• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.6
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• pp.543-552
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• 2014

This research covers correlation analysis between the machine data measured from EPB Shield TBM construction site and the ground condition during excavation, and figures out how the machine data are affected by the change of ground conditions through single and mixed parameter analysis. It was found that when the ground is changed from hard rock to soft rock, the ratio of the cutter torque to thrust force increases. The relationship between the ratio of the cutter torque to thrust force and the penetration rate shows that the ratio has a certain range of values for hard rock; on the other hand, it increases for soft rock. It means that we can recognize a sign of appearance of weak zone by assessing the ratio of the cutter touque to thrust force according to each penetration rate. Multiple regression analysis of the machine data showed that the cutter torque increases with the increases of the total thrust force, and it decreases with the increase of the uniaxial compressive strength of the ground.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.5
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• pp.657-673
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• 2019

A monitoring method based on acoustic emission (AE) sensor has been widely used to evaluate the damage of structures in underground rock. The acoustic emission signal generated from cracking in material is analyzed as various acoustic emission parameters in time and frequency domain. To investigate from initial crack generation to final failure of rock material, it is important to understand the characteristics of acoustic emission parameters according to the stress ratio and rock strength. In this study, uniaxial compression tests were performed using very strong and weak rock specimen in order to investigate the acoustic emission parameters when the failure of specimen occurred. In the results of experimental tests, the event, root-mean-square (RMS) voltage, amplitude, and absolute energy of very strong rock specimen were larger than those of the weak rock specimen with an increase of stress ratio. In addition, the acoustic emission parameters related in frequency were more affected by specification (e.g., operation and resonant frequency) of sensors than the stress ratio or rock strength. It is expected that this study may be meaningful for evaluating the damage of underground rock when the health monitoring based on the acoustic emission technique will be performed.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.6
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• pp.623-641
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• 2020

About 5 km length of tunnels were constructed by mechanized tunnelling method using closed type shield TBM. In order to avoid construction delay problems for ensuring timely electricity transmission, it is necessary to increase the prediction accuracy of the excavation process involving machines according to rock mass types. This is important to corroborate the project duration and optimum operation for various considerations involved in the machine. So, full-scale tunnelling tests were performed for developing the advance rate model to be appropriately used for 3.6 m diameter shield TBM. About 100 test cases were established and performed using various operational parameters such as thrust force and rotational speed of cuttterhead in representative uniaxial compressive strengths. Accordingly, relationships between normal force and penetration depth and, between UCS and torque were suggested which consider UCS and thrust force conditions according to weathered, soft, hard rocks. Capacity analysis of cutterhead was performed and optimum operational conditions were also suggested based on the developed model. Based on this study, it can be expected that the project construction duration can be reduced and users can benefit from the provision of earlier service.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.6
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• pp.573-584
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• 2014

In this study, the variations of cutter acting forces depending on cutting conditions were examined to obtain basic data for roadheader cutting head design. The linear cutting tests were performed in the condition of different attack angles, penetration depths, cutter spacings by using a slim conical pick for the light cutting condition. Cutter acting forces were measured by 3-directional load cell under different test conditions, and the analysis for cutting performance were carried out after calculating average values of the measured results. It is confirmed that the optimal cutting condition for the mortar specimen is the 50 degree attack angle, the cutter spacing of 12 mm, the cutting depth of 9 mm which are obtained from the analysis results. In addition, 50 degree attack angle is more effective than 45 degree attack angle to design optimal specifications of cutting head.

• Tunnel and Underground Space
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• v.28 no.3
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• pp.232-246
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• 2018

In this study, the relationship between in situ seismic wave velocities and RMR (rock mass rating) was investigated in a test bed for the examination of the basis of rock classification (RMR) based on seismic wave velocity. The seismic wave velocity showed a monotonous increase with depth. It was also found that there was no systematic correlation between the seismic wave velocity (Vp) and other parameters (RQD, joint spacing, UCS, rock core Vp, and RMR) collected at the same depth of the same borehole. However, correlative relation was observed among RMR, RQD, and joint spacing. On the other hand, when all the data in the borehole (three holes) are examined without considering the depth, Vp still shows no correlation with RMR parameters (e.g., correlative coefficient for uniaxial compressive strength and joint spacing are 0.039 and 0.091, respectively), but Vp shows weak correlative relation with RMR and RQD (correlative coefficient for RQD and RMR are 0.193 and 0.211, respectively). Thus, it is found that it is difficult to deduce physical properties of rock mass directly from seismic wave velocities, but the seismic wave velocity can be used as a tool to approximate rock mass properties because of weaker correlation between Vp and RMR with RQD. In addition, the velocity value of for soft and moderate rocks suggested by widely used construction standards is slower than that of the observed velocity, implying that the standards need to be examined and revised.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4C
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• pp.147-154
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• 2011

Currently NATM tunnels are designed by applying the initial ground loads caused during construction to the primary supports, conisting of shotcrete, steel ribs and rock bolts. For long term considerations, it is assumed that the primary supports lose its functionality and therefore the secondary support, i.e. concrete lining, is design to resist against the entire ground loads. But the steel ribs, usually applied to bad ground conditions, are embedded in shotcrete causing very little corrosion and therefore the assumption that the primary support will lose all of its functionality is too conservative. Also even though shotcrete carbonates in long term, excluding it from design is also too conservative. In this study, we have, through analytical and numerical analysis, set a rational level of support pressure and allowable relaxed rock mass height sustainable by the primary support for long term design. Changes in sectional forces of the concrete lining considering the calculated support pressure of the primary supports was also carried out. Shallow subway tunnels were considered in the analysis with weathered rock and soft rock ground conditions. The analysis results showed that, by considering the support pressure of steel ribs, an economical design of the concrete lining is possible.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.4
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• pp.457-471
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• 2015

A domestic cutterhead with the diameter of 3.6 m was designed and manufactured in this study. Then, it was attached to an existing earth-pressure balanced shield TBM to excavate a cable tunnel with the length of 1,275 m. Especially, the procedures for TBM cutterhead design and its corresponding performance prediction were also summarized. From field data analyses of the refurbished shield TBM, its maximum advance rate was recorded as 14.4 m/day. Penetration depths of disc cutters were found to be approximately 4 mm/rev, which is equal to the maximum penetration depth designed for the strongest rock strength condition in the target tunnel. Every TBM operating thrust and cutter normal force during TBM driving was much smaller than their corresponding maximum capacities. When cutter acting forces recorded in the field were analyzed, their prediction errors by the CSM model were very high for weak rock conditions. In addition, rock strength showed very close relationships with cutter normal force and penetration depth.

• Tunnel and Underground Space
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• v.11 no.3
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• pp.206-216
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• 2001

Many failures in cut slopes occur during and following road construction. Failures are caused, in part, by a lack of understanding of the characteristics of rock mass including its geologic structure. The stability of rock slopes is closely related to factors that include the type of rock, development of geological structures, weathering, characteristics of rock, and the shape of the geologic features. Therefore, it is very important to consider these characteristics of rock mass in the evaluation of rock slope stability. In spite of investigation from many slope failures, these information data were not systematically stored and not efficiently utilized. In this study, a Database system named DB/SLOPE was developed using Oracle for systematic management of cut slopes. The developed database system can be used to estimate of slope stability and to predict of slope failure.

• Journal of the Korean Geotechnical Society
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• v.28 no.8
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• pp.79-88
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• 2012

In this study, the tunnel loads acting on the concrete lining are analyzed by comparing three methods - Terzaghi table, Terzaghi formula and Ground-Lining Interaction (G.L.I) model. The tunnel loads are analyzed by FLAC 2D. And the G.L.I model is analyzed under various rock mass ratings, tunnel depths (20~80m) and in-situ stress ratios ($K_0$=0.5~2.0). Terzaghi's method can be applied only to weathered rocks and soils, and cannot reflect the effect of various tunnel depths and in-situ stress ratio. The proposed G.L.I model can not only be applied to various ground conditions, but also relieves the tunnel loads by up to 30%.

• Tunnel and Underground Space
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• v.26 no.6
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• pp.508-515
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• 2016

In this study, we compared the stability of the pillars by using room and pillar mining method with the four models with different stiffness and pillar overlap ratio. The experimental models consist of two plaster models (overlap ratio 0%, 100%) and two cement models(overlap ratio 0%, 100%). The soft and hard rocks are modeled by plaster and cement models respectively. In these experiments, the model materials with strength values reflecting the calculated scaled factors not been used, so it is not a true scaled model test that reproduces in situ state in the laboratory. Experimental results show that the different overlap ratio pillars are one of the factors that can affect the stability of the mine.