(사)한국터널지하공간학회
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- P-ISSN2233-8292
- E-ISSN2287-4747
- KCI
ISSN : 2233-8292
Vol.25 No.2
Abstract
With the concentration of the population in the city center and the saturation of the structures on the ground, the development of the underground structures becomes important and the construction of an adjoining tunnel that can reduce the overall problems is respected. In addition, it is necessary to apply the reinforcement construction method for the pillar part of the adjacent tunnel that can secure stability, economy and workability of the site. In this study, the tunnel pillar reinforcement method using prestress and grouting was reviewed. There are various reinforcement methods that can compensate for the problems of the side tunnel, but as the tunnel pillar construction method using prestress and grouting is judged to be excellent in field applicability, stability and economic feasibility, theoretical and numerical analysis of the actual behavior mechanism are conducted. Numerical analysis is divided into PC stranded wire + steel pipe reinforcement grouting + prestress (Case 1), pillar part tie bolt reinforcement (Case 2), pillar part non-reinforcement (Case 3) under the same ground conditions, and the maximum value of the celling displacement, internal displacement, and member force, the stability was confirmed. Through numerical analysis, it was confirmed that Case 1 which reinforced the PC stranded wire, was the best construction method and if it is verified and supplemented through field experiments later, it will be possible to derive superior results in terms of displacement control and member force than the currently applied reinforcement method was judged.
Abstract
The use of TBM (Tunnel boring machine) has increased worldwide due to its performance together with the benefit of being safely and environmentally friendly compared to conventional tunneling. In particular, EPB (Earth Pressure Balanced) TBM is widely used because it can be applied to various grounds compared to Open TBM. Also EPB TBM has a simple mechanical structure and advantages in cost, requires less ground area than Slurry TBM. EPB TBM has advantages in soft ground, and more importantly, can extend its applicability by use of appropriate soil conditioning, which improves mechanical and hydrological properties of excavated soil and increases the excavation performance of EPB TBM. Various studies suggested the proper mixing ratio and injection ratio, but almost they are limited to laboratory test under atmospheric pressure such as slump test. Actual field conditions may differ depending on the ground and mechanical condition. In this study, first the amount of used soil conditioning used in the field with various grounds from hard rock to soft ground was estimated through laboratory tests and compared with the estimate in design stage. And also it was compared with the amount used during actual excavation. In addition, experience of soil conditioning for the problems of cutter head clogging and groundwater inrush that occurred during excavation is discussed. Finally, lesson learned for the use of soil conditioning in difficult ground condition such as mixed ground are reviewed.
Abstract
Ground excavation inevitably causes ground displacement of adjacent ground, and structures and facilities exposed to ground displacement may suffer various damages. Therefore, in order to minimize the damage and damage to adjacent structures and facilities caused by excavation, ground displacement (settlement and horizontal displacement) in the adjacent ground caused by excavation must first be predicted. There is many ground displacement information induced by general braced cut excavation, but the information is not enough for circular shaft excavation. This study aims to provide information on the estimation of ground settlement caused by circular shaft excavation through the case analysis of circular shafts and comparison with braced cut excavation. From this study, it was found that the use of the settlement criterion of braced cut excavation as the settlement management criterion for circular shaft excavation is a conservative approach in terms of safety. But when considering the economic aspect, it may result in overdesign of the wall and therefore, a more reasonable settlement criterion can be needed for circular shaft excavation.
Abstract
Electrical resistivity survey have been widely conducted at diverse scales, from a few centimeters for laboratory tests to kilometers for field tests. It measures electrical resistance through relationship of electric potential difference and current between two electrodes penetrated on the surface of medium, and eventually quantifies electrical resistivity known as inherent properties of the medium. In field or full-scale test, it assumes the electrodes as equivalent half-sphere electrodes that have a same surface area with different electrodes for ease of calculation because the contact area between electrode and medium is small and sufficient distance between two electrodes. However, small-scale laboratory test is significantly affected by the electrode geometries (penetrated depth, height, radius of electrode and distance between electrodes), which change the equipotential surface and electric current flow. Indeed, the electrode geometries may eventually cause a difference of electrical resistivity value. This study reviews the theoretical electrical resistance derived with various electrode geometries (half-sphere, cylinder, cylindrical with half-spherical tip, cylindrical with conical tip) and verifies the developed numerical module by comparing results with the theoretical electrical resistance. The distributions of electrical resistance around electrodes and among electrodes are analyzed. In addition, it is discussed how the electrical characteristic of cylindrical electrode with conical tip widely used in field test has effect on the electric current flow.
Abstract
Various tunnels such as road, subway, and railway are under construction and operation. Various types of linings are used for structural stability of tunnel structures, and concrete segment linings are mainly installed in TBM tunnel construction. In this paper, when a fire occurs in a tunnel, the impact on the concrete segment lining, which is the structure in the tunnel, and related standards, fire resistance evaluation and fire resistance method are investigated through literature review and related contents are presented.Through this, it is intended to provide an information for practitioners to secure the safety of concrete segment linings against tunnel fires.
Abstract
Monitoring technology based on electrical resistivity is widely used for non-destructive data collection and health analysis of underground structures and tunnels. Vulnerable sections such as fault zone generates many problems during construction of the tunnel. These problems cause displacement and stress changes of the ground. Therefore, it is necessary to predict the state of the fault zone section to ensure the mechanical stability of the underground structure. Monitoring the size of joints and the porosity of the fillings is essential for rocks. Previous studies have not considered the variety of fillings in rock joints. In this study, electrical resistivity tests were conducted according to the particle mixing state of the sandy fillings. When the size of fillings is decreased at the constant porosity, the electrical resistivity tends to increase. The results of this study are expected to be useful as basic electrical resistivity data for predicting the ground conditions and evaluation of the ground behavior that is containing sandy fillings in the rock joint for tunnels.
Abstract
Although this site is designed with a non-vibration excavation method for a section of 265 m, there are concerns about decline of constructability and economic feasibility. For this reason, the low-vibration electronic detonator blasting method was suggested. To evaluate the applicability of the low-vibration electronic detonator blasting method, the damage range of blasting vibration of low-vibration electronic detonator blasting applied just before the site (suggestion Ⅰ) and low-vibration electronic detonator blasting constructed close range the subway like this site (suggestion Ⅱ) was analyzed. As a result of comparing the blasting vibration damage ranges of the two suggestions, the damage range of suggestion Ⅱ was calculated more conservatively. Considering the specificity of the close range of this site, suggestion Ⅱ was selected for design change for safer construction. As a result, it is predicted that there will be no damage to the structure even if the 72 m section out of the non-vibration excavation 265 m section is changed to the Low-vibration electronic detonator blasting. And it is evaluated that high economic benefits can be obtained because the total expected excavation period can be reduced by 144 days from 662.5 days.
Abstract
The buffer materials in disposal hole are exposed to the decay heat from spent nuclear fuels and groundwater inflow through adjacent rockmass. Since understanding of thermal-hydro-mechanical-chemical (T-H-M-C) interaction in buffer material is crucial for predicting their long-term performance and safety of disposal repository, it is necessary to investigate the heating-hydration characteristics and consequent T-H-M-C behavior of the buffer materials under disposal conditions considering geochemical factors. In response, the Korea Atomic Energy Research Institute developed a laboratory-scale ‘Lab.THMC’ experiment system, which characterizes the T-H-M behavior of buffer materials under different geochemical conditions by analyzing heating-hydration process and stress changes. This technical report introduces the detail design of the Lab.THMC system, summarizes preliminary experimental results, and outlines future research plans.