• Tunnel and Underground Space
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• v.20 no.5
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• pp.344-351
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• 2010

Slip along a frictional fracture can be approached as initiation and propagation of a mode II crack along its own plane. Fracture mechanics theories predict that under pure mode II loading initiation will occur when the energy release rate of the fracture attains a critical value ($G_{IIC}$), which is generally taken as a material property. For the past few years the rock mechanics group at Purdue University has investigated experimentally the dependence of $G_{IIC}$ on normal stress and on the frictional characteristics of a fracture. A number of experiments has been conducted first on acrylic, a material that, using photoelastic methods, allows visualization of the stress field ahead of the fracture tip; and later on gypsum, a rock model material with relatively low unconfined compression strength. The experimental investigation has been expanded to include other frictional materials with higher unconfined compression strength. Direct shear tests have been conducted on specimens made with cement paste. New observations together with previous experiments indicate that $G_{IIC}$ can only be considered a material property when the peak friction angle of the discontinuity is similar to the residual friction angle; otherwise the critical energy release rate increases with normal stress.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.4 s.74
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• pp.429-440
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• 2006

This paper comprises two specific objectives. The first is to examine the applicability of ordinary kriging interpolation(OK) to the p-adaptivity of the finite element method that is based on variogram modeling. The second objective Is to present the adaptive procedure by the hierarchical p-refinement in conjunction with a posteriori error estimator using the modified S.P.R. (superconvergent patch recovery) method. The ordinary kriging method that is one of weighted interpolation techniques is applied to obtain the estimated exact solution from the stress data at the Gauss points. The weight factor is determined by experimental and theoretical variograms for interpolation of stress data apart from the conventional interpolation methods that use an equal weight factor. In the p-refinement, the analytical domain has to be refined automatically to obtain an acceptable level of accuracy by increasing the p-level non-uniformly or selectively. To verify the performance of the modified S.P.R. method, the new error estimator based on limit value has been proposed. The validity of the proposed approach has been tested with the help of some benchmark problems of linear elastic fracture mechanics such as a centrally cracked panel, a single edged crack, and a double edged crack.

• Journal of Soil and Groundwater Environment
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• v.10 no.4
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• pp.33-44
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• 2005

On the basis of a stepwise and careful integration of various field and laboratory methods the analysis of groundwater flow characterization was performed with five boreholes (BH-1, -2, -3, -4, -5) on a pilot site of Natural Forest Park in Guemsan-gun, Chungcheongbook-do, Korea. The regional lineaments of NW-SE are primarily developed on the area, which results in the development of many fractures of NW-SE direction around boreholes made in the test site for the study. A series of surface geological survey, core logging, geophysical logging, tomography, tracer tests, and heat-pulse flowmeter logging were carried out to determine fracture characteristics and fracture connectivity between the boreholes. In the result of fracture connectivity analysis BH-1 the injection well has a poor connectivity with BH-2 and BH-3, whereas a good with BH-4 and BH-5. In order to analyse the hydraulic connectivity between BH-1 and BH-5, in particular, a conspicuous groundwater outflux in the depth of 12 m and influx in the depth of 65 m and 70 m, but partly in/outflux occurred in other depths in BH-5 were observed as pumping from BH-1. On the other hand, when pumping from BH-5 the strong outflux in the depths of 17 m and 70 m was occurred. The spatial connectivity between the boreholes was examined in the depth of 15 m, 67 m, and 71 m in BH-1 as well as in the depth of 15 m, 17 m, 22 m, 72 m, and 83 m in BH-5.

• Tunnel and Underground Space
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• v.9 no.4
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• pp.315-327
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• 1999

Rock fracture mechanics has been widely applied to blasting, hydraulic fracturing, rock slope and many other practical problems in rock engineering. But a measuring method for the fracture toughness of rock, one of the mort important parameters in fracture mechanics as an intrinsic property of rock, has not been yet well established. To obtain mode I rock fracture toughness, the more favorable disc-typed specimens such as CCNBD, SCB, chevron-notched SCB and BDT were used in this study. Rock fracture toughness under mixed-mode and mode II conditions was measured by using the STCA applied to the CCNBD specimen. Size effects such as specimen thickness, diameter and notch length on fracture toughness were investigated. From the mixed-mode results, fracture envelops were obtained by applying various regression curves. The mixed-mode results were also compared with three mixed-mode failure criteria. In each fracture toughness test, acoustic emission was measured to get the data for determining the load levels of different crack propagation patterns.

• Korean Journal of Materials Research
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• v.10 no.8
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• pp.551-557
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• 2000

Cu-based leadframe sheets were oxidized ic a hot alkaline solution to black-oxide layer on the surface and molded with epoxy molding compound(EMC), and finally machined to form sandwiched double-cantilever beam(SDCB) and sandwiched Brazil-nut(SBN)specimers to measure the adhesion strength of leadframe-EMC interface. The SDCB and the SBN specimens were designed to measure the adhesion strength in terms fracture toughness under puasi-mode I and mixed mode loadinf, respectively. After the tests, fracture surfaces were analyzed paths were observed in the SDCB-tested speciments, failure paths varied with crack speed and loading conditions.

• Magazine of the Korea Concrete Institute
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• v.11 no.2
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• pp.167-175
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• 1999

Many composite girder bridges have been constructed for about thirty five years. Nowadays they are aged or deteriorated because of the increase in traffic and vehicle loads. In this study, the effect of strengthening with glass fiber sheet is investigated to estimate the possibility for applying to damaged prestressed concrete bridges. One normal and eight cracked specimens which had been preloaded were tested. The cracked specimens were strengthened with either external prestressing or bonding glass fiber sheet, or using both methods. The results showed that the maximum loads are almost same for both methods. So it seems that the strengthening with glass fiber sheet can be used for strengthening damaged prestressed concrete girders. It is important that proper devices should be selected to prevent glass fiber sheet from premature bonding failure below its maximum load, which is similar to end anchorage problem in external prestressing method. It is proved that the devices proposed in this paper have sufficient anchoring capability to increase load carrying capacity.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.6
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• pp.612-617
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• 2001

A nondestructive evaluation technique for detecting internal defects of an hot forged Al-Si alloy part is established in this study. Ultrasonic characteristics of various internal planar defects are investigated by experiments for establishing a reliable test procedure. The effect of the angle between ultrasonic energy propagation directions and planar defects on the ultrasonic signal configuration is evaluated in the pulse-echo technique. A characteristic of ultrasonic signal for the internal planar defect located near the edge is also evaluated. The applicability of the through-transmission technique is also discussed. Reliability of the presented approach is validated by the destructive testing for more than 500 specimens.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.1
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• pp.105-116
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• 2002

In this paper, an analytical model to predict the resisting capacity of slender RC columns is introduced. Material and geometric nonlinearities are taken into account, and the layer approach is adopted to simulate the different material properties across the sectional depth. On the basis of the obtained numerical analysis results, an improved design equation as a function of concrete strength, slenderness ratio, steel ratio and eccentricity for slender RC columns, which can be used effectively in the preliminary design stage, is introduced. Finally, P-M interaction diagrams constructed by the introduced equation are compared with the ACI method with the objective of establishing the relative efficiencies of the introduced equation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.3
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• pp.602-607
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• 2009

Most of explorer robot in past has the fixed magnitude and communicate with wire communication method. In case of various range of pipe's width and various angle in pipe inter structure, the exploring work is very difficult. Thus, in this paper, we design as dealing with spring tension with pushing out pipe exterior, and applied RF communication. We can accept good performance both structure change and improvement of ability, monitor and collect the defaults data in pipe inter structure. Newly designed and developed pipe explorer robot is very advantageous to carrying and driving as being small and law weight.

• The Journal of Engineering Geology
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• v.22 no.1
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• pp.59-65
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• 2012

The purpose of this study is to analyze the direction of slope sliding that occurred at the highland ${\bigcirc}{\bigcirc}$ district in the Samcheok coalfield, using geological and structural detail surveys. The study area is dominated by the Paleozoic Pyong-an Group, and sliding is concentrated in zones of alternating sandstone and shale beds in the Geumcheon and Jangsung Formations. Discontinuities in the area have a strike of NE-SW and dip at 30~$80^{\circ}$ to the NW and 40~$80^{\circ}$ to the SE. However, some have strikes of NW-SE. In slide area group 1 (P1 to P4), en echelon tension gashes were caused by shearing. The surface in the areas of group 2 (P5 to P7) and group 3 (P8 and P9) is marked by step-type tension cracks that formed due to extension. This phenomenon caused anticlockwise rotation of the sliding slope. Otherwise, the cutting of the road side through the eastern slope of the mountain contributed to surface sliding due to geographical equilibrium loss.