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Keywords: circular tunnels, static, dynamic, single, twin, shear wave velocity.

Summary

The effect of different parameters on the static and dynamic behaviour of tunnels has been one of the main concerns in previous studies. The most important parameters are the type of the soil, tunnel depth and shape of the tunnel section.

One of the other main problems is the interaction of twin tunnels that have become of great importance in big cities. The distance between twin tunnels or their position has a significant effect on their behaviour.

The main aim of this paper is to investigate the effect of the shear wave velocity, tunnel depth and also the interaction between twin tunnels and surrounding soils.

Numerical modelling has been performed based on the finite difference method using the Flac 2D software. The circular tunnel is modelled assuming the excavation with a tunnel boring machine (TBM). The modelling procedure consists of creating the model geometry, considering material properties, applying the initial and boundary condition, static loading (excavating tunnels, stress relaxation and lining construction), dynamic loading and sensitivity analysis. Sensitivity analysis consists of the investigation of the effect of shear wave velocity, tunnel depth and also the distance between the twin tunnels and their interaction.

A Mohr-Coulomb model has been used for numerical modeling as an elastic-perfect plastic model. Four different soil conditions have been modelled based on the real seismic and geotechnical test results of different sites. These soil conditions are selected in such a way as to correspond to loose to very dense soils.

The diameter of the tunnels modeled is 10 metres and the analysis has been performed considering the tunnel center depths at 15 and 25 metres below the ground surface. In order to investigate the interaction between the twin tunnels, the ratio of the distance between tunnel centres to their diameters has been considered from 1.2 to 3.

Based on the dynamic and static analysis results, the lining axial force variations are mainly dependent on the tunnel depth and overburden pressure, while the moment variations are mainly dependent on the soil type and shear wave velocity without significant dependency on the tunnel depth.

Based on the static analysis results, the increase of the moment, axial force and settlements arising from the interaction of twin tunnels is considerable especially when there is a small distance between tunnels. Also the effect of soil type is considerable and lower shear wave velocity values will result in more intensified moments and settlements. Under dynamic loading, the interaction effects of twin tunnels on the increase of the axial forces is less in comparison with the static case, while the moment variations are also insignificant.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 96 PROCEEDINGS OF THE THIRTEENTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING Edited by: B.H.V. Topping and Y. Tsompanakis Paper 224 Analysis of Single and Twin Tunnels Interacting with Surrounding Alluvial Soils H. Shakib and O. Naeemifar Civil Engineering Faculty, Tarbiat Modares University, Tehran, Iran doi:10.4203/ccp.96.224 purchase the full-text of this paper Full Bibliographic Reference for this paper H. Shakib, O. Naeemifar, "Analysis of Single and Twin Tunnels Interacting with Surrounding Alluvial Soils", in B.H.V. Topping, Y. Tsompanakis, (Editors), "Proceedings of the Thirteenth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 224, 2011. doi:10.4203/ccp.96.224 Keywords: circular tunnels, static, dynamic, single, twin, shear wave velocity. Summary The effect of different parameters on the static and dynamic behaviour of tunnels has been one of the main concerns in previous studies. The most important parameters are the type of the soil, tunnel depth and shape of the tunnel section. One of the other main problems is the interaction of twin tunnels that have become of great importance in big cities. The distance between twin tunnels or their position has a significant effect on their behaviour. The main aim of this paper is to investigate the effect of the shear wave velocity, tunnel depth and also the interaction between twin tunnels and surrounding soils. Numerical modelling has been performed based on the finite difference method using the Flac 2D software. The circular tunnel is modelled assuming the excavation with a tunnel boring machine (TBM). The modelling procedure consists of creating the model geometry, considering material properties, applying the initial and boundary condition, static loading (excavating tunnels, stress relaxation and lining construction), dynamic loading and sensitivity analysis. Sensitivity analysis consists of the investigation of the effect of shear wave velocity, tunnel depth and also the distance between the twin tunnels and their interaction. A Mohr-Coulomb model has been used for numerical modeling as an elastic-perfect plastic model. Four different soil conditions have been modelled based on the real seismic and geotechnical test results of different sites. These soil conditions are selected in such a way as to correspond to loose to very dense soils. The diameter of the tunnels modeled is 10 metres and the analysis has been performed considering the tunnel center depths at 15 and 25 metres below the ground surface. In order to investigate the interaction between the twin tunnels, the ratio of the distance between tunnel centres to their diameters has been considered from 1.2 to 3. Based on the dynamic and static analysis results, the lining axial force variations are mainly dependent on the tunnel depth and overburden pressure, while the moment variations are mainly dependent on the soil type and shear wave velocity without significant dependency on the tunnel depth. Based on the static analysis results, the increase of the moment, axial force and settlements arising from the interaction of twin tunnels is considerable especially when there is a small distance between tunnels. Also the effect of soil type is considerable and lower shear wave velocity values will result in more intensified moments and settlements. Under dynamic loading, the interaction effects of twin tunnels on the increase of the axial forces is less in comparison with the static case, while the moment variations are also insignificant. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £130 +P&P)
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