• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.6
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• pp.587-596
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• 2015

Recent years have shown great advances in the feasibility of long subsea tunnels. Projects such as the Channel Tunnel, the Stoerebelt Tunnel or the Bosporus Crossing have pushed the boundaries of TBM tunneling technology and fueled the work on feasibility studies for even more challenging projects such as crossing the Qiongzhou or Gibraltar Straits. There are numerous geotechnical challenges such as wide variations of ground conditions, high operation pressures or long tunnel distances and finally geological uncertainties which must be solved in order to attempt such projects. Several operational challenges such as large muck quantities interventions under difficult conditions and long transport distances also have to be tackled. TBM manufacturer and construction industry have developed a number of approaches to these challenges which point into the right technical direction and have been proven successfully in recent experiences. Their further development will allow attempting several megaprojects which are currently under discussion.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.4
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• pp.561-571
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• 2019

Drilling and charging of the blast holes during NATM tunneling works take more than 30% of construction time among the whole tunneling work process. Prediction of ground condition ahead of tunnel face has been studied by several researchers by correlating percussion pressure and drilling speed during tunneling work with the ground condition and/or RMR values. However, most of the previous researches were conducted in the granite rock condition which is the most representative igneous rock in the Korean peninsula. In this study, drilling speeds in igneous rocks were analyzed and compared with those in sedimentary rocks (most dominantly composed of conglomerates, sandstones, and shales) under the similar RMR ranges; it was identified that the drilling speed is pretty much affected by rock types even in a similar RMR range. Under the similar RMR values, the drilling speed was faster in sedimentary rocks compared with that in igneous rock. Moreover, while the drilling speed was not much affected by change of the RMR values in igneous rocks, it became faster in sedimentary rocks as the RMR values got lower.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.1
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• pp.89-96
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• 2005

Due to fast development of digital equipments, various information techniques have been applied to the tunneling and a decision aid system based on IT has also been used during excavation stage. A PDA based informative tunneling method is, therefore, studied in this paper and the decision aids for tunneling using digital face mapping data as well as geologic information in terms of digital data is developed. For this, wireless network, mobile computer, CDMA and digital camera have been combined to generate the digital map of the tunnel face and reinforcement or excavation pattern can be estimated based on digitalized geologic conditions. Future studies will be concentrated on the enhancement of the PDA S/W so that reinforcement method as well as the amount of reinforcements can also be stored in the same DB. Furthermore, field application of the S/W will be undertaken and a virtual reality technique will also be introduced to visualize all the tunneling work on the computer monitor.

• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.2
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• pp.161-174
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• 2003

Applicability of the Decision Aids for Tunneling (DAT) technique is investigated in this study to better understand the efficiency of the decision making process during tunnel construction. For this, a traffic tunnel under construction is adopted and information on the construction procedure, i.e., overall geology, unit cost and construction time for each excavation process, is provided periodically. Various scattergrams in which cost-time simulation results are plotted are obtained according to the simulation methods and final prediction on the construction time/cost is made. It is found that the uncertainty in the cost distribution is greater than the uncertainty in the time distribution for each cycle simulation and the uncertainties in time and cost for the one time simulations are comparable. Future work will be concentrated on the updating scheme using the face mapping data and various parametric studies will also be performed.

• Journal of Korean Society of Disaster and Security
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• v.14 no.3
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• pp.51-63
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• 2021

This study is for the quality improvement of water-sealing & reinforcement grouting in tunnel of the construction of the underground transportation network underneath the city. Existing tunnel grouting process did not technically utilize P~q~t charts fully. It is due to the absence of technical methods to decide how P~q~t charts change in the presence of trouble and what the change represents in grouting. There were no standards to decide which chart pattern represents which ground characteristics, how to categorize ground types, and how to take measures according to the standards. This paper studies on the grouting type, ground characteristics, ground type categorizing method, and countermeasures for both general and algorithm-processed grouting in soil and rock layer to address the aforementioned problems. Newly improved P~q~t charts from grouting in soil was categorized into six different types. Different characteristics and categorization method was developed for each type. Countermeasures for each type of grouting process were developed so that on-site application can be readily available. Improved P~q~t charts for rock layer also have six different types of grouting. Each type was given the countermeasures for rock layer grouting process for easier applications. Therefore, it is expected to be used through out the entire process of grouting from preparation to the last report of the water-sealing & reinforcement grouting in tunnel of the construction of the underground transportation network underneath the city.

• Geomechanics and Engineering
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• v.37 no.1
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• pp.73-84
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• 2024

Owing to the high strength and abrasive characteristics of cobble-boulders, cutters are easily worn and damaged during shield tunneling, making construction inefficient. In the present work, the stress on the ripper and scraper on the cutterhead was analyzed by the PFC3D-FLAC3D coupling model of shield tunneling to get insight into the performance of the cutterhead for cutting underground cobble and boulders. The numerical calculation results revealed that the increase in trajectory radius leads to a rising stress on the cutters, and the stress on the front cutting surface is greater than that on the back of the cutters. Moreover, the correlation between cutter wear and stress is revealed based on field measurement data. The distribution of the cutter stress is consistent with the cutter wear and breakage characteristics in actual construction, in which more extensive cutter stress is exhibited, extreme cutter wear appears, and more cutter breakage occurs. Finally, the relationship between the cutterhead opening area's layout and cutter wear distribution was investigated, indicating that the cutter wear extent is the most severe in the region where the radial opening ratio dropped sharply.

• Journal of Korean Tunnelling and Underground Space Association
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• v.3 no.3
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• pp.31-43
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• 2001

In this study, we carried out investigation and analysis on damages in tunnels on order to provide the basic information for the safety assessment of tunnels and to minimize the potential damage of the same kind as investigated. The frequencies of occurrence in terms of 4 items, i.e., service life interval, type of the damage, cause of the damage, and geological condition, were examined and summarized based on 44 foreign and domestic cases of tunnel damages. Also, we carried out a survey research of which the content included 28 questions on the tunnel safety assessment. The answers collected from domestic experts in tunneling suggested that the most probable cause of the tunnel damages was cracking in tunnels at 42~58%. They also suggested that the poor constrution work strongly caused the damages. Therefore, to ensure tunnel safety, high quality of constrution should be maintained as examined. The types of damage and their extent of influence on the overall tunnel safety are of practical importance to be used in the artficial intelligent system for tunnel safety assessment.

• Geomechanics and Engineering
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• v.37 no.3
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• pp.213-222
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• 2024

Determination of jointed rock mass properties plays a significant role in the design and construction of underground structures such as tunneling and mining. Rock mass classification systems such as Rock Mass Rating (RMR), Rock Mass Index (RMi), Rock Mass Quality (Q), and deformation modulus (Em) are determined from the jointed rock masses. However, parameters of jointed rock masses can be affected by the tunnel depth below the surface due to the effect of the in situ stresses. In addition, the geomechanical properties of rocks change due to the effect of metamorphism. Therefore, the main objective of this study is to apply correlation analysis to investigate the relationships between rock mass properties and some parameters related to the depth of the tunnel studied. For this purpose, the field work consisted of determining rock mass parameters in a tunnel alignment (~7.1 km) at varying depths from 21 m to 431 m below ground surface. At the same excavation depths, thirty-seven rock types were also sampled and tested in the laboratory. Correlations were made between vertical stress and depth, horizontal/vertical stress ratio (k) and depth, k and Em, k and RMi, k and point load index (PLI), k and Brazilian tensile strength (BTS), Em and uniaxial compressive strength (UCS), UCS and PLI, UCS and BTS. Relationships were significant (significance level=0.000) at the confidence interval of 95% (r = 0.77-0.88) between the data pairs for the rocks taken from depths greater than 166 m where the ratio of horizontal to vertical stress is between 0.6 and 1.2. The in-situ stress parameters affected rock mass properties as well as metamorphism which affected the geomechanical properties of rock materials by affecting the behavior of minerals and textures within rocks. This study revealed that in-situ stress parameters and metamorphism should be reviewed when tunnel studies are carried out.

• Journal of Korean Tunnelling and Underground Space Association
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• v.4 no.4
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• pp.277-286
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• 2002

Most of the problems in dealing with the tunnel construction are the uncertainties and complexities of the stress conditions and rock strengths in ahead of the tunnel excavation. The limitations on the investigation technology, inaccessibility of borehole test in mountain area and public hatred also restrict our knowledge on the geologic conditions on the mountainous tunneling area. Nevertheless an extensive and superior geophysical exploration data is possibly acquired deep within the mountain area, with up to the tunnel locations in the case of alternative design or turn-key base projects. An appealing claim in the use of artificial neural networks (ANN) is that they give a more trustworthy results on our data based on identifying relevant input variables such as a little geotechnical information and biological learning principles. In this study, error back-propagation algorithm that is one of the teaching techniques of ANN is applied to presupposition on Rock Mass Ratings (RMR) for unknown tunnel area. In order to verify the applicability of this model, a 4km railway tunnel's field data are verified and used as input parameters for the prediction of RMR, with the learned pattern by error back propagation logics. ANN is one of basic methods in solving the geotechnical uncertainties and helpful in solving the problems with data consistency, but needs some modification on the technical problems and we hope our study to be developed in the future design work.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.1
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• pp.1-12
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• 2016

When utilizing a Tunnel Boring Machine (TBM) for tunnelling work, unexpected ground conditions can be encountered that are not predicted in the design stage. These include fractured zones or mixed ground conditions that are likely to reduce the stability of TBM excavation, and result in considerable economic losses such as construction delays or increases in costs. Minimizing these potential risks during tunnel construction is therefore a crucial issue in any mechanized tunneling project. This paper proposed the potential risk events that may occur due to risky ground conditions. A resistivity survey is utilized to predict the risky ground conditions ahead of the tunnel face during construction. The potential risk events are then evaluated based on their occurrence probability and impact. A TBM risk management system that can suggest proper solution methods (measures) for potential risk events is also developed. Multi-Criterion Decision Making (MCDM) is utilized to determine the optimal solution method (optimal measure) to handle risk events. Lastly, an actual construction site, at which there was a risk event during Earth Pressure-Balance (EPB) Shield TBM construction, is analyzed to verify the efficacy of the proposed system.