Shaking-Table Tests Study on the Seismic Dynamic Res-ponse of Underground Three-Dimensional Crossing Tun-nel Structures

This is the authors' abstract. We don't add key points for this paper.

To conduct an in-depth investigation into the dynamic response patterns of the intersecting tunnel structures under seismic loading, by establishing a vibration table test model with a similarity ratio of 1:30, three typical seismic waves, namely Kobe, Loma and Taft, were selected. Under different peak acceleration conditions of 0.1g, 0.2g and 0.3g, a systematic comparative analysis was conducted on the acceleration, strain and displacement responses of the free field system (FF) and the cross-tunnel system (STS), and the interaction factor (IF) was introduced as a comparative index to quantitatively evaluate the peak-response-level influence of structural interaction. The results show that the presence of the crossing tunnel structure reduces the system's equivalent stiffness, resulting in an approximately 13.8% reduction in natural frequency compared to the free-field condition. Additionally, the crossing tunnel structure significantly decreases the surface acceleration amplification coefficient by approximately 20%-30%, while localized amplification occurs above the cross junction due to wave reflection and interference. The overcrossing tunnel is significantly affected by the free surface effect, with its acceleration and displacement responses being relatively large overall. In contrast, the undercrossing tunnel exhibits more pronounced nonlinear characteristics and strain sudden increase phenomena under strong seismic forces. As the input seismic excitation increases, the interaction effect coefficient gradually approaches 1, indicating that the soil's nonlinearity weakens the modulation effect of the structure on the seismic excitation. Studies have shown that the seismic response of three-dimensional cross tunnels exhibits the characteristic of "amplification of the upper part response and enhancement of nonlinearity in the lower part", which can provide experimental basis for the seismic design and numerical analysis of complex underground space structures.