• Journal of Korean Tunnelling and Underground Space Association
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• v.4 no.2
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• pp.101-111
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• 2002

The purpose of this research is to develop improved model for joints of tunnel based on Disturbed State Concept (DSC) model. DSC model is verified with respect to comprehensive laboratory tests performed by Schneider and back prediction results. Based on results of this research, it can be stated that DSC model is capable of characterizing the strain softening and dilative behavior of rough granite joints under four different constant normal stresses.

• Journal of the Korean Geotechnical Society
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• v.15 no.5
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• pp.217-228
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• 1999

The three methods of analysis (i) REV(representative elemental volume), (ii) non-REV and (iii) joint network analysis are introduced in this paper to analyze the groundwater flow in jointed rock mass and the inflow into underground excavations. The results from those methods are compared one another to reveal their characteristics by varying the number of joints and the diameter of the opening. The pre-processor, the so-called sequential analysis, is introduced to predict the equivalent hydraulic conductivity of a jointed rock mass having a number of intersecting joints. Using the finite element mesh, joint map and sequential analysis, the equivalent hydraulic conductivities are calculated for all 445 elements. The hydraulic inhomogeneity and the determination of the representative properties of jointed rock masses are discussed. In the REV analysis where the entire rock mass is homogenized through the representative properties, the inflow is increased regularly and consistently by increasing the joint density, the opening size and the conductivity contrast value. Though the non-REV analysis showed irregular variation of the inflow due to the local inhomogeneity allowed to individual elements, the inflow approached the REV results as the characteristic length increases. The joint network analysis showed the most sensitive reaction to the joint density, the opening size and the presence of the network crossing the opening. The reliability of the network analysis depends on the geometric data of individual joints. In view of the limited field data on joint geometry and possible uncertainty the REV and non-REV methods are considered more practical and rational than the joint network analysis.

• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.61-70
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• 2013

This paper presents the results of a two-dimensional finite element analysis of end bearing capacity of single pile installed in fractured rock mass. A number of cases were analyzed using Hoek-Brown criterion that can consider the condition of rock joints. Considering a wide range of joint conditions in which the pile is embedded into the rock, GSI was set as a main parameter. And the effects of pile diameter, unconfined compressive strength of rock and Hoek-Brown constant $m_0$ were considered. Based on parameter study, end bearing load factor graphs were suggested.

• Tunnel and Underground Space
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• v.13 no.5
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• pp.331-343
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• 2003

Though the Grouting has been in use for a long time, it is still regarded as an technique rather than engineering. The study of ground improvement by grouting is rare especially in jointed rock mass. In this study, biaxial compression tests were performed in the jointed rock mass models with .ough surfBce joints assembled with blocks before and after grouting. The load-deformation curves of the jointed rock masses showed a non-linear relationship before grouting but showed a relatively linear deformaion behavior after grouting. Improvement ratio (deformation modulus after grouting/deformation modulus before grouting) decreased with increasing joint spacing and lateral stress. Improvement ratio decreased exponentially with increasing deformation modulus of the rock mass model before grouting. Three-dimensional FDM analysis was performed to a highway tunnel case using experimental data of grouted rock. The convergence of the tunnel predicted after grouting by the numerical modelling coincided with those attained from the field measurement.

• Journal of the Korean Geotechnical Society
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• v.15 no.5
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• pp.229-240
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• 1999

The groundwater flow and grout flow in individual rock joint and jointed rock mass are studied using various methods of analysis such as (i) the finite difference method, (ii) channel network analysis and (iii) joint network analysis. The flow behaviour is investigated in two distinguishable scales of observation: one for a rough joint of a laboratory scale having variable aperture, and the other for field- scale rock masses having three sets of intermittent joints. In the former case, the aperture-dependent channel flow is identified for both water and grout flows. The comparison of the flow rate in a rough joint is made between the finite difference analysis and existing analytical solution. In the latter case, the effects of increasing number of joints on the groundwater inflow into a circular opening of various diameters are analyzed using both the joint network method and Goodman's analytic solution. Comparisons are made between the two methods. The boundary effects in the joint network method are discussed. The inhomogeneity of joint network and its impacts on the groundwater inflow are also discussed.

• 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.

• Tunnel and Underground Space
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• v.8 no.3
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• pp.200-208
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• 1998

This research is intended to investigate the behavior of the jointed rock under various loading conditions: static or dynamic load. The distributed state concept (DSC) is based on the idea that the response of the joint can be related to and expressed as the response of the reference states : relative intact (RI) and fully adjusted (FA) states. In the DSC, an initially RI joint modifies continuously through a process of natural self-adjustment, and a part of it approaches the FA state at randomly disturbed locations in the joint areas. In this study, based on the DSC concept, RI state, FA state, and disturbance function (D) are defined for characterizing the behavior of rock joint. From the results of this research, it can be stated that DSC model is capable of capturing the physical behavior of jointed rock such as softening and hardening and considering the size of joint and roughness of joint surface.

• Proceedings of the KSEEG Conference
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• 2001.04a
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• pp.175-180
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• 2001

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.229-239
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• 2013

Elastic modulus in rockmass is an important factor to represent the characteristic of rock deformation and is frequently used to estimate the displacement induced due to tunnel excavation or other activities in rockmass. Nevertheless, the study to estimate the elastic modulus, which considers the rock type and joint characteristics (joint shear strength and joint inclination angle), has been done in less frequency. Accordingly, this study is aimed at estimating of elastic modulus in jointed rockmass. For this purpose, numerical parametric studies have been carried out with a consideration of rock and joint conditions. Tunnel displacement results have been used to estimate the elastic modulus of jointed rockmass using the elastic theory of circular tunnel. From this study, the results would be expected to have a great practical use for estimating the displacement induced due to tunnel excavation or other activities in jointed rockmass.

• Proceedings of the KSEG Conference
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• 2002.04a
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• pp.201-210
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• 2002

서울시 북동부의 서울화강암에 대한 암반 공학적 특성 중 터널과 도로 건설시 중요하게 취급되는 절리의 방향성, 절리간격, 절리밀도, 암석의 일축압축강도, 그리고 RQD 값을 수락산과 불암산지역으로 구분하여 비교, 분석하였다. 이 중 절리의 방향성, 절리간격과 절리밀도는 선조사법, 원형조사법, 그리고 면적조사법을 이용하여 야외에서 직접 측정하였다. 암석의 일축압축강도와 RQD의 측정은 시추코아의 표본이 필요하지만 이번 연구에서는 간단히 응용할 수 있는 대비공식을 이용하여 계산하였다. 측정된 대표적인 절리의 방향성은 두 지역에서 모두 3조의 방향성이 나타났으며 즉 2조의 수직정방절리와 저각으로 경사하는 1조의 판상절리로 판명되었으며 두 지역에서 서로 유사한 방향성을 갖는다. 측정된 절리밀도는 0.039-0.066/cm이었으며, 평균절리길이는 1.30-4.52m, 그리고 평균절리간격은 10.3cm에서 최대 59.6cm로 측정된 절리의 방향에 따라 변화가 심하다 또한 슈미트 해머 타격값에 근거한 절리면의 일축압축강도는 217 MPa에서 335 MPa로 매우 강한 암체였으며, 평균절리간격에 기초하여 계산된 이론적 RQD 값은 73.1-98.7%의 값을 갖는 것으로 나타났다.