• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.513-525
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• 2018

A 3 dimensional numerical analysis for shield TBM tunnel should take into account various characteristics of the shield TBM excavation, such as gap, tail void, segment installation, and backfill injection. However, analysis method considering excavation characteristics are generally mixed with various method, resulting in concern of consistency and reliability degradation of the analytical results. In this paper, a parametric study is carried out by using actually measured ground settlement data on various methods that can be used for 3 dimensional numerical analysis of shield TBM tunneling. As a result, we have analyzed and arranged an analytical method to predict similarly the behavior of ground settlement and tunnel face pressure at the design stage. Skin plate pressure, backfill pressure and soil model have been identified as the most significant influences on the ground settlement. The grout pressure model is considered to be applicable when there is no volume loss information on the excavated ground, such as seabed tunnels, or when it is important to identify the behavior around a tunnel, such as surface settlement as well as face pressure. And it is considered that designers can use these guidelines as a base material to perform a reasonable 3 dimensional numerical analysis that reflects the ground conditions and the features of the shield TBM tunneling.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.4
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• pp.303-314
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• 2024

Recently, the consecutive shield tunnel boring machine (TBM) has gained attention for its potential to enhance TBM penetration rates. However, its development requires a thorough risk assessment due to the unconventional nature of its equipment and hydraulic systems, coupled with the absence of design or construction precedents. This study investigated the causal relationships between four accidents and eight relevant sources associated with the consecutive shield TBM. Subsequently, risk levels were determined based on expert surveys and a risk matrix technique. The findings highlighted significant impacts associated with collapses or surface settlements and the likelihood of causal combinations leading to misalignment. Specifically, this study emphasized the importance of proactive mitigation measures to address collapses or surface settlements caused by inadequate continuous tail void backfill or damaged thrust jacks. Furthermore, it is recommended to develop advanced non-destructive testing technology capable of comprehensive range detection across helical segments, to design a sequential thrust jack propulsion system, and to determine an optimal pedestal angle.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.2
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• pp.105-118
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• 2008

Shotcrete is one of the main support materials in tunnelling. Its bonding state on excavated rock surfaces controls the safety of the tunnel: De-bonding of shotcrete from an excavated surface decreases the safety of the tunnel. Meanwhile, the bonding state of shotcrete is affected by blasting during excavation at tunnel face as well as bench cut. Generally, the bonding state of shotcrete can be classified as void, de-bonded, or fully bonded. In this study, the state of the back-surface of shotcrete is investigated using impact-echo (IE) techniques. Numerical simulation of IE technique is performed with ABAQUS. Signals obtained from the IE simulations were analyzed at time, frequency, and time-frequency domains, respectively. Using an integrated active signal processing technique coupled with a Short-Time Fourier Transform (STFT) analysis, the bonding state of the shotcrete can be evaluated accurately. As the bonding state worsens, the amplitude of the first peak past the maximum amplitude in the time domain waveform and the maximum energy of the autospectral density are increasing. The resonance frequency becomes detectable and calculable and the contour in time-frequency domain has a long tail parallel to the time axis. Signal characteristics with respect to ground condition were obtained in case of fully bonded condition. As the ground condition worsens, the length of a long tail parallel to the time axis is lengthened and the contour is located in low frequency range under 10 kHz.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.433-452
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• 2018

The shield tunneling method can minimize surface settlements by preventing the deformation of tunnel face and tunnel intrados due to tunnel excavation. For this purpose, it is very important to control the operating conditions of shield TBM. The face pressure and backfill pressure for tail void grouting should be the most important and immediate measure not only to restrain surface settlement, but also to influence the effective stress and pore water pressure around the circumstance of tunnel during excavation. The reaction of the ground to the application of face pressure and backfill pressure relies on the stiffness and permeability of ground. Especially, the reaction of saturated clayey ground formations, which shows the time-dependent deformation, is different from the permeable ground. Hence, in this paper it was investigated how the TBM operating conditions, ground stiffness, and permeability impact on the surface settlement of saturated clayey ground. For this purpose, a series of parametric studies were carried out by means of the stress-pore water pressure coupled FE analysis. The results show that the settlement of soft clayey ground is divided into the immediate settlement and consolidation settlement. Especially, the consolidation settlement depends on the ground stiffness and permeability. In addition, the existence of critical face pressure and backfill pressure was identified. The face pressure and backfill pressure above the critical value may cause an unexpected increase in the ground settlement.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.3
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• pp.183-198
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• 2021

The EPB (Earth Pressure Balanced) shield TBM method restrains the ground deformation through continuous excavation and support. Still, the significant surface settlement occurs due to the ground conditions, tunnel dimensions, and construction conditions. Therefore, it is necessary to clarify the settlement behavior with its influence factors and evaluate the possible settlement during construction. In this study, the analytical model of surface settlement based on the influence factors and their mechanisms were proposed. Then, the parametric study for controllable factors during excavation was conducted by numerical method. Through the numerical analysis, the settlement behavior according to the construction conditions was quantitatively derived. Then, the qualitative trend according to the ground conditions was visualized by coupling the numerical results with the analytical model of settlement. Based on the results of this study, it is expected to contribute to the derivation of the settlement prediction algorithm for EPB shield TBM excavation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.71-83
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• 2009

Shotcrete is an important primary support for tunnelling in rock. The quality control of shotcrete is a core issue in the safe construction and maintenance of tunnels. Although shotcrete may be applied well initially onto excavated rock surfaces, it is affected by blasting, rock deformation and shrinkage and can debond from the excavated surface, causing problems such as corrosion, buckling, fracturing and the creation of internal voids. This study suggests an effective non-destructive evaluation method of the tunnel shotcrete bonding state applied onto hard rocks using the impact-echo (IE) method and ground penetration radar (GPR). To verify previous numerical simulation results, experimental study carried out. Generally, the bonding state of shotcrete can be classified into void, debonded, and fully bonded. In the laboratory, three different bonding conditions were modeled. The signals obtained from the experimental IE tests were analyzed at the time domain, frequency domain, and time-frequency domain (i.e., the Short- Time Fourier transform). For all cases in the analyses, the experimental test results were in good agreement with the previous numerical simulation results, verifying this approach. Both the numerical and experimental results suggest that the bonding state of shotcrete can be evaluated through changes in the resonance frequency and geometric damping ratio in a frequency domain analysis, and through changes in the contour shape and correlation coefficient in a time-frequency analysis: as the bonding state worsens in hard rock condition, the autospectral density increases, the geometric damping ratio decreases, and the contour shape in the time-frequency domain has a long tail parallel to the time axis. The correlation coefficient can be effectively applied for a quantitative evaluation of bonding state of tunnel shotcrete. Finally, the bonding state of shotcrete can be successfully evaluated based on the process suggested in this study.