• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.2
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• pp.109-120
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• 2007

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 $1{\sim}2$ 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.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.1206-1215
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• 2008

In this study, the equivalent pressure acting on the face of drilled hole was determined by back analysis. This analysis was continued until the difference between the displacement directly measured during field test construction of CGS and the displacement evaluated by numerical analysis was below 10 percent, and the affect of diaphragm wall adjacent to grout bulb was evaluated by numerical analysis using the equivalent pressure. From the analysis results, it was observed that the increase of the pressure acting on the diaphragm wall was greater at reclaimed sandfill layer than silty clay layer during the installation of CGS. Two methods were adopted to reduce the pressure acting on the diaphragm wall. One is installing of trench between diaphragm wall and grout bulb, the other is pre-installing of CGS before construction of diaphragm wall. From the numerical analysis results, above two methods can be considered as an effective method to reduce the pressure. It was analyzed that the amount of reduction of the pressure and the displacement are 689.8% and 564.6%, respectively, in the case of adopting the trench method, and 463.7% and 214.0%, respectively, in the case of adopting pre-installing of 3 columns CGS.

• Journal of the Korean Geophysical Society
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• v.5 no.2
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• pp.75-86
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• 2002

A TSP(Tunnel Seismic Prediction) survey which is modified VSP(Vertical Seismic Profiling) survey applied in tunnel was carried out at Pyongtaek and Incheon liquefied petroleum gas(LPG) storage cavern during excavation. The TSP survey in Pyongtaek LPG storage cavern which is located below Namyangho was performed to confirm the location and orientation of the fault detected at pre-investigation stage. The TSP survey was carried out in access tunnel, construction tunnel, and watercurtain tunnel to characterize 3 dimensional figure of the fault. The results of TSP survey are compared four in vestigation boreholes drilled in shelter of access tunnel. The fault was also detected by borehole survey and the location was coincided with the result of TSP survey. Depending on the result of TSP survey and core logging, the design such as cavern layout and length was changed. Another TSP survey was performed in Incheon LPG storage cavern which is located below sea. Because of poor geological information at pre-investigation stage and suffering from heavy leakage of groundwater, the TSP survey to detect fracture zone was carried out. The support and grouting design was reflected by the result of TSP survey.

• Geomechanics and Engineering
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• v.13 no.1
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• pp.173-194
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• 2017

Access shaft is of critical importance to the construction and operation of underground rock caverns. It usually has a relatively large cross-section and penetrates through fill materials, soil layers, and weathered rocks before reaching the caverns excavated in solid bedrock. In this paper, the design and construction of vertical shafts are reviewed in terms of diameter, depth, geological conditions, and support structure. Three shaft alternatives, namely alternative I: vertical shaft with spiral roads, alternative II: upper shaft with spiral roads & lower tunnels, alternative III: plain shaft, are proposed based on a simplified geological profile of the Jurong formation, Singapore. The advantages and limitations of the three types of shafts are discussed. The key issues relating to shaft design and construction, such as the shaft sinking, water control, support structure, are also discussed with a series of solutions provided, such as the sequential excavation, pre-grouting and diaphragm walls.

• Geomechanics and Engineering
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• v.20 no.4
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• pp.359-370
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• 2020

Prestressed ground anchors are important structural elements in geotechnical engineering. Despite their widespread usage, the design process is often significantly simplified. One of the major drawbacks of commonly used design methods is the assumption that skin friction is mobilized uniformly along an anchor's fixed length, one consequence of which is that a progressive failure phenomenon is neglected. The following paper introduces an alternative design approach - a computer algorithm employing the load-transfer method. The method is modified for the analysis of anchors and combined with a procedure for the derivation of load-transfer functions based on commonly available laboratory tests. The load-transfer function is divided into a pre-failure (hardening) and a post-failure (softening) segment. In this way, an aspect of non-linear stress-strain soil behavior is incorporated into the algorithm. The influence of post-grouting in terms of radial stress update, diameter enlargement, and grout consolidation is included. The axial stiffness of the anchor body is not held constant. Instead, it gradually decreases as a direct consequence of tensile cracks spreading in the grout material. An analysis of the program's operation is performed via a series of parametric studies in which the influence of governing parameters is investigated. Finally, two case studies concerning three investigation anchor load tests are presented.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.1752-1759
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• 2007

In the new Seoul-Busan high speed railroad construction specially city center passage roadbed establishment is recommended the staibility for the existing subway tunnel segments of Busan subway line No. 1 and No.2. regarding the appearance condition, a quality condition and the durability of the objective facility site exact inspection, and it evaluates the numerical analysis which uses MIDAS GTS it leads and there is the objective of the place where the stability of the objective facility and this tunnel it investigates. To immediacy of the on-the-spot inspection result whole facility it is a condition where the reinforcement which is simple not to be hindrance is necessary, 2nd Line case it is a condition which transfer is good but the general defect and the damage which occur from the tunnel of NATM type were confirmed part. While roadbed establishment constructing that the continuous maintenance is necessary, it is judged. The result of 1st, 2nd Line maximum sinkage, unequal sinkage and the lining stress of numerical analysis are within permission and the damage degree is appearing with the fact that the degree it will can disregard it is slight. But it enforces necessary Pre-grouting in order to minimize an actual tunnel face conduct and when the tunnel is excavated it is judged with the fact that necessary to minimize the outflow possibility.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.241-244
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• 2007

Cement-grouts are injected into limestone cavities beneath the road in the project area, in order to improve strength and reduce permeability; the extent to which grout has penetrated in cavities need to be monitored in order to determined effectiveness of cement-grout. Geophysical approaches, offer great potential for monitoring the grout injection process in a fast and cost-effective way as well as showing whether the grout has successfully achieved the target. This paper presents the ability of surface electrical resistivity to investigate the verification of the grout placement. In order to image the cement-grout, time-lapse surface electrical resistivity surveys were conducted to compare electrical resistivity images before and after injection. Cement-grout was imaged as anomalies exhibiting low resistivity than the surrounding rocks. In accordance with field monitoring, laboratory study was also designed to monitor the resistivity changes of cement-grout specimens with time-lapse. Time-lapse laboratory measurements indicated that electrical methods are good tool to identify the grouted zone. Pre-and post grouting electrical images showed significant changes in subsurface resistivity at grouted zone. The study showed that electrical resistivity imaging technology can be a useful tool for detecting and evaluating changes in subsurface resistivity due to the injection of the grout.

• Journal of the Korean Geosynthetics Society
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• v.20 no.4
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• pp.19-32
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• 2021

In this study, evaluation and consideration of domestic/overseas design, construction, and quality control performed by the authors on the deep cement mixing method were performed, and improvements for the development of the DCM method were suggested in the future. As a result of this study, it was found that the cross-sectional area correction for strength is required during the laboratory test of mix proportion, and caution is required because the extrapolation method may lead to different results from the actual one. Applicable design methods should be selected in consideration of both the improvement ratio and the type of improvement during design, and it was confirmed that the allowable compressive strength to which the safety factor was applied refers to the standard value for stability review and not the design parameters. In the case of the stress concentration ratio, rather than applying a conventional value, it was possible to perform economical design by calculating the experimental and theoretical stress concentration ratio reflecting the design conditions. In the case where pre-boring is expected during construction, if the increased water content is not large compared to the original, there were cases where a major problem did not occur even if the result that did not consider the increase in water content was used. In addition, it was confirmed that when the ratio of the top treatment length to the improved length is high, a small amount of design cement contents per unit length can be injected during construction. In the case of quality control, it was evaluated that D/4~2D/4 for single-axis and D/4 point for multi-axis were optimal for coring of grouting mixtures. As an item for quality control, it is judged that the standard that considers the TCR along with the unconfined compressive strength of grouting mixtures is more suitable for the domestic situation.

• Tunnel and Underground Space
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• v.13 no.2
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• pp.77-86
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• 2003

The finite element method and statistics of the convergence measurement are useful method of the stability analysis of the tunnel adjacent to the pier. It is the purpose of the this case study to certificate of validity of the application of those methods. The safety of the pilot tunnel method and LW pre-grouting has been evaluated from the FEM analysis. The three-dimensional finite element method is carried out for the decision of the level of stress redistribution at the two-dimensional numerical analysis. An analysis of the convergence is carried out by the estimation of preceding convergence at tunnel excavation. F-examination is applied for this estimation. As results of that analysis, The F-value is from 10.81 to 158.74 and the coefficient of determination is from 0.82 to 0.99. An analysis of convergence is carried out by using regression analysis. Consequently, it is shown that the convergence can be modeled as following function C(t)=a[1-exp(-bt)].

• Journal of the Korean Geophysical Society
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• v.7 no.4
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• pp.313-324
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• 2004

The finite element method and statistics of the convergence measurement are useful method of the stability analysis of the tunnel adjacent to the pier. It is the purpose of the this case study to certificate of validity of the application of those methods. The safety of the pilot tunnel method and LW pre-grouting has been evaluated from the FEM analysis. The three-dimensional finite element method is carried out for the decision of the level of stress redistribution at the two-dimensional numerical analysis. An analysis of the convergence is carried out by the estimation of preceding convergence at tunnel excavation. F-examination is applied for this estimation. As results of that analysis, The F-value is from 10.81 to 158.74 and the coefficient of determination is from 0.82 to 0.99. An analysis of convergence is carried out by using regression analysis. Consequently, it is shown that the convergence can be modeled as following function C(t) = a[1-exp(-bt)].