Effect of excitation frequency on segmental tunnels in sand using 1 g shaking table tests

Abstract

Two physical models of 1 g shaking table tests are conducted to investigate the effect of excitation frequency on dynamic responses of segmental tunnels in sand ground. Contained by a laminar shear box, the free-field model is a sand ground of 2 m in depth, while the soil-tunnel model has a miniature tunnel embedded within the ground. The tunnel is deliberately designed to imitate the structural features of typical segmental linings of shield-driven tunnels. To both physical models, ramped harmonic excitations are applied with three amplitudes at five frequencies, respectively. Interpretation of the test results is performed directly on the original model scale to avoid uncertainties brought up by scaling laws. Analysis of the free-field responses reveals that dynamic characteristics of the ground are highly dependent on the amplitudes and frequencies of the input motions due to the modulus reduction of the sand. As for the soil-tunnel model, responses of the segmental tunnel are much stronger when subjected to excitations of frequencies close to the eigenfrequency of the ground or of lower frequencies with large amplitudes. The former case could be attributed to the resonance effect. The latter one is caused by the larger shear strains induced by low-frequency excitations, as elaborated by an analytical solution. Thus, this study could offer helpful insights into the soil nonlinearity in 1 g shaking table tests and its influence on the soil-tunnel interactions.