• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.2
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• pp.61-76
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• 2021

As the number of existing road tunnels increases every year, collapse and floor heaving accidents occur frequently during construction. The collapse among tunnel accidents dominates, so that studies related to the floor heaving are relatively insufficient. Accordingly, many studies to reinforce the lower part of the tunnel have been conducted, but the analysis on the effect of the curvature of the tunnel floor is insufficient. Therefore, in this study, the effects of the upper analysis area height and the coefficient of lateral earth pressure of the tunnel located on a tuff deterioration zone with a large rock cover, as well as the floor curvature, were examined through sensitivity analysis. As a result of the analysis, it turned out that the overall stability of the tunnel increases as the floor curvature increases, the coefficient of lateral earth pressure decreases, and the upper analysis region increases.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.1
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• pp.37-45
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• 2021

The construction of the tunnel portal should be careful because cover depth is shallow and it is difficult to exhibit the arching effect. Tunnel stability may be reduced with additional embankment above the portal of tunnel. In this study, in order to examine the stability of the tunnel according to additional embankment above the portal of tunnel, numerical analysis was performed while changing the ground conditions and height of embankment. As a result of the numerical analysis, it was found that the allowable flexural compressive stress of shotcrete and allowable axial force of rockbolts were exceeded when the height of additional embankment was 12 m in rock mass rating V. When considering the displacement, the range of the plastic region and the behavior of the support materials, the tunnel stability seems to be greatly reduced if the height of additional embankment above the portal of tunnel exceeds 10 m.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.85-95
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• 2009

In urban areas, blast excavation adjacent to tunnels is carried out frequently. It is generally required to secure static and dynamic stability of nearby tunnel structures for any such activities. Although there is some national guidelines for static safety, there is little guides to risk zoning controling the dynamic behavior of the underground structures. In this study, impacts on the blast-induced vibration are investigated using numerical study. An attempt to define the restricted area of blast adjacent to subway tunnels was also made. Particular concerns were given to tunnel depth and ground types. By carrying out the parametric study on depth and ground patterns, the envelope of blast distance of which dynamic response on the lining is controlled under 1 cm/sec, is established. It is shown that the increase in depth has increased the required safety distance slightly until the distance of 3.5 times of the tunnel diameter. Despite small changes in safety distance, it can be generally said that the effects of depth and stiffness of the ground is not significant in controlling the particle velocity of the tunnel linings.

• Journal of the Korean Geotechnical Society
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• v.30 no.2
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• pp.5-18
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• 2014

Depending on the underground load support mechanism, anchors are classified as friction anchors, bearing plate anchors and the recently developed combined friction-bearing plate anchors which combine the characteristics of both the friction and bearing plate type anchors. Even though numerous studies have been performed on bearing plate anchors, there were only few studies performed to observe the failure surface of bearing plate anchors. Furthermore most of the soil materials used on these tests were not real sand but carbon rods. In this study, sand was placed in the soil tank and laboratory tests were performed with bearing plate anchors installed with an embedment depth (H/h) ranging from 1~6. The variation in the pullout capacity and the behaviour of soil with the embedment depth (H/h) were observed. Ground deformation analysis program was also used to analyze soil displacement, zero extension direction, maximum shear strain contours. It was determined from the analysis of the results that at ultimate pullout resistance the deformation was 5 mm and the failure surface occurred in a narrower area when compared with results of the previous researches. It was also observed that the width of the fracture surface gradually becomes wider and expands up to the surface as the deformation increases from 10 mm to 15 mm.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.1
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• pp.97-103
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• 2020

The newly improved multistep steel pipe grouting method was applied to an existing steel pipe-reinforced grouting method. It was applied in order to prevent a damage caused by ground failure from excessive grouting pressure in a tunnel construction. The tunnel goes under a highway and a ramp connected to a rest area on OO highway with 11.3~12.1 m depth cover and is a part of roadbed facility construction section ordered by OO public corporation. The improved grouting method provides pre-construction work condition assessment technique through new water injection limit test and grouting effect assessment technique by grouting type assessment. It also includes assessments on interval of joints, appropriate grouting pressure, and optimal operation time to be applied to current operations. Application of the grouting method allowed the smooth road management in shallow-depth grouting construction area located upper part of tunnel excavation. Moreover, the possibility of the application of the method not only to shallow-depth grouting construction but also to various steel pipe-reinforced grouting constructions was confirmed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.1
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• pp.141-150
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• 1987

The Soyanggang Dam completed in 1973 was well instrumented during construction period. The measured results for stresses and movements of the embankment have already been published elsewhere, but theoretical analyses have not been made until now. This study intends to analyze the stress and deformation behavior of the embankment numerically which have been subjected to the load of materials during construction and water load during impounding. The constitutive law used for the analyses is hyperbolic model developed by Duncan et al., and a nonlinear incremental finite element analysis simulating its contruction steps is. used in this study. Hyperbolic parameters for each Zone are estimated from literature. The results obtained from the theoretical analyses clearly show deformation characteristics and stress vectors in arbitrary section of the dam. The analytical results ate well agreed with the measured deformations at the maximum cross section, however, there are some discrepancy in horizontal movements and in stresses generated in the core zone. From the numerical analyses and its comparison with the measured values, it is charaterized that relatively large construction settlements occurred in core zone, overburden pressure in the core zone was considerably reduced by arching effect, and tension zones might occur near both abutments because of the large horizontal displacement.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.10
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• pp.24-30
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• 2018

As the demand for underground space increases, many researchers have been studying the load reduction method using high compressible materials to solve for the stability problem of the overhead load and for the increase of the earth pressure which decreases the function of the underground structure. This paper determines the optimum soft zone and the effect of the using EPS Geofoam as a load reduction material to arch structures. A finite element analysis program, ABAQUS, is used to analyze the soil-structure interaction and the behavior of buried arch structures considering different four EPS Geofoam forms to confirm the most conservative shape. The optimum cross-sectional shape was determined by comparing the results of earth pressure reduction rate in accordance with the change of span-rise ratio and span length of the arch structure. It was confirmed that the earth pressure generated in the arch structure using the optimal soft zone selected by the numerical analysis was reduced by an average of 78%. In this study, the effect of EPS Geofoam on soil pressure reduction and its applicability to underground arch structures will provide an economical and conservative way to design underground structures and will help to increase the usability of deep underground space.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.375-392
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• 2018

The shield TBM method is widely adopted for tunneling works in urban area because it has more beneficial ways to control settlement at ground surface than conventional mined tunneling. In the shield tunneling, backfill grouting at tail void is crucial because it is supposed not only to restraint ground deformation around tail void during excavation but also to compensate precedent ground settlement by pushing up the ground with highly pressurized grout. However, the tail void grouting has been found to be ineffective for settlement compensation particularly in sandy ground, which might be caused by complicate interaction between ground and tail void grouting. In this paper, the effects of tail void grouting on behavior of ground in shield TBM tunneling were investigated based on 3-dimensional finite element analyses. The results of numerical analyses indicated that backfill grouting actually reduces settlement by degrading settlement increasing rate in excavation, which means decrease of volume loss. Meanwhile, the grouting could not contribute to compensate the precedent settlement, because reduction of volume loss by grouting was found to be counterbalanced by volume change of ground.

• Journal of Korea Water Resources Association
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• v.50 no.6
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• pp.429-440
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• 2017

A series of multispectral high-resolution Korean Multi-Purpose Satellite (KOMPSAT) images were analyzed to detect the geographical changes in four different tidal flats in the west coast of South Korea. The method of unsupervised classification was used to generate a series of land use/land cover (LULC) maps from the satellite images, which were used as the input of the temporal trajectory analysis to detect the temporal change of coastal wetlands and its association with natural and anthropogenic activities. The accurately classified LULC maps extracted from the KOMPSAT images indicate that these multispectral high-resolution satellite data is highly applicable to generate good quality thematic maps for extracting wetlands. The result of the trajectory analysis showed that, while the tidal flat area of Gyeonggi and Jeollabuk provinces was estimated to have changed due to tidal effects, the reductive trajectory of the wetland areas belonging to the Saemangeum province was caused by a high degree of human-induced activities including large reclamation and urbanization. The conservation of the Jeungdo Wetland Protected Area in Jeollanam province revealed that the social and environmental policies can effectively protect coastal wetlands from degradation. Therefore, monitoring for wetland change using high resolution KOMPSAT is expected to be useful to coastal environment management and policy making.

• Tunnel and Underground Space
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• v.8 no.3
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• pp.209-225
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• 1998

Recently, Umbrella Arch Method(UAM), one of the auxiliary techniques for tunnelling, is used to reinforce the ground and improve stability of tunnel face. Because UAM combines the advantages of a modern forepoling system with the grouting injection method, this technique has been applied in subway, road and utility tunnel sites for the last few years in Korea. Also, several research results are reported on the examination of the roles of inserted pipes and grouted materials in UAM. But, because of its empirical design and construction methodology, more qualitative and systematic design sequences are needed. Therefore, above sequences using numerical analysis are proposed and, the effects of some design parameters were studied in this research. In order to acco,mplish these objects, first, the roles of pipe and grouting materials, steel-rib and the others in ground improving mechanism of UAM are clarified. Second, the effects of design parameters are investigated through parametric studies. Design parameters are as follows; 1) ground condition, 2) overburden, 3) geometrical formulation of pipes, 4) grouting region and 5) characteristics of pipes.