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CONTENTS
Volume 15, Number 3, June30 2018
 

Abstract
Chip size distribution can be used to evaluate the cutting efficiency and to characterize the cutting behavior of rock during cutting and fragmentation process. In this study, a series of linear cutting tests was performed to investigate the effect of cutting conditions (specifically cut spacing and penetration depth) on the production and size distribution of rock chips. Linyi sandstone from China was used in the linear cutting tests. After each run of linear cutting machine test, the rock chips were collected and their size distribution was analyzed using a sieving test and image processing. Image processing can rapidly and cost-effectively provide useful information of size distribution. Rosin-Rammer distribution pamameters, the coarseness index and the coefficients of uniformity and curvature were determined by image processing for different cutting conditions. The size of the rock chips was greatest at the optimum cut spacing, and the size distribution parameters were highly correlated with cutter forces and specific energy.

Key Words
chip size distribution; image processing; linear cutting machine (LCM) test; pick cutter; rock powder; cutting efficiency

Address
Hoyoung Jeong and Seokwon Jeon: Department of Energy Systems Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea

Abstract
The most important issue during shield TBM tunneling in soft ground formations is to appropriately control ground surface settlement. Among various operational conditions in shield TBM tunneling, the face pressure and backfill pressure should be the most important and immediate measure to restrain surface settlement during excavation. In this paper, a 3-D hydro-mechanical coupled FE model is developed to numerically simulate the entire process of shield TBM tunneling, which is verified by comparing with real field measurements of ground surface settlement. The effect of permeability and stiffness of ground formations on tunneling-induced surface settlement was discussed in the parametric study. An increase in the face pressure and backfill pressure does not always lead to a decrease in surface settlement, but there are the critical face pressure and backfill pressure. In addition, considering the relatively low permeability of ground formations, the surface settlement consists of two parts, i.e., immediate settlement and consolidation settlement, which shows a distinct settlement behavior to each other.

Key Words
TBM; face pressure; backfill pressure; consolidation; tunneling

Address
Kiseok Kim: Department of Civil and Environmental Engineering, University of Illinois, IL, U.S.A.

Juyoung Oh: Samsung C&T Corporation, Seoul, Korea

Hyobum Lee, Dongku Kim and Hangseok Choi: School of Civil, Environmental and Architectural Civil Engineering, Korea University, Seoul, Korea

Abstract
Dynamic behaviour of a tunnel is one of the most important issues for the safety and it is generally subjected to the seismic response of the surrounding soil. Relative displacement occurred in tunnel lining during earthquake produces severe damage. Generally, it concentrates at the connecting area when two tunnels are connected in the ground. A flexible segment is a useful device for the mitigation of seismic loads on tunnel lining. In this study, 1-g shaking table tests are performed to investigate the acceleration response for the verification of the effect of flexible segment and to determine the optimum location of the flexible segment for connected tunnels. Four different seismic waves are considered; as a result, peak acceleration is reduced to 49% in case that flexible segment is implemented adjacent to connecting area. It also exhibited that the mitigation of acceleration response is verified in all seismic waves. Additionally, 3-dimensional numerical analysis is performed to compare and verify the results. And the numerical results show good agreement to those of the experimental study.

Key Words
dynamic behavior; flexible segment; 1-g shaking table test; 3-dimensional numerical analysis

Address
Changwon Kwak: Civil & Architectural Engineering Group, KDHEC, Gyeonggi-do, 13591, Korea

Dongin Jang and Innjoon Park: Department of Civil Engineering, Hanseo University, 360, Choongnam, 32158, Korea

Kwangho You: School of Civil Environment Energy Engineering, University of Suwon, Gyeonggi-Do, 18323, Korea

Abstract
The purpose of a rock bolt is to improve the mechanical performance of a jointed-rock mass. The performance of a rock bolt is generally evaluated by conducting a field pullout test, as the analytical or numerical evaluation of the rock bolt behavior still remains difficult. In this study, wide range of field test was performed to investigate the pullout resistance of rock bolts considering influencing factors such as the rock type, water bearing conditions, rock bolt type and length. The test results showed that the fully grouted rock bolt (FGR) in water-bearing rocks can be inadequate to provide the required pullout resistance, meanwhile the inflated steel tube rock bolt (ISR) satisfied required pullout resistance, even immediately after installation in water-bearing conditions. The ISR was particularly effective when the water inflow into a drill hole is greater than 1.0 l/min. The effect of the rock bolt failure on the tunnel stability was investigated through numerical analysis. The results show that the contribution of the rock bolt to the overall stability of the tunnel was not significant. However, it is found that the rock bolt can effectively reinforce the jointed-rock mass and reduce the possibility of local collapses of rocks, thus the importance of the rock bolt should not be overlooked, regardless of the overall stability.

Key Words
pullout resistance; rock bolt; tunnel; water inflow

Address
Ho-Jong Kim, Kang-Hyun Kim and Jong-Ho Shin: Department of Civil Engineering, Konkuk University, Seoul 05029, Korea

Hong-Moon Kim:Department of Geotechnical & Tunnel Engineering, Pyunghwa Engineering, Anyang 13949, Gyeonggi-do, Korea

Abstract
There are two primary causes of the ground movement due to tunnelling in urban areas; firstly the lost ground and secondly the groundwater depression during construction. The groundwater depression was usually not considered as a cause of settlement in previous research works. The main purpose of this study is to analyze the combined effect of these two phenomena on the transverse settlement trough. Centrifuge model tests and numerical analysis were primarily selected as the methodology. The characteristics of settlement trough were analyzed by performing centrifuge model tests where acceleration reached up to 80g condition. Two different types of tunnel models of 180 mm diameter were prepared in order to match the prototype of a large tunnel of 14.4 m diameter. A volume loss model was made to simulate the excavation procedure at different volume loss and a drainage tunnel model was made to simulate the reduction in pore pressure distribution. Numerical analysis was performed using FLAC 2D program in order to analyze the effects of various groundwater depression values on the settlement trough. Unconfined fluid flow condition was selected to develop the phreatic surface and groundwater level on the surface. The settlement troughs obtained in the results were investigated according to the combined effect of excavation and groundwater depression. Subsequently, a new curve is suggested to consider elastic settlement in the modified Gaussian curve. The results show that the effects of groundwater depression are considerable as the settlement trough gets deeper and wider compared to the trough obtained only due to excavation. The relationships of maximum settlement and infection point with the reduced pore pressure at tunnel centerline are also suggested.

Key Words
volume loss; excavation; groundwater depression; settlement trough; centrifuge model test

Address
Jonguk Kim, Jungjoo Kim, Jaekook Lee and Hankyu Yoo: Department of Civil and Environmental Engineering, Hanyang University, 55 Hanyangdeahak-ro, Ansan, 15588, Republic of Korea

Abstract
Recent occurrences of earthquakes in Korea have increased the importance of considering how horizontal loads affect foundation structures as a result of wind and dynamic impact. However, to date, there are few studies on tunnelling-induced behaviour of ground and pile structures simultaneously subjected to horizontal and vertical loads. In this research, therefore, the behaviour of ground and single piles due to tunnelling were investigated through a laboratory model test. Three cases of horizontal loads were applied to the top of the pile. In addition, a numerical analysis was carried out to analyse and compare with the results from the laboratory model test.

Key Words
single pile, horizontal and vertical loads, tunnelling, laboratory model test, numerical analysis

Address
Dong-Wook Oh, Ho-Yeon Ahn and Yong-Joo Lee: Department of Civil Engineering, Seoul National University of Science and Technology,232 Gongneung-ro, Nowon-gu,
Seoul 01811, Republic of Korea


Abstract
The continually growing demand for underground space in dense urban cities is also driving the demand for underground highways. Building the underground highway tunnel, however, can involve complex design and construction considerations, particularly when there exists divergence or convergence in the tunnel. In this study, interaction between two asymmetric noncircular tunnels-that is, a larger main tunnel and a smaller tunnel diverging from the main tunnel, was investigated by examining the distributions of the principal stresses and the strength/stress ratio for varying geometric conditions between the two tunnels depending on diverging conditions using both numerical analysis and scale model test. The results of numerical analysis indicated that for the 0o, 30o, 60o diverging directions, the major principal stress showed an initial gradual decrease and then a little steeper increase with the increased distance from the left main tunnel, except for 90o where a continuous drop occurred, whereas the minor principal stress exhibited an opposite trend with the major principal stresses. The strength/stress ratio showed generally a bell-shaped but little skewed to left distribution over the distance increased from the left larger tunnel, similarly to the variation of the minor principal stress. For the inter-tunnel distance less than 0.5D, the lowest strength/stress ratio values were shown to be below 1.0 for all diverging directions (0o, 30o, 60o and 90o). The failure patterns observed from the model test were found to be reasonably consistent with the results of numerical analysis.

Key Words
underground highway; noncircular tunnel; principal stress; diverging condition; strength-stress ratio

Address
You-Sung La, Bumjoo Kim, Yeon-Soo Jang and Won-Hyuk Choi: Department of Civil and Environmental Engineering, Dongguk University, 30, Pildong-ro 1-gil, Jung-gu, Seoul, Republic of Korea

Abstract
Probability-based design codes have been developed to sufficiently confirm the safety level of structures. One of the most acceptable probability-based approaches is Load Resistance Factor Design (LRFD), which measures the safety level of the structures in terms of the reliability index. The main contribution of this paper is to calibrate the load and resistance factors of the design code for tunnels. The load and resistance factors are calculated using the available statistical models and probability-based procedures. The major steps include selection of representative structures, consideration of the limit state functions, calculation of reliability for the selected structures, selection of the target reliability index and calculation of load factors and resistance factors. The load and resistance models are reviewed. Statistical models of resistance (load carrying capacity) are summarized for strength limit state in bending, shear and compression. The reliability indices are calculated for several segments of a selected circular tunnel designed according to the tunnel manual report (Tunnel Manual). The novelty of this paper is the selection of the target reliability. In doing so, the uniform spectrum of reliability indices is proposed based on the probability paper. The final recommendation is proposed based on the closeness to the target reliability index.

Key Words
load and resistance factor; reliability analysis; target reliability; tunnels

Address
Seyed Hooman Ghasemi: Department of Civil Engineering, Qazvin Branch, Islamic Azad University, Qazvin 1477893855, Iran

Andrzej S. Nowak: Department of Civil Engineering, Auburn University, Auburn, AL 36849, U.S.A.

Abstract
Backfilling of mine stopes with waste rocks or tailings is commonly done to enhance ground stability. It is also an alternative for mining wastes disposal. A successful application of underground backfilling requires an accurate evaluation of the stress distribution in stopes. Over the years, various analytical solutions have been proposed to assess these stresses. Most of them were based on the arching theory, considering uniform stresses across horizontal layer elements. The vertical and horizontal stresses in vertical stopes are principal stresses only along the vertical center line, but not close to the walls where there is rotation of the principal stresses. A few solutions use arc layer elements that follow the iso-contours of the minor principal stresses, based on numerical solutions. In this paper, a modified analytical solution is developed for the stresses in vertical backfilled stopes, considering a circular arc distribution. The proposed solution is calibrated with a few numerical modeling results and then validated by additional numerical simulations under different conditions.

Key Words
backfill; arching effect; analytical solution; stresses; arc layer element

Address
El-Mustapha Jaouhar, Li Li and Michel Aubertin: 1.) Research Institute on Mines and Environment (RIME UQAT-Polytechnique)
2.) Department of Civil, Geological and Mining Engineering, École Polytechnique de Montréal, C.P. 6079,
Succursale Centre-Ville, Montréal, QC, H3C 3A7, Canada


Abstract
Terrace deposits are often encountered in portal areas and tunnels with low overburden. They are challenging to excavate considering their great mechanical and spatial heterogeneity and a very high stiffness contrast within the ground. Terrace deposits are difficult to characterize, considering that samples for laboratory testing are almost unfeasible to obtain, and laboratory tests may not be representative due to scale effects. This paper presents the approach taken for their characterization during the design stage and their posterior validation performed during construction. Lessons learned from several tunnels excavated on terrace deposits on the Bogota-Villavicencio road (central-east Colombia), suggest that based on numerical simulations, laboratory testing and tunnel system behaviour monitoring, an observational approach allows engineers to optimize the excavation and support methods for the encountered ground conditions, resulting in a more economic and safe construction.

Key Words
alluvial deposits; terrace; complex terrain; ground characterization; ground behaviour, back analysis, observational method

Address
Julio E. Colmenares: Department of Civil and Agricultural Engineering, Universidad Nacional de Colombia, Carrera 30 No. 45-03 - Bogotá D.C., Colombia

Juan M. Dávila and Jairo Vega: EDL SAS, Calle. 26 No. 59 - 41 - Bogotá D.C., Colombia

Jong-Ho Shin: Department of Civil Engineering, Konkuk University, 120 Neungdong-ro, Jayang 1(il)-dong, Gwangjin-gu, Seoul, Korea

Abstract
This paper concerns a numerical investigation on the effect of construction sequence on three-arch (3-Arch) tunnel behavior. A three-arch tunnel section adopted in a railway tunnel construction site was considered in this study. A calibrated 3D finite element model was used to conduct a parametric study on a variety of construction scenarios. The results of analyses were examined in terms of tunnel and ground surface settlements, shotcrete lining stresses, loads and stresses developed in center column in relation to the tunnel construction sequence. In particular, the effect of the side tunnel construction sequence on the structural performance of the center structure was fully examined. The results indicated that the load, thus stress, in the center structure can be smaller when excavating two side tunnels from opposite direction than excavating in the same direction. Also revealed was that no face lagging distance between the two side tunnels impose less ground load to the center structure. Fundamental governing mechanism of three-arch tunnel behavior is also discussed based on the results.

Key Words
3-arch tunnel; 3D finite element analysis; construction sequence; face lagging distance; center column load

Address
C. Yoo and J. Choi: School of Civil and Architectural Engineering, Sungkyunkwan University, Suwon, Korea

Abstract
Stress-strain responses of weak-to-strong carbonate rocks used for tunnel construction were studied. The analysis of applicability of exponential stress-strain models based on Haldane\'s distribution function is presented. It is revealed that these exponential equations presented in transformed forms allow us to predict stress-strain relationships over the whole pre-failure strain range without mechanical testing of rock samples under compression using a press machine and to avoid measurements of axial failure strains for which relatively large values of compressive stress are required. In this study, only one point measurement (small strain at small stress) using indentation test and uniaxial compressive strength determined by a standard Schmidt hammer are considered as input parameters to predict stress-strain response from zero strain/zero stress up to failure. Observations show good predictive capabilities of transformed stress-stress models for weak-to-strong (sigmac <100 MPa) heterogeneous carbonate rocks exhibiting small (< 0.5 %), intermediate (< 1 %) and large (> 1 %) axial strains.

Key Words
stress-strain model; failure strain; uniaxial compressive strength; carbonate rocks

Address
Vyacheslav Palchik: Department of Geological and Environmental Sciences, Ben-Gurion University, POB 653, Beer-Sheva 84105, Israel

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