• Geomechanics and Engineering
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• v.22 no.4
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• pp.329-337
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• 2020

Polyacrylamide (PAM) possesses high water absorption capacity and a unique pH-dependent behavior that confer large potential to enhance the engineering performance of clays. In this study, calcium bentonite was treated with a nonionic PAM. Flexible-wall permeability test and the consolidation test were performed at different pH values to evaluate the effects of PAM treatment on the hydraulic and consolidation properties. Test results demonstrate that index properties are affected by the adsorbed PAM on clay surface: a decrease in specific gravity, a decrease in net zeta potential, and an increase in liquid limit are observed due to the PAM treatment. At a given pH, the compressibility of the treated clay is greater than that of the untreated clay. However, the compression indices of untreated and treated clays can be expressed as a single function of the initial void ratio, regardless of pH. Hydraulic conductivity is reduced by PAM treatment about 5 times at both neutral and alkaline pH conditions under similar void ratios, because of the reduction in size of the water flow channel by PAM expansion. However, at acidic pH, the hydraulic conductivity of the treated clay is slightly higher than the untreated clay. This reflects that the treated bentonite with PAM can be beneficially used in barrier system for highly alkaline residues.

• Journal of the Korean Geotechnical Society
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• v.27 no.9
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• pp.37-46
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• 2011

The compression index, which represents the compressibility of clay, is generally obtained from the consolidation test, or has been predicted by empirical correlations with soil properties. In this study, the results of consolidation tests on natural and reconstituted Busan and Inchon clays are analyzed to figure out the sedimentation state and its effect on empirical correlations. Results of analysis show that the void index of Busan clay is higher than SCL while the void index of Inchon clay is lower than SCL. By comparing prediction errors with ${\Delta}e_r$, which represents the sedimentation state of clay, it is shown that errors predicting the compressibility based on the liquid limit and plasticity index decrease as ${\Delta}e_r$ increases. Supplemented correlations predicting the compression index of Busan and Inchon clays are suggested using these relationships.

• Journal of the Korean Geotechnical Society
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• v.27 no.5
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• pp.5-15
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• 2011

Recent increase of large scale construction near costal area has also increased the application of soft ground treatment. As a result, solidification with cement and lime which increases stability and durability of soils, is frequently used for surface layer stabilization in soft ground site. While stabilization of very soft clay with high plasticity and compressibility has widely been studied, studies on silty clay with low plasticity and compressibility are relatively rare. In this study, after stabilizing low plasticity silty clay of Songdo area with cement and lime under various water contents, mixing ratio, and curing time, uniaxial compression test and plate load test were performed. Strength properties from both tests were considerably consistent. And trackability of construction equipment on the treated surface layer of dredged land was estimated. Finally, optimum mixing condition for Songdo silty clay was proposed.

• Geomechanics and Engineering
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• v.18 no.3
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• pp.299-313
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• 2019

This research investigated the nonlinear compressibility, permeability, the yielding due to structural degradation and their effects on consolidation behavior of structured soft soils. Based on oedometer and hydraulic conductivity test results of natural and reconstituted soft clays, linear log (1+e) ~ $log\;{\sigma}^{\prime}$ and log (1+e) ~ $log\;k_v$ relationships were developed to capture the variations in compressibility and permeability, and the yield stress ratio (YSR) was introduced to characterize the soil structure of natural soft clay. Semi-analytical solutions for one-dimensional consolidation of soft clay under time-dependent loading incorporating the effects of soil nonlinearity and soil structure were proposed. The semi-analytical solutions were verified against field measurements of a well-documented test embankment and they can give better accuracy in prediction of excess pore pressure compared to the predictions using the existing analytical solutions. Additionally, parametric studies were conducted to analyze the effects of YSR, compression index (${\lambda}_r$ and ${\lambda}_c$), and permeability index (${\eta}_k$) on the consolidation behavior of structured soft clays. The magnitude of the difference between degree of consolidation based on excess pore pressure ($U_p$) and that based on strain ($U_s$) depends on YSR. The parameter ${\lambda}_c/{\eta}_k$ plays a significant role in predicting consolidation behavior.

• Geomechanics and Engineering
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• v.21 no.5
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• pp.413-422
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• 2020

The choice of eco-friendly materials for ground improvement is a necessary way forward for sustainable development. Adapting naturally available biopolymers will render the process of soil stabilization carbon neutral. An attempt has been made to use β-glucan, a natural biopolymer for the stabilization of lean clay as a sustainable alternative with specific emphasis on comprehending the effect of confining stresses on lean clay through triaxial compression tests. A sequence of laboratory experiments was performed to examine the various physical and mechanical characteristics of β-glucan treated soil (BGTS). Micro-analysis through micrographs were used to understand the strengthening mechanism. Results of the study show that the deviatoric stress of 2% BGTS is 12 times higher than untreated soil (UTS). The micrographs from Scanning Electron Microscopy (SEM) and the results of the Nitrogen-based Brunauer Emmett Teller (N₂-BET) analysis confirm the formation of new cementitious fibres and hydrogels within the soil matrix that tends to weld soil particles and reduce the pore spaces leading to an increase in strength. Hydraulic conductivity (HC) and compressibility reduced significantly with the biopolymer content and curing period. Results emphases that β-glucan is an efficient and sustainable alternative to the traditional stabilizers like cement, lime or bitumen.

• 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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• 2000.11a
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• pp.303-310
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• 2000

A new stress path testing scheme with back pressure equalization process is proposed, to compute the settlement of clay soils based on their probable deformation mode. The proposed testing scheme minimizes the efforts for testing, otherwise numerous testing works are required to simulate the probable stress paths in the field. Furthermore, the proposed testing scheme can supply anisotropic stress paths for consolidation which cannot be possible in a conventional way. The validity and effectiveness of the proposed testing scheme was investigated and confirmed with test results on remolded kaolinite clay soils. Conclusively, it is suggested that the proposed testing scheme is a very effective tool to compute settlement of clay soils and it is also very useful to investigate the anisotropic characteristics of deformation of clay soils.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.1
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• pp.183-194
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• 2004

It's essential process to study non-linear material function related to characteristics of compressibility and permeability when we predict the consolidation behavior of soft clay ground. In this study, laboratory tests were conducted to find out the material function using marine clay. Standard oedometer test and Rowe cell test were performed with conditions, which were classified into vertical drainage only, radial drainage only and vertical-radial drainage case. Modified oedometer test equipment was developed to find out the material function and special extrusion device was originated to minimize the sample disturbance effect. Reliability of the results in modified oedometer test could be confirmed by comparing with the Rowe cell's one. Effective stress - void ratio - permeability relations were analyzed using all testing results. As a result, void ratio with effective stress level could be expressed by the power function and permeability with void ratio could be expressed by exponential function. In soft clay with high initial water content and low shear strength, non-linear characteristics related to compressibility and permeability varied with wide range by the effective stress levels. It's important to note that non-linearity of the material function should be considered at prediction of the consolidation behavior.

• Geomechanics and Engineering
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• v.20 no.6
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• pp.505-516
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• 2020

In recent years, Nano-technology significantly invaded the field of Geotechnical engineering, particularly in soil stabilisation techniques. Stabilisation of weak soil is envisioned to modify various soil characteristics by the addition of natural or synthetic materials into the virgin soil. In the present study, laboratory experiments were executed to investigate the influence of nano-silica particles in the consistency limits, compressive strength of the soft clay blended with cement. The results revealed that the high compressibility behaviour of soft clay modified to medium-stiff condition with fewer dosages of cement and nano-silica. The mechanism behind the strength development is verified with the previous researches as well as from Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction test (XRD) and Scanning Electron Microscopy (SEM) analysis. Based on the results, the presence of nano-silica in soft clay blended with cement has a positive effect on the behaviour of soil. This technique proves to be very economical and less detrimental to the environment.

• Geomechanics and Engineering
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• v.20 no.6
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• pp.537-546
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• 2020

Oil and natural gas reserves have been recognised abundantly in clayey rich rock formations in deep costal reservoirs. It is necessary to understand the sedimentary history of those reservoir rocks to well explore these natural resources. This work designs a group of laboratory experiments to mimic the physical process of the sedimentary clay-rich rock formation. It presents characterisation results of the physical properties of the artificial clayey rocks synthesized from illite clay, quartz sand and brine water by high-pressure consolidation tests. Special focus is given on the effects of illite clay content and high-stress consolidation on the physical properties. Multi-step loaded consolidation experiments were carried out with stress up to 35 MPa on mixtures constituting of the illite clay, quartz sand and brine water with five initial illite clay contents (w=85%, 70%, 55%, 40% and 25%). Compressibility and void ratio were characterised throughout the physical compaction process of the mixtures constituting of five illite clay contents and their water permeability was measured as well. Results show that the applied stress induces a great reduction of clayey rock void ratio. Illite clay contents has a significant influence on the compressibility, void ratio and the permeability of the physically synthesized clayey rocks. There is a critical illite clay content w=70% that induces the minimum void ratio in the physically synthesised clayey rocks. The SEM study indicates, in the high-pressure synthesised clayey rocks with high illite clay contents, the illite clay minerals are located in layers and serve as the material matrix, and the quartz minerals fill in the inter-mineral pores or are embedded in the illite clay matrix. The arrangements of the minerals in microscale originate the structural anisotropy of the high-pressure synthesised clayey rock. The test findings can give an intuitive physical understanding of the deep-buried clayey rock basins in energy reservoirs.