• Tunnel and Underground Space
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• v.25 no.5
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• pp.423-434
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• 2015

Scaled model tests were performed to investigate the influence of pillar width, rock strength and isotropy/anisotropy on the stability of twin tunnels. Test models had respectively different pillar widths, uniaxial compressive strengths of modelling materials and model types, where both the deformation behaviors around tunnels and the biaxial pressure data at a time of pillar cracking were analysed. The cracking pressures of the higher strength models were higher than the lower strength models, whereas the percentage of cracking pressure to uniaxial compressive strength of modelling materials showed an opposite tendency. The cracking pressures of the shallower pillar width models were lower than the thicker models, moreover the percentage of that showed a same tendency. It has been found that the pillar width was one of the main factors influencing on the stability of twin tunnels. Model types such as isotropy/anisotropy also influenced on the stability of twin tunnels. The anisotropic models showed lower values of both cracking pressures and the percentage of that than the isotropic models, where the pillar cracks of anisotropic models were generated with regard to the pre-existing joint planes.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.3
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• pp.189-204
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• 2015

This paper presents the results of reduced scale model tests on the effect of fault zone characteristics on the tunnel deformation behavior. A series of model tests were carried out on deep tunnels considering different fault zone orientations and offset distance. The tunnelling process was simulated in the model tests using compressed air technique. During the tests, the tunnel and ground deformation were mainly monitored while reducing the pressure inside the tunnel and the relationship between the pressure level and the tunnel deformation were established. The results indicate that for a given offset distance the tunnel behavior is influenced the most when the fault zone dips vertically while smallest influence occurs when the fault zone dips 45 degrees.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.6
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• pp.623-635
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• 2015

Double-deck tunnels beneath the groundwater table have relatively large volume and commonly constructed as watertight tunnels. In this case, it requires to secure stability of the tunnels for buoyant force. Generally the contact force between lining and ground is sufficient to resist the buoyant force. However in the long-term the contact force could be reduced because of structural deterioration. In this study the effect of long-term buoyant force acting on the double-deck tunnel is investigated. The results has shown that the buoyant force has increased invert deformation and stress. It is indicated that the contact resilience between lining and ground needs to be kept during tunnel operation.

• Tunnel and Underground Space
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• v.33 no.4
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• pp.265-280
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• 2023

Water leakage in tunnels is a defect that can affect tunnel stability and the ground movement by changing the stress and pore water pressure of the surrounding ground. Long-term or large-scale water leaks may lead to damage of tunnel structure and the surrounding environment, such as tunnel lining instability and ground surface settlement. The present study numerically investigated the effects of water leakage on the structural stability of a tunnel and the ground behavior. The tunnel was assumed to be under undrained conditions for preventing the inflow of the surrounding water and leaks occurred in the concrete lining after completion of the tunnel construction. A coupled hydro-mechanical analysis using a TOUGH-FLAC simulator developed in Python was conducted for assessing the leakage induced-behavior of the tunnel structure and ground under different conditions of the amount and location of water leak. Additionally, the effect of hydro-mechanical coupling terms on the results of coupled response was investigated and discussed.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.3
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• pp.315-325
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• 2009

The thickness of the material can be thinned because arch cut-and-cover tunnel has the support mechanism by the axial force, and the ground reaction force due moderate deformation can be expected thereby making it be dynamically advantageous, therefore the arch cut-and-cover tunnel has become more widely used. An important characteristic of the arch cut-and-cover tunnel is that the thickness of the material can be thinned because precast arch type has the support mechanism by the axial force. However, there is a different stress state surrounding the structures between normally excavated tunnels and cut-and-cover tunnels, it should be considered at designing. Therefore, finite element method was carried out to examine the mechanical behavior of the precast arch cut-and-cover tunnel considering construction procedure.

• Tunnel and Underground Space
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• v.18 no.3
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• pp.214-218
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• 2008

Dynamic fracturing of anisotropic granite was investigated by SHPB (Split Hopkinson Pressure Bar). Energy absorption during the test and maximum stress were increased as strain rate increased. Maximum stresses in every direction were dependent on the strain rate but not so sensitive to anisotropy. Elastic wave velocity was decreased as strain rate increased and dependent on strain rate in every direction. Especially, elastic wave velocity decreased more rapidly in a strong rock.

• Journal of the Korean Geotechnical Society
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• v.26 no.6
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• pp.57-70
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• 2010

Recent earthquakes have demonstrated that the tunnels, which were once considered to be highly resistant to earthquakes, are susceptible to substantial damage under severe seismic loading. Among various modes of deformation under an earthquake loading, the response of the tunnel in the transverse direction is known to be the critical mode. This paper investigates the seismic response of the tunnel in the transverse direction using the method of seismic displacement, which is a type of pseudo-static analysis. Firstly, the methods of calculating the ground deformation are compared. It is shown that the single and double cosine may not provide an accurate estimation of the ground deformation, and that a one-dimensional site response analysis needs to be performed for a more reliable evaluation. Secondly, the tunnel responses are calculated using the simplified, analytical, and numerical solutions. It is demonstrated that the simplified method provides poor estimates of the tunnel response ground deformation. The analytical solution is shown to be effective in modeling circular tunnels in uniform ground, but has serious limitation in modeling tunnel response in non-uniform ground. Numerical analyses are shown to be applicable to all cases, and give the most accurate estimates of the tunnel response. It is also demonstrated that the linear solutions can be so conservative that the soil nonlinearity needs to be accounted for more accurate evaluation of the tunnel response.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2011.09a
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• pp.281-287
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• 2011

• Proceedings of the Korean Geotechical Society Conference
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• 1998.06b
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• pp.91-122
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• 1998

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.3
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• pp.249-257
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• 2005

There are basically two methods for the seismic design of underground structures ; analytical or pseudo-static, and dynamical method. In pseudo-static analysis approach, the ground deformations are imposed as a static load and soil-structure interaction does not include dynamic or wave propagation effects. However the behavior of soil structure interaction is nonlinear, it needs to consider nonlinear soil-structure interaction effects. In this study simplified seismic analysis method to consider soil-structure interaction by iterative procedure is proposed and the results are compared and analyzed by a finite difference computer program.