Abstract: In this paper, both physical tests and numerical simulation were conducted to study the dynamic response characteristics of the tunnels with horseshoe cross-section under high-speed train loads. Based on time domain and frequency domain analysis, the frequency response function (FRF) and peak particle acceleration (PPA) are used as evaluation indicators. Under the train vibration loads, the dynamic response of tunnels is analyzed at the speeds of 300 km/h and 350 km/h in the physical tests, respectively. The numerical model is developed by FLAC3D to study the dynamic response of the tunnel under moving loads of high-speed train. Results show that the dynamic response of the tunnel is not attenuated in the circumferential direction as the distance from the vibration source increases. The tunnel response shows a clear attenuation from the inverted arch to the arch. However, there is an increasing trend from the arch to the vault. The test results also show that dynamic response of the horseshoe cross-section tunnel is greater than dynamic response of the circular tunnel, and the average difference is about 3.8 dB in frequency range of 40?200 Hz. It indicates that the tunnel cross-section greatly affects the dynamic response of the tunnel, which should be considered in design. Furthermore, the PPA of the tunnel is the largest at the inverted arch under single-point excitation load. The peak acceleration is the smallest at the tunnel dome. The PPA of the tunnel at monitoring points shows obvious periodic effect under moving train loads of high-speed train. The PPA reaches the highest value when the train travels at the monitoring section. The PPA of the tunnel under moving train loads shows a clear amplification compared with tunnel response under the single-point excitation load. Therefore, it is important to consider the effect of moving trains when studying the tunnel dynamic behaviour under train induced vibration loads.

Key words: horseshoe cross-section tunnel, high-speed train, vibration load, physical test, FLAC3D, dynamic response