• Journal of the Korean Geotechnical Society
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• v.34 no.10
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• pp.61-74
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• 2018

In this study, the pull-out behavior of tunnel type anchorage of suspension bridges was analyzed based on results from laboratory size model tests and numerical analysis. Tunnel type anchorage has found its applications occasionally in both domestic and oversea projects, therefore design method including failure mode and safety factor is yet to be clearly established. In an attempt to improve the design method, scaled model tests were conducted by employing simplified shapes and structure of the Ulsan grand bridge's anchorage which was the first case history of its like in Korea. In the model tests, the anchorage body and the surrounding rocks were made by using gypsum mixture. The pull-out behavior was investigated under plane strain conditions. The results of the model tests showed that the tunnel type anchorage underwent wedge shape failure. For the verification of the model tests, numerical analysis was carried out using ABAQUS, a finite element analysis program. The failure behavior predicted by numerical analysis was consistent with that by the model tests. The result of numerical analysis also showed that the effect of Poisson's ratio was negligible, and that a plugging type failure mode could occur only when the strength of the surrounding rocks was 10 times larger than that of anchorage body.

• The Journal of Engineering Geology
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• v.23 no.4
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• pp.457-465
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• 2013

We integrated and correlated datasets from surface and subsurface geophysics, drilling cores, and engineering geology to identify geological interfaces and characterize the joints and fracture zones within the rock mass. The regional geometry of a geologically weak zone was investigated via a fence projection of electrical resistivity data and a borehole image-processing system. Subsurface discontinuities and intensive fracture zones within the rock mass are delineated by cross-hole seismic tomography and analyses of dip directions in rose diagrams. The dynamic elastic modulus is studied in terms of the P-wave velocity and Poisson's ratio. Subsurface discontinuities, which are conventionally identified using the N value and from core samples, can now be identified from anomalous reflection coefficients (i.e., acoustic impedance contrast) calculated using a pair of well logs, comprising seismic velocity from suspension-PS logging and density from logging. Intensive fracture zones identified in the synthetic seismogram are matched to core loss zones in the drilling core data and to a high concentration of joints in the borehole imaging system. The upper boundaries of fracture zones are correlated to strongly negative amplitude in the synthetic trace, which is constructed by convolution of the optimal Ricker wavelet with a reflection coefficient. The standard deviations of dynamic elastic moduli are higher for fracture zones than for acompact rock mass, due to the wide range of velocities resulting from the large numbers of joints and fractures within the zone.

• Journal of the Mineralogical Society of Korea
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• v.21 no.2
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• pp.183-192
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• 2008

Stone cultural heritages in Korea are mostly situated out door without any notable protection thus there are severe damage from chemical and biological weathering. This in turn, causes deformation and structural damage. To counter act this problem and to increase durability, various kinds of conservation materials are used in the conservation and restoration treatment. However, there are not many practical and technological experiment done on this subject. This paper attempts quantitative evaluation of effectiveness of ethylsilicate based resin for Namsan granite in Gyeongju. When two different materials with different ethylsilicate concentration were compared, the result indicated decrease of absorption and porosity with increase of ultrasonic velocities, uniaxial compressive strength, elastic constant, tensile strength and Poisson's ratio. In addition, comparison of physical characteristic of the conservation material resulted favorably toward ones with higher concentration of ethylsilicate. This is due to the ethylsilicates characteristic to fill the internal pores of stone. There is discolouration of stone surface after treatment with conservation material. This was more prominent with the product of higher ethylsilicate concentration.

• The Journal of Engineering Geology
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• v.8 no.2
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• pp.131-143
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• 1998

The study area, Beulgok-myon Nonsan-goon Chungcheongnan-do is consist of Changri slate(Och, okcheon system), lithic tuff(Kslt, kyoungsang system), granite (Kqb, kyoungsang system) and quartz porphyry(Kgf, kyoungsang system). More than 3000 joints were measured and classified by direction. Main dipdirection/dips of Kqb are 228~257/73~88, 010~150/70~85, Och are 134~164/40~90, 214~249/55~89, Kslt are 291~332/75~82, 235~241/73~71. But Kgf are not appeared distinct directions of joint. In field, p-wave velocities(Vp) are measured on the bed rock. Vp of Kgf are $5000m(240^{\circ})~2380(360^{\circ})m/s$, Kqb are $3846(210^{\circ})~1408(150^{\circ})m/s$, Kslt are $5000(360^{\circ})~2323(150^{\circ})m/s$ and Och are $6657(180^{\circ})~2000(030^{\circ})m/s$. Also P-wave velocities on specimen are measured. It is slightely higher than it's measured on the bed rock. For engineering properties of rock, we measured Poisson's ratio, rigidity, Young's modulus and bulk modulus by dynamic method.

• Geophysics and Geophysical Exploration
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• v.16 no.4
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• pp.250-256
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• 2013

Using shear wave velocity is more reasonable to estimate strength and integrity of rock compared with using compressional wave. It is often ambiguous to pick the dominant frequency caused by torsional wave when evaluating $V_S$ of rock specimen from FFRC method. It is also sometimes ambiguous to pick the first arrival point of S wave compared with P wave in the signals acquired from ultrasonic velocity method. Otherwise, the procedure of evaluating $V_P$ using ultrasonic velocity method and $V_L$ using FFRC method is relatively stable. Through the relationship between elastic modulus, poisson's ratio and $V_S$ can be obtained from $V_P$, $V_L$. Applicability was checked using model specimens having different material property and length and rock specimens sampled in mine area, and usefulness of proposed procedure was verified.

• Journal of the Korean Geophysical Society
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• v.3 no.1
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• pp.37-48
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• 2000

In order to investigate in-line ground motions caused by earthquakes, we examine the multicomponent complex trace analysis method (MCTAM) for the synthetic data and apply it to real earthquake data. An experimental result for synthetic data gives correct information on the arrival times, duration of individual phases, and approaching angles for body waves. Rayleigh waves are also easily identified with the MCTAM. A deep earthquake with magnitude of 7.3 was chosen to test various polarization attributes of ground motions. For P waves, instantaneous phase difference between the vertical and the in-line horizontal components ${\phi}(t)$, instantaneous reciprocal ellipticity ${\rho}(t)$, and approaching angle ${\tau}(t)$ are computed to be ${\pm}180^{\circ},\;0{\sim}0.25,\;and\;-30^{\circ}{\sim}-45^{\circ}$, respectively. For S waves, ${\phi}(t)$ tends to vary while ${\rho}(t)$ have values of $0{\sim}0.3\;and\;{\tau}(t)$ remains near vertical, respectively. A relatively low frequency signal registered just prior to the S wave event is interpreted as a P-wave phase based on its polarization characteristics. Velocities of P and S waves are computed to be 8.633 km/s and 4.762 km/s, and their raypath parameters 0.074 s/km and 0.197 s/km. Dynamic Poisson's ratio is obtained as 0.281 from the velocities of P and S waves.

• The Journal of Engineering Geology
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• v.30 no.1
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• pp.31-42
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• 2020

Electrical resistivity and downhole seismic surveys were conducted together with bore investigations and well-logging to examine subsurface structures in small-scale landslides at Sinjindo-ri, Geunheung-myeon, Taean-gun, Chungcheongnam-do, Republic of Korea in 2014. On the basis of the low N-values at depths of 5~7 m in borehole BH-2, downhole seismic and electrical dipole-dipole resistivity surveys were performed to delineate geological weak zones. The low-resistivity zones (<150 Ω·m) measure ~8 m in thickness and show a close depth correspondence to weathered soils consisting mainly of silty clays as identified from the bore investigations and well-logging data. Compared with weak zones in borehole BH-1, weak zones in BH-2 are characterized by lower densities (1.6~1.8 g/㎤) and resistivities (<150 Ω·m) and greater variation in Poisson's ratio. These observations can be explained by the presence of wet silty clays rich in weathered soil material that have resulted from heavy rainfall and rises in groundwater level. Downslope movements are probably caused by the sliding of wet clay that acts to reduce the strength of the weathered soil.

• Journal of the Korea Concrete Institute
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• v.29 no.2
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• pp.149-157
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• 2017

As the amount of construction wastes increase, reuse of recycled materials is being considered in research areas. While there are many experimental investigations focusing on development of mortar and concrete using the recycled materials, the studies regarding the fiber-reinforced cement composites (FRCCs) using recycled materials are still limited. In this paper, an experimental attempt has been made to investigate the effect of recycled fine aggregates and fly ash on the mechanical properties of PVA FRCCs. The cement and natural sand were respectively replaced by fly ash and recycled fine aggregates at two content levels, 25% and 50%. Ten types of PVA FRCCs mixes were fabricated and tested to investigate the flexural, compressive and direct tensile behaviors. The test results show that flexural, compressive and direct tensile strength were decreased with increase in fly ash content at all ages. In particular, flexural, compressive and direct tensile strengths of specimens, containing 50% recycled fine aggregates and 50% fly ash, showed the lowest values. The modulus of elasticity of specimens showed similar trend to the 28-day compressive strength. Poisson's ratio was increased with increase in fly ash and recycled fine aggregates content.

• Journal of the Korean Ceramic Society
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• v.50 no.3
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• pp.206-211
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• 2013

The effect of a $WO_3$ or $Ga_2O_3$ addition on the densification, phase evolution, optical reflectance, and elastic and dielectric properties of $Y_2O_3$-doped AlN ceramics sintered at $1800^{\circ}C$ for 3 h is investigated. The investigated compositions of the additives are 4.5 wt% $Y_2O_3$ (YA), 3.5 wt% $Y_2O_3$-1.0 wt% $Ga_2O_3$ (YGA), and 3.5 wt% $Y_2O_3$-1.0 wt% $WO_3$ (YWA). $YAlO_3$ and $Y_4Al_2O_9$ form as the secondary phases in all of the investigated compositions, whereas $W_2B$ appears additionally in the YWA. In the YGA, Ga is detected in the AlN grains, indicating that the dissolution of $Ga_2O_3$ into the AlN lattice occurs. The addition of $WO_3$ blackens the specimen more significantly than that of $Ga_2O_3$ does. In all of the investigated specimens, the linear shrinkage and the apparent density are above 20 percent and in the range of 3.34-3.37 $g/cm^3$, respectively. The elastic modulus, Poisson's ratio, the dielectric constant, and the dielectric loss are in the ranges of 335-368 GPa, 0.146-0.237, 8.60-8.63, $2.65-3.95{\times}10^{-3}$, respectively. The sinterability and the properties of $Y_2O_3$-doped AlN ceramics are not much altered by the addition of $WO_3$ or $Ga_2O_3$.

• The Journal of Engineering Geology
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• v.30 no.2
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• pp.161-173
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• 2020

This study is to examine the engineering characteristics of colunmar joints in Mudeugsan National Park, a global geopark. For these purposes, physical and mechanical properties of Mudeungsan Tuff, evaluation for the weathering degree of columnar joints, and crack behavior monitoring in columnar joints were conducted. The physical properties of Mudeungsan tuff were 1.02% for the average porosity, 0.38% for the average absorption, 2.69 g/㎤ for the average specific gravity, and 4,948 m/s for the average elastic wave velocity. Its mechanical properties were 337 MPa for the average uniaxial compressive strength, 68 GPa for the average elastic modulus, 0.29 for the average Poisson's ratio, 41.3 MPa for the average cohesion strength, and 62.8° for the average friction angle. the average rebound Q-value of the silver Schmidt hammer for the three columnar joint blocks at the Ipseok-dae was shown as 49.3. when this value is converted into uniaxial compressive strength, it becomes 70.5 MPa, which is about 21% of the uniaxial compression strength of Mudeungsan tuff. In addition, according to the results of crack monitoring measurements for the three columnar joint blocks at the Ipseok-dae, the crack behavior is less than 1 mm, so it is believed that its behavior in Ipseak-dae columnar joints has hardly occured to date.