• Tunnel and Underground Space
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• v.34 no.3
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• pp.185-195
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• 2024

The Incheon Metro Line 1 Geomdan Extension Phase 1 is the first project in South Korea where both a roadheader and TBM (Tunnel Boring Machine) are being used together. The shield TBM tunnel section is 1,057 m long, and is mostly composed of rock, including the section beneath the Airport Railroad and the Gyeongin Ara Waterway. A 7.8 m earth pressure balance shield TBM was used for tunnel excavation. The average monthly advance rate for both the North and South tracks is 239.1 m, with a maximum monthly advance rate of 334.5 m. This technical article comprehensively evaluates the productivity of the shield TBM, focusing on the TBM excavation performance. Above all, it aims to provide useful reference material for the successful execution of shield TBM tunnel construction.

• 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.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.5
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• pp.281-302
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• 2021

Railway projects have been consistently increasing in Korea. In relation to this trend, the mechanized tunneling using Tunnel Boring Machine (TBM) is preferably applied for mining urban areas and passing under rivers. The TBM tunneling under difficult grounds like mixed faces with high water pressure could require ground improvements for stable TBM advance or safe cutter head intervention (CHI). In this study, pre-grouting works for CHI in Daegok-Sosa railway project are presented in terms of the grouting zone design, the executions and the results, the lessons learned from the experience. It should be mentioned that the grouting from inside TBM was carried out several times and turned out to be inefficient in the project. Therefore, grouting experiences from the surface are highlighted in this study. Jet grouting was implemented on CHI points on land, while permeation grouting off shore in the Han River, which mostly allow to access the cutter head of TBM in free air with stable faces. The results of CHI works have been analyzed and the lesson learned are suggested.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.424-442
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• 2005

In this paper a design of a large shield Tunnel through weathered soil and weathered rock in 703 section of seoul subway line No.7 extension project is presented. The geological investigation results show that the projecet region consists mostly of weathered soil with some local weathered rock in the tunnel excavation level. A EPB shield TBM is selected as a optimal excavation machine for the large shield Tunnel considering the geological and site conditions. Also, the shield machine head and cutter for the large shield tunnel type are designed considering site geological conditions and average advance rate in similar projects.

• Proceedings of the KSR Conference
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• 2003.10b
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• pp.569-578
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• 2003

In this paper a determination of the optimal excavation method and machine type for a tunnel under the Han river between the Sungsoo-dong, Sungdong-Gu and the Chungdaw-dong, Kangnam-Gu in the Bundang railway. The geological investigation results show that some fractured zones exist locally under the northern boundary of the Han river bed, but the other regions consist mostly of hard rocks of good quality in the tunnel excavation level. Also, a hign water pressure of $5kgf/cm^2$ and a flash inflow of river water due to old boring holes are expected during tunnel excavation. A EPB shield TBM is selected as a optimal excavation machine for the Han river tunnel considering the geological and ,site conditions.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.6
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• pp.1049-1060
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• 2018

Soil conditioning is one of the key factors for successfull tunnel excavations utilizing the earth pressure-balanced (EPB) shield tunnel boring machine (TBM) by increasing the tunnel face stability and extraction efficiency of excavated soils. In this study, conditioning agents are mixed with the weathered granite soils which are abundant in the Korean peninsula and the workability of the resulting mixture is evaluated through the slump tests to derive and propose the most suitable conditioning agent as well as the most appropriate agent mix ratios. However, since it is cumbersome to perform the slump tests all the time either in the laboratory or in-situ, a simpler test may be needed instead of the slump test; the fall cone test was proposed as a substitute. In this paper, the correlation between the slump value obtained from the slump test and the cone penetration depth obtained from the proposed fall cone test was obtained. Test results showed that a very good correlation between two was observed; it means that the simpler fall cone test can be used to assess the suitability of the conditioned soils instead of the more cumbersome slump test.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.4
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• pp.233-252
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• 2021

This paper is a study to improve the efficiency of mixing technology in the shield TBM chamber. Currently, the number of construction cases using the TBM method is increasing in Korea. According to the increasing use of TBM method, research on TBM method such as Disc Cutter, Cutter bit, and Segment also shows an increasing trend. However, there is little research on the mixing efficiency in chamber and chamber. In order to improve the smooth soil treatment and the behavior of the excavated soil, a study was conducted on the change of the mixing efficiency according to the effective mixing bar arrangement in the chamber. In the scale model experiment, the ground was composed using plastic materials of different colors for ease of identification. In addition, the mixing bar arrangement was different and classified into 4 cases, and the particle size distribution was classified into single particle size and multiple particle size, and the experiment was conducted with a total of 8 cases. The rotation speed of the cutter head of all cases was the same as 5 RPM, and the experiment time was also carried out in the same condition, 1 minute and 30 seconds. In order to check the mixing efficiency, samples at the upper, middle (left or right), and lower positions of each case were collected and analyzed. As a result of the scaled-down model experiment, the mixing efficiency of Case 4 and Case 4-1 increased compared to Case 1 and Case 1-1, which are actually used. Accordingly, it is expected that the mixing efficiency can be increased by changing the arrangement of the mixing bar in the chamber, and it is considered to be effective in saving air as the mixing efficiency increases. Therefore, this study is considered to be an important indicator for the use of shield TBM in Korea.

• KEPCO Journal on Electric Power and Energy
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• v.6 no.3
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• pp.305-313
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• 2020

The use of cable tunnels for electric power transmission as well as their construction in difficult conditions such as in subsea terrains and large overburden areas has increased. So, in order to efficiently operate the small diameter shield TBM (Tunnel Boring Machine), the estimation of advance rate and development of a design model is necessary. However, due to limited scope of survey and face mapping, it is very difficult to match the rock mass characteristics and TBM operational data in order to achieve their mutual relationships and to develop an advance rate model. Also, the working mechanism of previously utilized linear cutting machine is slightly different than the real excavation mechanism owing to the penetration of a number of disc cutters taking place at the same time in the rock mass in conjunction with rotation of the cutterhead. So, in order to suggest the advance rate and machine design models for small diameter TBMs, an EPB (Earth Pressure Balance) shield TBM having 3.54 m diameter cutterhead was manufactured and 19 cases of full-scale tunneling tests were performed each in 87.5 ㎥ volume of artificial rock mass. The relationships between advance rate and machine data were effectively analyzed by performing the tests in homogeneous rock mass with 70 MPa uniaxial compressive strength according to the TBM operational parameters such as thrust force and RPM of cutterhead. The utilization of the recorded penetration depth and torque values in the development of models is more accurate and realistic since they were derived through real excavation mechanism. The relationships between normal force on single disc cutter and penetration depth as well as between normal force and rolling force were suggested in this study. The prediction of advance rate and design of TBM can be performed in rock mass having 70 MPa strength using these relationships. An effort was made to improve the application of the developed model by applying the FPI (Field Penetration Index) concept which can overcome the limitation of 100% RQD (Rock Quality Designation) in artificial rock mass.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.2
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• pp.91-111
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• 2024

Most of utility cable tunnels are constructed utilizing shield TBM as part of the underground transmission line project. The TBM chamber is the only space inside the tunnel that encounters rock and soil, and is the place with the highest frequency of accident exposure, such as collapse and collision accidents. Since there is currently no way to measure the disc cutter wear from outside the chamber, frequent inspection by workers is essential. Accordingly, in this study, in order to prevent safety accidents inside the TBM chamber and expect the effect of shortening the construction period by reducing the number of chamber openings, the concept of disk cutter wear measurement technology was established and a prototype was produced. By considering prior technology and determining that magnetic sensors are most suitable for the excavation environment, wear measurement sensor package were developed integrating magnetic sensors, wireless communication modules, power supply, external casing, and monitoring systems. To verify the performance of the prototype in an actual excavation environment, a full-scale tunnelling test was performed using a 3.6 m EPB shield TBM. Based on the full-scale tests, five prototypes were operated normally among eight prototypes. It was analyzed that sensor measurement, wireless communication, and durability performance were secured within a maximum thrust of 3,000 kN and a rotation speed of 1.5 RPM.

• Geomechanics and Engineering
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• v.38 no.5
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• pp.507-515
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• 2024

An accurate estimation of the geotechnical parameters in front of tunnel faces is crucial for the safe construction of underground infrastructure using tunnel boring machines (TBMs). This study was aimed at developing a data-driven model for predicting the rock quality designation (RQD) of the ground formation ahead of tunnel faces. The dataset used for the machine learning (ML) model comprises seven geological and mechanical features and 564 RQD values, obtained from an earth pressure balance (EPB) shield TBM tunneling project beneath the Han River in the Republic of Korea. Four ML algorithms were employed in developing the RQD prediction model: k-nearest neighbor (KNN), support vector regression (SVR), random forest (RF), and extreme gradient boosting (XGB). The grid search and five-fold cross-validation techniques were applied to optimize the prediction performance of the developed model by identifying the optimal hyperparameter combinations. The prediction results revealed that the RF algorithm-based model exhibited superior performance, achieving a root mean square error of 7.38% and coefficient of determination of 0.81. In addition, the Shapley additive explanations (SHAP) approach was adopted to determine the most relevant features, thereby enhancing the interpretability and reliability of the developed model with the RF algorithm. It was concluded that the developed model can successfully predict the RQD of the ground formation ahead of tunnel faces, contributing to safe and efficient tunnel excavation.