• Geomechanics and Engineering
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• v.16 no.2
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• pp.151-157
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• 2018

The constrained conditions of roof and floor for the coal pillar affect the strength of coal pillar very seriously. To analyze the influence of rock mass for the roof and floor on the stability of coal pillar comprehensively, one method based on the mechanical method for the composite rock mass was proposed. In this method, the three rock layers of roof, floor and coal pillar are taken as the bedded composite rock mass. And the influence of rock mass for the roof and floor on the elastic core of coal pillar has been analyzed. This method can obtain not only the derived stress by the cohesive constraining forces for the coal pillar, but also the derived stress for the rock mass of the roof and floor. Moreover, the effect of different mechanical parameters for the roof and floor on the stability of coal pillar have been analyzed systematically. This method can not only analyze the stability of strip coal pillar, but also analyze the stability of other mining pillars whose stress distribution is similar with that of the strip coal pillar.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.4
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• pp.443-453
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• 2013

This study aims to evaluate the mechanical behaviors of unsupported rock pillars in a room-and-pillar underground structure by a series of numerical analyses. In addition, rock pillar strengths estimated by a few empirical equations proposed for underground mines are compared with those from numerical analyses. Based on the results from the numerical analysis, the ratio of pillar strength to rock mass strength increases as the ratio of the width of a pillar to its height becomes bigger. It means that higher ratio of pillar width to its height is much more favorable for stabilizing a room-and-pillar underground structure. Especially, unsupported pillar strengths estimated from numerical analyses are higher than rock mass strength when the ratio of pillar width to height is approximately over 1.5. It is also found that the choice of an empirical equation appropriate for a given geometric condition of a pillar is important for its feasible application to the stability analysis of a pillar in the room-and-pillar method.

• Journal of Industrial Technology
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• v.24 no.A
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• pp.139-155
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• 2004

A room and pillar mining method has been adopting at the Jeungsun limestone mine. To check stability of pillar with multiple and irregular openings, the size, shape and spacing of rib pillar were first designed using some empirical suggestions. The Finite Difference Method(FDM)was used to analyze the pillar stability. Twelve different cases with the variation of K(horizontal/vertical stress)values, different height and different spacing of pillar were used in this study. Finally Mohr-Coulomb criterion was adopted to calculate the safety factors. Horizontal and vertical displacement, maximum and minimum principal stresses, range of plastic zone and safety factors were calculated at each case. As a result of analysis, the size of one block is 160m long, 70m wide, 40m high with 20m wide rib pillar and 20m square column pillar. The overall recovery at this case can be estimated about 40%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.3
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• pp.1002-1007
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• 2012

The manufacturing method of the pillar is one of the main process where it is used in vacuum glazing and semi-conductor display field. Pillar can be arranged by screen printing method. However it may unable to spread all pattern of metal mask according to the ingredient of the mixture. In addition, spreaded mixture doesn't maintain the original shape according to the viscosity. In this research, the pillar tried to be arranged through the screen printing by using the inorganic compound of the alumina and silica base. This study suggested a method in which it can decrease the test frequency and design the composition of the vacuum glass pillar by using the mixture design.

• Tunnel and Underground Space
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• v.30 no.3
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• pp.226-241
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• 2020

The stability of underground mine cavity is closely related with pillar strength. The vulnerability of pillars can be judged and reinforced if the pillar strength is known. The pillar strength is affected by characteristics of discontinuities and shape of a pillar. The change of pillar strength due to a discontinuity passing through the center of a pillar, width-to-height ratio of a pillar and small joints existing within a pillar was analyzed using PFC 3D. The result showed that the pillar strength is influenced by dip angle of a discontinuity and it increases as width-to-height ratio of a pillar increases. The pillar strength decreases as the number of contained joints increases. The relationship between total trace length observable from the pillar surface and the pillar strength was regressed with exponential function. The correlation coefficient of the regression was high enough so that pillar strength can be predicted using total trace length if a joint set exists in a pillar. Lastly, the method to estimate the strength of a pillar that includes two joint sets was proposed if the joint dip angles are 60°, 30°. The method also need total trace lengths of two joint sets.

• Explosives and Blasting
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• v.35 no.3
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• pp.1-8
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• 2017

In this paper, parametric studies are conducted to evaluate the contribute effect of multi layered room and pillar mine structures by underground accidental explosions. Influence of PPV(Peak Particle Velocity) obtained from large explosion at a multi layered room and pillar mine was numerically simulated by using AUTODYN. Parameters for contribution rate Analysis was analyzed by the robust design method. Orthogonal array is $L_9(3^4)$, which was adopted in this study, the parameters were pillar height, pillar width, mine span and sill pillar of 3 levels. Results of analysis showed that bottom mine of vertical direction from explosion point are most affected by pillar height, followed by sill pillar thickness, mine span and pillar width. Parameters affecting adjacent mine of horizontal direction from explosion are in the order of pillar width, mine span, pillar height and sill pillar thickness.

• Geomechanics and Engineering
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• v.30 no.2
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• pp.107-121
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• 2022

Coal pillar assessment is of broad importance to underground engineering structure, as the pillar failure can lead to enormous disasters. Because of the highly non-linear correlation between the pillar failure and its influential attributes, conventional forecasting techniques cannot generate accurate outcomes. To approximate the complex behavior of coal pillar, this paper elucidates a new idea to forecast the underground coal pillar stability using combined unsupervised-supervised learning. In order to build a database of the study, a total of 90 patterns of pillar cases were collected from authentic engineering structures. A state-of-the art feature depletion method, t-distribution symmetric neighbor embedding (t-SNE) has been employed to reduce significance of actual data features. Consequently, an unsupervised machine learning technique K-mean clustering was followed to reassign the t-SNE dimensionality reduced data in order to compute the relative class of coal pillar cases. Following that, the reassign dataset was divided into two parts: 70 percent for training dataset and 30 percent for testing dataset, respectively. The accuracy of the predicted data was then examined using support vector classifier (SVC) model performance measures such as precision, recall, and f₁-score. As a result, the proposed model can be employed for properly predicting the pillar failure class in a variety of underground rock engineering projects.

• Journal of IKEEE
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• v.25 no.2
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• pp.344-349
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• 2021

This paper proposes a structure in which Trench SiO₂ is grown inside of Super Junction IGBT P-Pillar. When observing the electric field in 3D, we checked the region where the electric field have not affected inside of the P-Pillar. The pillar region's portion resistance is varied by the breakdown voltage and size of each pillar, which reduces the size by growing SiO₂ after trenching has no field effect inside of that. At 4.5kV the same breakdown voltage, it was confirmed that the On-state voltage drop improved by about 58%, 19% compared to Field Stop IGBT and conventional Super Junction IGBT.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.6
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• pp.585-597
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• 2013

In this study, in order to evaluate stability of the room-and-pillar underground structure, a series of preliminary numerical analyses were performed. Design concept and procedure of an underground structure for obtaining a space are proposed, which should be different from structural design for the room-and-pillar in mine. With assumed material properties, a series of numerical analyses were performed by varying size ratios of room and pillar and then the failure modes and location at yielding initiation were investigated. From the results, relationship between the ratio of pillar width to the roof span (w/s) and overburden pressure at failure initiation shows a relatively linear relation, and the effect of w/s on structural stability is much more critical than the ratio of pillar width and height (w/H) which is a crucial parameter in design of the room-and-pillar mining. It means that roof tensile failure and shear failure at shoulder and pillar are necessary to be considered together for confirming overall structural stability of the room-and-pillar structure, rather than considering the pillar stability only in mining. Failure modes and location at failure initiation were varied with respect to the ratio of room and pillar widths. Therefore, it is necessary to simultaneously consider stability of both roof span and pillar for design of underground structure by the room-and-pillar method.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.3
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• pp.27-32
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• 2010

For the flip chip joints processed using Cu pillar bumps and Sn pads, thermal cycling and high temperature storage reliabilities were examined as a function of the Sn pad height. With increasing the height of the Sn pad, which composed of the flip chip joint, from 5 ${\mu}m$ to 30 ${\mu}m$, the contact resistance of the flip chip joint decreased from 31.7 $m{\Omega}$ to 13.8 $m{\Omega}$. Even after thermal cycles of 1000 times ranging from $-45^{\circ}C$ to $125^{\circ}C$, the Cu pillar flip chip joints exhibited the contact resistance increment below 12% and the shear failure forces similar to those before the thermal cycling test. The contact resistance increment of the Cu pillar flip chip joints was maintained below 20% after 1000 hours storage at $125^{\circ}C$.