Experimental and numerical studies on dynamic responses of tunnel and soils due to train traffic loads

Abstract

This paper outlines an experimental and numerical hybrid analysis of dynamic responses generated by train traffic loading in an urban metro tunnel. It presents a set of measurements of the wheel loads, track bed vibrations and pore pressures right below the tunnel to describe the excitation induced by train traffic loading and the propagation of dynamic responses in the railway system and surrounding soil. A key aim of this paper is to provide a set of dynamic response records that researchers can use for further investigation and the validation of numerical prediction models. The experimental analysis of vibration responses reveals that the resonance frequency of the track system (P2 resonance frequency) of 64 Hz in monolithic track bed coincides with the frequency where the largest track bed vibration occurs. There are residual pore pressures in some surrounding saturated soil during and after train passages, and the amplitudes of residual pore pressure grow with the train speeds. The serial number of the vehicles corresponding to the maximum excess pore pressure is relative to the train speed. The numerical analysis reveals that the extent of excess pore pressure build-up in tunnel surrounding soil during train passage is also determined by the ratio of train speed c and the soil Darcy permeability kD. For a tunnel buried at a deep depth like nearly 20 m, the shear stress is too small to excite the rotation of principal stress. The increase value of c/kD brings small but adverse implications in terms of the potential for soil failure. For the tunnel substratum soil, the initial stress state (i.e. K0) is a more dominant factor to determine the likelihood of failure than underground train traffic load.