• Tunnel and Underground Space
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• v.18 no.6
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• pp.447-456
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• 2008

Open-pit mine slope design must be carried out from the economical efficiency and stability point of view. The overall slope angle is the primary design variable because of limited support or reinforce options available. In this study, the slope angle and critical slope height of large coal mine located in Pasir, Kalimantan, Indonesia were determined from safety point of view. Failure time prediction based on the monitored displacement using inverse velocity was also conducted to make up fir the uncertainty of the slope design. From the study, critical slope height was calculated as $353{\sim}438m$ under safety factor guideline (SF>1.5) and $30^{\circ}$ overall slope angle but loom is recommended as a critical slope height considering the results of sensitivity analysis of strength parameters. The results of inverse velocity analysis also showed good agreement with field slope cases. Therefore, failure of unstable slope can be roughly detected before real slope failure.

• Tunnel and Underground Space
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• v.20 no.4
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• pp.292-298
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• 2010

The purpose of this study is to evaluate an effect of ground vibration caused by blasting on the concrete brick structure. For the purpose, dynamic response time-history of the structure assumed single degree of freedom (SDOF) system and vibration time-history directly measured from the structure were examined, using Newmark $\beta$ method based on data measured at ground. The time-history was interpreted from the measured data of ground and structure in single hole blasting. Vibration magnitude between ground vibration and structure in single hole blasting and 20 ms interval blasting was about three times and was shown larger vibration on the structure. By time-history analysis of structure dynamic response, the value was almost the same one with the data measured from the structure. It indicates that the vibration characteristics of structures may be predicted on the basis of the ground vibration data measured from the sub-ground of structure.

• Tunnel and Underground Space
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• v.14 no.6 s.53
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• pp.411-422
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• 2004

Sinkhole subsidence occurs over abandoned mine workings and can be detrimental to human lives, damage to properties and other surface structures. In this study, simulation of sinkhole development process is performed using special finite element procedure. Especially, creation of mine voids due to roof falls and generation of goaf from broken rocks are simulated using active-passive-active finite elements. An active or solid element can be made passive or void once the tensile failure criterion is satisfied in the specified sinkhole formation zone. Upon completion of sinkhole development process, these passive elements in again be made active to simulate goal region. Several finite element models are analyzed to evaluate the relationships between sinkhole formation with width of gallery. depth of mine, roof condition and bulking factor of roof rocks. This study demonstrates that the concept of passive elements in numerical analysis can be used effectively for analyzing sinkhole formation or roof fall phenomenon in general.

• Tunnel and Underground Space
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• v.15 no.4 s.57
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• pp.296-304
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• 2005

This study is to observe stray currents generated around the steel tower by domestic transmission network system and analysis stability of electric detonator. It is measured the stay current of each ten place at steel tower of 765 kV, 345 tV, 154 tV transmission line among domestic transmission network system. Stay currents measured a total of 40m at intervals of 4m toward a line direction and a line vertical direction centering around steel tower. Temperature of the surface, EC, water content also are measured. Although stay currents show the highest values, that is 12 percent of at 4m and less than 1 percent of 40m with Institute of Makers of Explosives(IME) regulations. It is shown correlation between stay currents and water content$\cdot$EC$\cdot$temperature of the surface. Stay currents measured at line direction and line vertical direction were little different and the shape of diminution was also shown a similar aspect.

• Tunnel and Underground Space
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• v.11 no.4
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• pp.352-361
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• 2001

Mode I fracture toughness ( $K_{IC}$) of the frozen rocks and that of the frozen-thawed rocks were obtained by using BDT and CCNBD specimens. The test temperatures ranged from +$25^{\circ}C$ to -16$0^{\circ}C$. Wet and air-dry specimens of granite and sandstone were used in order to investigate the effect of water and porosity on fracture toughness. The SEM images of the frozen-thawed rocks were also analysed to check the density of thermal cracks. The $K_{IC}$ of the frozen rocks increased as the test temperature went down. The rate of increase was higher in wet condition than in dry condition and the rate of increase for wet granite was higher than that for wet sandstone. The $K_{IC}$ of the frozen-thawed rocks varied within 15% from the $K_{IC}$ of the rocks at room temperature. After one freeze-thaw process, thermal crack occurred in granite but no thermal cracks occurred in sandstone. And the crack density was increased as the temperature went down.n.

• Tunnel and Underground Space
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• v.11 no.4
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• pp.301-310
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• 2001

Gypsum blocks with sixteen flaws have been prepared and tested in uniaxial compression. Results from these experiments are compared with observations from the same material with two and three flaws. The results indicate that the cracking pattern observed in specimens wish multiple flaws is analogous to the pattern obtained in specimens with two and three flaws such as initiation and propagation of wing, and secondary cracks and coalescence. Wing cracks initiate at an angle with the flaw and propagate in a stable manner towards the direction of maximum compression. Secondary cracks initiate and propagate in a stable manner. As the load is increased, secondary cracks may propagate in an unstable manner and produce coalescence. Two types of secondary cracks are observed: quasi-coplanar, and oblique secondary cracks. Coalescence is produced by the linkage of two flaws: wing and/or secondary cracks. From the sixteen flaws test, four types of coalescence are observed. Observed types of coalescence and initiation stress of wing and secondary crackle depend on flaw geometries, such as spacing, continuity, flaw inclination angle, ligament angle, and steppings.

• Tunnel and Underground Space
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• v.13 no.4
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• pp.287-293
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• 2003

A long vertical duct is an essential installation for extracting smoke to the ground level when a fire occurs in an underground space. Due to the limitations of its basic assumptions, the existing two-layer zone model is unsuitable to model smoke dispersion through a long vertical duct. Therefore, an assessment was made to investigate the applicability of the field model, which is based on the computational fluid dynamics (CFD). A similar configuration to the published experimental work was modeled to test the validity. It is clear that under a consistent decision criterion based on the mass fraction, the field model (CFD) is able to predict that the diffusion front progresses up the shaft with exactly the same rate as that in the empirical correlation equation. This result is for better than the mathematically obtained equations in previously published research. Therefore, it can be said that the field model is an excellent option to predict the smoke dispersion through the long vertical shaft.

• Tunnel and Underground Space
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• v.11 no.4
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• pp.362-367
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• 2001

The stiff top layer in a soil profile, which can happen in winter, may change the isolation effect of the wave barrier. The research scope of this paper is the investigation of the propagation of surface waves in layered soil with a stiff layer on its top, and the isolation effect of the solid stiff wave barrier. The investigations have been performed numerically by the Boundary-Element Method as a two-dimensional problem. A strip foundation vibrated harmonically in vertical direction was considered as the vibration source. Three soil profiles, a homogeneous half-space, two profiles with different thickness of stiff top layer, with two different types of wave barriers were investigated. The profiles with a stiff top layer show considerable reductions of the amplitude of the vibration in comparison to the homogeneous soil profile. The layered soil profiles with a stiff top layer do not show wave propagation velocities as high as they are expected from the material properties. Furthermore the vibration amplitudes in a frozen soil are much smaller with distance than in a non-frozen soil.

• Tunnel and Underground Space
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• v.26 no.4
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• pp.327-337
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• 2016

In this study, laboratory hydraulic fracturing tests are carried out to evaluate the effects of the cleavage anisotropy of Pocheon granite. Breakdown pressure is smaller when cracks are generated to the direction of rift plane in constant pressurization rate condition because of higher microcracks density. Besides not only injection rate changes but also the amount of injection pressure for fracture initiation and crack expansion is detected while testing due to internal deformation. Pressurization rate is higher while hydraulic fracture testing with constant injection rate condition in case of the specimen which has rift plane perpendicular to borehole because there are much flow paths to penetrate compared to the specimen which has hardway plane perpendicular to borehole. Observation by X-ray CT scanning shows that almost all of cracks due to hydraulic fracturing are generated to the direction of plane which has higher microcrack density that is rift plane or grain plane.

• Tunnel and Underground Space
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• v.26 no.4
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• pp.316-326
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• 2016

The purpose of this study is to investigate the influence of cleavages on indirect tensile strength (ITS) of the granite. Brazilian disc tests and ring tests with three different hole sizes were performed. 2D DEM (Discrete Element Method) simulation was employed to further understand the failure process during the tests and the mechanism behind. Results show that ITS decreases across hardway, grain and rift cleavage. Measured average ITS from ring tests is about 2.5 ~ 6.4 times of those measured from Brazilian disc tests, and it decreases with increasing ratio of diameters of inner hole and specimen. Failure pattern in ring tests is influenced by both hole size and relative positions of cleavages parallel and perpendicular to the loading direction.