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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of Korean Tunnelling and Underground Space Association
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Journal DOI :
Korean Tunnelling and Underground Space Association (KTA)
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Volume & Issues
Volume 9, Issue 4 - Dec 2007
Volume 9, Issue 3 - Sep 2007
Volume 9, Issue 2 - Jun 2007
Volume 9, Issue 1 - Mar 2007
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Comparison and validation on shotcrete modelling method for the quantitative stability estimation of a tunnel
You, Kwang-Ho ; Lee, Min-Ho ; Park, Yeon-Jun ;
Journal of Korean Tunnelling and Underground Space Association, volume 9, issue 2, 2007, Pages 99~107
A method was suggested by You et al. (2000) to calculate safety factor of a tunnel based on numerical analysis with the shear strength reduction technique. In the method, the shotcrete is assumed to fail when its stress exceeds the allowable stress. The proposed method had been steadily developed by You et al. (2005) and Han et al. (2006). In this study, the previous routine was corrected so that tunnel construction sequences could be considered in calculating the safety factor of a tunnel. In addition, a proper way to model shotcrete is to be suggested by comparing with the previous studies.
Numerical analysis of pre-reinforced zones in tunnel considering the time-dependent grouting performance
Song, Ki-Il ; Kim, Joo-Won ; Cho, Gye-Chun ;
Journal of Korean Tunnelling and Underground Space Association, volume 9, issue 2, 2007, Pages 109~120
Auxiliary support systems such as the reinforced protective umbrella method have been applied before tunnel excavation to increase ground stiffness and to prevent the large deformation. However, determination procedure of geotechnical parameters along the construction sequence contains various errors. This study suggests a method to characterize the time-dependent behavior of pre-reinforced zones around the tunnel using elastic waves. Experimental results show that shear strength as well as elastic wave velocities increase with the curing time. Shear strength and strength parameters can be uniquely correlated to elastic wave velocities. Obtained results from the laboratory tests are applied to numerical simulation of tunnel considering its construction sequences. Based on numerical analysis, initial installation part of pre-reinforcement and portal of tunnel are critical for tunnel stability. Result of the time-dependent condition is similar to the results of for
days of the constant time conditions. Finally, suggested simple analysis method combining experimental and numerical procedure which considering time-dependent behavior of pre-reinforced zone on tunnel would provide reliable and reasonable design and analysis for tunnel.
Characteristics of velocity-dependent shear behavior of saw-cut rock joints at different shear velocities
Park, Byung-Ki ; Lee, Chang-Soo ; Jeon, Seok-Won ;
Journal of Korean Tunnelling and Underground Space Association, volume 9, issue 2, 2007, Pages 121~131
Recently, the probability of rock joints being exposed to free faces is getting higher for the scale of rock mass structures gets larger. Also, the frequency of occurring dynamic events such as earthquakes and blasting has been increasing. Thus, the shear behavior of rock joints under different conditions needs to be investigated. In this study, a series of direct shear tests were carried out under various conditions to examine the velocity-dependent shear behavior of saw-cut rock joints. Two types of direct shear test were carried out. The first was to examine the velocity-dependent shear behavior of saw-cut rock joints at seven different shear velocities, each with three different normal stresses. The second was to examine the shear behavior of saw-cut rock joints when three different instantaneous shear velocities changed. As a result, the coefficient of friction was affected by normal stress. The breakpoint velocity, the point when the change of shear velocity starts to affect the frictional behavior, became lower as normal stress increased. Also, as the shear velocity became lower, the degree of stress-drop on stick-slip behavior became larger. As a result of examining the changes of friction coefficient, velocity weakening (decrease of friction coefficient) was observed. The decrement of friction coefficient due to the changes of shear velocity under slow shear velocity was larger than that under fast shear velocity.
Defining the hydraulic excavation damaged zone considering hydraulic aperture change
Park, Jong-Sung ; Ryu, Chang-Ha ; Lee, Chung-In ; Ryu, Dong-Woo ;
Journal of Korean Tunnelling and Underground Space Association, volume 9, issue 2, 2007, Pages 133~141
The excavation damaged zone (EDZ) is an area around an excavation where in situ rock mass properties, stress condition, displacement, groundwater flow conditions have been altered due to the processes induced by the excavation. Various studies have been carried out on EDZ, but most studies have focused on the mechanical bahavior of EDZ by in situ experiment. Even though the EDZ could potentially form a high permeable pathway of groundwater flow, only a few studies were performed on the analysis of groundwater flow in EDZ. In this study, the 'hydraulic EDZ' was defined as the rock zone adjacent to the excavation where the hydraulic aperture has been changed due to the excavation by using H-M coupling analysis. Fundamental principles of distinct element method (DEM) were used in the analysis. In the same groundwater level, the behavior of hydraulic aperture near the cavern was analyzed for different stress ratios, initial apertures, fracture angles and fracture spacings by using a two-dimensional DEM program. We evaluate the excavation induced hydraulic aperture change. Using the results of the study, hydraulic EDZ was defined as an elliptical shape model perpendicular to the joint.
A rational estimating method of the earth pressure on a shaft wall considering the shape ratio
Shin, Young-Wan ; SaGong, Myung ;
Journal of Korean Tunnelling and Underground Space Association, volume 9, issue 2, 2007, Pages 143~155
The earth pressure acting on a circular shaft wall is smaller than that acting on the wall in plane strain condition due to the three dimensional axi-symmetric arching effect. Accurate estimation of the earth pressure is required for the design of the shaft wall. In this study, the stress model considering the decrease of earth pressure due to the horizontal and vertical arching effect and the influence of shape ratio (shaft height/radius) is proposed. In addition, model test on the sandy soil is conducted and a comparison is made between the stress model and the test results. The comparison shows that the proposed stress model is in agreement with test results; decrease of shape ratio (increase of radius) leads to stress state equal to the plane strain condition and approximate stress distribution is found between stress model and model test results.
Alteration of mechanical properties of tunnel structural members after a tunnel fire accident
Chang, Soo-Ho ; Choi, Soon-Wook ; Kwon, Jong-Wook ; Kim, Sang-Hwan ; Bae, Gyu-Jin ;
Journal of Korean Tunnelling and Underground Space Association, volume 9, issue 2, 2007, Pages 157~169
This study aimed to quantify the deterioration of tunnel structural members such as concrete lining and shotcrete lining after a tunnel fire accident by measuring their mechanical properties between
. From the experiments, it was revealed that the critical temperature where mechanical properties start to decrease linearly was approximately
. In addition, the other critical temperature where macro-cracks are induced in specimens was around
. From a series of regression analysis, the optimum regression function with correlation coefficients over 0.99 for mechanical properties at different temperature levels was obtained as the Boltzmann function. Finally, a schematic diagram to estimate temperature distribution inside structural members as well as their mechanical properties at corresponding temperature levels quantitatively was newly proposed for RABT and RWS fire scenarios.
Design on the large section of station tunnel under shallow overburden
Jeong, Yun-Young ; Choi, Hae-Joon ; Kim, Byung-Ju ; Yu, Bong-Won ; Kim, Yong-Il ; Oh, Sung-Jin ;
Journal of Korean Tunnelling and Underground Space Association, volume 9, issue 2, 2007, Pages 171~182
For minimizing the effect on the focus of civil traffic and environment conditions related to the excavation at the traffic jamming points, an underground station tunnel was planned with 35.5 m in length and bigger area than
in sedimentary rock mass. It faced the case that the overburden was just under 13 m. Not based on a pattern design but on the case histories of similar projects and arching effect, the design of large section tunnel under shallow overburden was investigated on three design subjects which are shape effect on the section area, application method of support pressure, and supporting and tunnel safety. According to the mechanical effect from section shape, a basic design and a preliminary design was obtained, and then supporting method of large section was planned by the supporting of NATM and a pipe roof method for subsidence prevention and mechanical stability. From the comparative study between both designs, it was found that the basic design was suitable and acceptable for the steel alignment of tunnel lining, safety and the design parameter restricted by the limit considered as partition of the excavation facilities. Through the analysis result of preliminary design showing the mechanical stability without stress concentration in tunnel arch level, it also was induced that shape effect of the large section area and yielding load obtained from deformation zone in the surrounding rock mass of tunnel have to be considered as major topics for the further development of design technique on the large section tunnel.
The ground reaction curve of underwater tunnels considering seepage forces
Shin, Young-Jin ; Kim, Byoung-Min ; Shin, Jong-Ho ; Lee, In-Mo ;
Journal of Korean Tunnelling and Underground Space Association, volume 9, issue 2, 2007, Pages 183~204
When a tunnel is excavated below groundwater table, the groundwater flows into the excavated wall of tunnel and seepage forces are acting on the tunnel wall. Such seepage forces significantly affect the ground reaction curve which is defined as the relationship between internal pressure and radial displacement of tunnel wall. In this paper, seepage forces arising from the ground water flow into a tunnel were estimated quantitatively. Magnitude of seepage forces was decided based on hydraulic gradient distribution around tunnel. Using these results, the theoretical solutions of ground reaction curve with consideration of seepage forces under steady-state flow were derived. A no-support condition and a supported condition with grouted bolts and shotcrete lining were considered, respectively. The theoretical solution derived in this study was validated by numerical analysis. The changes in the ground reaction curve according to various cover depths and groundwater table conditions were investigated. Based on the results, the application limit of theoretical solutions was suggested.
Analysis of dynamic behavior for underground structures under earthquake loading
Park, Seong-Yong ; Lee, Jae-Jin ; Choi, Seung-Ho ; Kim, Soo-Il ; Park, Inn-Joon ;
Journal of Korean Tunnelling and Underground Space Association, volume 9, issue 2, 2007, Pages 205~217
The behavior characteristics of underground structures are reported as they are not affected by their dynamic characteristics such as surface structures, but by dynamic characteristics of soil and rock surrounding the underground structures. Therefore, dynamic behavior of surrounding soil and rock dominates the dynamic behavior of the underground structure. The purpose of this paper is to analyze the dynamic response (longitudinal deformation and ovaling deformation) of the underground structure under earthquake loading. The dynamic responses of the underground structures were evaluated with varying earthquake conditions, soil conditions, and structural conditions using conventional closed-form solution of seismic behavior of underground structure. In addition, shaking table tests were conducted to simulate the earthquake loading and the dynamic behavior of the model was analyzed.