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Keywords: random height, seismic acceleration, transfer function, surface displacement, probabilistic.

Summary

Seismic excitations create waves that are transmitted through surrounding soil and influence structures such as neighbouring buildings [1,4]. The study of buried structures in soil has a certain number of complications inherent to structures (rigidity, geometry, discontinuity) and soil (geometry, infinity, uncertainty).

The BEM is an appropriate numerical method for the resolution of such problem because it's necessites only the discretization of frontiers, and hence significantly decreases the dimension of the problem. However, this procedure requires the determination of fundamental functions called "Green's functions" that are known analytically only for simple cases. This obstacle is overcome by using the Thin Layer Method [3] to obtain Green's function that are ideal for the case of dynamic loads in a horizontally stratified medium. To this obstacle, the random characteristics of the geological and mechanical properties, which implies the use of probabilistic methods based on simulation techniques, must be considered.

In the present paper, a tunnel (Algiers, Algeria) in a multi-layered soil is subjected to the Boumerdes May 21st 2003 earthquake (magnitude 6.5) seismic excitation. The acceleration considered is that located at Keddara station (located at 12 km from Boumerdes), because it is located directly at the bedrock . Accelerations in one horizontal direction EW are considered and will focus on the SH wave propagation. The height of the bottom layer is uncertain and normally distributed. One hundred samples are considered to calculate the mean and the standard deviation of the ground surface displacement and transfer function of seismic acceleration [2].

The present study shows the influence of the randomness of the geological properties of layered soil on the surface displacement and the transfer function with the presence of a tunnel.

The maximum of the mean ground surface displacement is located approximately at the fundamental frequency of the signal and at a distance to the axis of the tunnel corresponding to the extremity of the tunnel. The standard deviation of the displacements is important for the lower frequencies and for the fundamental frequency.

The frequency content of the signal is not influenced by the tunnel, and the location of the maximum displacement is at the extremity of the tunnel. The mean transfer function is importance for the eigenfrequencies of the system and the maximum is located at the extremity of the tunnel.

References

1: M. Badaoui, "Investigation analytique et numérique du phénomène d'interaction dynamique dans les systèmes sol multicouches - structures multiples". Master Thesis, Dept. of Civ. Eng., 1998.
2: Badaoui M., Nour A., Slimani A. and Berrah M.K., "Stochastic Seismic Investigation of Heterogeneous Soil Profile having Uncertain Depth", in Proceedings of The Fourth International Conference on Engineering Computational Technology, B.H.V. Topping and C.A. Mota Soares, (Editors), Civil-Comp Press, Stirling, United Kingdom, paper 114, 2004. doi:10.4203/ccp.80.114
3: E. Kausel and R. Peek, "Dynamic Loads in the Interior of Layered Stratum: an explicit solution", Bull. Seism. Soc. Am., 72(5), 1459-1481, 1982.
4: A.L. Pais,. "Dynamic Coupling of Multiple Structures Through Soil", PhD. Thesis, MIT, Dept. of Civ. Eng., 1988.

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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: 81 PROCEEDINGS OF THE TENTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING Edited by: B.H.V. Topping Paper 226 Influence of the Soil Profile Uncertainty on the Tunnel - Layered Soil Interaction Subject to Seismic Acceleration M. Badaoui+ and M.K. Berrah* +Department of Civil Engineering, USTHB, Algiers, Algeria Ecole Nationale Polytechnique, Algiers, Algeria doi:10.4203/ccp.81.226 purchase the full-text of this paper Full Bibliographic Reference for this paper M. Badaoui, M.K. Berrah, "Influence of the Soil Profile Uncertainty on the Tunnel - Layered Soil Interaction Subject to Seismic Acceleration", in B.H.V. Topping, (Editor), "Proceedings of the Tenth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 226, 2005. doi:10.4203/ccp.81.226 Keywords:* random height, seismic acceleration, transfer function, surface displacement, probabilistic. Summary Seismic excitations create waves that are transmitted through surrounding soil and influence structures such as neighbouring buildings [1,4]. The study of buried structures in soil has a certain number of complications inherent to structures (rigidity, geometry, discontinuity) and soil (geometry, infinity, uncertainty). The BEM is an appropriate numerical method for the resolution of such problem because it's necessites only the discretization of frontiers, and hence significantly decreases the dimension of the problem. However, this procedure requires the determination of fundamental functions called "Green's functions" that are known analytically only for simple cases. This obstacle is overcome by using the Thin Layer Method [3] to obtain Green's function that are ideal for the case of dynamic loads in a horizontally stratified medium. To this obstacle, the random characteristics of the geological and mechanical properties, which implies the use of probabilistic methods based on simulation techniques, must be considered. In the present paper, a tunnel (Algiers, Algeria) in a multi-layered soil is subjected to the Boumerdes May 21st 2003 earthquake (magnitude 6.5) seismic excitation. The acceleration considered is that located at Keddara station (located at 12 km from Boumerdes), because it is located directly at the bedrock . Accelerations in one horizontal direction EW are considered and will focus on the SH wave propagation. The height of the bottom layer is uncertain and normally distributed. One hundred samples are considered to calculate the mean and the standard deviation of the ground surface displacement and transfer function of seismic acceleration [2]. The present study shows the influence of the randomness of the geological properties of layered soil on the surface displacement and the transfer function with the presence of a tunnel. The maximum of the mean ground surface displacement is located approximately at the fundamental frequency of the signal and at a distance to the axis of the tunnel corresponding to the extremity of the tunnel. The standard deviation of the displacements is important for the lower frequencies and for the fundamental frequency. The frequency content of the signal is not influenced by the tunnel, and the location of the maximum displacement is at the extremity of the tunnel. The mean transfer function is importance for the eigenfrequencies of the system and the maximum is located at the extremity of the tunnel. References 1 M. Badaoui, "Investigation analytique et numérique du phénomène d'interaction dynamique dans les systèmes sol multicouches - structures multiples". Master Thesis, Dept. of Civ. Eng., 1998. 2 Badaoui M., Nour A., Slimani A. and Berrah M.K., "Stochastic Seismic Investigation of Heterogeneous Soil Profile having Uncertain Depth", in Proceedings of The Fourth International Conference on Engineering Computational Technology, B.H.V. Topping and C.A. Mota Soares, (Editors), Civil-Comp Press, Stirling, United Kingdom, paper 114, 2004. doi:10.4203/ccp.80.114 3 E. Kausel and R. Peek, "Dynamic Loads in the Interior of Layered Stratum: an explicit solution", Bull. Seism. Soc. Am., 72(5), 1459-1481, 1982. 4 A.L. Pais,. "Dynamic Coupling of Multiple Structures Through Soil", PhD. Thesis, MIT, Dept. of Civ. Eng., 1988. 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 £135 +P&P)
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