• The Journal of Engineering Geology
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• v.23 no.1
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• pp.67-77
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• 2013

We conducted a Tunnel Seismic Prediction (TSP) survey in a spillway tunnel at Juam Dam to predict the locations of major discontinuities ahead of the tunnel face. We compared the results of the TSP survey with those from pre-construction inspections (including a surface resistivity survey and borehole investigations) as well as with direct tunnel-face mapping during excavation. The TSP method predicted the locations of major fracture zones that were unnoticed in the pre-construction inspections. The reinforcement patterns planned on the basis of pre-construction inspections were changed on the basis of the TSP results. The results demonstrate that TSP surveys are a cost-effective and reliably accurate method of predicting the locations of fracture zones. Although the TSP method has some limitations, these results suggest that the method is generally useful for predicting geological conditions prior to tunnel face construction.

• Journal of the Korean GEO-environmental Society
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• v.19 no.3
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• pp.35-45
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• 2018

It is essential to predict ground conditions ahead of the tunnel face during tunnel excavation. Various studies on tunnel prediction method of the ground condition ahead of the tunnel face have already been done and applied to in mechanized tunnelling job sites. So, all the methods used in mechanized tunnelling to predict ground conditions ahead of the tunnel face were reviewed. A questionnaire surveying Tunnel Boring Machine (TBM) operators with at least 10 years' experience in TBM operation was used to determine the requirements for prediction methods as well as the distance from the tunnel face that must be assessed. Based on the result of questionnaire survey, the most feasible prediction methods applicable to mechanized tunnelling job-sites are suggested. One of the prediction methods applicable to mechanized tunnelling job-sites might be the electrical resistivity survey by utilizing the disk cutter on the cutterhead as electrode. So, in this study, laboratory tests were performed to evaluate the feasibility of prediction method utilizing electrical resistivity survey at mechanized tunnelling job-sites. It was found that geological condition ahead of 0.3 times of TBM's diameter from tunnel face could be predicted.

• Journal of the Korean GEO-environmental Society
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• v.3 no.3
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• pp.5-13
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• 2002

In tunnel design, geotechnical survey of over 200m tunnel depth is required because of its characteristical topography. For this reason, there are difficulties in collecting information of basic data in tunnel design because of large-scale costs in borehole tests, of limits to a geotechnical analysis by the existing refraction seismic survey and of analytical errors in steep mountainous area. Seismic tomography has many advantages as follows; 1) seismic velocity as absolute value is more reliable than electrical resistivity, 2) geotechnical analysis in deep tunnel depth is available by seismic velocity, 3) analytical errors is reduced in steep mountainous area. In this paper, it was found out a correlation of seismic velocity and Q in tunnel design in the neighborhood of the National Capital region and the reduction effect of tunnel construction cost using reliable rock quality by seismic tomography compared with by borehole data and electricity resistivity data.

• Tunnel and Underground Space
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• v.14 no.4
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• pp.275-286
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• 2004

It is studied to select the reinforcement method of an abandoned tunnel which are intersected under the new roadway line. In the various decision makings, the reasonability for the reinforcement method of an abandoned tunnel was estimated using the pair-wise comparison and the fuzzy approximate reasoning to simplify the process of survey research. And there is reflected all the qualitative and quantitative characterizations by investigation items. In order to select the reinforcement method of an abandoned tunnel, 4 characteristic factors of construction, economical efficiency, safety and maintenance were used. Using the simple survey research and pair-wise comparison matrix, the weight of 4 factors was decided. The fuzzy approximate reasoning was used to calculate the quantitative value of each factor And then reflecting each weight to these results, the final reinforcement method of an abandoned tunnel could be determined.

• Tunnel and Underground Space
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• v.6 no.2
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• pp.131-143
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• 1996

In-situ survey and laboratory rock test were carried out for rating rock mass around the tunnel that some failures had been occurred in Danyang limestone quarry. For rating rock mass, several methods such as RMR, Q-system, rock strength etc. were applied. The stability analysis on tunnel was evaluated by numerical method FLAC. And The block theory using streographic projection was also applied for stability analysis. The 3-4 major discontinuity sets are distributed in rock mass around tunnel.

• Tunnel and Underground Space
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• v.15 no.3 s.56
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• pp.177-184
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• 2005

The Sapaesan tunnel, the longest twin tube tunnel (4km) in Korea with 4 lanes each, is under construction with two years of delayed schedule because of the strong opposition from environmental bodies. Therefore, maximizing the construction efficiency was needed in tunnel project to compensate for time delay. This study includes improvements in the construction of the Sapaesan tunnel such as increasing excavation length and changing excavation sequence. In this paper the system for predicting tunnel face ahead is also introduced. Bulk-Emulsion explosive and Cylinder-Cut method were adopted in tunnel blasting to increase the excavation length. Optimum tunnel excavation step was designed to make up delayed time. Tunnel foe mapping, TSP survey and geological prediction system using computerized jumbo-drill were performed fnr safe construction of long and large twin tube tunnel.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.93-100
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• 2007

During tunnel excavation, drawdown of groundwater table or discharge from tunnel faces may not only reduce stability of tunnel and work efficiency but cause environmental problems. We have investigated the applicability of electrical resistivity survey for the establishment of the monitoring system for groundwater behavior and detecting flow channel of groundwater during tunnel excavation. The groundwater level was continuously measured at several points for 1 year. Survey was conduted at every 3 months using preinstalled electrical resistivity cables on site. The results show that observed changes in resistivity ratios in the area can be explained with observed changes in groundwater level. Thus, we believed that electrical resistivity analysed together with groundwater data can be applied for the monitoring of groundwater in tunnel area.

• Tunnel and Underground Space
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• v.19 no.2
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• pp.132-145
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• 2009

Faults in rock mass have strong influences on the behaviors of rock structure such as rock slope, tunnel and underground space. Thus, it is very important to analyse for the characteristics of fault rocks in design for tunnel. But, due to the limitation of geotechnical investigation in design stages, tunnel engineers have to carry out the face mapping and additional geological survey during tunnel excavation to find the distribution of faults and the engineering properties of faults for support and reinforcement design of tunnel. In this study, various geological survey and field tests were carried out to analyse the characteristics of the large thrust fault zone through the large sectional tunnel is constructed in mica-schist region. Also, the distribution of structural geology, the shape of thrust faults and the mechanical properties of fault rock were studied for the reasonable design of the reinforcement and support method for the highly fractured fault zone in the large-span tunnel.

• Geophysics and Geophysical Exploration
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• v.7 no.1
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• pp.62-69
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• 2004

The objective of this study is to estimate the distribution of a zone disturbed by excavation (EDZ) around tunnels that have been excavated at about 500 m depth in pre-Tertiary hard sedimentary rock. One of the most important tasks is to evaluate changes in the dynamic stability and permeability of the rock around the tunnels, by investigating the properties of the rock after the excavation. We performed resistivity and acoustic tomography using two boreholes, 5 m in length, drilled horizontally from the wall of a tunnel in pre-Tertiary hard conglomerate. By these methods, we detected a low-resistivity and low-velocity zone 1 m in thickness around the wall of the tunnel. The resulting profiles were verified by permeability and evaporation tests performed at the same boreholes. This anomalous zone matched a high-permeability zone caused by open fractures. Next, we performed resistivity monitoring along annular survey lines in a tunnel excavated in pre-Tertiary hard shale by a tunnel-boring machine (TBM). We detected anomalous zones in 2D resistivity profiles surrounding the tunnel. A low-resistivity zone 1 m in thickness was detected around the tunnel when one year had passed after the excavation. However, two years later, the resistivity around the tunnel had increased in a portion, about 30 cm in thickness, of this zone. To investigate this change, we studied the relationship between groundwater flow from the surroundings and evaporation from the wall around the tunnel. These features were verified by the relationship between the resistivity and porosity of rocks obtained by laboratory tests on core samples. Furthermore, the profiles matched well with highly permeable zones detected by permeability and evaporation tests at a horizontal borehole drilled near the survey line. We conclude that the anomalous zones in these profiles indicate the EDZ around the tunnel.

• Geophysics and Geophysical Exploration
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• v.18 no.1
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• pp.14-20
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• 2015

Three-dimensional (3D) resistivity method is an effective tool in the engineering site survey because it can provide a 3D resistivity distribution of the site. In this study, we tried to find out faults, fractures and coal seams that can cause the collapse of the tunnel. We carried out 2D resistivity survey along 5 parallel lines and 11 cross lines and merged all the apparent resistivity data for 3D inversion. Finally, from the 3D resistivity image and drilling data we presented the 3D distribution of faults, fractures and coal seams that are considered the main cause of the tunnel collapse.