• Tunnel and Underground Space
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• v.16 no.3 s.62
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• pp.203-208
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• 2006

This report is to introduce an article to compare 3 kinds of methods as RMR, Q-system and RMi published in Tunnel and Tunnelling Technology 2003. As rock mass classification is applied to estimate the amount of the support as an empirical design method, an attempt has been made to evaluate the parameters for classifications and their variations by Professor Nilsen and his team in Norway. Representability and reproducibility in measuring the field parameters are discussed and sensitivity of rating values in the three methods is also analyzed in this research. Although some parameters have high variation in rating among the 5 observers, the rock mass class has been found to be quite similar.

• Geomechanics and Engineering
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• v.27 no.5
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• pp.511-525
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• 2021

In the design of underground excavation, the shear strength (SS) is a key characteristic. It describes the way the rock material resists the shear stress-induced deformations. In general, the measurement of the parameters related to rock shear strength is done through laboratory experiments, which are costly, damaging, and time-consuming. Add to this the difficulty of preparing core samples of acceptable quality, particularly in case of highly weathered and fractured rock. This study applies rock index test to the indirect measurement of the SS parameters of shale. For this aim, two efficient artificial intelligence methods, namely (1) adaptive neuro-fuzzy inference system (ANFIS) implemented by subtractive clustering method (SCM) and (2) support vector regression (SVR) optimized by Harmony Search (HS) algorithm, are proposed. Note that, it is the first work that predicts the SS parameters of shale through ANFIS-SCM and SVR-HS hybrid models. In modeling processes of ANFIS-SCM and SVR-HS, the results obtained from the rock index tests were set as inputs, while the SS parameters were set as outputs. By reviewing the obtained results, it was found that both ANFIS-SCM and SVR-HS models can provide acceptable predictions for interlocking and friction angle parameters, however, ANFIS-SCM showed a better generalization capability.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.1
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• pp.55-77
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• 2012

A Modern Rock TBM is a tunnel excavation method combining the conventional tunnelling method with the mechanized tunnelling method. It is a hybrid system that excavates a tunnel with TBM and supports the ground by ring beam, wire mesh, rock bolt, shotcrete, i.e., conventional tunnelling method. In the Modern Rock TBM, a ring beam is similar to a steel rib in NATM in the way that uses H-beam. But using a ring beam is more effective than a steel rib because it is installed in a closed-circle. Therefore, improving the performance of the ring beam is a key factor for achieving tunnel stability. In this respect, this study introduces a pressurized ring beam that might be functioning more effectively by confining convergence during tunnel excavation. In order to verify the effect of the pressurized ring beam, a three-dimensional numerical analysis was conducted. The numerical analysis confirms an increase in the minimum principal stress and reduction in the plastic strain that triggers excessive displacement. The analysis result also indicates a decrease in the relative displacement occurring after installing the ring beam, and expansion in spacing between the ring beams.

• Geomechanics and Engineering
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• v.14 no.2
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• pp.151-159
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• 2018

Annually, the global production of construction aggregates reaches over 40 billion tons, making aggregates the largest mining sector by volume and value. Currently, the aggregate industry is shifting from sand to hard rock as a result of legislation limiting the extraction of natural sands and gravels. A major implication of this change in the aggregate industry is the need for understanding rock fragmentation and energy absorption to produce more cost-effective aggregates. In this paper, we focused on incorporating dynamic rock and soil mechanics to understand the effects of loading rate and water saturation on the rock fragmentation and energy absorption of three different sandstones (Red, Berea and Buff) with different pore sizes. Rock core samples were prepared in accordance to the ASTM standards for compressive strength testing. Saturated and dry samples were subsequently prepared and fragmented via fast and dynamic compressive strength tests. The particle size distributions of the resulting fragments were subsequently analyzed using mechanical gradation tests. Our results indicate that the rock fragment size generally decreased with increasing loading rate and water content. In addition, the fragment sizes in the larger pore size sample (Buff sandstone) were relatively smaller those in the smaller pore size sample (Red sandstone). Notably, energy absorption decreased with increased loading rate, water content and rock pore size. These results support the conclusion that rock fragment size is positively correlated with the energy absorption of rocks. In addition, the rock fragment size increases as the energy absorption increases. Thus, our data provide insightful information for improving cost-effective aggregate production methods.

• Geomechanics and Engineering
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• v.22 no.6
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• pp.509-518
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• 2020

Multi-layered primary linings have been proved to be highly effective for tunneling in severe squeezing grounds. But there still has not existed well-established design method for it. Basically, there are two main critical problems in this method, including determinations of allowable deformation and distribution of support stiffness. In order to address such problems, an attempt to investigate the mechanical response of a circular tunnel with double primary linings is performed in this paper. Analytical solutions in closed form for stresses and displacements around tunnels are derived. In addition, the effectiveness and reliability of theoretical formulas provided are well validated by using the numerical method. Finally, based on the analytical solutions, a parametric investigation on the effects of allowable deformation and distribution of support stiffness on tunnel performance is conducted. Results show that the rock pressure and displacement are significantly affected by these two design parameters. It can be found that rock pressure decreases as either allowable deformation increases or stiffness of the first primary lining decreases, but rock displacement shows an opposite trend. This paper can provide a useful guidance for the design of multi-layered primary linings.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.19 no.1
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• pp.75-85
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• 2021

Evaluating the quantitative damage to rocks through acoustic emission (AE) has become a research focus. Most studies mainly used one or two AE parameters to evaluate the degree of damage, but several AE parameters have been rarely used. In this study, several data-driven models were employed to reflect the combined features of AE parameters. Through uniaxial compression tests, we obtained mechanical and AE-signal data for five granite specimens. The maximum amplitude, hits, counts, rise time, absolute energy, and initiation frequency expressed as the cumulative value were selected as input parameters. The result showed that gradient boosting (GB) was the best model among the support vector regression methods. When GB was applied to the testing data, the root-mean-square error and R between the predicted and actual values were 0.96 and 0.077, respectively. A parameter analysis was performed to capture the parameter significance. The result showed that cumulative absolute energy was the main parameter for damage prediction. Thus, AE has practical applicability in predicting rock damage without conducting mechanical tests. Based on the results, this study will be useful for monitoring the near-field rock mass of nuclear waste repository.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.10a
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• pp.96-103
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• 2002

In this study, design concepts of Seoul Subway Construction (901∼914) are reviewed in relation to the cases for temporary soil support wall systems which are revealed in highly developed design competitions such as Turnkey and Alternative based on. Especially soil and rock properties, various design schemes for dealing with soil and water pressures, new technology adopted etc are discussed very profoundly and broadly for the better understanding and additional clues for constructing new design technologies.

• Tunnel and Underground Space
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• v.9 no.3
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• pp.204-213
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• 1999

NATM(New Austrian Tunnelling Method) uses a support system of shotcrete, rockbolt and steel support, which are installed after tunnel excavation. Recently, a lattice girder among these support system is used in tunnelling. A lattice girder is a new steel support developed in Europe for the replacement of an existing H-shaped steel set, which is reported to have some problems in installation. This is a triangular shape welded with steel rods and is a light-weight support system which enables fast and easy installation of porepolling. The major advantage of a lattice girder is the good bonding with shotcrete. In this study, to evaluate the applicability of a lattice girder in tunnelling in Korea, field tests were performed at a high speed railway tunnel with a large section. Also, features of lattice girder in field tests were compared with those of a H-shaped steel set respectively. Field tests proved that a lattice girder fully supported the initial earth pressure developed right after excavation and limited ground deformation effectively.

• Tunnel and Underground Space
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• v.13 no.1
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• pp.1-5
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• 2003

The United States Antarctic program (USAP) through its principal Support Contractor Raytheon polar Services Co. (RPSC), has recently finished a 3 years projects, almost 936m length of underground utility tunnels at Amundsen-Scott station. It accommodates the piping that conveys fresh water from current well sites, as well as waste water to repositories in abandoned wells. The under snow tunnels allow year-round access for system operations and maintenance.

• Journal of the Korean GEO-environmental Society
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• v.24 no.4
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• pp.13-22
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• 2023

In this paper, through experimental research, the period when rock bolts exert support effects is presented as grout strength and through numerical analysis, the rock bolt pull-out behavior according to ground conditions and strength reduction factors is analyzed. As a result, it is determined that rock bolts exhibit their reinforcing effect at a grout strength of 5 MPa (cured for 18 hours). The influence of the boundary interface strength reduction factor was found to be significant for rock bolt displacement in weak ground conditions, for shear stress between grout and ground in highly elastic ground conditions, and for grout stress in all ground conditions. These findings are expected to contribute to the establishment of specific standards for rock bolt testing and numerical analysis, and to facilitate improved design and implementation of rock bolt reinforcement.