• Geomechanics and Engineering
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• 제19권1호
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• pp.93-104
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• 2019

Anomalies and/or fractured grounds not detected by the surface geophysical and geological survey performed during design stage may cause significant problems during tunnel excavation. Many studies on prediction methods of the ground condition ahead of the tunnel face have been conducted and applied in tunneling construction sites, such as tunnel seismic profiling and probe drilling. However, most such applications have focused on the drill and blast tunneling method. Few studies have been conducted for mechanized tunneling because of the limitation in the available space to perform prediction tests. This study aims to predict the ground condition ahead of the tunnel face in TBM tunneling by using an electrical resistivity tomography survey. It compared the characteristics of each electrode array and performed an investigation on in-situ tunnel boring machine TBM construction site environments. Numerical simulations for each electrode array were performed, to determine the proper electrode array to predict anomalies ahead of the tunnel face. The results showed that the modified dipole-dipole array is, compared to other arrays, the best for predicting the location and condition of an anomaly. As the borehole becomes longer, the measured data increase accordingly. Therefore, longer boreholes allow a more accurate prediction of the location and status of anomalies and complex grounds.

• Geomechanics and Engineering
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• 제19권2호
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• pp.153-165
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• 2019

A case study of monitoring and analysis of surface settlement induced by tunneling of Tabriz metro line 2 (TML2) is presented in this paper. The TML2 single tunnel has been excavated using earth pressure balanced TBM with a cutting-wheel diameter of 9.49 m since 2015. Presented measurements of surface settlements, were collected during the construction of western part of the project (between west depot and S02 station) where the tunnel was being excavated in sand and silt, below the water table and at an average axis depth of about 16 m. Settlement readings were back-analyzed using Gaussian formula, both in longitudinal and transversal directions, in order to estimate volume loss and settlement trough width factor. In addition to settlements, face support and tail grouting pressures were monitored, providing a comprehensive description of the EPB performance. Using the gap model, volume loss prediction was carried out. Also, COB empirical method for determination of the face pressure was employed in order to compare with field monitored data. Likewise, FE simulation was used in various sections employing the code Simulia ABAQUS, to investigate the efficiency of numerical modelling for the estimating of the tunneling induced-surface settlements under such a geotechnical condition. In this regard, the main aspects of a mechanized excavation were simulated. For the studied sections, numerical simulation is not capable of reproducing the high values of in-situ-measured surface settlements, applying Mohr-Coulomb constitutive law for soil. Based on results, for the mentioned case study, the range of estimated volume loss mostly varies from 0.2% to 0.7%, having an average value of 0.45%.

• Geomechanics and Engineering
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• 제18권2호
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• pp.215-224
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• 2019

Excavation of long tunnels by shielded TBMs is a safe, fast, and efficient method of tunneling that mitigates many risks related to ground conditions. However, long-distance tunneling in great depth through adverse geological conditions brings about limitations in the application of TBMs. Among various harsh geological conditions, squeezing ground as a consequence of tunnel wall and face convergence could lead to cluttered blocking, shield jamming and in some cases failure in the support system. These issues or a combination of them could seriously hinder the performance of TBMs. The technique of excavation has a strong influence on the tunnel response when it is excavated under squeezing conditions. The Golab water conveyance tunnel was excavated by a double-shield TBM. This tunnel passes mainly through metamorphic weak rocks with up to 650 m overburden. These metamorphic rocks (Shales, Slates, Phyllites and Schists) together with some fault zones are incapable of sustaining high tangential stresses. Prediction of the convergence, estimation of the creeping effects and presenting strategies to overcome the squeezing ground are regarded as challenging tasks for the tunneling engineer. In this paper, the squeezing potential of the rock mass is investigated in specific regions by dint of numerical and analytical methods. Subsequently, several operational solutions which were conducted to counteract the challenges are explained in detail.

• Geomechanics and Engineering
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• 제20권6호
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• pp.475-484
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• 2020

The prediction of the ground conditions ahead of a tunnel face is very important, especially for tunnel boring machine (TBM) tunneling, because encountering unexpected anomalies during tunnel excavation can cause a considerable loss of time and money. Several prediction techniques, such as BEAM, TSP, and GPR, have been suggested. However, these methods have various shortcomings, such as low accuracy and low resolution. Most studies on electrical resistivity tomography surveys have been conducted using numerical simulation programs, but laboratory experiments were just a few. Furthermore, most studies of scaled model tests on electrical resistivity tomography were conducted only on the ground surface, which is a different environment as compared to that of mechanized tunneling. This study performed a laboratory experimental test to extend and verify a prediction method proposed by Lee et al., which used electrical resistivity tomography to predict the ground conditions ahead of a tunnel face in TBM tunneling environments. The results showed that the modified dipole-dipole array is better than the other arrays in terms of predicting the location and shape of the anomalies ahead of the tunnel face. Having longer upper and lower borehole lengths led to better accuracy of the survey. However, the number and length of boreholes should be properly controlled according to the field environments in practice. Finally, a modified and verified technique to predict the ground conditions ahead of a tunnel face during TBM tunneling is proposed.

• 화약ㆍ발파
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• 제26권2호
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• pp.64-76
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• 2008

기계화 장전시스템을 이용한 Bulk Emulsion은 외국에서는 보편화된 장약시스템으로 최근에는 국내에 보급되어 점차 사용이 증가하고 있다. 이런 Bulk Emulsion은 안전하고, 장전밀도를 증가시켜 파쇄도를 향상시킬 수 있으며, 터널발파에서 굴진효율을 향상시킬 수 있고, 발파 유해가스의 농도를 최소한 저감하여 환경친화적인 제품이라 할 수 있다. 또한, 그 종류에는 노천용과 터널용이 있으며, 사용현장 및 목적에 따라 폭약의 구성이 차이가 있으나 장전원리는 동일하다. 본 연구에서는 터널용 벌크에멀젼을 이용하여 국내 10여개 터널현장에서 본발파 및 시험발파를 실시하였고, 주요 현장의 발파 결과는 다음과 같다. 먼저, 카트리지와 비교하여 장전밀도를 $35{\sim}60%$ 증가시킬 수 있으며, 천공수는 약 $10{\sim}30%$의 절감효과가 있고, 굴진능률은 약 $8{\sim}20%$, 파쇄도는 30cm이하의 적정상차 입도 사이즈를 기준으로 약 30%정도의 증대 효과가 있었다. 또한, 발파 후가스는 약포형 에멀젼폭약의 경우 CO가 평균 34.44ppm이었으나 Bulk Emulsion의 경우 20.13ppm으로 기존 폭약 대비 58.45%수준이었고, NOx은 2ppm이하로 검측되지 않았다. 이러한 벌크 에멀젼 폭약을 이용한 기계화 장전시스템은 향후 대형 대단면 터널 현장과 $4m{\sim}5m$이상의 굴진장을 확보할 수 있는 장대터널의 장공발파현장 및 급속 시공을 요하는 현장에서 다양하게 적용될 것으로 판단된다.

• Geomechanics and Engineering
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• 제37권3호
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• pp.223-241
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• 2024

Evaluating the performance of Tunnel Boring Machines (TBMs) stands as a pivotal juncture in the domain of hard rock mechanized tunneling, essential for achieving both a dependable construction timeline and utilization rate. In this investigation, three advanced artificial neural networks namely, gated recurrent unit (GRU), back propagation neural network (BPNN), and simple recurrent neural network (SRNN) were crafted to prognosticate TBM-rate of penetration (ROP). Drawing from a dataset comprising 1125 data points amassed during the construction of the Alborze Service Tunnel, the study commenced. Initially, five geomechanical parameters were scrutinized for their impact on TBM-ROP efficiency. Subsequent statistical analyses narrowed down the effective parameters to three, including uniaxial compressive strength (UCS), peak slope index (PSI), and Brazilian tensile strength (BTS). Among the methodologies employed, GRU emerged as the most robust model, demonstrating exceptional predictive prowess for TBM-ROP with staggering accuracy metrics on the testing subset (R² = 0.87, NRMSE = 6.76E-04, MAD = 2.85E-05). The proposed models present viable solutions for analogous ground and TBM tunneling scenarios, particularly beneficial in routes predominantly composed of volcanic and sedimentary rock formations. Leveraging forecasted parameters holds the promise of enhancing both machine efficiency and construction safety within TBM tunneling endeavors.

• Geomechanics and Engineering
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• 제32권5호
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• pp.503-512
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• 2023

In tunneling projects, a significant part of the costs is spent on segment production. By more economically producing, the cost of tunnel construction can be greatly reduced, especially in long and large-diameter tunnels. In the present study, the effect of using the Carousel method in the improvement of the production system performance compared to the conventional Static system has been studied. To carry out the research, a quantitative comparison of cost and production time was carried out for two production methods using the available documentation. The opinions of experts have been obtained using questionnaires and qualitative comparison of cost, time and production quality was done by implementation of statistical analysis. The SPSS software and the univariate t-test were used to analyze the questionnaires. According to the results of statistical analysis with SPSS, the use of the Carousel method will reduce production time and costs along with increasing manufacturing quality. According to the documentation analysis, the Carousel method reduces the cost of production by almost 30% and leads to a reduction of the production time to approximately 40% of the Static moulds system. The Carousel method has a higher production rate, efficiency, and better performance. Research into quantifying the benefits of Carousel method in the production system performance is very limited. This comparison is based on real information from the under construction Tabriz Metro project. This article can be very helpful in choosing the best production method.

• 한국터널지하공간학회 논문집
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• 제23권5호
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• pp.281-302
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• 2021

철도망 구축이 확대되는 추세 속에 도심지나 한강을 통과하기 위해 TBM 굴착공법 적용사례가 증가하고 있다. 특히, 도심지나 한강하저를 통과하는 경우 불량한 지반 및 지하수조건을 조우하게 되며 안정적인 굴진 및 커터교체(Cutter Head Intervention, CHI)를 위해서 그라우팅을 적용하고 있다. 본 논문에서는 TBM 굴착공법을 적용한 철도 터널 시공 시 적용한 그라우팅에 대하여 소개하고자 한다. 특히, CHI를 위해 그라우팅을 수행한 사례에 대한 소개나 분석이 많지 않은 것으로 판단하여 CHI를 위한 그라우팅 범위산정, 수행결과, 고찰 및 제언(Lessons Learned)을 기술하고자 한다. 그라우팅은 막장안정성을 확보하는 목적이 있으며, 작업위치에 따라 지상(수직)그라우팅과 TBM 장비 내에서 수행하는 갱내 그라우팅으로 나눌 수 있다. 갱내그라우팅을 수행한 결과 공기 및 보강효과 측면에서 지상(수직) 그라우팅에 비해 비효율적이라고 판단되어 지상그라우팅으로 계획을 변경하였다. 한강하저 구간의 경우 슬러지 발생으로 인한 환경오염, 주입재 유실 등이 우려되어 고압분사그라우팅을 적용할 수 없었으며 대안으로 수중불분리 주입재를 적용한 저압그라우팅을 적용하였다. 육상구간은 지상 작업부지를 확보할 수 있어 고압분사그라우팅을 적용하였다. 실제 그라우팅을 수행한 결과를 소개함으로써 향후 쉴드 TBM을 적용한 터널 시공 중 CHI 시 지반조건에 따른 적합한 그라우팅 공법 및 방법을 결정하는데 기초자료로 활용될 수 있을 것으로 기대된다.

• Geomechanics and Engineering
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• 제16권3호
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• pp.295-308
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• 2018

The excavation of twin tunnels is a process that destabilizes the ground. The stability of the tunnel lining, the control of ground displacements around the tunnel resulting from each excavation and the interaction between them must be controlled. This paper provides a new approach for replacing the costly 3D analyses with the equivalent 2D analyses that closely reflects the in-situ measurements when excavating twin tunnels. The modeling was performed in two dimensions using the FLAC2D finite difference code. The three-dimensional effect of excavation is taken into account through the deconfinement rate ${\lambda}$ of the soil surrounding the excavation by applying the convergence-confinement method. A comparison between settlements derived by the proposed 2D analysis and the settlements measured in a real project in Algeria shows an acceptable agreement. Also, this paper reports the investigation into the changes in deformations on tunnel linings and surface settlements which may be expected if the twin tunnels of T4 El-Harouche Skikda were constructed with a tunneling machine. Special attention was paid to the influence of the excavation phase shift distance between the two mechanized tunnel faces. It is revealed that the ground movements and the lining deformations during tunnel excavation depend on the distance between the tunnels' axis and the excavation phase shift.

• 터널과지하공간
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• 제29권3호
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• pp.148-156
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• 2019

최근 도심지에서의 터널 및 지하공간 개발에 있어 TBM을 비롯한 다양한 형태의 기계식 굴착장비의 적용이 증가하고 있다. 한편 기존의 전통적인 암석절삭방식에서 변형된 언더커팅방식 적용한 암반의 기계식 굴착공법에 대한 연구가 선진국을 중심으로 수행되어 소개된 바 있다. 따라서 국내에서도 기존의 암반기계굴착에 대한 연구를 지속적으로 수행함과 동시에 최신 기술에 대한 연구가 요구된다. 본 연구에서는 언더커팅에 대한 기초연구로서 해당 기술의 원리 및 굴착방식에 대한 소개와 더불어 해외 선진 기관들의 연구 현황을 조사하였다. 언더커팅공법은 터널 및 지하공간의 개발을 위한 단독공법으로 적용이 가능할 뿐만 아니라 터널의 확공 및 기존 공간의 확장을 위한 보조공법으로의 활용성도 우수한 것으로 판단되었다.