Effect of Inclined Soil Layers on Surface Vibration from Underground Railways Using the Thin-Layer Method

Noise and vibration from underground railways is a documented disturbance for individuals living or working near subways. Numerical models are used to investigate and understand vibration propagation from these underground railways, although the models commonly include simplifying assumptions (i.e., assuming the soil is a horizontally layered, homogenous half-space). Such simplifying assumptions add a level of uncertainty to the predictions that is not well understood. The goal of the current paper is to quantify the effect of including layer inclination angles up to 5 in relation to the surface. The thin-layer method (TLM) is introduced as an efficient and accurate means of simulating vibration from underground railways in arbitrarily layered half-spaces. The TLM is an element-based approach that uses the analytical wave equation to describe vibration in the horizontal direction, whereas assuming displacements in the vertical direction can be described by using a linear shape-function. The method is used to simulate a half-space with an inclined layer and is shown to be both accurate and computationally faster than a boundary-element model in predicting surface RMS velocities. The sensitivity of surface vibrations to inclination angle is also investigated, and the results suggest that small inclination angles of 5 degrees or less can cause significant variation in RMS response of approximately 5 dB. DOI:10.1061/(ASCE)EM.1943-7889.0000292. (C) 2011 American Society of Civil Engineers.