Centrifuge Modelling of the Dynamic Behavior of Square Tunnels in Sand

Abstract

The Chapter summarizes representative experimental results from dynamic centrifuge tests that were performed on square model-tunnels embedded in dry sand. Two model-tunnels were used, a rigid and a flexible one, with the latter model collapsing during the test. The tests were carried out at the geotechnical centrifuge facility of the University of Cambridge, within the Transnational Access action of the SERIES Research Project (TA Project: TUNNELSEIS). The experimental data is presented in terms of acceleration in the soil and on the tunnel, earth pressures on the side walls of the tunnel and internal forces of the tunnel lining. The collapse mechanism of the flexible tunnel is presented and discussed based on the recorded response. The goal of this program is two fold: to better understand the seismic behaviour of this type of structures, and to use the high quality data to validate the numerical models, which should be used for the design of rectangular embedded structures. The interpretation of the results reveals (i) “rocking” response of the tunnels in addition to racking, (ii) existence of residual values on the earth pressures on the side walls and on the internal forces after shaking, affected significantly by the flexibility of the tunnels, and (iii) modification of the induced shear wave field from the presence of the shallow tunnel, which in turn is affecting its seismic response. These issues are not well understood and often are not considered by simplified seismic analysis methods.