• Tunnel and Underground Space
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• v.17 no.5
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• pp.389-410
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• 2007

For moderately jointed to massive rock masses, the failure and deformation behaviors around an excavated opening are absolutely influenced by the initial rock stress and strength of in-situ rock mass. The localized and progressive brittle failure around an opening does not mean whole collapse of an excavated opening. But, for many cases, it may induce temporary stopping of excavation works and reexamination of the current supporting system, which can result in delay of the entire construction works and additional construction cost. In this paper, the characteristics of the brittle failure around an opening with stress level and tunnel shape was studied by the biaxial compressive test using scaled specimen and by the numerical simulation with $PFC^{2D}$. The biaxial test results were well coincided with the stress induced failure patterns around the excavated openings observed and monitored in the in-situ condition. For the circular part of the opening wall, the stress induced cracks initially occurred at the wall surface in the direction of the minimum principal stress and contributed to the localized notch shaped failure region having a certain range of angle. But for the corner and straight part of the opening wall, the cracks initiated at sharp corners were connected and coalesced each other and with existing micro cracks. Further they resulted in a big notch shaped failure region connecting two sharp corners.

• Economic and Environmental Geology
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• v.41 no.2
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• pp.201-210
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• 2008

The mixing treatment process using lime (CaO) and limestone ($CaCO_3$) as the immobilization amendments was applied for heavy metal contaminated filmland soils around Goro abandoned Zn-mine, Korea in the batch and pilot scale continuous column experiments. For the batch experiments, with the addition of 0.5 wt.% commercialized lime or limestone, leaching concentrations of As, Cd, Pb, and Zn from the contaminated filmland soil decreased by 70, 77, 94, and 95 %, respectively, compared to those without amendments. For the continuous pilot scale column experiments, the acryl column (30 cm in length and 20 cm in diameter) was designed and granulated lime and limestone were used. From the results of column experiments, with only 2 wt.% of granulated lime, As, Cd, and Zn leaching concentrations decreased by 63%, 97%, and 98%, respectively. With 2 wt.% of granulated limestone, As leaching concentration reduced from 135.6 to 30.2 ${\mu}g/L$ within 5 months and maintained mostly below 10 ${\mu}g/L$, representing that more than 46% diminution of leaching concentration compared to that without the amendment mixing. For Cd and Zn, their leaching concentrations with only 2 wt.% of limestone mixing decreased by 97%, respectively compared to that without amendment mixing, suggesting that the capability of limestone to immobilize heavy metals in the filmland soil was outstanding and similar to that of lime. From the column experiments, it was investigated that if the efficiency of limestone to immobilize heavy metals from the soil was similar to that of lime, the limestone could be more available to immobilize heavy metals from the soil than lime because of low pH increase and thus less harmful side effect.

• Journal of Dental Rehabilitation and Applied Science
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• v.28 no.2
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• pp.147-161
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• 2012

This study is to assess the effect of horizontal misfit of an implant supported 3-unit fixed prosthodontics on the stress development at the marginal cortical bone surrounding implant neck. Two finite element models consisting of a three unit fixed prosthodontics and an implant/bone complex were constructed on a three dimensional basis. The three unit fixed prosthodontics were designed either shorter (d=17.8mm model) or longer (d=18.0mm model) by 0.1mm than the span of two implants placed at the mandibular second premolar and second molar areas 17.9mm apart. Fitting of the fixed prosthodontics onto the implant abutments was simulated by a total of 6 steps, that is to say, 0.1mm displacement per each step, using DEFORM 3D (ver 6.1, SFTC, Columbus, OH, USA) program. Stresses in the fixed prosthodontics and implants were evaluated using von-Mises stress, maximum compressive stress, and radial stress as necessary. The d=17.8mm model assembled successfully on to the implant abutments while d=18.0mm model did not. Regardless if the fixed prosthodontics fitted onto the abutments or not, excessively higher stresses developed during the course of assembly trial and thereafter. On the marginal cortical bone around implants during the assembly, the peak tensile and compressive stresses were as high as 186.9MPa and 114.1MPa, respectively, even after the final sitting of the fixed prosthodontics (for d=17.8mm model). For this case, the area of marginal bone subject to compressive stresses above 55MPa, equivalent of the $4,000{\mu}{\varepsilon}$, i.e. the reported threshold strain to inhibit physiological remodeling of human cortical bone, extended up to 2mm away from implant during the assembly. Horizontal misfit of 0.1mm can produce excessively high stresses on the marginal cortical bone not only during the fixed prosthodontics assembly but also thereafter.