• The Journal of Engineering Geology
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• v.24 no.1
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• pp.111-122
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• 2014

For accurate laboratory evaluations of soil deposits, it is essential that the samples are undisturbed. An artificial ground-freezing system is the one of the most effective methods for obtaining undisturbed samples from sand deposits. The objective of this study is to estimate the shear strengths and the characteristics of elastic waves of frozen-thawed and unfrozen specimens through the undrained triaxial compression test. For the experiments, Jumunjin standard sands are used to prepare frozen and unfrozen specimens with similar relative densities (60% and 80%). The water pluviation method is used to simulate the fully saturated condition under the groundwater table. When thawing the frozen specimens, the temperature is measured every minute. After the specimens are completely thawed, undrained triaxial compression tests are conducted using the same procedures as for the unfrozen specimens. During the triaxial tests (saturation, consolidation, and shear phase), compressional and shear waves are measured. The results show that the freeze-thaw process has minor effects on the peak deviatoric stress and shear strength values, and that the process does not affect the internal friction angle. The compressional wave velocity increases with increasing B-value to 1800 m/s in the saturation phase, but tends to remain constant in the process of consolidation and shearing. The shear wave velocity decreases with increasing B-value in the process of saturation, but changes velocity in accordance with the change in effective stress in the processes of consolidation and shearing. The compressional wave velocity has similar values regardless of the freeze-thaw process, but values of shear wave velocity are slighly lower in frozen-thawed specimens than in unfrozen specimens. This study is a preliminary experiment for estimating the shear strength and characteristics of elastic wave velocity in undisturbed frozen specimens that have been obtained using the artificial ground-freezing method.

• Journal of the Korean Magnetics Society
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• v.15 no.3
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• pp.191-197
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• 2005

In the fabrication process of Fe-based amorphous alloy powder cores by pulverization of the melt-spun ribbons and cold compaction, the effects of powder preparation method on the magnetic & electric properties, powder shapes and microstructure of cores have been investigated. The powder cores made by using rotor mill showed low effective permeability as compared to the cores prepared by ball milling. However the frequency dependence and quality factor properties were superior in the case of rotor-milling. Further the powders prepared by rotor mill had homogeneous and round shapes through strong shearing in the sieve ring, while the ball milled powders were inhomogeneous and relatively small. The lower permeability of the powder cores fabricated with rotor mill was considered to be due to the high internal stress occurred by very intensive shearing. Moreover the powder cores produced by rotor-milling showed lower core loss and good frequency dependence of effective permeability possibly due to the higher electrical insulation between magnetic particles. The dc bias property of the powder cores made by rotor-milling was better than the one by ball-milling.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.247-256
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• 2003

FEM analyses which are based on modified Cam-clay theory have been generally used in such cases as analyses of stability and displacement fur embankment construction on soft clays. However, the Modified Cam Clay Model can generate some problems in anisotropic stress conditions of field because the critical state theory has been developed through many laboratory tests in isotropic conditions. Thus, the applicability on the prediction of undrained shear strength and pore water pressure which was based on the critical state theory was evaluated by triaxial tests and numerical analyses in isotropic and anisotropic conditions. Used samples often come out in domestic area, together with general low plastic clays which are showing dilatant behavior in shearing process. They were evaluated by laboratory tests and FEM based on MCCM. From the results of test and numerical analysis, the predictions of undrained strength in low plastic clays well coincided with each other in both isotropic and anisotropic conditions. However, the generation of porewater pressure was often overestimated during undrained shearing in anisotropic conditions. The results can generate the errors in the prediction of stress path of field sites during loading such as construction of embankment on soft clays because the field is subjected to anisotropic conditions during loading.

• Tunnel and Underground Space
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• v.29 no.5
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• pp.292-304
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• 2019

Limestone joint surfaces with smooth roughness were experimented by means of both the individual direct shear tests based on the KSRM standard test method and the multi-stage direct shear test to apply the stepwise vertical stresses. Changes in the roughness of the joint surfaces before and after the shear tests were examined and the difference between the two kinds of tests mentioned above was analyzed. In both tests, the shear resistance increased as the joint roughness increased and the maximum shear stress required for shearing the joint surface increased as the vertical stress increased. The peak friction angle obtained by the multi-stage direct shear tests was only 63% of that obtained by the individual direct shear tests. In the multi-stage direct shear test, the initial engagement of the concave-convex parts changes frequently during stepwise shearing process, which deforms the original roughness of a joint surface. Accordingly, the individual direct shear test is thought to be more effective when obtaining the friction angle of the rock joint surfaces. Limestone joint surfaces with smooth roughness of JRC value 4~8 were found to have peak friction angle of $47^{\circ}$, residual friction angle of $38^{\circ}$ and cohesion of 37 kPa.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.5
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• pp.320-333
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• 2019

In this study, a physics-based 3D morphology model for the estimation of an erosion rate of nourished beach is newly proposed. As a hydrodynamic module, IHFOAM toolbox having its roots on the OpenFoam is used. On the other hand, the morphology model comprised a transport equation for suspended sediment, and Exner type equation derived from the viewpoint of sediment budget with the bed load being taken to accounted. In doing so, the incipient motion of sediment is determined based on the Shields Diagram, while the bottom suspended sediment concentration, the bed load transport rate is figured out using the bottom shearing stress directly calculated from the numerically simulated flow field rather than the conventional quadratic law and frictional coefficient. In order to verify the proposed morphology model, we numerically simulate the nonlinear shoaling, breaking over the uniform beach of 1/m slope, and its ensuing morphology change. Numerical results show that the partially skewed, and asymmetric bottom shearing stresses can be successfully simulated. It was shown that sediments suspended and eroded at the foreshore by wave breaking are gradually drifted toward a shore and accumulated in the process of up-rush, which eventually leads to the formation of swash bar. It is also worth mentioning that the breaker bar formed by the sediments dragged by the back-wash flow which commences at the pinnacle of up-rush as the back-wash flow gets weakened due to the increased depth was successfully duplicated in the numerical simulation.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.3
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• pp.6-14
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• 2014

Touch panels are widely used in the modern display industry as the cover glass of smart mobile phones and tablet PCs. Glass cutting machines are commonly used to cut the panels into their proper sizes. Vibration of these glass cutting machines is assumed to be the main factor leading to the creation of burrs, notches, cracks, scratches and chips on the cut surfaces, eventually causing defects of the cover glass. In this study, the vibrations of a glass cutting machine used for the shearing of cover glass components were analyzed through an experiment and a computer simulation. The structural properties leading to vibration were also analyzed in an effort to determine design alterations which can suppress these vibrations. Moreover, each design alteration was applied to a computer simulation model to determine the effect of different alteration on suppressing vibration. The results show that simple design alterations can substantially suppress vibrations of glass cutting machines.

• Journal of the Korea Concrete Institute
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• v.23 no.1
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• pp.57-65
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• 2011

Both shear and torsional moments apply shear stresses on cross-section of a member, which need to be considered in the design. But in the current Korean Building Code, the design equations for shear and torsional moments are expressed in terms of the sectional strength with different units, causing figures to be drawn separately in two axes. If the design equations are expressed in terms of stresses, then the stresses of shear and torsional moments can be added, allowing figures to be drawn in one axis for easy recognition of the design procedure and the final design results. Moreover, the current code's design equations for shear and torsional moments are considered separately with the intention of summing the area of stirrups with respect to unit length for shear moment ($A_{\upsilon}/s$) and torsional moment ($2A_t/s$). Since the size or type of vertical stirrups are predetermined in the design process, the design equations are expressed in terms of the spacing of stirrups rather than the $A_{\upsilon}/s$ and $2A_t/s$ terms, clarifying various design steps and a design process.

• Korean Journal of Food Science and Technology
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• v.31 no.4
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• pp.1011-1016
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• 1999

This study was performed to search a physical method having high yield and quality and minimum environmental pollution for extraction of pectin from apple pomace. Based on the physical solubilization of plant cell wall under the condition of high temperature, pressure and shearing stress, apple pomace was treated by a corotating intermeshing type twin-screw extruder with the diameter-to-length ratio of 1/20. The specific mechanical energy of extruder was introduced as system parameter for extrusion process modeling and the shaft speed, feed rate and moisture content as process variables. The yield, average molecular weight and galacturonic acid content of water-soluble polysaccharides obtained by extrusion were, respectively, modeled with the linear functions of the system parameter which was of the form as a linear function of process variables. The specific mechanical energy increased with increase of shaft speed and with decrease of feed rate and moisture content. Out of process variables, moisture content had the greatest effect on specific mechanical energy. The yield increased with increase of specific mechanical energy while the average molecular weight and galacturonic acid content increased with its decrease. In aspects of yield and quality of pectin, the results from this study showed the possibility to replace a traditional acidic method with the extrusion treatment of this study.

• Tunnel and Underground Space
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• v.26 no.2
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• pp.68-86
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• 2016

Understanding the frictional properties of rock discontinuities is crucial to ensure the stability of underground structures. In particular, the frictional behavior at depth depends on the complex interaction among mechanical, hydraulic, thermal and chemical characteristics and their coupled effects. In this study, a series of shear tests were carried out in a triaxial compression chamber to investigate the shearing behavior of saw-cut granite surface and rough shear surface of synthetic rocks. The test results were analyzed using Coulomb's shear strength criterion. The frictional behavior of saw-cut granite surface showed little variation at different confining, water pressures and temperature conditions, however in case of synthetic rocks, the frictional behavior showed different trend depending on normal stress level. In addition, the variation of stiffness and dilation at different testing conditions were analyzed, and the stiffness and dilation showed little variation at different water pressures and temperature conditions.

• Geomechanics and Engineering
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• v.22 no.6
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• pp.529-540
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• 2020

Water inrush is a major hazard for mining and excavation in deep coal seams or rock masses. It can be attributed to the coalescence of rock fractures in rock mass due to the interaction of fractures, hydraulic flow and stress field. One of the key technical challenges is to understand the course and mechanism of fluid flows in rock joint networks and fracture propagation and hence to take measures to prevent the formation of water inrush channels caused by possible rock fracturing. Several case observations of fluid flowing in rock joint networks and coupled fracture propagation in underground coal roadways are shown in this paper. A number of numerical simulations were done using the recently developed flow coupling function in FRACOD which simulates explicitly the fracture initiation and propagation process. The study has demonstrated that the shortest path between the inlet and outlet in joint networks will become a larger fluid flow channel and those fractures nearest to the water source and the working faces become the main channel of water inrush. The fractures deeper into the rib are mostly caused by shearing, and slipping fractures coalesce with the joint, which connects the water source and eventually forming a water inrush channel.