Society
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    • v.20 no.5
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    • pp.39-46
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    • 2019
  • Most of the soil used for reclamation is marine clay generated from dredging construction.The soft ground made of dredged clay has high water content and high compressibility, so the bearing capacity of the ground is very weak and it is difficult to enter the ground improvement equipment. Therefore, surface hardening treatment method is used to enter equipment prior to full-scale civil engineering work, and stabilizer is mainly used for cement series. Cement-based stabilizers have the advantage of improving the ground in a short period of time and have excellent economic efficiency, but they are disadvantageous in that they cause environmental problems due to leaching of heavy metals such as hexavalent chromium. In this study, environmental effects evaluation of dredged clay mixed with normal portland cement and environmentally friendly stabilizer was evaluated, and uniaxial compressive strength test and indoor model test were conducted to confirm the bearing capacity characteristics of the solidified layer.