• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.833-841
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• 2008

Recently, the upheaval generation in the road which is under service had been reported. Due to the upheaval generation, total 4 lanes were forced to curtail to 3 lanes, and traffic was delayed. In normal situation of cut-slopes in korea, that condition is hard to detect since most cut-slopes contain discontinuous material, that is rock. Common collapses in rock-slopes is wedge failure, plane failure and toppling failure which is all individual mechanism of discontinuous rock mass. In contrast, such upheaval in the road in front of cut-slope can be generated only when circular movement is triggered within the cut-slope. In this sense, rock-slopes barely show any kind of movement in the road locates at the front of them. Numerical analysis is general method in simulation of slope displacement and evaluation of safety. However, numerical analysis programs which are related with rock-slopes are not able to simulate such upheaval movement because that programs are based on discontinuous modeling mechanism. In addition, although numerical analysis programs which are based on FEM/FDM and thus utilize continuous modeling mechanism are able to simulate circular movement and upheaval situation, they have weakness in reflecting discontinuities of rock-slope itself. In this study, detailed in-site investigation and numerical analysis based on in-site condition were performed in order to expect upheaval movement in the road. In this procedure, the FLAC program which uses continuous modeling method was utilized, and new approach reflecting discontinuity developed toward the road with a ubiquitous joint model was tried to derive reliable analysis result.

• Journal of the Korean Geosynthetics Society
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• v.8 no.4
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• pp.9-17
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• 2009

This research was intended to verify the stability of landfill final cover using SRSL(Self Recovering Sustainable Liner) with regard to differential settlements due to the degradation of waste and so on in a waste landfill. Numerical analysis was performed using FLAC 2D software program with input parameters based on soil characteristic tests and reference data after the blank was designed in order to represent the decomposition condition of waste. The maximum settlement of landfill cover was calculated to investigate the structural stability of landfill cover with the different condition of settlement width, settlement depth, and number of differential settlements. The allowable maximum deformation rate of SRSL, which was calculated using field permeability tests, was 6 mm. The analysis showed that SRSL was stable in case of a differential settlement width not exceeding 24.5% of total cover width.

• Journal of the Korean Geotechnical Society
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• v.15 no.5
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• pp.29-41
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• 1999

This Paper applied a simple strength parameter averaging method to double layered systems consisting of the strong sand layer overlying the soft clay deposit. This study derived a formula which defines a critical depth as the strength parameters, and used the correction parameter, $\alpha$ to reduce an error of the strength parameter averaging method. The results of the method were presented in the form of dimensionless charts and were compared with the results of several solutions proposed by Satyanarayana & Grag, Sreenivasulu, and Meyerhof & Hanna. The results of the proposed method coincided with the method of Meyerhof & Hanna and the results obtained from FLAC. But the Satyanarayana & Grag method and the Sreenivasulu method overestimated the bearing capacity. Consequently, the bearing capacity of foundation on sand layer overlying soft clay layer can be approximately estimated by using the proposed dimensionless charts.

• Journal of the Korean Geotechnical Society
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• v.16 no.1
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• pp.243-250
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• 2000

The mechanical behavior of the underground box culvert constructed by the open cut method depends mainly on the earth pressure acting on it. In this study, the earth pressure on the underground box culverts constructed by the open cut method during and after the construction sequence was numerically analysed by using FLAC. The results are compared with those of the Marston-Spangler's theory, silo theory, and the model tests. The results showed that the vertical earth pressure on the upper slab of the box structure was not uniform. It was as large as the overburden in the middle part of the slab but was smaller or larger than that at its end part depending on the slope of the excavation, the depth of the cover, and the width of the side refill. The horizontal earth pressure on the side wail was much smaller than the earth pressure at rest and grew nonlinearly with the depth.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.783-790
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• 2004

In this study, a newly modified soil nailing technology named as the PSN(pretensioned soil nailing) system, is developed to reduce both facing displacements and ground surface settlements in top-down excavation process as well as to increase the global stability. Up to now, the PSN system has been investigated mainly focusing on an establishment of the design procedure. In the present study, the analytical procedure and design technique are proposed to evaluate maximum pretension force and stability of the PSN system. Also proposed arc techniques to determine the required thickness of a shotcrete facing and to estimate probability of a failure against the punching shear. Based on the proposed procedure and technique, effects of the radius of a influence circle and dilatancy angle on the thickness of a shotcrete facing, bonded length and safety factors arc analyzed. In addition, effects of the reduction of deformations expected by pretensioning of the soil nails are examined in detail throughout an illustrative example and $FLAC^{2D}$ program analysis. And a numerical approach is further made to determine a postulated failure surface as well as a minimum safety factor of the proposed PSN system using the shear strength reduction technique with the $FLAC^{2D}$ program. Global minimum safety factors and local safety factors at various excavation stages computed in case of the PSN system arc analyzed throughout comparisons with the results expected in case of the general soil nailing system. The efficiency of the PSN system is also dealt with by analyzing the wall-facing deformations and the adjacent ground surface settlements.

• Structural Engineering and Mechanics
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• v.57 no.6
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• pp.1125-1142
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• 2016

Tunneling is one of the challenging tasks in civil engineering because it involves a variety of decision making and engineering judgment based on knowledge and experience. One of the challenges is to construct tunnels in risky areas under shallow overburden. In order to prevent the collapse of ceilings and walls of a large tunnels, in such conditions, either a sequential excavation method (SEM) or ground reinforcing method, or a combination of both, can be utilized. This research deals with the numerical modeling of L-profiles and pipe fore-poling pre-support systems in the adit tunnel in northwestern Iran. The first part of the adit tunnel has been drilled in alluvial material with very weak geotechnical parameters. Despite applying an SEM in constructing this tunnel, analyzing the results of numerical modeling done using FLAC3D, as well as observations during drilling, indicate the tunnel instability. To improve operational safety and to prevent collapse, pre-support systems, including pipe fore-poling and L-profiles were designed and implemented. The results of the numerical modeling coupled with monitoring during operation, as well as the results of instrumentation, indicate the efficacy of both these methods in tunnel collapse prevention. Moreover, the results of modeling using FLAC3D and SECTION BUILDER suggest a double angle with equal legs ($2L100{\times}100{\times}10mm$) in both box profile and tee array as an alternative section to pipe fore-poling system while neither $L80{\times}80{\times}8mm$ nor $2L80{\times}80{\times}8mm$ can sustain the axial and shear stresses exerted on pipe fore-poling system.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.5
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• pp.389-399
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• 2016

Efficiency for estimation of subsea tunnel safety can be increased through reflecting back analysis algorithm to displacement measurements besides other measurement information such as stress, water pressure and ground stiffness degradation. In this study, the finite difference code FLAC3D built-in FISH language is used. In addition, the stability of the tunnel lining will be evaluated from the development of displacement-based algorithm and its expanded algorithm with conformity of several parameters such as stress measurements, water pressure measurements, tunnel lining degradation measurements and ground stiffness degradation measurements. By using additional measurement information to assess the stability of subsea tunnel, it was confirmed that the error rate is reduced to the tunnel back analysis.

• Explosives and Blasting
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• v.26 no.2
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• pp.20-28
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• 2008

In the design stage of a tunnel, the wall convergence is commonly estimated through an elasto-plastic analysis of the tunnel, which has been a topic drawing many researcher's attention so far. Despite its importance, however, the elasto-plastic behavior of a circular tunnel excavated in a generalized Hoek-Brown rockmass is still poorly understood. In this study, a simple munerical method based on Lee & Pietruszczak (2008) for the elasto-plastic analysis of a circular tunnel surrounded by reinforced annulus is proposed. It is assumed that the tunnel is excavated in a strain-softening rockmass obeying the generalized Hoek-Brown failure condition. The commercial code FLAC is used for the verification of the proposed method. The influence of the Hoek-Brown strength parameter a and the thickness of the reinforcement annulus on the elasto-plastic behavior around the tunnel was discussed by conducting some example analyses. The results show that the influence of these two parameters on the distribution of stresses and displacements is substantial.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.147-154
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• 2000

The influence of the mined-out caves on the stability of the high speed railway tunnel was investigated with a series of geological logging and in-situ tests on the one hand, and with the rock mass classification using the multiple regression analysis on the other hand. The rock mass in this area can be classified as 'fair', and the condition of the discontinuities plays the most important role in the classification of the rock mass. The results of the analysis obtained by the FLAC showed that the western part of the tunnel locating at 50m above the mine cavities could be affected by subsidence associated with a considerable deformation, the magnitude of which might depend on the properties of the rock mass. Key word : multi regression analysis, subsidence, mine cavities

• Tunnel and Underground Space
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• v.10 no.3
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• pp.441-446
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• 2000

Numerical analysis using FLAC3D has been conducted to estimate the stability of a large underground hall that is to be excavated in a mined area and constructed as an unit of a resort park. Numerical modelling is divided into two stages. The first stage is related to the analysis of the mechanical stability of the hall itself and the second to that of the influence of an adjacent mined cavity upon the hall. In the first stage, the stability of the hall is judged from the interpretation of numerical results in three respects: convergence of the unbalanced force of the model, occurrence of plastic zones and distribution of the displacement. In the second stage, variation of the stress state around the underground hall due to the existence of the cavity is compared to that in the case of the absence of the cavity. Through these analyses, it could be known that the large underground hall is not exposed to any mechanical problems and also not affected by the adjacent cavity.