• Journal of the Korean Geotechnical Society
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• v.24 no.7
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• pp.5-16
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• 2008

Most of roadway tunnels have been constructed in the form of parallel twin tunnel in Korea. If parallel twin tunnel does not have a sufficient separation distance between tunnels, the problem of tunnel stability can occur. Generally, it is reported that tunnels are not influenced by each other when a center distance between tunnels is two times longer than tunnel diameter under the complete elastic ground and five times under the soft ground. In this study, the scaled model tests of closely-spaced parallel twin tunnel using homogeneous material are performed and induced displacements are measured around the tunnel openings during excavation. The influence of separation distance between tunnels on the behavior of closely-spaced tunnel is investigated. The experimental results are expressed by the induced displacement vector and progress of crack during construction and at failure. The results show that based on the analysis of induced displacement at the crown during construction, the additional displacement of the preceding tunnel induced by the excavation of following tunnel decreases as the separation distance between twin tunnel increases until the center to center distance is two times of tunnel diameter. Beyond this point, however, the additional displacement has become stabilized.

• Journal of the Korean Geotechnical Society
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• v.20 no.8
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• pp.135-145
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• 2004

In this study, the behavior of unpropped diaphragm walls on decomposed granite soil was investigated through centrifugal and numerical modelling. Centrifuge model tests were performed by changing the interval distance of surcharge. Excavation was simulated during the centrifuge tests by operating a solenoid valve that allowed the zinc chloride solution to drain from the excavation. In these tests, ground deformation, wall displacement and bending moment induced by excavation were measured. FLAC program which can be able to apply far most geotechnical problems was used in the numerical analysis. In numerical simulation, Mohr-Coulomb model fur the ground model, an elastic model for diaphragm wall were used for two dimensional plane strain condition. From the results of model tests, failure surface was straight line type, the ground of retained side inside failure line had downward displacement to the direction of the wall, and finally the failure was made by the rotation of the wall. The angle of failure line was about 67 ∼ 74$^{\circ}$, greater than calculated value. The locations of the maximum ground settlement obtained from model tests and analysis results are in good agreements. The displacement of wall and the change of the embedment depth is likely to have linear relationship.

• Journal of Korean Tunnelling and Underground Space Association
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• v.4 no.1
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• pp.27-35
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• 2002

For the excavation of the rock, blast method is put into operation in most of the construction site in Korea. In comparison to other methods of excavation, blast method has many merits such as improvement in efficiency in operation, reducement of operation period, and etc. However, blast operation also creates much loss due to the blast vibration, noise, and fly rocks. Thus, in this study, we have examined main features, rock fragmentation effect and the application of plasma method the one of shallow vibration method. In this study, the attenuation exponent of blast method operated in the site was 1.39~1.40 and that of the plasma method was analysed to be 1.45~2.23. From the location where the distance between excavation location and observation location was over 15 m, most of excavation vibration were measured to be less than 0.2 kine(cm/sec), which is also the allowed standard value of sensitive buildings, such as cultural assets and computer facilities. According to the result of FFT(Fast Fourier Transform) analysis, the frequency measured through blast method in this site was 30~50 Hz and the frequency of plasma method ranges in between 30~130 Hz.

• The Journal of Engineering Geology
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• v.32 no.4
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• pp.725-733
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• 2022

This study applied a hydraulic rock splitting system equipped with a hybrid packer to the bench-cut method. The hybrid packer system is an improvement of the packer developed in previous studies; it is designed efficiently to reduce vibration and noise during rock excavation by combining the two functions of inducing hydraulic fractures using injection pressure and then expanding and extending them using a rubber packer. Field experiments assessed the efficiency of rock excavation with respect to the injection conditions; the adjusted experimental conditions included the distance from the free surface and the test holes drilled at the top of the slope and the injection settings. Using a separation of 5 m left some unexcavated parts, but using a separation of 1 m left no unexcavated parts. The hydraulic fractures generated by the injection pressure developed generally parallel to the free surface and expanded and extended as the rubber packer expanded, thus facilitating bench-cut excavation. For hydraulic rock splitting to be broadly applicable to bench-cut rock excavation, it is important to accumulate results from many field experiments conducted under varying experimental conditions for various types of rockmass.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.1
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• pp.59-78
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• 2024

In tunnel construction, the stability is evaluated by the settlement of adjacent structures and ground, but the shear strain of the ground is the main factor that determines the failure mechanism of the ground due to the tunnel excavation and the change of the operating load, and can be used to review the stability of the tunnel excavation and to calculate the reinforcement area. In this study, a twin tunnel excavation was simulated on a soft ground in an urban area through a laboratory model test to analyze the behavior of the twin tunnel excavation on the adjacent pile grouped foundation and adjacent ground. Both the displacement and the shear strain of ground were obtained using a close-range photogrammetry during laboratory model test. In addition, two-dimensional finite element numerical analysis was performed based on the model test. The results of a back-analysis showed that the maximum shear strain rate tends to decrease as the horizontal distance between the pillars of the twin tunnel and the vertical distance between the toe of the pile group and the crown of the tunnel were decreased. The impact of the second tunnel on the first tunnel and pile group was decreased as the horizontal distance between the pillars of the twin tunnel was increased. In addition, the vertical distance between the toe of the pile group and the crown of the tunnel had a relatively greater impact on the shear strain results than the horizontal distance of the pillars between the twin tunnels. According to the results of the close-range photogrammetry and numerical analysis, the settlement of adjacent pile group and adjacent ground was measured within the design criteria, but the shear strain of the ground was judged to be outside the range of small strain in all cases and required reinforcement.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.6
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• pp.1105-1123
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• 2018

The main risk factors of tunnel excavation through urban areas are ground settlement and surface sink which caused by ground conditions, excavation method, groundwater condition, excavation length, support method, etc. In the process of ground settlement assessment, the numerical analysis should be conducted considering the displacement and stress due to tunnel excavation. Therefore a technique that can simplify such process and easily evaluate the influence of tunnel excavation is needed. This study focused on the tunnelling-induced ground settlement which is main consideration of underground safety impact assessment. The parametric numerical analyses were performed considering such parameters as ground conditions, tunnel depth, and lateral distance from tunnel center line, etc. A simplified ground settlement evaluation chart was suggested by analyzing tendency of ground subsidence, lateral influence area and character by depth. The applicability of the suggested settlement evaluation chart was verified by comparative numerical analysis of settlement characteristics.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.5
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• pp.395-409
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• 2022

To overcome the limitation of conventional rock excavation methods, the excavation with abrasive waterjet has been actively developed. The abrasive waterjet excavation method has the effect of reducing blasting vibration and enhancing the excavation efficiency by forming a continuous free surface on the rock. However, the waterjet cutting performance varies with rock fracturing characteristics. Thus, it is necessary to analyze the cutting performance for various rocks in order to effectively utilize the waterjet excavation. In this study, cutting experiments with the high pressure waterjet system were performed for basalt and granite specimens. Water pressure, standoff distance, and traverse speed were determined as effective parameters for the abrasive waterjet cutting. The cutting depth and width of basalt specimens were analyzed to compare with granite results. The averaged cutting depth of basalt was shown in 41% deeper than granite; in addition, the averaged cutting width of basalt was formed by 18.5% narrower than granite. The results of this study are expected to be useful basic data for applying rock excavation site with low strength and high porosity such as basalt.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.189-198
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• 2008

Lots of roadway tunnel have been almost constructed in forms of closely-spaced tunnel in korea. If closely-spaced tunnel is not constructed at a sufficient distance between tunnels, the problem of stability can occur. However, the case that can not secure a sufficient distance between tunnels can occur due to a difficulty in buying a lot and an issue of popular complaint and environmental disruption. Generally, tunnels are not influenced by each other when a center distance between tunnels is two times longer than tunnel diameter under the complete elastic ground and five times under the soft ground. In this study, the scaled model tests of closely-spaced tunnel by using homogeneous material were performed and induced displacements were measured around the tunnel openings during excavation. The influence of distance between tunnels on the behavior of closely-spaced tunnel was investigated.

• Tunnel and Underground Space
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• v.4 no.3
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• pp.256-260
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• 1994

HLW canister array was designed by FLLSSM program, considering the thermal concentration. Rock properties were chosen as those of granite, the most possible bedrock for the repository in Korea. It was shown that repository area and excavation volumes can be determined by the pitch or distance between canisters. Pitch can be reduced to 0.6 m assuming the tolerance temperature as 200$^{\circ}C$. Thermal concentration was reduced as storage time for cooling the canister passed. After 10 years of storage the thermal problems seemed to be negligible.

• Geotechnical Engineering
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• v.6 no.3
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• pp.5-12
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• 1990

In this paper, ground vibration and other properties measurements were conducted to deter mine empirical equation based on careful test blasting with crawler drill(diameter 70-75mm). The empirical euqations for ground vibration are obtained as follows where V is peak particle velocity in cm 1 sec, D is distance in m and W is maximum charge weight per delay in kg