• Journal of the Korean Recycled Construction Resources Institute
• /
• v.5 no.4
• /
• pp.421-426
• /
• 2017

In this paper, the effect of freezing-thawing action on the dynamic modulus and porosity was examined by ultrasonic pulse velocity (UPV) measurement. UPV was measured every 30 cycles during the freezing-thawing test, and dynamic modulus and porosity of cement mortar were calculated by relationship among UPV, porosity and dynamic modulus. Porosity analysis was also performed to compare with calculated porosity by mercury intrusion porosimetry (MIP). From the test, it was found that dynamic modulus of cement mortar was decreased 13% after 300 cycles. The calculated porosity was increased about 30% compared with the initial porosity before freezing-thawing action. The calculated porosity showed similar increase tendency with the porosity measured by MIP. So, it can be concluded that the porosity change of cementitious materials by freezing-thawing action can be predicted by UPV measurement.

• Journal of Mechanical Science and Technology
• /
• v.15 no.7
• /
• pp.1032-1040
• /
• 2001

It is widely accepted that the pressure variation of interstitial fluid is one of the most important factors in bone physiology. In order to understand the role of interstitial fluid on porous bony structure, a consideration for the biomechanical interactions between fluid and solid constituents within bone is required. In this study, a poroelastic theory was applied to investigate the elastic behavior of calf vertebral trabecular bone composed of the porous solid trabeculae and the viscous bone marrow. The poroelastic behavior of trabecular bone in a uniaxial stress condition was simulated using a commercial finite difference analysis software (FLAC, Itasca Consulting Group, USA), and tested for 5 different strain rates, i.e., 0.001, 0.01, 0.1, and 10 per second. The material properties of the calf vertebral trabecular bone were utilized from the previous experimental study. Two asymptotic poroelastic responses, the drained and undrained deformations, were predicted. From the predicted results for the simulated five strain rates, it was found that the pore pressure generation has a linearly increasing behavior when the strain rate is the highest at 10 per second, otherwise it showed a nonlinear behavior. The pore pressure generation with respect to the strain was found to be increased as the strain rate increased. The elastic moduli predicted at each strain were 208.3, 212.2, 337.6, 593.1, and 602.2 MPa, respectively. Based on the results of the present study, it was suggested that the calf vertebral trabecular bone could be modeled as a poroelastic material and its strain rate dependent material behavior could be predicted.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.20 no.2
• /
• pp.95-103
• /
• 2007

An analytical closed-form solution for wave propagation velocity and damping in saturated porous media is presented in this paper The fully coupled field model with compressible solid Brains and pore water were used to derive this solution. An engineering approach for the analysis of fully saturated porous media was adopted and closed-form solutions for one dimensional wave propagation in a homogeneous domain were derived. The solution is highly versatile in that it considers compression of the solid grains, compression of the pore water, deformation of the porous skeleton, and spatial damping and can be used to compute wavespeeds of first and second kind and damping coefficients in various geologic materials. This solution provides a means of analyzing the influence of material property variations on wavespeed and attenuation. In Part 2 of this work the theoretical solution is incorporated into the numerical code and the code is used in a parametric study on wave propagation velocity and damping.

• Journal of the Korea Concrete Institute
• /
• v.25 no.6
• /
• pp.675-682
• /
• 2013

In this study, to enhance the quality of concrete surface by removing the surplus water, permeable liner attached the euroform was applied for manufacturing concrete specimens. Various kinds of concrete mixtures with different water to binder ratios were applied and the strength properties of the hardened concrete surfaces were evaluated at different heights. Experimental results showed that the rebound values by schmidt hammer test and the compressive strengths on the surfaces of concrete specimens were increased as proportion to the amount of mixture water which is dependent on the water to binder ratio of each concrete mixture, and more enhancements were observed on the middle and lower specimen surfaces than the upper region. SEM analysis also showed that much denser hydrate structures were observed on the specimen surfaces by the application of the permeable liner while similar hydrate formations were occurred regardless of surface treatment conditions. From the MIP test results of the concrete surfaces, it was observed that, by the application of permeable liner, the pore volume below $0.01{\mu}m$ was decreased with a maximum of 50% resulting in the densification of pore structures.

• Journal of the Korean Geotechnical Society
• /
• v.29 no.1
• /
• pp.13-22
• /
• 2013

This paper presents the results of a numerical investigation into the behavior of retaining wall subject to cycles of wetting and drying due to rainfall. The stress-pore pressure coupled finite element modeling strategy was first established for stimulating the wall behavior. A series of finite element analyses were then performed on a range of conditions including different rainfall and backfill conditions. The results indicated that the rainfall intensity was the primary influencing factor for the wall behavior. Also revealed was that the pre-rainfall condition determines the magnitudes and the distribution of matric suction which in fact has a significant impact on the behavior of wall during a major rainfall. This result demonstrates the importance of incorporating the pre-rainfall condition for numerical modeling of walls during heavy rainfall. Practical implications of the findings from this study are discussed in great detail.

• Journal of the Korean Geotechnical Society
• /
• v.33 no.4
• /
• pp.5-15
• /
• 2017

Three-hinge failure occurs in a jointed rock slope with a joint set parallel with slope and a conjugate joint set. Limit Equilibrium Method (LEM) and Finite Element Method (FEM) which are commonly used for slope design, are not suitable for evaluating stability against three-hinge failure, and this study performed parametric study to analyze the failure mechanism and to find influence factors causing three-hinge failure using UDEC which is a commercial two-dimensional DEM based numerical program. Numerical analyses were performed for various joint structural conditions and joint properties as well as ground water conditions. It was found that pore water pressure is the main factor triggering the three-hinge failure and the mode of failure depends on friction angle of basal joint and bedding joint set. The results obtained from this study can be used for adequate and economic footwall slope reinforcement design and construction.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.18 no.1
• /
• pp.53-60
• /
• 2016

This study analyzed a monitoring data, based on the initial limit values of monitoring in subway, of earth pressure and pore water pressure. The data is obtained from 8 sections of the Seoul metropolitan subway line No 6, 7 and 9 in about 5 years. Also, a research is performed to set up the limit values of management monitoring, which will be applied to management monitoring in tunnel, through comparing the limit values of overseas management monitoring data and that of domestic management monitoring data. And the result obtained from comparison show that the safety phase is 60% of allowable pressure, the attention phase is 80% of allowable pressure and the precision analysis phase is 100% of allowable pressure. Also, we presented a method of management monitoring by the absolute value which can be easily applied easily in practical affairs.

• Geomechanics and Engineering
• /
• v.22 no.4
• /
• pp.319-328
• /
• 2020

This paper investigates the effect of the width of failure and tension crack (TC) on the stability of cohesive-frictional soil slopes in three dimensions. Working analytically, the slip surface and the tension crack are considered to have spheroid and cylindrical shape respectively, although the case of tension crack having planar, vertical surface is also discussed; the latter was found to return higher safety factor values. Because at the initiation of a purely rotational slide along a spheroid surface no shear forces develop inside the failure mass, the rigid body concept is conveniently used; in this respect, the validity of the rigid body concept is discussed, whilst it is supported by comparison examples. Stability tables are given for fully drained and fully saturated slopes without TC, with non-filled TC as well as with fully-filled TC. Among the main findings is that, the width of failure corresponding to the minimum safety factor value is not always infinite, but it is affected by the triggering factor for failure (e.g., water acting as pore pressures and/or as hydrostatic force in the TC). More specifically, it was found that, when a slope is near its limit equilibrium and under the influence of a triggering factor, the minimum safety factor value corresponds to a near spherical failure mechanism, even if the triggering factor (e.g., pore-water pressures) acts uniformly along the third dimension. Moreover, it was found that, the effect of tension crack is much greater when the stability of slopes is studied in three dimensions; indeed, safety factor values comparable to the 2D case are obtained.

• Journal of The Korean Society of Integrative Medicine
• /
• v.7 no.4
• /
• pp.223-230
• /
• 2019

Purpose : Wellness tourism is defined as travel for the purpose of promoting health and well-being through physical, psychological, or spiritual activities. The development and verification of a comprehensive wellness program for health care for workers is needed. The purpose of this study is to investigate the wellness and skin health effects of skin health programs in order to develop high-value health care services. Methods : The subjects were 15 middle-aged women who understood the research and volunteered and participated in the two-day skin health wellness program. Participants were measured to determine their wellness index and skin health twice: before and after participating in the program. Wellness index measures include comprehensive wellness, physical wellness, mental wellness, emotional wellness, social/cultural wellness, financial wellness, and environmental wellness. Skin health measurement items consisted of skin oil, skin water, skin pore, skin elasticity, skin wrinkle, and skin pigment. The skin wellness program included aerobic exercise, endurance exercise, functional food, cosmetics, herbal tea, massages, spa treatments, meditation, and marine leisure sports. The t-test analysis was used to compare the difference between wellness index and skin health measurement items before and after the program. Results : Among the wellness index items, the comprehensive wellness index (p<.05), mental wellness index (p<.05) and environmental wellness index (p<.05) showed statistically significant differences. Among skin health items, skin oil (p<.05), skin elasticity (p<.01) and skin wrinkle (p<.01) all showed statistically significant differences. There was no statistically significant difference in physical wellness, emotional wellness, social/cultural wellness, financial wellness, skin water, skin pore and skin pigment. Conclusion : This study confirmed that the two-day complex wellness program is an effective program for some items of wellness index and skin health.

• Korean Journal of Materials Research
• /
• v.23 no.12
• /
• pp.722-726
• /
• 2013

Freeze drying of a porous Cu-Sn alloy with unidirectionally aligned pore channels was accomplished by using a composite powder of CuO-$SnO_2$ and camphene. Camphene slurries with CuO-$SnO_2$ content of 3, 5 and 10 vol% were prepared by mixing with a small amount of dispersant at $50^{\circ}C$. Freezing of a slurry was done at $-25^{\circ}C$ while the growth direction of the camphene was unidirectionally controlled. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green bodies were hydrogen-reduced at $650^{\circ}C$ and then were sintered at $650^{\circ}C$ and $750^{\circ}C$ for 1 h. XRD analysis revealed that the CuO-$SnO_2$ powder was completely converted to Cu-Sn alloy without any reaction phases. The sintered samples showed large pores with an average size of above $100{\mu}m$ which were aligned parallel to the camphene growth direction. Also, the internal walls of the large pores had relatively small pores. The size of the large pores decreased with increasing CuO-$SnO_2$ content due to the change of the degree of powder rearrangement in the slurry. The size of the small pores decreased with increase of the sintering temperature from $650^{\circ}C$ to $750^{\circ}C$, while that of the large pores was unchanged. These results suggest that a porous alloy body with aligned large pores can be fabricated by a freeze-drying and hydrogen reduction process using oxide powders.