(사)한국터널지하공간학회
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- P-ISSN2233-8292
- E-ISSN2287-4747
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ISSN : 2233-8292
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e-SubmissionVol.22 No.4
Abstract
Traffic jam and congestion in urban areas has caused the need to improve the utility ofunderground space. In response, research on underground structures is increasinglybeing conducted. Notably, a double-deck tunnel is one of the most widely used of allthose underground structures. This double-deck tunnel is separated by the middle slabinto the upper and lower roadways. Both vehicle load and earthquake load cause themiddle slab to exhibit dynamic behavior. Earthquake-related response characteristics,in particular, are highly complex and difficult to interpret in a theoretical context, andthus experimental research is required. The aim of the present study is to assess thestability of a double-deck tunnel’s middle slab of the Collapse Prevention Level andSeismic Category 1 with regard to the presence of vibration-damping Rubber Bearings. In vibration table tests, the ratio of similitude was set to 1/4. Linings and vibratingplatforms were fixed during scaled model tests to represent the integrated behavior ofthe ground and the applied models. In doing so, it was possible to minimize relativebehavior. The standard TBM cross-section for the virtual double-deck tunnel wasselected as a test subject. The level of ground motion exerted on the bedrock was setto 0.154 g (artificial seismic wave, Collapse Prevention Level and Seismic Category 1). A seismic wave with the maximum acceleration of 0.154 g was applied to the vibrationtable input (bedrock) to analyze resultant amplification in the models. As a result, theseismic stability of the middle slab was evaluated and analyzed with respect to thepresence of vibration-damping rubber bearings. It was confirmed that the presence ofvibration-damping rubber bearings improved its earthquake acceleration dampingperformance by up to 40%.
Abstract
In order to resolve traffic problems in urban areas and to increase the area of greenspaces, tunnels in downtown areas are being increased. Additionally, the applicationof large port smoke extraction ventilation systems is increasing as a countermeasureto smoke extraction ventilation for tunnels with high potential for traffic congestion. It is known that the smoke extraction performance of the large port smoke extractionsystem is influenced not only by the amount of the extraction flow rate, but also byvarious factors such as the shape of the extraction port (damper) and the extractionair velocity through a damper. Therefore, in this study, the design standards andinstallation status of each country were investigated. When the extraction air flow ratewas the same, the smoke extraction performance according to the size of the damperwas numerically simulated in terms of smoke propagation distance, compared andevaluated, and the following results were obtained. As the cross-sectional area of thesmoke damper increases, the extraction flow rate is concentrated in the damper closeto the extraction fan, and the smoke extraction rate of the damper in downstreamdecreases, thereby increasing the smoke propagation distance on the downstream side. In order to prevent such a phenomenon, it is necessary to reduce the cross-sectionalarea of the smoke damper and increase the velocity of passing air through the damperso that the pressure loss passing through the damper increases, thereby reducing thenon-uniformity of smoke extraction flow rate in the extraction section. In this analysis,it was found that when the interval distance of the extraction damper was 50 m, the airvelocity passing through damper was 4.4 m/s or more, and when the interval distance of the extraction dampers was 100 m, the air velocity passing through damper was greater than 4.84 m/s, it was foundto be advantageous to ensure smoke extraction performance.
Abstract
This paper presents the seal material mixing ratio of tunnel umbrella arch reinforcementmethod. Currently, there is no clear standard for the proper gelation time and curingtime of the Seal material in Korea, and the quality control is also difficult because itcannot be verified. In response, the ratio of the mixture of the seal material wascomposed of four types of indoor experiments, and the amount of gelation time andbleed was checked. In addition, a non-cart penetration test confirmed the curing timeand compared the ratio of each combination. Further experiments on W/C 120%identified the effect of mixing speed and time on the seal material. A total of three fieldexperiments were conducted based on indoor experiments, and the size and strength ofbulb formation were compared by checking the curing time of the specimen and maininjection. Comparisons show that the lower W/C, the stronger the strength, the largerthe size of the bulb, and the faster the hardening time appears. Based on the results ofthe gelation time and curing time, it was deemed that the mixing ratio of W/C 120%is most appropriate when applied to the actual site.
Abstract
Optimizing the spacing of the disc cutter is a key element in the design of the TBMcutter head, which determines the drilling performance of the TBM. The full-scalelinear cutting test is known as the most reliable and accurate test for calculating thespacing of the disc cutter, but it has the disadvantage of costly and time-consuming forthe full-scale experiment. In this study, through the numerical analysis study based onthe discrete element method, the tendency between Specific Energy-S/P ratio accordingto uniaxial compression strength and penetration depth of rock was analyzed, and theoptimum spacing of 17-inch disc cutter was derived. To examine the appropriatenessof the numerical analysis model, the rolling force acting on the disc cutter wascompared and reviewed with the CSM model. As a result of numerical analysis for thelinear cutting test, the rolling force acting on the disc cutter was analyzed to be similarto the rolling force derived from the theoretical formula of the CSM model. From thenumerical analysis on 5 UCS cases (50 MPa, 70 MPa, 100 MPa, 150 MPa, 200 MPa),it is found that the range of the optimum spacing of the disc cutter decreases as the rockstrength increases. And it can be concluded that 80~100 mm of disc cutter spacing isthe optimum range having minimum specific energy regardless of rock strength. Thistends to coincide with the optimal spacing of previously reported disk cutters, which underpins the disk cutter spacing calculated through this study.
Abstract
As an increasing demand for rapid railway transportation, the construction of sidetrackis inevitable to operate local and express trains simultaneously. However, the currenttechnologies for the sidetrack construction method require a long construction periodby interrupting the operation of the existing subway line, as well as cause a hugeeconomic loss. Thus, it is necessary to study the sidetrack construction method underthe special situation that the subway is in operation and to analyze the risk of theexisting tunnel enlargement process for the sidetrack construction. Therefore, in thispaper, the Government Complex Gwacheon station on Subway Line 4 was consideredas a target station for the virtual sidetrack construction and the optimal sidetrackconstruction plan was derived. Subsequently, the application of risk managementprocess was carried out in the order of identifying risk, risk response planning,performing a risk analysis, risk monitoring and control for potential risk events duringthe construction of sidetrack under the subway operation. A total of eight potential riskevents and risk mitigation methods were selected, and a risk assessment matrix was established using the five-step risk probability and impact level criteria to perform the risk assessment includingresidual risks. Based on the results of the risk assessment, the risk grade and the reduction effect of each risk mitigationmethod were confirmed.
Abstract
In this study, the damage parameters of Mazars model for KURT (KAERI UndergroundResearch Tunnel) granite are measured form uniaxial compressive and Brazilian testsunder the simulated coupled condition of a deep geological disposal. The tests areconducted in three different temperatures (15°C, 45°C, and 75°C) and dry/saturatedconditions. Major model parameters such as maximum effective tensile strain (), At,Bt, Ac, and Bc differ from the typical reference values of concrete specimens. This islikely due to the difference in elastic modulus between rock and concrete. It is foundthat the saturation of specimens causes an increase in value of Bt and Bc while, the risein temperature increases and Bt and decreases Bc. The damage model obtained fromthis study will be used as the primary input parameters in the development of coupledThermo-Hydro-Mechanical Damage numerical model in KAERI.
Abstract
The divergence section of a double-deck tunnel can be divided into a ‘wideningpre-divergence section’, a large cross-section with a cap shape and a ‘post-divergencesection’ where the separation between the main and the branch tunnel is made. Sincethe cross-section of the widening pre-divergence section is considerably larger thanthat of the post-divergence section, the influence of excavation due to the differentsizes and shapes in the cross-section should be considered in the examination of thetunnel stability. In this study, the effect of the preceding excavation, that is theexcavation of the widening pre-divergence section, on excavation stability of thepost-divergence section was examined by varying the excavation methods and benchlengths through 3D finite element analysis. The results showed that although theeffects of the excavation methods and the bench lengths are not significant on thevariation of principal stresses, the preceding excavation causes a relatively largevariation on the stresses which may have an impact on the stability of thepost-divergence section from the comparison of Stress-Strength Ratio (SSR) betweenthe cases with and without the consideration of the preceding excavation effect by 2Dfinite element analysis.
Abstract
Aging tunnels with small cross-sections can cause chronic traffic jams. This problemcan be solved by widening the tunnel. In general, when the tunnel is expanded, theouter portion of the existing tunnel is excavated through a mechanical or blastingmethod. Such excavation affects not only the surrounding ground but also the existingtunnel. The application of the pre-cutting method can be a solution to these problemseffectively. Therefore, if the widening of tunnel is performed by applying pre-cuttingmethod, analysis of the impact of this method must be performed. In this study, in orderto analyze the effect of applying pre-cutting in tunnel widening, numerical analysis isperformed at six ground grades, from grade I to weathered rock. The analysis isperformed with the expanding lane and the excavation length of pre-cutting asvariables. In addition, the analysis is focused on the displacement of crown of theexisting tunnel and the enlarged tunnel. As a result, the crown displacement of theenlarged tunnel is confirmed to converge at the same value regardless of theexcavation length of the pre-cutting when the tunnel widening is completed. In thecase of existing tunnels, uplift of crown occurs within 5 m of the front of the tunnelsurface, and the shorter the excavation length of pre-cutting is found to be effective inpreventing the occurrence of uplift.
Abstract
This study focused on shielding through inflatable structure in the event of suddenwater inflow into the submerged floating tunnels. Currently, there is a lack of measuresto deal with unexpected water in tunnels in Korea. Although water treatment facilitiessuch as waterproofing and floodgates in tunnels are installed, there are limitations tothe sudden inflow of large amounts of seawater or underground water. Also, floodgatescannot respond quickly to sudden damage due to slow blocking time. Accordingly, astudy was conducted on the shielding rate and axial movement distance for inflatablestructure. The results of the reduced model experiment confirmed that the number ofinflatable structure and internal pneumatic pressure influence on the shielding rate. Asthe number of inflatable structure increased from one to two, the shielding rateincreased by about 35 up to 40 percent. It was also confirmed that the shielding rateincreased by about 4 percent as the internal pneumatic pressure increased from 0.2 barto 0.3 bar. If we verify and further develop the results identified in this study througha real-size experiment, it will be able to be used as an effective waterproof measure forsudden water inflow into the undersea tunnels or underwater tunnels.