• Tunnel and Underground Space
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• v.27 no.6
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• pp.366-376
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• 2017

In this paper, we investigated the subsidence possibility and countermeasures according to the current mining method through investigation of the subsidence condition in operation mine. Most of the metal mine were broken, investigating to subsidence pattern of the Sink-hole. Coal mines are becoming more and more deep, investigating to Trough type subsidence patterns in existing mining areas. History of nonmetallic mines have not been developed for over 30 years, but large and small ground deformation problems have been investigated. Mining also has ground subsidence functionality due to time dependence by relying more heavily on empirical methods than technical methods. Therefore, it is necessary to carry out the various researches on systematic development method and prevention of subsidence of nonmetallic mines.

• Tunnel and Underground Space
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• v.9 no.1
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• pp.56-63
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• 1999

Rock behaves in a complex way due to the discontinuities. To describe the complicated failure and deformation behavior of rock, many researches were focused on the development of crack models. This study discusses the validity of the sliding and shear crack model to systematically fractured rock, i.e. coal. The model was also implemented into a numerical analysis. For that, a finite element program was modified in several ways. To describe the transverse isotropy in two-dimensional analysis, the stress-strain relationship was modified for the direction of the axis of symmetry. Also, the changes of the effective elastic moduli according to the crack growth were calculated. A simple example of two-dimensional laboratory uniaxial compression test was analyzed. The results coincided with the observations obtained from the laboratory tests.

• Journal of Veterinary Clinics
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• v.34 no.1
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• pp.54-57
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• 2017

A 1-year-old castrated male Schnauzer dog was presented with heart murmur. Auscultation revealed systolic murmur located at the left heart base (grade 5/6). There were no remarkable findings on thoracic radiographs. Two-dimensional echocardiography revealed subaortic tunnel-like obstruction at the entrance to the left ventricular outflow tract. Anterior mitral valve leaflet appeared to be tethered to septum with minimal motion. Chordae tendineae was abnormally thickened. Color Doppler analysis revealed turbulent flow starting below the aortic valve. Mitral regurgitation was presented during systole. Spectral Doppler recordings revealed high velocity flow through the aorta and mitral regurgitation. Based on echocardiographic examination, the dog was diagnosed with subaortic stenosis concurrent with mitral dysplasia. The patient was medicated with ${\beta}-blocker$ and diuretics. It has been doing well without apparent clinical signs at 2 year after the diagnosis.

• Geomechanics and Engineering
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• v.16 no.6
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• pp.619-626
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• 2018

A simple prediction procedure was investigated for calculating the stresses and displacements of a circular opening. Unlike existed approaches, the proposed approach starts each step with a radius increment. The stress for each annulus could be obtained analytically, while strain increments for each step can be determinate numerically from the compatility equation by finite difference approximation, flow rule and Hooke's law. In the successive manner, the distributions of stresses and displacements could be found. It should be noted that the finial radial stress and displacement were equal to the internal supporting pressure and deformation at the tunnel wall, respectively. By assuming different plastic radii, GRC and the evolution curve of plastic radii and internal supporting pressures could be obtained conveniently. Then the real plastic radius can be calculated by using linear interpolation in the evolution curve. Some numerical and engineering examples were performed to demonstrate the accuracy and validity for the proposed procedure. The comparisons results show that the proposed procedure was faster than that in Lee and Pietrucszczak (2008). The influence of annulus number and dilation on the accuracy of solutions was also investigated. Results show that the larger the annulus number was, the more accurate the solutions were. Solutions in Park et al. (2008) were significantly influenced by dilation.

• Tunnel and Underground Space
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• v.10 no.2
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• pp.180-195
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• 2000

Grouting has been practiced as a reliable technique to improve the mechanical properties of rock mass. But, the study of ground improvement by greeting is rare especially in jointed rock mass. In this study, joint compression test and direct shear test were performed on pure rock joint and cement milk grouted rock joint to examine the grouting effect on the property of rock joint. In the pure rock joint compression test, joint closure varied non-linearly with normal stress. But after cement milk grouting, the normal deformation characteristics of the joint was linear at the low normal stress level. As normal stress increased. deformation of the sample rapidly increased due to the stress concentration at the joint asperities. Peak shear strength of the grouted joint in low normal stress was higher than that of non-grouted joint due to the cohesion, decreased exponetially as the grout thickness increased. Thus after cement milk grouting, the failure envelope modified to a curve that has cohesion due to grout material hydration with decreased friction angle. Shear stiffness and peak dilation angle of the grouted joint decreased as the grout thickness increased. The peak shear strength from the direct shear test on grouted rock joint was represented by an empirical equation as a fuction of grout thickness and roughness mean amplitude.

• Tunnel and Underground Space
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• v.23 no.6
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• pp.493-505
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• 2013

This numerical study investigates seismicity and fault slip induced by fluid injection in deep geothermal reservoir with pre-existing fractures and fault. Particle Flow Code 2D is used with additionally implemented hydro-mechanical coupled fluid flow algorithm and acoustic emission moment tensor inversion algorithm. The output of the model includes spatio-temporal evolution of induced seismicity (hypocenter locations and magnitudes) and fault deformation (failure and slip) in relation to fluid pressure distribution. The model is applied to a case of fluid injection with constant rates changing in three steps using different fluid characters, i.e. the viscosity, and different injection locations. In fractured reservoir, spatio-temporal distribution of the induced seismicity differs significantly depending on the viscosity of the fracturing fluid. In a fractured reservoir, injection of low viscosity fluid results in larger volume of induced seismicity cloud as the fluid can migrate easily to the reservoir and cause large number and magnitude of induced seismicity in the post-shut-in period. In a faulted reservoir, fault deformation (co-seismic failure and aseismic slip) can occur by a small perturbation of fracturing fluid (<0.1 MPa) can be induced when the injection location is set close to the fault. The presented numerical model technique can practically be used in geothermal industry to predict the induced seismicity pattern and magnitude distribution resulting from hydraulic stimulation of geothermal reservoirs prior to actual injection operation.

• Tunnel and Underground Space
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• v.33 no.3
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• pp.150-168
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• 2023

The anisotropic behavior of rocks is primarily attributed to the directional arrangement of rock-forming minerals and the distribution characteristics of microcracks. Notably, sedimentary and metamorphic rocks often exhibit distinct transverse isotropy in terms of their strength and deformation characteristics. Consequently, it is crucial to gain accurate insights into the deformation and failure characteristics of transversely isotropic rocks during rock mechanics design processes. The deformation of such rocks is described by five independent elastic constants, which are determined through laboratory testing. In this study, the characteristics of the directional variation of apparent elastic constants in transversely isotropic rocks were investigated using experimental data reported in the literature. To achieve this, the constitutive equation proposed by Mehrabadi & Cowin was introduced to calculate the apparent elastic constants more efficiently and systematically in a rotated Cartesian coordinate system. Four transversely isotropic rock types from the literature were selected, and the influence of changes in the orientation of the weak plane on the variations of the apparent elastic modulus, apparent shear modulus, and apparent Poisson's ratio was analyzed. Based on the investigation, a new constraint on the elastic constants has been proposed. If the proposed constraint is satisfied, the directional variation of the apparent elastic constants in transversely isotropic rocks aligns with intuitive predictions of their tendencies.

• The Journal of Engineering Geology
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• v.20 no.3
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• pp.329-338
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• 2010

The foundation area for tram contains biotite gneiss, quartzo-feldspathic gneiss, calc-silicate rock, and porphyroblastic gneiss of the pre-Cambrian Kyeonggi gneiss complex. These rocks record at least three stages of deformation, as indicated by fold sets of contrasting orientations (D1-D3). Joints are generally steeply dipping and strike NW-SE to WNW-ESE. The Gonjiam Fault, which strikes WNW-ESE, follows a river in the area. The fault possesses a 3-m-wide fracture zone, a 10-m-wide damage zone, and is 15 km long. Two tunnels have been constructed through the biotite gneiss. The geometric relationship between discontinuities (e.g., joints and foliation) and tunneling direction reveals that set 3 of the AA tunnel is unstable but that BB tunnel is relatively safe.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.4
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• pp.295-306
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• 2010

Contrary to an intact rock, the jointed rock mass shows strain-dependent deformation characteristics (elastic modulus and damping ratio). The maximum elastic modulus of a rock mass can be obtained from an elastic wave-based exploration in a small strain level and applied to seismic analyses. However, the assessment and application of the non-linear characteristics of rock masses in a small to medium strain level ($10^{-4}{\sim}0.5%$) have not been carried out yet. A non-linear dynamic analysis module is newly developed for FLAC3D to simulate strain-dependent shear modulus degradation and damping ratio amplification characteristics. The developed module is verified by analyzing the change of the Ricker wave propagation. Strain-dependent non-linear characteristics are obtained from disks of cored samples using a rock mass dynamic testing apparatus which can evaluate wave propagation characteristics in a jointed rock column. Using the experimental results and the developed non-linear dynamic module, seismic analyses are performed for the intersection of a shaft and an inclined tunnel. The numerical results show that vertical and horizontal displacements of non-linear analyses are larger than those of linear analyses. Also, non-linear analyses induce bigger bending compressive stresses acting on the lining. The bending compressive stress concentrates at the intersection part. The fundamental understanding of a strain-dependent jointed rock mass behavior is achieved in this study and the analytical procedure suggested can be effectively applied to field designs and analyses.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.71-83
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• 2009

Shotcrete is an important primary support for tunnelling in rock. The quality control of shotcrete is a core issue in the safe construction and maintenance of tunnels. Although shotcrete may be applied well initially onto excavated rock surfaces, it is affected by blasting, rock deformation and shrinkage and can debond from the excavated surface, causing problems such as corrosion, buckling, fracturing and the creation of internal voids. This study suggests an effective non-destructive evaluation method of the tunnel shotcrete bonding state applied onto hard rocks using the impact-echo (IE) method and ground penetration radar (GPR). To verify previous numerical simulation results, experimental study carried out. Generally, the bonding state of shotcrete can be classified into void, debonded, and fully bonded. In the laboratory, three different bonding conditions were modeled. The signals obtained from the experimental IE tests were analyzed at the time domain, frequency domain, and time-frequency domain (i.e., the Short- Time Fourier transform). For all cases in the analyses, the experimental test results were in good agreement with the previous numerical simulation results, verifying this approach. Both the numerical and experimental results suggest that the bonding state of shotcrete can be evaluated through changes in the resonance frequency and geometric damping ratio in a frequency domain analysis, and through changes in the contour shape and correlation coefficient in a time-frequency analysis: as the bonding state worsens in hard rock condition, the autospectral density increases, the geometric damping ratio decreases, and the contour shape in the time-frequency domain has a long tail parallel to the time axis. The correlation coefficient can be effectively applied for a quantitative evaluation of bonding state of tunnel shotcrete. Finally, the bonding state of shotcrete can be successfully evaluated based on the process suggested in this study.