• Tunnel and Underground Space
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• v.22 no.5
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• pp.330-338
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• 2012

Though the uniaxial compressive strength (UCS) of rock material is one of the key properties for rockmass characterization purposes, core samples for the test cannot always be obtained from the field. Indirect tests such as the point load test (PLT) can be a useful alternative. In this study, correlation between the UCS and the point load strength index of limestone of Imgye area was analyzed, and the linear regression equation obtained from regression analysis of two variables was suggested. The results of this study were also compared with previous studies on limestone. It was suggested that conversion factors for the same rock type from diverse areas in Korea may have different values, and more data should be obtained to increase the accuracy of regression analysis.

• Tunnel and Underground Space
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• v.24 no.1
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• pp.46-54
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• 2014

Direct shear tests have been initiated to understand the characteristics of joints which crucially affect the stability of rock mass. In this research, numerical approach in direct shear tests has been initiated using 3DEC on the basis of 3D distinct element method. Normal loads were altered in four different levels on artificial joint tests depending on the sawtooth angle and strengths on constant normal stress conditions, measuring the peak shear strength according to the direct shear tests under laboratory condition. Also results obtained from mechanical properties through laboratory test were used to perform numerical modeling, and shear strength obtained from the modeling was used to compare with laboratory direct shear test. As a result numerical analysis from distinct element method can simulate well on the shear behavior of rockmass.

• Tunnel and Underground Space
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• v.19 no.4
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• pp.355-365
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• 2009

This paper proposes an elasto-plastic finite difference method which is useful for the stability evaluation of concrete lining installed in a deep circular tunnel. Mohr-Coulomb criterion is assumed for the condition of yielding in both the rock mass and concrete lining. In order to take into account the installation delay of lining after the excavation, the outer boundary pressure acting on the lining was calculated with the consideration of the convergence occurred before the lining installation. The distributions of stress and displacement in the rock mass and lining were calculated based on the method proposed Lee & Pietruszczak (2008). The applicability of the proposed method was demonstrated by conducting the elasto-plastic analysis of concrete lining supporting an imaginary compressed air storage tunnel. The analysis result revealed that the exact determination of the boundary pressures acting on the concrete lining is of importance in the stability analysis of concrete lining.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2003.03a
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• pp.13-30
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• 2003

In this paper, a new systematic method will be introduced, in which a Rock-mass Prediction System(RPS) predicts the geological conditions and rock mass movements before tunnel excavation and the appropriate counter-measures are taken in the expected weak zones during tunnel construction. The Rock-mass Prediction System(RPS) consists of the LIM, a horizontal core drilling and a seismic exploration method(TSP/HSP). In the Rock-mass Prediction System(RPS), the seismic exploration method (TSP/HSP) gives information on the locations of the weak zones such as major faults and voids in wide-range, and the horizontal core drillings are utilized to find exact location and widths of the faults or voids near the weak zones which was predicted by the seismic exploration method (TSP/HSP). The LIM is used to find the hardness of the rock mass and small weak zones near the excavation face. The Rock-mass Prediction System (RPS) was successfully applied to the Sol-An Tunnel and the effectiveness of the system was verified.

• The Journal of Engineering Geology
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• v.32 no.4
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• pp.725-733
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• 2022

This study applied a hydraulic rock splitting system equipped with a hybrid packer to the bench-cut method. The hybrid packer system is an improvement of the packer developed in previous studies; it is designed efficiently to reduce vibration and noise during rock excavation by combining the two functions of inducing hydraulic fractures using injection pressure and then expanding and extending them using a rubber packer. Field experiments assessed the efficiency of rock excavation with respect to the injection conditions; the adjusted experimental conditions included the distance from the free surface and the test holes drilled at the top of the slope and the injection settings. Using a separation of 5 m left some unexcavated parts, but using a separation of 1 m left no unexcavated parts. The hydraulic fractures generated by the injection pressure developed generally parallel to the free surface and expanded and extended as the rubber packer expanded, thus facilitating bench-cut excavation. For hydraulic rock splitting to be broadly applicable to bench-cut rock excavation, it is important to accumulate results from many field experiments conducted under varying experimental conditions for various types of rockmass.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2C
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• pp.95-107
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• 2010

To calculate the end bearing capacity of a drilled Shaft socketed into the rockmass, the unconfined compression strength could be used. But it is difficult to find the unconfined compression strength because it is impossible to get undisturbed samples in weathered soils and rocks. So, to calculate the end bearing capacity, the existing bearing formula could not be used. In this study, for five zones (near pile tip, tip~lower 1D, tip~lower 2D, upper 1D~lower 1D, upper 1D~lower 2D), the relationships between the characteristic values of in-situ tests(SPT, DCPT PMT, BST) and the end bearing capacity of drilled shafts were analysed. As a result, DCPT results were represented the best credibility. Also, a design chart of end bearing capacity using DCPT was suggested.

• The Journal of Engineering Geology
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• v.19 no.1
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• pp.63-70
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• 2009

The optical fiber cable acting as a sensor was embedded in the underground research tunnel and portal area in order to monitor their stability and the spatial temperature variation. This system includes two types of sensing function to monitor the distributed strain and temperature along the line, where sensor cable is installed, not a point sensing. According to the results of one year monitoring around the KURT, there is no significant displacement or movement at the tunnel wall and portal slope. However, it would be able to aware of some phenomena as an advance notice at the tunnel wall which indicates the fracturing in rockmass and shotcrete fragmentation before rock falls accidently as well as movement of earth slope. The measurement resolution for rock mass displacement is 1 mm per 1 m and it covers 30 km length with every 1m interval in minimum. In temperature, the cable measures the range of $-160{\sim}600^{\circ}C$ with $0.01^{\circ}C$ resolution according to the cable types. This means that it would be applicable to monitoring system for the safe operation of various kinds of facilities having static and/or dynamic characteristics, such as chemical plant, pipeline, rail, huge building, long and slim structures, bridge, subway and marine vessel. etc.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.3
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• pp.221-232
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• 2008

Rock bolts have been installed into rockmass as a main support system. In order to evaluate the rock bolt integrity using non-destructive technique, the transmission method of the guided ultrasonic wave has been successfully performed. For the transmission method, however, the source for the generation o# guided ultrasonic waves should be installed at the end of the steel bar during construction of the rock bolt in the field. The purpose of this study is to suggest a reflection method that the source and the receiver are installed on the head of the steel bar. The reflection method is compared with the transmission method using non-embedded rock bolts and rock bolts embedded in concrete block. In this experiment, the piezo disc element is used as the source and the AE sensor is used as the receiver. The wavelet transform is applied to determine the energy velocity. The experimental studies show that the reflection method produces almost identical value of the transmission method, and the energy velocity increases with the defect ratio. This study suggests that the reflection method of the guided ultrasonic wave may be a suitable method fur the rock bolt integrity evaluation in the field.

• Tunnel and Underground Space
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• v.22 no.6
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• pp.462-470
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• 2012

Implementing the generalized Hoek-Brown failure criterion in the framework of the Mohr-Coulomb criterion requires the calculation of the equivalent friction angle and cohesion. In the conventional method based on the Balmer (1952)'s theory, the tangential instantaneous friction angle and cohesion are expressed in terms of the minimum principal stress ${\sigma}_3$, which does not provide the information about the dependency of the equivalent parameters on the hydrostatic pressure and the stress path. In this study, this defect of the conventional method has been overcome by representing the equivalent parameters in terms of stress invariants. Through the example implementation of the new method, the influence of the magnitude of the hydrostatic pressure and the Lode angle on the tangential instantaneous friction angle and cohesion is investigated. It turns out that the tangential instantaneous friction angle is maximum when the stress condition is triaxial extension, while the tangential cohesion is maximum when the stress condition is triaxial compression. The dependency of the equivalent Mohr-Coulomb strength parameters on the hydrostatic pressure and the Lode angle tends to be more substantial for the favorable rockmass of larger GSI value.

• Journal of the Korean Geotechnical Society
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• v.30 no.7
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• pp.17-26
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• 2014

Tunneling-induced displacement in a jointed rock mass is an important factor to control tunnel stability and to secure a demanded space and construction quality. The magnitude of the inducible displacements is significantly affected by an elastic modulus and therefore, in a rock mass where a joint controls tunnel behavior, it is very important to estimate an elastic modulus of jointed rock mass reliably. Elastic modulus of jointed rock mass is affected by many factors such as rock type, joint condition, and loading condition. Nevertheless, most existing studies were focused on rough empirical relationships based on compressive loading conditions, which are different from tunnel excavation loading conditions, without a systematic approach of rock, joint, and loading conditions together. Therefore, this study considered rock and joint conditions systematically to estimate an elastic modulus of jointed rock mass under tunnel excavation loading. The controlled factors considered in this study are rock types and joint conditions (joint shear strength, joint inclination angle, number of joint sets, and joint spacing). Numerical parametric studies have been carried out with a consideration of different rock and joint conditions; the results have been compared with existing empirical relationships; and charts of elastic modulus change of different rock and joint conditions have been provided. The results are expected to have a great practical use for estimating the convergence induced by tunnel excavation in jointed rockmass.