• Geotechnical Engineering
• /
• v.10 no.4
• /
• pp.119-132
• /
• 1994

Undrained cyclic triaxial tests were performed on silt contained in the sand in order to investigate the effect of silt contents on the liquefaction strength and shear characterist ifs of the sand. As the result of this experiment, the weakest percentage of silt contained in the sand was 30% for all the relative density considered in the test. Also, the same bests were performed to find the effect of cyclic speed applied ranging from 0.1Hz to 5Hz on the liquefaction strength. The more the silt is contained in the sand, the greater the liquefaction strength was affected by cyclic speed, While the silt -containing sand was far less influenced by the cyclic speed than clay containing sand. These results are believed to be caused by the change of pore water pressure of the effective stress path.

• Journal of the Korean Geosynthetics Society
• /
• v.7 no.2
• /
• pp.23-29
• /
• 2008

The purpose of this research is to assess the application of recycled-aggregate that is gained from construction wastes as the material of compaction pile method. At the same time, the development of the new technique rectifies defects of the existing compaction pile method for soft ground improvement. In this research, laboratory chamber tests were carried out analyzing the effect of the soft ground improvement by porous concrete pile using recycled aggregate. Through the results of the laboratory chamber tests, the variations of settlement, excess pore pressure, and increment of the vertical stress with time and the behavior of the composite ground were elucidated.

• Journal of the Korean Geosynthetics Society
• /
• v.7 no.4
• /
• pp.25-36
• /
• 2008

This paper presents the results of numerical investigation on support mechanism of geogrid-encased stone columns for use in soft ground. A number of cases were analyzed using a axial-and 3D stress-pore pressure coupled model that can effectively model construction sequence and drainage as well as reinforcing effects of geogrid-encased stone columns. The results indicated that the geogrid encasement tends to significantly improve the load carrying of a stone column. Also revealed was that such a confinement effect depends on encasement length and stiffness of geogrid. It is also shown that there exist critical encasement length and stiffness of geogrid for a given condition.

• Journal of the Korean GEO-environmental Society
• /
• v.13 no.12
• /
• pp.51-57
• /
• 2012

In this study, numerical analysis was carried out for both partially penetrated SCP(sand compaction pile) and fully penetrated SCP constructed into the ground. Midas GTS was used as a FEM analysis program, which is widely used in geotechnical engineering. For the analysis, ground displacement, effective stress and pore water pressure at the time both just after embankment on the ground and 365days later were compared and analyzed. As the results, the effect regarding partially penetrated SCP was similar to the effect regarding fully penetrated SCP under the bottom of the center of embankment when considering the safety towards shear failure.

• 한국신재생에너지학회:학술대회논문집
• /
• 2010.11a
• /
• pp.76.1-76.1
• /
• 2010

Recently, many efforts to solve the durability problem of PEM fuel cell are carried on constantly. However, despite this attention, durability researches of gas diffusion layer (GDL) are not much reported yet. Generally, GDL of PEM fuel cell experiences three external attacks, which are dissolution of water, erosion of gas flow, corrosion of electric potential. In this study, among these degradation factors, carbon corrosion of electric potential was focused and investigated with accelerated carbon corrosion test. Through the test, it is confirmed that carbon corrosion occurred at GDL, and corroded GDL decreased a performance of operating fuel cell. The property changes of GDL were measured with various methods such as air permeability meter, pore distribution analyzer, thermo gravimetric analyzer, and tensile stress test to discover the effects of carbon corrosion. Carbon corrosion caused not only loss of weight and thickness, but also degradation of mechanical strength of GDL. In addition, to analysis the reason of GDL property changes, a surface and a cross section of GDL were observed with scanning electron microscope. After 100 hours test, the GDL showed serious damage in center of layer.

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

• Computers and Concrete
• /
• v.16 no.6
• /
• pp.847-864
• /
• 2015

This study aimed to develop models of sulfate diffusion and ettringite content profile in cement paste for the predication of the damage behavior in cement paste subject to external sulfate. In the models, multiphase reaction equilibrium between ions in pore solution and solid calcium aluminates phases and the microstructure changes in different positions of cement paste were taken into account. The distributions of expansive volume strain and expansion stress in cement paste were calculated based on the ettringite content profile model. In addition, more sulfate diffusion tests and SEM analyses were determined to verify the reliability and veracity of the models. As the results shown, there was a good correlation between the numerical simulation results and experimental evidences. The results indicated that the water to cement ratio (w/c) had a significant influence on the diffusion of sulfate ions, ettringite concentration profile and expansion properties in cement paste specimens. The cracking points caused by ettringite growth in cement paste specimens were predicted through numerical methods. According to the simulation results, the fracture of cement paste would be accelerated when the specimens were prepared with higher w/c or when they were exposed to sulfate solution with higher concentration.

• Journal of the Korean Geotechnical Society
• /
• v.17 no.6
• /
• pp.235-244
• /
• 2001

Liquefaction may be caused by sudden decrease in the soil strength under undrained conditions. This loss of soil strength is related to the development of excess pore pressures. During this study, fines content affects the maximum and minimum void ratios are investigated. The results of static and cyclic triaxial test on silty saturated sands are presented. These tests are performed to evaluate liquefaction strength and static and cyclic behavior characteristics. The samples are obtained from Saemangeum and drying on air. The main results are summarized as follows : 1) The maximum and minimum void ratio lines follow similar trends. 2) Maximum and minimum void ratios are established at 20~30% fines content. 3) As confining pressures and overconsolidation ratio are increased, the resistance to liquefaction are increased. 4) Instability friction angles are increased with increasing initial relative density. 5) The resistance to liquefaction are decreased with increasing effective stress ratio.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.48 no.6
• /
• pp.69-77
• /
• 2006

In this study, the large scaled model test improved by sand drain was carried out to clarify the internal behavior of the three-dimensional consolidation under different secondary consolidation periods. From the results of model test, the void ratio in the undrained side was lager than in the drained side. In addition, the unconfined compressive strength in the long-term consolidated specimen was larger than that in the short-term consolidated one. It was also found that the unconfined compressive strength was larger in the drained side than in the undrained side. These reasons are considered to be due to the large effective stress by quick pore water pressure dissipation by the short drainage distance in the drained side. Furthermore, in order to investigate the three-dimensional consolidation behavior of clay ground improved by the vertical drain method, the numerical analysis obtained from the three-dimensional elasto-viscous consolidation theory proposed by author (2006) were compared with the test results. It was found that during the three-dimensional consolidation process not only vertical displacement but also radial displacement occurs inside the specimen.

• Geomechanics and Engineering
• /
• v.11 no.3
• /
• pp.421-438
• /
• 2016

Explosions inside transportation tunnels might result in failure of tunnel structures. This study investigated the failure mechanisms of circular cast-iron tunnels in saturated soil subjected to medium internal blast loading. This issue is crucial to tunnel safety as many transportation tunnels run through saturated soils. At the same time blast loading on saturated soils may induce residual excess pore pressure, which may result in soil liquefaction. A series of numerical simulations were carried out using Finite Element program LS-DYNA. The effect of soil liquefaction was simulated by the Federal Highway soil model. It was found that the failure modes of tunnel lining were differed with different levels of blast loading. The damage and failure of the tunnel lining was progressive in nature and they occurred mainly during lining vibration when the main event of blast loading was over. Soil liquefaction may lead to more severe failure of tunnel lining. Soil deformation and soil liquefaction were determined by the coupling effects of lining damage, lining vibration, and blast loading. The damage of tunnel lining was a result of internal blast loading as well as dynamic interaction between tunnel lining and saturated soil, and stress concentration induced by a ventilation shaft connected to the tunnel might result in more severe lining damage.