• The Journal of Engineering Geology
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• v.28 no.2
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• pp.297-312
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• 2018

In order to assess the safety diagnosis and grouting reinforcement effect of old reservoir facility, local governments and public offices mainly use electrical resistivity survey. However, electrical resistivity survey is a qualitative evaluation that varies the resistivity value by various exploration conditions. It is also difficult to grasp the stiffness change directly related to the stability of reservoir, thus an electrical resistivity survey is not applicable to continuous stability monitoring after grouting. The purpose of this study is to investigate and validate the quantitative evaluation of reinforcement effect of reservoir with cement grouting through shear velocity (Vs), which is closely related to the stiffness (${\mu}$) of the ground. This study was carried out on two reservoir facilities. The reinforcement effect was evaluated by comparing the permeability test, standard penetration test, down-hole test and MASW(Multi-channel Analysis of Surface wave) survey before and after cement grouting. Shear wave velocity changes before and after grouting were analyzed by phase velocity difference and inversion analysis, respectively, and the reliability of the analytical results was evaluated by comparing with field test results. Shear wave velocity increases to 5~10% in case of the D levee, and 10~20% in the levee of H reservoir. These results are showed similar pattern to the field test results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.2
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• pp.175-181
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• 2020

This paper suggests a proper hydraulic filling method in downtown areas. Road subsidence on roadways and sidewalks in downtown areas can result in vehicle damage and casualties. The representative cause of road subsidence is the fraudulent construction in nearby construction sites. A deficiency of excavation restoration causes approximately 25~49% of subsidence. This is performed by equipment or manpower. Hydraulic filling is used in backfilling narrow pipe conduits and spaces between structures. On the other hand, standard specifications and quality assurance standards regarding hydraulic filling principles and construction conditions are insufficient. Therefore, in-door model experiments on hydraulic filling principles, backfilling material, and compaction efficiency were performed. This paper suggests guidelines by investigating and analyzing construction status. In conclusion, thrown backfilling material has a particle size distribution and permeability coefficient as major factors, and detailed standards of the factors are suggested. To improve the compaction efficiency, 90% or more, compaction by the floor should be in units of 0.3m while ensuring a lower drainage layer. When an H-shape stabilizing pile is pulled out after filling, additional hydraulic filling should be in the disturbance range.

• Journal of Korean Tunnelling and Underground Space Association
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• v.2 no.3
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• pp.25-36
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• 2000

The purpose of this research work is to propose an analytical method of tunnel design based on reasonable site data. Therefore the proposed design method consists of monitoring data and Modified In Situ Rock Model. Also the Rock Mass Rating for very poor quality rock is very difficult to estimate, the balances between the ratings may no longer gives a reliable basis for the rock mass strength. But in reality Rock Mass Rating is only the property which can be obtained from face mapping records of the exposed tunnel face during construction stage. Evaluation of rock parameters for the actual design prior to tunnel construction should be corrected during tunnelling process in particularly complex ground conditions. This study intends to investigate application of in-situ rock model to soft rock tunnelling (weathered rock) by face mapping results and site measurement data that are obtained at the costraction site of Seoul Subway Tunnel. For the preparation of more reliable ground parameters, the Rock Mass Rating values for the weathered rocks were modified and readjusted in accordance with the measurement data. The modified input parameters obtained by the proposed method are used for the prediction of the tunnel behavior at subsequent construction stages. The results of this study revealed that more reasonable feed back tunnel analysis can be possible as suggested. Ample measurement data would be able to confirm the new proposed technique in this research work.

• 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 Korean Society for Marine Environment & Energy
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• v.19 no.3
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• pp.218-226
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• 2016

Field observations were used to study the characteristics and influence of groundwater level fluctuations on vegetation development on the natural beach of a sandy barrier island, in the Nakdong River estuary. The spatial/temporal fluctuations of the groundwater level and the interactions with the external forces (weather, ocean wave and tide) were analyzed. The results indicated that when it rains the groundwater level rises. During summer, when precipitation intensity is greater than 20 mm/hour, it rose rapidly over 20 cm. Subsequently, it fell gradually during periods of no precipitation. Seasonal characteristics indicated that the groundwater level was high during the summer rainy season and tended to fall in the winter dry season. The time-averaged groundwater level, observed from the four observations over 3 years (2012-2014), was about 1.47 m, higher than mean sea level (M.S.L.). It was shown that the average annual groundwater level rises toward the land rather than showing intertidal patterns observation. Differences in the presence or absence of a coastal sand dunes affected the progress of vegetation. In other words, in environments of saltwater intrusion where the groundwater level varies, dependent on the distance from the shoreline and bottom slope, sand dunes can be provided to affect soil conditions and groundwater, so that vegetation can be grown reliably.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.9
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• pp.914-923
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• 2009

Helix antennas have been widely applied to satellite TT&C, data communication and GPS receiver systems onboard military, remote sensing and communication purpose satellites. The helix antennas are known to be convenient to control impedance and radiation coverage characteristics with a maximum directivity in satellite z-axis. Waveguide horn is commonly used for radar system that needs ultra-wideband pulse for exploration ground radar and electromagnetic disability measurement etc. It has high efficiency and low reflection characteristics provided by the low-profile shape and suppressed radiation distortion. In this paper, a waveguide horn structure incorporated with helix antenna design is proposed for satellite applications that require ultra-wideband pulse radar and high rate RF data communication link to ground station over wide coverage area. The main design concern is to synthesize variable beam forming pattern based on modified horn-helix combination helicone structure such that multi-mission antenna is implemented applicable for TT&C, earth observation, high data rate transmission. Waveguide horn helps to reduce the overall antenna structure size by introduction fold type reflector connected to the tapered helix antenna. The next generation KOMPSAT satellite currently under development requires high-performance precision attitude control system. We present an initial design of a hybrid hern-helix antenna structure suitable for efficient RF communication module design of multi-purpose satellite systems.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.891-894
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• 2008

This study was performed to investigate how to design, where to construct, why to degrade, what plan to use systematically the underground structures such as underpass, underground passageways. About 50% of the underground structures are located on Seoul, Kyungi-Do. In design of the underground structures such as underpass, underground passageways, the required conditions are defined. And also in construction stage, the conditions of soil, required structure depth, site characteristics, reasonable construction method, are investigated. In the selection of details for underground structure, the items mainly considered, are the wall and column type, the sidewalk type, anchoring-system type, the water-proofing method, entranc shape. The reason and the adequate measures for the degradation of concrete structure are also investigated. The initial cracking properties due to the thermal characteristic are considered. The state of the art report on the new technologies are reviewed. The recent project for the systematically application to the underground structures is reviewed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1529-1539
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• 2013

Recent case studies in Japan have shown that rockbolts are commonly installed at an oblique angle to the excavation direction of the tunnel, instead of at a right angle, due to restriction of the working space. In particular, in the case of expansion in an existing tunnel, the working space can be very small, due to the large protective structures necessary to operate within an existing tunnel. In this case, where both the current use of the existing tunnel, and the reinforcement of the ground around the tunnel are required, the effects of installation angles and patterns of rockbolts are important factors in the design process. Therefore, in this study, a total number of 24 model tests are performed, to investigate the reinforcing effects of system bolting installed obliquely from the excavation direction of the tunnel, by changing the installation angle of bolts, longitudinal distance, and bonded length of bolts. The model test results indicate that the relaxed load ratio decreases, with the increase of both the bonded lengths and the number of the installed bolts, resulting in the decrease of the supported area by one bolt. Two-dimensional numerical analysis, which considered the reinforcement effect of inclined system bolting as the change of engineering properties near the tunnel, demonstrated that the deflection patterns at the tunnel crown in the numerical simulations, show a similar tendency to those measured in the model tests.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1499-1508
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• 2013

Freeze-thaw tests were performed on gneiss samples collected from Terra Nova Bay, Antarctica in order to examine the engineering properties of rocks with slightly weathered (SW) and moderately weathered (MW). The tests were conducted under temperature ranging from $20{\pm}2^{\circ}C$ to $-20{\pm}2^{\circ}C$. A cycle of test consisted of 5 hours of freezing followed by another 5 hours of thawing under full saturation. In this paper, total 200 cycles of freeze-thaw test were performed with measurements of porosity, absorption, ultrasonic velocity, and shore hardness per each 20 cycle and that of uniaxial compressive strength (UCS) per each 50 cycle. The UCS of the SW rocks approximately decreased 0.07 MPa per a single cycle, while that of MW rocks decreased around 0.2 MPa per a single cycle. During the 200 cycles of SW rocks, the absorption increased from 0.23% to 0.39%, the P-wave velocity decreased from 4,054 m/s to 3,227 m/s and S-wave velocity decreased from 2,519 m/s to 2,079 m/s. Similarly, those of MW rocks changed from 0.65% to 1.6%, 3,207 m/s to 2,133 m/s and 2,028 m/s to 1,357 m/s. In conclusion, it was inferred that the properties of SW rocks experienced approximately 200-300 cycles of freeze-thaw process become close to those of MW rocks.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.6
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• pp.597-604
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• 2015

When a tunnel is constructed by drilling and blasting operation, the excavated perimeter becomes uneven due to overbreak at the drill holes so that the thickness of shotcrete tends to be irregular. In this case, the conventional stress analyses for tunnel lining of a uniform thickness cannot be readily applicable. In this study, the profile of tunnel perimeter assumed to be sinusoidal in order to simulate the uneven tunnel perimeter and to control the thickness of shotcrete by using the amplitude and wavelength. By adopting the sinusoidal function to a theoretical solution of stress analysis for uniform lining, the range of axial stress of irregular shotcrete can be estimated. The applicability of the approximate solution has been verified by performing a series of numerical analyses for various conditions. It is shown that the axial stress of shorcrete is highly dependent upon the irregularity of shotcrete, together with the ground property and initial stress conditions. It is also shown the shear stress is dependent upon the wavelength, and the stress condition becomes unfavorable where the thickness of shotcrete is relatively small. The approach developed in this study shows that the stress state where the thickness is relatively small is unfavourable, and it is necessary to take complementary measures when installing shotcrete after blasting.