(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.16 No.5
Abstract
In this paper case studies of artificial ground freezing, which have not been applied in Korea, have been investigated for the water cut-off in a subsea tunnel under high water pressure and the most commonly used cooling mediums of brine and liquid nitrogen are examined. Since sea water with pressure has the lower freezing point than pure water, the lower temperature cooling medium is required in the application of subsea tunnel. Also, the cooling medium must have refrigeration safety and is able to reduce executing time. Brine freezing system can reuse cooling medium and is safer than liquid nitrogen freezing. But it takes more time to freeze ground and needs complex circulation plants. On the other hand, liquid nitrogen freezing system can’t recycle cooling medium and may cause breathingproblemsorasphyxiationthroughoxygendeficiency. But, freezing with liquid nitrogen is fast and requires simple refrigeration equipment. Principal elements of design for ground freezing in subsea tunnel have been extracted and these elements are needed further research
Abstract
The displacement data monitored during tunnel construction play a crucial role in predicting the behaviour of ground around and ahead of excavation face. However, the management criteria for monitoring data are not well established especially for the reliable analysis on varying aspect of displacement data along with chainage. In this study, we evaluated the applicability of x-MR control chart method, which is kind of applied statistical management method, for the analysis of displacement monitoring data in terms of prediction of possible collapse or induced cracks. As a result, a possible abnormal behaviour could be predicted beforehand at 5 ~ 13 m ahead or on at least one day before it occurred by using x-MR control chart method. In addition, it is noted that the moving range for the x-MR control chart should be set to 5 ~ 10 for this pur
Abstract
Now-a-days, the trend in constructing tunnels is to build more deeper, more longer tunnels of greater cross-sections. That’s why, the demand of “Early-high-strength shotcrete” is very high because of their advantage of attaining higher strength immediately after excavation, which controls the ground subsidence. So, this study reveals the supporting phenomena of early-high-strength shotcrete, using three-dimensional numerical analysis. The crux of this study can be applied practically in construction sites also. Support Performance of two different qualities of shotcrete was checked out, by keeping the general shotcrete’s thickness constant and comparing it with early-high-strength shotcrete’s thickness decreasing it gradually in five steps, and analysing/comparing the support performance in all cases. Effect of using early-high-strength shotcrete was analysed to save the cost of steel sets, which are widely used for supporting the ground before the hardening of general shotcrete. The results of numerical analysis on the performance of early-high-strength shotcrete show that, it behaves more effectively under worse ground conditions and it can support the ground more conveniently than steel sets, before the shotcrete is hardened.
Abstract
The monitoring method of geotechnical structures using acoustic emission(AE) and microseismicity(MS) isto detect the microscopic deformation and fracture behavior in the inner structures by measuring induced acoustics andvibrations. It can identify a pre-indication of failure by taking advantage of the characteristics that the amount and occurrencerates of AE and MS increase rapidly prior to large scale destruction of the target structures. The monitoring system consistingof high-quality sensors, high-speed data acquisition device and the operation program is required for the practical applicationof this method. Recently, the AE and MS monitoring systems have been localized. In particular, the developed operationsoftware which can analyze and interpret the measured signals was demonstrated through a number of applications todomestic fields. This report introduces the configuration and features of developed monitoring system, then the challengesand future direction of AE monitoring in geotechnical structures are discussed.
Abstract
In this study, in order to suggest the design method for supports in the room-and-pillar underground structure,the case study was carried out. In the case study, shape of rock pillar and room was mainly considered. From the analysis,a displacement at the roof, the maximum principle stress and plastic state were examined. To optimize variables in the casestudy, cases from the Seoul metro station were analyzed, then a target depth of the underground structure and groundconditions were determined. And the height of rock pillar and room were chosen from the assumed purpose of undergroundspace, i.e. living/office and warehouse. Total cases of analysis was 180 cases including 3 types of ground condition, 5 typesof rock pillar and 6 types of roof span. It is expected that results from analysis can be used to determine the installation ofsupport in room-and-pillar underground structure with stability, utilization efficiency of underground space andapplicability of vehicles.
Abstract
In this study, analysis results described in the companion paper was used to determine shapes ofroom-and-pillar underground structure. To select optimized shapes, structural stability, space applicability and vehicleapplicability were considered. In the structural stability step, ratio between strength and stress of the pillar and the criticalstrain at the roof span were adopted. The space applicability was used to retain the sufficient space of underground structureas its purpose is for human activity. The vehicle applicability was used to consider a radius for rotation of constructionequipments in the room-and-pillar underground structure. From the given procedure in this study, proper shapes of rockpillar and room can be selected to design supports at the pillar and roof.