• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.56-59
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• 2004

This paper presents the consideration of design guideline for underground HCS system, composite spancrete slab, under axial and bending force. Serviceability design requirements for continuous composite spancrete slab subjected axial force, which are allowable stress and deflection, are compared. Flexural strengths are evaluated by design guideline using strain-compatibility method. The results showed that stresses of spancrete and topping concrete, especially at the ends of beam, have much effect on design loads. Maximum service loads for tested specimens are proposed by allowable stress.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.115-121
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• 2003

Discrete joint network approach has widely been used to investigate the hydraulic behavior of jointed rock masses. In general, joints will undergo deformation due to stress redistribution induced by construction of underground openings, hence joint aperture is often assumed to have a probability distribution rather than to be a constant value. In real situations, however, it is more reasonable to take into account the effect of stress change on aperture values by calculating joint deformation. In this report, a mechanical process has been developed to determine the joint opening or closure based on a statistically generated joint network model. By performing numerical analyses, some significant results on the hydro-mechanical behavior of jointed rock masses have been summarized.

• Tunnel and Underground Space
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• v.8 no.2
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• pp.96-106
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• 1998

Rock contains discontinuities at all scales. These discontinuities make rock behave in a complex way. This paper discusses a new approach to underground design based on the theory of rock fracture mechanics. The mechanism of deformation and failure of coal was studied by observing the distributions of length, orientation and spacing of the pre-existing as well as stress-induced cracks. Different types of crack information. The crack information is dependent on the scale used. The cracks propagate along the intersections of the pre-existing cracks, and both extensile and shear crack growth occur depending on the direction of the load relative to the bedding planes. An analytical model that takes into account both shear and extensile crack growth was developed to predict the nonlinear stress-strain behavior of coal including strain-hardening and strain-softening.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1997.04a
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• pp.79-86
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• 1997

In this study, pre-postprocessing toolbox is developed to perform elasto-plastic analyze of underground structures with transient ground water flow. This toolbox is composed of three modules. The first is the data input processor for the structural analysis. The preprocessing Is using GUI (Graphic User Interface), which is consist of dialog box, pull down, and short-cut icon, etc. The second is the structural analysis module. The analysis is based on the elasto-plastic finite element method involving additional options such as ground excavation effect, transient ground water flow, and rock bolts behavior. The last is the postprocessing module. The postprocessing is able to verify the result of the structural analysis by the graphical simulation which visualizes the element mesh, the node displacements, the element stress states, the stress contour, the ground water surface, and the rock bolt stresses. Since various options are considered separately in this toolbox, it is easy to modify the module of each processing, and to update other functional modules for the given analysis conditions.

• Tunnel and Underground Space
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• v.6 no.1
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• pp.10-18
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• 1996

Arched openings are generally excavated in underground construction works. Since stress distribution around openings depends on geological structure in rock mass, any shape of arched openings fully conformed with in-situ stress condition should be recommended to maintain mechanical safety of structures. Shape of arched openings is specified by both roof curvature and height-width ratio, and especially this report presents deformation behaviors related with roof curvature. Scale model tests and numerical studies of various shaped openings are conducted, where rectangular opening shows the greatest convergence. Through the anlayses of various arched opengings, as radius of roof curvature is increased, roof lowering and sidewall closure are remarkably increased, whereas floor heaving is increased little by little. By the way, it is useful that displacements of openings are roughly estimated in the stage of preliminary investigation. To find out elastic displacements of arched openings with any roof curvature, regressional formula and charts by least square method are represented. In addition elastoplastic deformation behavoirs of arched openings concerning associated adn non-associated flow rule are discussed.

• Geomechanics and Engineering
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• v.30 no.1
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• pp.93-105
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• 2022

With the exploitation of natural resources in China, underground resource extraction and underground space development, as well as other engineering activities are increasing, resulting in the creation of many defective rocks. In this paper, uniaxial compression tests were performed on rocks with double holes and fractures at different angles using particle flow code (PFC2D) numerical simulations and laboratory experiments. The failure behavior and mechanical properties of rock samples with holes and fractures at different angles were analyzed. The failure modes of rock with defects at different angles were identified. The fracture propagation and stress evolution characteristics of rock with fractures at different angles were determined. The results reveal that compared to intact rocks, the peak stress, elastic modulus, peak strain, initiation stress, and damage stress of fractured rocks with different fracture angles around holes are lower. As the fracture angle increases, the gap in mechanical properties between the defective rock and the intact rock gradually decreased. In the force chain diagram, the compressive stress concentration range of the combined defect of cracks and holes starts to decrease, and the model is gradually destroyed as the tensile stress range gradually increases. When the peak stress is reached, the acoustic emission energy is highest and the rock undergoes brittle damage. Through a comparative study using laboratory tests, the results of laboratory real rocks and numerical simulation experiments were verified and the macroscopic failure characteristics of the real and simulated rocks were determined to be similar. This study can help us correctly understand the mechanical properties of rocks with defects and provide theoretical guidance for practical rock engineering.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.6
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• pp.764-769
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• 2014

This paper describes sheath voltage limiter(SVL) transient characteristics by switching overvoltage considering single point bonding in underground transmission cables. The crossbonding system is generally used for grounding methods of underground transmission system. However, the single point bonding system is used in selective area which is difficult to consist of crossbonding major section. The sheath voltage limiters are connected between joints in the single point bonding. Specially, the high overvoltage might be generated in that section as well as the aging of sheath voltage limiter might be progressed by various electrical stress including lightning overvoltage, switching overvoltage and power frequency overvoltage. Therefore, in this paper, the switching overvoltage characteristics in underground cables are firstly analysed using EMTP simulation. Then, the switching overvoltage of sheath voltage limiter is also studied in single point bonding. Finally, the reduction method of sheath voltage limiter switching overvoltage is proposed by various simulation studies including circuit breaker operating order.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.10a
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• pp.11-17
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• 2002

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.5
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• pp.487-495
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• 2014

In this study, in order to suggest the design method for supports in the room-and-pillar underground structure, the case study was carried out. In the case study, shape of rock pillar and room was mainly considered. From the analysis, a displacement at the roof, the maximum principle stress and plastic state were examined. To optimize variables in the case study, cases from the Seoul metro station were analyzed, then a target depth of the underground structure and ground conditions were determined. And the height of rock pillar and room were chosen from the assumed purpose of underground space, i.e. living/office and warehouse. Total cases of analysis was 180 cases including 3 types of ground condition, 5 types of rock pillar and 6 types of roof span. It is expected that results from analysis can be used to determine the installation of support in room-and-pillar underground structure with stability, utilization efficiency of underground space and applicability of vehicles.

• Safety and Health at Work
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• v.9 no.2
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• pp.149-158
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• 2018

Background: Work comfort studies have been extensively conducted, especially in the underground and meteorological fields resulting in an avalanche of recommendations for their evaluation. Nevertheless, no known or universally accepted model for comprehensively assessing the thermal work condition of the underground mine environment is currently available. Current literature presents several methods and techniques, but none of these can expansively assess the underground mine environment since most methods consider only one or a few defined factors and neglect others. Some are specifically formulated for the built and meteorological climates, thus making them unsuitable to accurately assess the climatic conditions in underground development and production workings. Methods: This paper presents a series of sensitivity analyses to assess the impact of environmental parameters and metabolic rate on the thermal comfort for underground mining applications. An approach was developed in the form of a "comfort model" which applied comfort parameters to extensively assess the climatic conditions in the deep, hot, and humid underground mines. Results: Simulation analysis predicted comfort limits in the form of required sweat rate and maximum skin wettedness. Tolerable worker exposure times to minimize thermal strain due to dehydration are predicted. Conclusion: The analysis determined the optimal air velocity for thermal comfort to be 1.5 m/s. The results also identified humidity to contribute more to deviations from thermal comfort than other comfort parameters. It is expected that this new approach will significantly help in managing heat stress issues in underground mines and thus improve productivity, safety, and health.