• Journal of the Korean Geotechnical Society
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• v.22 no.6
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• pp.27-40
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• 2006

Damage of cut-and-cover tunnel lining can be attributed to physical and mechanical factors. Physical factors include material property, reinforcement corrosion, etc. while mechanical factors include underground water pressure, vehicle loads, etc. This study is limited to the modeling of rigid circular cut and cover tunnel constructed at a depth of $1.0{\sim}1.5D$ in loose sandy ground and subjected to a vibration frequency of 100 Hz. In this study, only damages due to mechanical factors in the form of additional loads were considered. Among the different types of additional, excessive earth pressure acting on the cut-and-cover tunnel lining is considered as one of the major factors that induce deformation and damage of tunnels after the construction is completed. Excessive earth pressure may be attributed to insufficient compaction, consolidation due to self-weight of backfill soil, precipitation and vibration caused by traffic. Laboratory tunnel model tests were performed in order to determine the earth pressure acting on the tunnel lining and to investigate the applicability of existing earth pressure formulas. Based on the difference in the monitored and computed earth pressure, a factor of safety was recommended. Soil deformation mechanism around the tunnel was also presented using the picture analysis method.

• Journal of the Korean Geosynthetics Society
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• v.16 no.3
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• pp.21-30
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• 2017

Cement grouting method is generally applied for the purpose of reinforcement of deteriorated reservior. Problems have been raised due to the limit of the injection material. In order to solve these problems, various grout materials have been developed. However, there are many cases in which the grounds are disturbed in actual field. In this study, the physical properties of hybrid grout with high fineness and high viscosity characteristics were analyzed to enable penetration into the ground. Optimum inflation agent was selected and mixed with the grout. The pressure and compaction effect on expansion was examined and its effectiveness was verified. From the result of confirming expansion ratio, uniaxial compressive strength, expansion pressure and compaction effect, the HI-E (2%) sample was analyzed to be excellent in improvement effect by the inflation agent. Hence, hybrid grout can be effectively applied for the impermeable and reinforcement method of deterioration reservoir and tide embankment.

• Journal of the Korean Geotechnical Society
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• v.31 no.3
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• pp.27-38
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• 2015

Triaxial tests on sand-silt mixture specimens under low and high confining pressures were performed to understand their shear behaviors. The fines content in the mixture is lower than the threshold value. A series of tests under different conditions including fines contents (0%, 9.8%, 14.7%, 19.6%), density of specimen (controlled by different compaction energies of $E_c=22kJ/m^3$, $E_c=504kJ/m^3$), confining pressure (100 kPa, 1 MPa, 3 MPa, 5 MPa) were performed to investigate influences of these factors. Based on the test results, the threshold fines content, where the dominant structure of mixture changes from sand-matrix to fines-matrix, decreases with the increase of confining pressure. Under very high confining pressures, as a result of sand particle crushing, the behavior of the dense specimen is similar to that of the loose specimen which shows hardening, compression behavior, and shear strength increases with increase of fines content. In conclusion, silt is granular material like sand, and its influence on shear behavior of sand-silt mixture is very different from that of plastic fines on sand-fines mixture.

• Journal of Powder Materials
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• v.21 no.4
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• pp.256-259
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• 2014

A magnetic powder, M-type barium hexaferrite (BaFe12O19), was consolidated with the spark plasma sintering process. Three different holding temperatures, $850^{\circ}C$, $875^{\circ}C$ and $900^{\circ}C$ were applied to the spark plasma sintering process with the same holding times, heating rates and compaction pressure of 30 MPa. The relative density was measured simultaneously with spark plasma sintering and the convergent relative density after cooling was found to be proportional to the holding temperature. The full relative density was obtained at $900^{\circ}C$ and the total sintering time was only 33.3 min, which was much less than the conventional furnace sintering method. The higher holding temperature also led to the higher saturation magnetic moment (${\sigma}_s$) and the higher coercivity ($H_c$) in the vibrating sample magnetometer measurement. The saturation magnetic moment (${\sigma}_s$) and the coercivity ($H_c$) obtained at $900^{\circ}C$ were 56.3 emu/g and 541.5 Oe for each.

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

• Advances in materials Research
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• v.6 no.1
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• pp.79-91
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• 2017

In the present work, a design of experiment (DOE) technique using Taguchi method, has been applied to optimize the properties of ODS tungsten heavy alloys(WHAs). In this work Taguchi method involves nine experiments groups for four processing parameters (compaction pressure, sintering temperature, binding material type, and oxide type) with three levels was implemented. The signal-to-noise (S/N) ratio and analysis of variance (ANOVA) were employed to obtain the optimal process parameter levels and to analyze the effect of these parameters on density, electrical conductivity, hardness and compressive strength values. The results showed that all the chosen factors have significant effects on all properties of ODS tungsten heavy alloys samples. The density, electrical conductivity and hardness increases with the increase in sintering temperature. The analysis of the verification experiments for the physical properties (density and Electrical conductivity) has shown that Taguchi parameter design can successfully verify the optimal parameters, where the difference between the predicted and the verified values of relative density and electrical conductivity is about 1.01% and 1.15% respectively.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.940-950
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• 2010

In case of uneven surcharge like backfill or embankment after constructing caisson applied on the deep soft marine deposits, lateral deformation of soft soils would happen due to plastic deformation of soil particles by increase of excess pore water pressure. Lateral deformation of soil will result in the caisson displacement which affects soft soil-caisson structure safety. Soft soil was improved by soil compaction pile method, and then gravity caisson was installed. Soil deformations were monitored and analyzed with step by step backfill and embankment behind the caisson. Amount and speed of lateral deformation after the installation of caissons were closely related with the time of backfill and embankment. The relationship between maximum lateral displacement($\Delta_y$) in front of caisson and settlement($\Delta_s$) can be expressed as $\Delta_y=(0.0871)\Delta_s+122.95$. Soft soil depth did not affect the lateral displacement of caisson in this study, which can be explained the soft soil improvement under the caisson by S.C.P. method. Substantially the amount and speed of the lateral deformation of caisson were closely related with the uneven surcharging rate behind caisson.

• Journal of Powder Materials
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• v.20 no.1
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• pp.7-12
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• 2013

The effect of particle size distribution on green and sintered properties of Fe-Cr-Mo prealloy powder was investigated in this study. For the study, prealloyed Fe-Cr-Mo powders with different particle sizes were mixed as various ratios and cold compacted at various pressure and sintered at $1250^{\circ}C$ for 30 min, $90%N_2+10%H_2$ atmosphere in the continuous sintering furnace. The results shows that the powders with large particle size distribution have high compressibility and low ejection force. However the green strength are much less than those with small particle size distribution. Tensile prperties of the sintered specimes with large particles size also have high strength and elongation.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.838-845
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• 2006

Recently construction work in Korea, demands of favorable condition ground had been increased with industrialization acceleration and economic growth. However, because of limited land space, it was so hard to ensure favorable condition grounds that construction work proceeds until soft ground area on plans of road, railroad and industrial complex. In this case, soft ground improvement was required such as a stone column method. Stone column method, making a compaction pile using crushed stone, is a soft ground improvement method. However, stone column method is difficult to apply to the ground which is not mobilized enough lateral confine pressure because no bulging failure resistance. Hence, in present study, evaluates the stone columns reinforced by geogrid for settlement reduction and wide range of application of stone columns. Triaxial compression tests were conducted for evaluation which is about behavior characteristics of stone column on replacement rate. Then, 3-dimensional numerical analysis were conducted for application of stone column reinforced by geogrid as evaluate behavior characteristics and settlement reduction effect of stone column reinforced by geogrid on reinforcing depth change of geogrid.

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.195-200
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• 2006

Laboratory creep experiments show that compaction of unconsolidated shale is an irrecoverable process caused by viscous time-dependent deformation. Using Perzyna's viscoplasticity framework combined with the modified Cam-clay theory, we found the constitutive equation expressed in the form of strain rate as a power law function of the ratio between the sizes of dynamic and static yield surfaces. We derived the volumetric creep strain at a constant hydrostatic pressure level as a logarithmic function of time, which is in good agreement with experimental results. The determined material constants indicate that the yield stress of the shale increases by 6% as strain rate rises by an order of magnitude. This demonstrates that the laboratory-based prediction of yield stress (and porosity) may result in a significant error in estimating the properties in situ.