• Proceedings of the KSR Conference
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• 2004.10a
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• pp.1089-1094
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• 2004

Numerical methods to estimate behaviors of jointed rock mass can be roughly divided into two method : discontinuous model and continuum model. Generally, distinct element method (DEM) is applied in discontinuous model, and finite element method (FEM) or finite difference method (FDM) is utilized in continuum model. To predict a behavior of discontinuous model by DEM, it is essential to understand characteristics of joints developed in rock mass through field tests. However, results of field tests can not provide full information about rock mass because field tests is conducted in limited area. In this paper, discontinuous analysis by UDEC and continuous analysis by FLAC is utilized to estimate a behavior of a tunnel in jointed rock mass. For including discontinuous analysis in continuous analysis, joints in rock mass is considered by reducing rock mass properties obtained by RMR and decreasing shear strength of rock mass. By comparing and revising two analysis results, analysis results similar with practical behavior of a tunnel can be induced and appropriate support system is decided.

• Journal of the Korean Society for Railway
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• v.8 no.1
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• pp.82-86
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• 2005

Numerical methods to estimate behaviors of jointed rock mass can be roughly divided into two methods : continuous and discontinuous model. Generally, distinct element method(DEM) is applied in discontinuous model, and finite element method(FDM) or finite difference method(FDM) is utilized in continuum model. To predict a behavior of discontinuous model by DEM, it is essential to understand characteristics of joints developed in rock mass through field tests. However, results of field tests can not provide full information about rock mass because field tests are conducted in limited area. In this paper, discontinuous analysis by UDEC and continuous analysis by FLAC are utilized to estimate a behavior of a tunnel in jointed rock mass. For including discontinuous analysis in continuous analysis, joints in rock mass is considered by reducing rock mass properties obtained by RMR and decreasing shear strength of rock mass. By comparing and revising two analysis results, analysis results similar with practical behavior of a tunnel can be induced and appropriate support system is decided.

• Tunnel and Underground Space
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• v.25 no.1
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• pp.68-75
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• 2015

Rock mass includes such discontinuities as fault, joint, bedding, crack, schistosity, cleavage. The rock mass behavior, therefore, is influenced by the discontinuity behavior. In this study, a stability and deformation analysis method considering discontinuities in rock mass is proposed, and then applied to the rock collapse disaster site. As the method, the stability analysis by the stereographic projection method was carried out in an actual site, the deformation analysis program by the finite element method including the joint element was developed, and performed. To demonstrate the applicability of this developed stability and deformation analysis method considering discontinuities in rock mass, the analysis results are examined and compared with the failure behavior at the rock mass.

• Proceedings of the Korean Geotechical Society Conference
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• 1994.09a
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• pp.209-216
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• 1994

Rock mass classifications have played an indispensable role in underground construction for several decades. An important issue in rock mass classifications is the selection of the parameters of greatest significance. There appears to be no single parameter that can fully describe a jointed rock mass for underground construction design. In this paper. We find some problems shen applied rock mass classification for underground construction in domestic, analyze the most significant parameters and parameters correlation influencing the behavior of a rock mass, and suggest the Simplied Rock Mass Rating system based on RMR method for effective underground supports.

• Tunnel and Underground Space
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• v.15 no.3 s.56
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• pp.185-194
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• 2005

Recently, the surrounding rock mass is understood as the major support system for the tunnel constructed in the rock mass. Generally, the rock mass contains many discontinuity planes such as joints, and thus, the tunnel behavior in the rock mass is governed by the characteristics of the discontinuity planes. In this study, the behavior of tunnel in jointed rock mass is studied by model tests and numerical analyses. The results shows that the behavior of tunnel depends on the different initial stress conditions, in case that the tunnel is excavated in the ground without any joints. When a joint is located near the tunnel, the pound stress and displacement tend to increase between the tunnel and the joint.

• Economic and Environmental Geology
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• v.39 no.4 s.179
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• pp.451-471
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• 2006

Major projects and research topics in the field of rock mechanics are analyzed to obtain the following results: $\cdot$ Rock mechanics deals with the behavior of deformation, failure and displacement of the rock and rock mass on the basis of geological basics. Discontinuities in the rock mass are the most important parameters to control the behavior of rock mass around underground openings. $\cdot$ The objective of site investigation and testing is to determine the strength properties of the rock mass and the in situ stress regime. Specimens for laboratory and in situ tests are to be selected in order that the results of the tests give the representative properties oi the rock mass of the site in question. $\cdot$ The result of a numerical model would be better evaluated not quantitatively but qualitatively. The displacement behavior of the rock mass has to be monitored properly for the NATM (New Austrian Tunneling Method) principles. $\cdot$ The stability of rock slope is to be evaluated preferably by back analysis with strength parameters, such as cohesion and friction angle.

• Geomechanics and Engineering
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• v.29 no.2
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• pp.99-111
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• 2022

Instability of bolted rock mass has been a major hazard in the underground coal mining industry for decades. Developing effective support guidelines requires understanding of complex bolted rock mass failure mechanisms. In this study, the dynamic failure behavior, mechanical behavior, and energy evolution of a laboratory-scale bolted specimens is studied by conducting laboratory static-dynamic coupled loading tests. The results showed that: (1) Under static-dynamic coupled loading, the stress-strain curve of the bolted rock mass has a significant impact velocity (strain rate) correlation, and the stress-strain curve shows rebound characteristics after the peak; (2) There is a critical strain rate in a rock mass under static-dynamic coupled loading, and it decreases exponentially with increasing pre-static load level. Bolting can significantly improve the critical strain rate of a rock mass; (3) Compared with a no-bolt rock mass, the dissipation energy ratio of the bolted rock mass decreases exponentially with increasing pre-static load level, the ultimate dynamic impact energy and dissipation energy of the bolted rock mass increase significantly, and the increasing index of the ratio of dissipation energy increases linearly with the pre-static load; (4) Based on laboratory testing and on-site microseismic and stress monitoring, a design method is proposed for a roadway bolt support against dynamic load disturbance, which provides guidance for the design of deep underground roadway anchorage supports. The research results provide new ideas for explaining the failure behavior of anchorage supports and adopting reasonable design and construction practices.

• Tunnel and Underground Space
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• v.18 no.6
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• pp.465-479
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• 2008

For the quantitative identification of rock behavior in shallow tunnels, we recommend using the rock behavior index (RBI) by the analytic hierarchy process (AHP) and the Rock Engineering Systems (RES). AHP and RES can aid engineers in effectively determining complex and un-structured rock behavior utilizing a structured pair-wise comparison matrix and an interaction matrix, respectively. Rock behavior types are categorized as rock fall, cave-in, and plastic deformation. Seven parameters influencing rock behavior for shallow depth rock tunnel are determined: uniaxial compressive strength, rock quality designation (RQD), joint surface condition, stress, pound water, earthquake, and tunnel span. They are classified into rock mass intrinsic, rock mass extrinsic, and design parameters. An advantage of this procedure is its ability to obtain each parameter's weight. We applied the proposed method to the basic design of Seoul Metro Line O and quantified the rock behavior into RBI on rock fall, cave-in, and plastic deformation. The study results demonstrate that AHP and RES can give engineers quantitative information on rock behavior.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5C
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• pp.359-368
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• 2006

After construction, time-variant seepage and long-term underground motion are representative factors to understand the abnormal behavior of tunnels. In this study, numerical models have been developed to analyze the behavior of tunnels associated with seepage and long-term underground motion. Possible scenarios have been investigated to establish causes-and-results mechanisms. Various parameters such as permeability of tunnel filter, seepage condition, water table, long-term rock mass load, size of damaged zone due to excessive blasting have been investigated. These are divided into two sub-parts depending on the tunnel type and major loading mechanisms depending on the types. For the soft ground tunnels, the behavior associated with seepage conditions has been studied and the effect of permeability change in tunnel-filter and the effect of water-table change which are seldom measurable are investigated in detail. For the rock mass tunnels, tunnel behavior associated with the visco-plastic behavior of rock mass has been studied and the long-term rock mass loads as a result of relaxation and creep have been considered.

• Computers and Concrete
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• v.18 no.2
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• pp.235-266
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• 2016

A rock mass containing non-persistent joints can only fail if the joints propagate and coalesce through an intact rock bridge. Shear strength of rock mass containing non-persistent joints is highly affected by the both, mechanical behavior and geometrical configuration of non-persistent joints located in a rock mass. Existence of rock joints and rock bridges are the most important factors complicating mechanical responses of a rock mass to stress loading. The joint-bridge interaction and bridge failure dominates mechanical behavior of jointed rock masses and the stability of rock excavations. The purpose of this review paper is to present techniques, progresses and the likely future development directions in experimental and numerical modelling of a non-persistent joint failure behaviour. Such investigation is essential to study the fundamental failures occurring in a rock bridge, for assessing anticipated and actual performances of the structures built on or in rock masses. This paper is divided into two sections. In the first part, experimental investigations have been represented followed by a summarized numerical modelling. Experimental results showed failure mechanism of a rock bridge under different loading conditions. Also effects of the number of non-persistent joints, angle between joint and a rock bridge, lengths of the rock bridge and the joint were investigated on the rock bridge failure behaviour. Numerical simulation results are used to validate experimental outputs.