Seismic analysis of underground structures

Abstract

The present paper describes a soil-structure interaction analysis of underground tunnels. Use has been made of available computer codes in order to study the problem in the three significant sections through the three coordinate planes.

The seismic environment consists of a combination of S- and P-waves obtained by conventional methods based on the theory of one-dimensional wave propagation through linearly viscoelastic layered systems. The response of the soil-structure system has been analysed by linearly viscoelastic finite elements.

Results of Section A across the tunnel axis indicated only a low level of tunnel-soil interaction, and this only in the high frequency range. Consequently the stresses obtained were small.

Results of Section B along a vertical plane through the tunnel axis revealed strong soil-structure interaction as well as important effects of the buildings response on to that of the tunnel. Significant stresses which will govern the structural design were also obtained.

The behaviour of the tunnel in a horizontal plane through the axis was studied in Section C. Although some tunnel-soil interaction was observed, the calculated stresses were not as high as in Section B.

Comparison of the finite element stresses and the stresses obtained by simplified methods provided reasonable upper and lower limits for the finite element results.