Showing papers by "Hem Hunt published in 2007"

Vibration from railways: can we achieve better than +/-10dB prediction accuracy?

Abstract: This paper examines the sources of uncertainly in models used to predict vibration from underground railways. It will become clear from this presentation that by varying parameters by a small amount, consistent with uncertainties in measured data, the predicted vibration levels vary significantly, often by more than 10dB. This error cannot be forecast. Small changes made to soil parameters (Compressive and Shear Wave velocities and density), to slab bending stiffness and mass and to the measurement position give rise to changes in vibration levels of more than lOdB. So if 10dB prediction error results from small uncertainties in soil parameters and measurement position it cannot be sensible to rely on prediction models for accuracy better than 10dB. The presentation will demonstrate in real time the use of the new - and freely-available - PiP software for calculating vibration from railway tunnels in real time.

A model for calculating vibration from a railway tunnel buried in a full-space including rigid bedrock

Abstract: Subway induced vibration has become an important environmental problem. Ground borne noise and vibration have a signi cant impact on the comfort of inhabitants of buildings near railway tunnels. Therefore, legislation has become strict and the design of vibration countermeasures is of increasing importance. Engineers need accurate and fast running models. Over the last 10 years a computationally ef cient model, known as the Pipe-in-Pipe (PiP) model, has been developed. In its basic formulation, the PiP model accounts for a tunnel in a full space. Two methods are presented in this paper to account for a rigid bedrock underneath the tunnel. The rst is the mirror-image method and takes the bedrock into account by mirroring the tunnel and the applied load around the soil-bedrock interface. Vibration generated by the mirrored load represents the re ected wave eld. The mirror image method is very ef cient but it is only an approximation of the real boundary condition at the soil-bedrock interface. The second method is a new development of the PiP model and is based on the assumption that the near eld displacements are not in uenced by the existence of the rigid bedrock. Green's functions for a full space are used to calculate the internal source in a full space that would produce the same displacements at the tunnel-soil interface as calculated by the original PiP model (e.g. a tunnel in a full-space). This internal source is then used to calculate the far eld displacement by using Green's functions for a half-space with a xed surface. The two different methods are compared with an alternative Finite Element-Boundary Element (FE-BE) model, from which it is concluded that the modi ed PiP model produces more accurate results then the mirror-image method. ICSV14 • 9–12 July 2007 • Cairns • Australia

Modelling of floating-slab tracks with discontinuous slabs in underground railway tunnels

Abstract: Floating-slab tracks are known as effective means for isolating vibration from underground railway tunnels. Slabs are supported on tunnels via rubber bearings or steel springs. The slab can be continuous or discontinuous. Continuous slab is cast in-situ and discontinuous slab is constructed in discrete pre-cast sections. A track with discontinuous slab exhibits more resonances due to constructive interference of waves that reflect at both ends of the slab. This paper presents a new method for modelling floating-slab tracks with discontinuous slabs in underground railway tunnels. The track is subjected to a harmonic moving load. The model consists of two sub-models. The first is an infinite track with periodic double-beam unit formulated as a periodic infinite structure. The second is modelled with a new version of the Pipe-in-Pipe (PiP) model that accounts for a tunnel wall embedded in a half-space. The two sub-models are coupled by writing the force transmitted from the track to the tunnel as a continuous function using Fourier series representation and satisfying the displacement compatibility. The displacements at the free surface are calculated for a track with discontinuous slab and compared with those of a track with continuous slab. The results confirm that the far-field vibration can significantly be increased due to resonance frequencies of slab for tracks with discontinuous slabs.