• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.5C
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• pp.201-208
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• 2010

In this study, the ground settlement was investigated by using monitoring data of the test sites where vacuum consolidation method and surcharge method were applied for improving deep soft soil. The monitoring data are chosen in ${\bigcirc}{\bigcirc}$ area port construction site reclaimed with very soft dredged clay. These data are analyzed to compare the consolidation characteristics between the different loading methods for soil improvement. Through analysis of the loading time, it is shown that the ground settlement reaches its allowable value under vacuum consolidation loading by about 45% faster than that of the surcharge loading consolidation. This could be explained that vacuum consolidation method makes the isotropic consolidation condition so that the time for reaching a certain final preloading without soil failure can be shortened.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.217-222
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• 2000

An understanding of the behaviour of soft clay soils is important in a large number of civil engineering applications, including dredging operations, land reclamation and slurry management such as disposal and storage. Although the details of the behaviour depend on parameters such as the soil mineralogy, the pore water chemistry, the organic content and the microbiology, there are general features that are typical in many cases. The purpose of this paper is to present and discuss some of evaporation and desiccation observed in laboratory experiments under controlled conditions. Desiccation of dredged material is basically removal of water by evaporation which is controlled by weather and material type, etc. This study shows that (1) solar radiation, (2) wind velocity, (3) material depth, (4) trench depth are important factors in desiccation of dredged ultra soft clay.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.918-927
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• 2008

The problems associated with constructing high-speed concrete track embankments over soft compressible soil has lead to the development and/or extensive use of many of the ground improvement techniques used today. Drains, surcharge loading, and geosynthetic reinforcement, have all been used to solve the settlement and embankment stability issues associated with construction on soft soils. Geosynthetic-reinforced embankment supporting piles method consist of vertical columns that are designed to transfer the load of the embankment through the soft compressible soil layer to a firm foundation and one or more layers of geosynthetic reinforcement placed between the top of the columns and the bottom of the embankment. In the paper, the evaluations of a seismic performance of geosynthetic-reinforced embankment piles for a ultra soft ground during earthquake were studied. the equivalent linear analysis was performed by SHAKE for soft ground. A seismic performance analysis of Piles was performed by GROUP PILE and PLAXIS for geosynthetic-reinforced embankment piles. Guidelines is required for pile displacement during earthquake. Conclusions of the studies come up with a idea for soil stiffness, conditions of pile cap, pile length and span.

• Journal of the Korean Geosynthetics Society
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• v.7 no.3
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• pp.41-49
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• 2008

This study was carried out the model experiment in laboratory to evaluate the bearing capacity improvement of soft ground as altered constraint condition of reinforcements according to geotextile, georid, steel bar. As a results, the value of BCR was increased linearly as improvement of the stiffness of reinforcements, and the factor governed the increasement of BCR was the increasement of frictions between reinforcement and clay as far as the constrain conditions increased until T=85.6kg. Moreover, An angle of inclination, ${\theta}$, between reinforcement and horizontal surface was distributed from $38^{\circ}$ to $50^{\circ}$ for Geotextile, from $45^{\circ}$ to $50^{\circ}$ for Geogrid and from $14^{\circ}$ to $16^{\circ}$ for steel bar. A radius of heaving, r, of clay ground by vertical weight at side was distributed from 0.6m to 0.7m for Geotextile, from 0.5m to 0.8m for Geogrid, and from 2.4m to 3.0m for steel bar. In case of steel bar, r was 4 times that of Geotextile.

• Journal of the Korean GEO-environmental Society
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• v.10 no.6
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• pp.19-25
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• 2009

The current study developed light-weighted mixed soil that can solve problems related with soft soil such as ground subsidence, sliding and lateral displacement of ground. By reducing weight of reclaimed soil through mixing phosphogypsum and recycled EPS beads with the weathered granite soil. A series of geotechnical laboratory tests including physical index test, compaction test, CBR test, and direct shear test were performed and engineering properties were reviewed in order to assess applicability of the light-weighted mixed soil for roads and abutment and various back-filling materials at the reclamation area. Based on the laboratory test results, it was found that the maximum dry unit weight of the light-weighted soil ranges $14.32{\sim}15.79kN/m^3$ and the optimum water content ranges 21.91~24.23%, which means there is 11~19.3% weight decrease effect when comparing with general weathered granite soil. Also it was found that the corrected CBR value ranges 10.4~18.4% satisfying the domestic regulations on road subgrade and back-filling material. In addition, as for shear strength parameter, cohesion ranges 10.79~18.64 kPa and internal frictional angle ranges $35.4{\sim}37.2^{\circ}$, which are similar with those of general construction soil and back-filling material used in Korea. So it can be concluded that light-weighted mixed soil with phosphogypsum can be used effectively for soft reclamation ground as actual filling material and back-filling material. From the current study, it was found that light-weighted mixed soil with phosphogypsum has not only weight reduction effect, but also has no special problems in shear strength and bearing capacity. Therefore, it is expected that phosphogypsum can be recycled in bulk as road subgrade and back-filling material at the reclamation area.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.1
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• pp.9-15
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• 2005

Dredged soil from sea has much higher water content than liquid limit of clay and even if small loads apply, it will suffer a great settlement. Therefore it is very difficult to perform a consolidation test with general consolidation apparatus because of high water content. In this study Rowe cell apparatus consolidation tests have been performed with 5 slurry clays of a water content of 100%, 110%, 120%, 133%, and 150%. From the test results the consolidation characteristics such as compression index, secondary compression index, consolidation coefficient, and strain have been investigated with a variation of water content of dredged soil. The equations to get consolidation constants such as a compression index, a coefficient of consolidation, and strain have been proposed with the field water content.

• Proceedings of the KSR Conference
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• 2001.05a
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• pp.408-415
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• 2001

Hardening agent has been the traditional material for surface soil stabilization of soft ground. The aim of this study if to determine optimal mixture ratio of hardening agent in accordance with the required design specifications. Hardening agent consists of fly ash, gypsum, slag and cement for the ettringite hydrates and if effective for early stabilization of unconsolidated soil. The raw ground material is the clay that is widely found here and there in Korea. In this study, preliminary tests were performed to get optimal mixture ratio of stabilizer ingredient and marine clay in Jinhae was used to get physical and chemical properties. Laboratory tests of 50 stabilized soils were performed to get optimal mixture ratio for 16-stabilizer materials of 6 types, and mixture ratio of stabilizer ingredient and marine clay was determined.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.491-498
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• 2002

Dredged and reclaimed soft clays form slurry state which is very high water content and very low shear strength, experience large self-weight consolidation, nonlinear compressibility and permeability phenomenon would take place. In this case, a material functions which represent variety effective stress-void ratio-permeability relation (especially very low effective stress), are should be determined to predict nonlinear finite strain consolidation phenomenon forehand In this study, large slurry consolidometer with a 380mm diameter and a 1400mm height which is able to consolidation and permeability test, was developed to determine material function of very soft clay with a 500% initial water content clay, self-weight consolidation and low stress level consolidation (1Kpa, 3Kpa, 6Kpa, 12Kpa) was conducted and after each consolidation step permeability test also conducted. after final consolidation step, a constant rate of strain consolidation was conducted with undisturbed sample obtained from the large consolidometer. On the above result, material function was determined and laboratory test was modelled to evaluate its validity, numerical analysis on th field was compared to other method.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.731-738
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• 2002

Recently, as large constructions on the coast are performed frequently, surface layer stabilization method which Is one of the improvement methods for dredged soft clay has been applied. However, there have been few studies about the surface layer stabilization method. The purpose of this study is to clarify characteristics of ultra-soft marine clay and hardening agent. Also, optimal mixture ratio of hardening agent was verified through the laboratory tests such as statistical analysis and pilot tests. Laboratory tests were performed with proper hardening agent and test soil and standard mixing tables of hardening agent were determined according to ground conditions through statistical analysis. Also, applicability of surface layer stabilization method to field was verified by pilot tests. From the results of the tests, it was found that hardening agent materials such as cement, slag, fly-ash, inorganic salts, arwin, gypsum etc. affect on the appearing compressive strength. It was defined optimal mixture ratio which satisfies the required compressive strength from the statistical analysis. Also, It was compared the effect of ground improvement by cements and hardening agents through the pilot tests. This study will serve as data for design or construction criteria of stabilization of surface layer on ultra-soft marine clay.

• Journal of the Korean GEO-environmental Society
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• v.13 no.5
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• pp.13-24
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• 2012

In this study, the in-situ model test has been conducted and used to estimate and analyze consolidation behavior of the ground by using the miniature test that reconstructs economically geotechnical behavior of in-situ full scale structure. To analogize the relation among effective stress, void ratio and coefficient of permeability at the self-weight consolidation stage, the low stress seepage consolidation test has been conducted and the involution function of constitutive equation had been obtained from the result of the curve fitted seepage consolidation test result. As a result of the numerical analysis that had been conducted on the representative section using a constitute equation, final settlement was similar with those of self-weight consolidation of the centrifugal model test. But, it was more or less smaller. It seems that these trends are caused by the difference between estimated values.