• 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.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2001.10a
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• pp.375-378
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• 2001

This study was peformed to understand permeability characteristic of clays with various pH values. A serious of physical properties and permeability tests, consolidation tests was performed on a clay and a marine clay. Results of the study are as follows. As pH values were decreased, coefficient of permeability was increased because of increase in effective void caused by decrease in thickness of diffuse double layer besides change in soil structures and effective grain size. As pH values were increased, coefficient of permeability of marine clay was increased. Variation of coefficient of permeability of marine clay was increased. Variation of coefficient of permeability of marine clay was largely related because of higher clay contents.

• Geotechnical Engineering
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• v.3 no.1
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• pp.7-24
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• 1987

Preloading surcharge method along with vertical drains was adopted to improve the performance of a very soft marine clay deposit. The onshore deposit, located in the Ulsan Bay area, consists of a 2 to 10m thick, very soft, highly compressible marine clay layer developed just below. the sea water level. The initial undrained shear strength of the clay layer was about 0.6 ton/m2. But, the deposit was designed after treatment to support some auxiliary facilities for a new ilo refinery plant, requiring bearing capacities of 3.6 to 5.4 ton/m2 and maximum allowablee settlement of less than 7.5cm. A total of 35, 000 wick drains Ivas installed to expedite drainage during preloading, and surcharge loads of up to 5m above the original ground level were applied in a step-by-step loading sequence to prevent ground failure by excess surcharge loads. An extensive program of field instrumentation was implemented to monitor the behavior of the clay deposit. Measurers!ends included settlements, excess pore pressure and its dissipation, ground farmer level fluctuation, and lateral movement of the so(t clay layer under the preloads. This paper describes the design concepts, construction methods and control procedures used for improvement of the clay layer. It also presents the ground behavior measured during construction, rind comparisons with theoretical predictions.

• Proceedings of the Korean Geotechical Society Conference
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• 2007.09a
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• pp.3-38
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• 2007

The depositional characteristics of Busan clay are initially described in this paper. The deposits of the Nakdong River estuary are composed of some different layers, which have been affected by marine transgression and regression. The upper clay layer is thick and soft. The lower clay layer and some depth of the upper clay layer have been leached by artesian pressure existing in an aquifer below. The clay shows unique physical and engineering characteristics due to leaching. Several large-scale reclamation projects have been performed in this delta area. The preloading method using long vertical drains has been applied for soft ground improvement. Experiences obtained from ground improvement are mentioned in connection with the depositional characteristics of the clay layers.

• Journal of Ocean Engineering and Technology
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• v.18 no.4 s.59
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• pp.46-51
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• 2004

The surface layer in dredged and reclaimed marine clay is improved by mixing of shallow soils and hardening agents, which is made of cement, containing some other special admixtures. Tests in both laboratory and field settings are performed to investigate the improvement effect and strength properties of cement-stabilized soils. The test results show that the hardening agent sufficiently improves the soil properties of the surface layer, while increasing the load-carrying capacity. The strength of cement-stabilized soils depends, primarily, on water-to-cement ratio and curing temperature. That is, the higher curing temperature and the longer curing time, the higher the strength in cement-stabilized soils. The high ratio of water-ta-cement results in a lower strength.

• Journal of the Korean Geotechnical Society
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• v.16 no.4
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• pp.149-156
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• 2000

Sedimentation and self-weight consolidation tests in cylinder and large model tank and field measurement such as settlement and pore water pressure at each layer by wireless automatic instrumentation system were carried out to investigate the behaviour of dredged marine clay fill. The consolidation behaviour for each reclaimed layer was analyzed from these measured data and numerical analysis result using finite strain consolidation theory. It was fond from this study that the consolidation behaviour of dredged clay fill is heavily dependent on the filling process.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.33-43
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• 2002

Recently, as large constructions on the coast increase, an application of a surface layer stabilization method which is one of the improvement methods for dredged soft clay has increased. However, there are few studies about this. The purpose of this study is clarifying characteristics of ultra-soft marine clay and hardening agent. Also, it is verifying an optimal mixture ratio of hardening agent through the laboratory tests according to designed experiments and proving by statistical analysis and pilot tests. Laboratory tests were performed with proper hardening agent and test soil in accordance with the design of experiments. Regression equations between hardening agents materials and unconfined compressive strength were derived from the tests. The applicability of regression equations were also verified by pilot tests. From the test results, it was found that hardening agent materials(cement, slag, fly-ash, inorganic salts, arwin, gypsum etc.) have some effect upon compressive strength. The optimal mixture ratio which satisfies the required compressive strength was derived from the statistical analysis. The effect of ground improvement by cements and hardening agents was confirmed through the pilot tests. This study will suggest data for design or construction criteria of stabilization of surface layer on ultra-soft marine clay.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1435-1440
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• 2009

Geotechnical variability is a complex feature that results from many independent sources of uncertainties, and is mainly affected by inherent variability and measurement errors. This study evaluates the coefficient of variation (COV) of soil properties at Song-do region in Korea for evaluating inherent soil variability. Since soil variability is sensitive to soil layers and soil types, the COVs by soil layers (reclaimed layer and marine layer) and the COVs by soil types (clay and silt) were separately evaluated. It is observed that geotechnical variability of marine layer and clay is relatively smaller than that of reclamation layer and silt.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.499-506
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• 2004

The use of dredged soft marine clay is increasing due to a shortage of coarse material available. This paper presents a stabilization method that can increase shear strength of the surface layer of a dredged clay deposit at dates much earlier than usual. The desiccation of the upper soft 1-2m layer can be accelerated by interrupting water seeping from its bottom with impervious geotextile. Just below the geotextile, enough pervious material is provided so that the underlying deposit can be drained through it. This scheme is proved to be effective through theoretical analysis.

• Geotechnical Engineering
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• v.14 no.6
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• pp.45-56
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• 1998

In order to select a proper ground improvement technology and to assess the quality and rate of improvement in the soft deposits. it is essential to characterize in-situ properties of the soft marine clay layer that may have many thin silt or sand seams. In this paper, both piezocone and flat dilatometer tests were performed to characterize in situ properties of a marine clay. Both tests provided quite similar site classifications, and in both tests the penetration pore water pressure was the better indicator for the classification of marine clay layer, especially in which sand or silt seams are frequently interbedded. Undrained strengths determined by both the cone tip resistance and the excess pore water pressure measured from piezocone were very similar in clayey soil layers. And the untrained strength determined by dilatometer had an approximately average value of undiained strengths obtained from piezocone. In addition, the theoretical time factor that can consider pore pressure dissipation effect during cone penetration may provide a reliable estimation of the coefficient of consolidation, especially for a coastal site which includes many silt or sand fractions or seams.