The stiffening of soft soils on railway lines

Dong, Kaitai; Connolly, David; Laghrouche, Omar; Woodward, Peter Keith; Costa, Pedro Alves

doi:10.1016/j.trgeo.2018.09.004

Cited by 46 publications

(33 citation statements)

References 46 publications

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“…where i = √−1 and K0-5 are given in [11]. Finally, frequency independent hysteric damping is simulated using complex functions for Lames elastic constants: = (1 + 2 ) and = (1 + 2 ), where is the damping ratio for dilatational waves and is the damping ratio for shear waves.…”

Section: Soilmentioning

confidence: 99%

“…Where, ( , ) is a function that scales the load transmitted from guideway to ground using the equivalent stiffness and lower track displacement [11]. Finally, the ground displacement response in the frequency-wavenumber domain is converted to the time-space domain using:…”

Section: Guideway Modelmentioning

confidence: 99%

“…lime or cement) is sometimes required to further increase shear wave velocities (e.g. [11]). This is expensive and thus challenging to justify over larger distances (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Geodynamics of very high speed transport systems

Connolly

Costa

2020

Soil Dynamics and Earthquake Engineering

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This work reveals the existence of a new dynamic load amplification mechanism due to ground surface loads. It is caused by the interaction between a moving vehicle's axle configuration and the vibration characteristics of the underlying soil-guideway system. It is more dominant than the traditionally considered 'critical velocity' dynamic amplification mechanism of the guidewayground structure, and is of relevance to very high speed transport systems such as high speed rail. To demonstrate the new amplification mechanism, first a numerical model is developed, capable of simulating ground-wave propagation in the presence of a series of discrete high speed loads moving on a soil-guideway system. The model couples analytical equations for the transportation system guideway with the thin-layer element method for ground simulation. As a practical example, it is validated using high speed railroad field data and then used to analyse the response of a generalised single moving load at high speed. Next the effect of multiple discrete vehicle-guideway contact points is studied and it is shown that dynamic amplification is highly sensitive to load spacing when the speed is greater than the critical velocity. In particular, large resonant effects occur when the axle/magnet loading frequency and the propagating wave vibration frequency of the soil-guideway structure are equivalent. As an example, it is shown that for an individual case, although critical velocity might increase displacements by 50-100%, for the same scenario, axle configuration can increase displacements by 400%. It is also shown that resonance is sensitive to the total number of loading points and the individual frequencies excited by various spacings. The findings are important for current (e.g. high speed railway) and potential future (e.g. hyperloop) transport systems required to operate at speeds either close-to, or greater than the critical velocity of their supporting guideway-soil structure. In such situations, it is important to design the vehicle and supporting structure(s) as a combined system, rather than in isolation.

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Section: Soilmentioning

confidence: 99%

Section: Guideway Modelmentioning

confidence: 99%

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Geodynamics of very high speed transport systems

Connolly

Costa

2020

Soil Dynamics and Earthquake Engineering

Self Cite

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“…Figure 19 and Figure 20 show the effect of train speed on the vibration response caused by a negative pulse defect. The train speeds are chosen to be significantly lower than the critical velocity of the soil to prevent low frequency amplification [45], [61] [62]. One-third octaves, MTVV and PPV are again shown.…”

Section: Model Validationmentioning

confidence: 99%

A 2.5D time-frequency domain model for railway induced soil-building vibration due to railway defects

Connolly

Galvín

Olivier

et al. 2019

Soil Dynamics and Earthquake Engineering

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“…This occurred because the track was constructed over soft ground, with a sandwiched layer of uncharacteristically soft organic clay. The detailed track and ground properties, including soil degradation curves, are given in [14], [16] and [17]. Figure 4 shows the time history response of the field the TLM signals at a train speed of 70 km/h.…”

Section: Validationmentioning

confidence: 99%

Soil Non-Linearity on High Speed Railway Lines

Dong¹,

Costa

Laghrouche

et al. 2019

Proceedings of the 7th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (COM

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Increases in operational train speed have resulted in an elevated probability that dynamic effects will occur inside the railway track and subgrade structure. This is problematic because it causes soil non-linearity, thus resulting in reduced soil stiffness. Therefore, this paper outlines a numerical semi-analytical frequency domain model to compute and analyse non-linear stiffness degradation below railway lines. An equivalent linear approach is used to incorporate non-linear stiffness and damping changes into a thin-layer element frequency-wavenumber domain formulation. The model is validated using published data and then used to analyse nonlinearity. It is shown that non-linearity plays an important role in track-ground response, with track displacements increasing significantly in magnitude. It is also shown that the critical velocity can be reduced significantly, which is important because many high speed lines set their dynamic threshold at 70% of the linearly calculated value. Similar findings are made for track velocities and soil strain levels, thus indicating it is vital to consider soil non-linearity when modelling high speed rail track behaviour.

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The stiffening of soft soils on railway lines

Cited by 46 publications

References 46 publications

Geodynamics of very high speed transport systems

Geodynamics of very high speed transport systems

A 2.5D time-frequency domain model for railway induced soil-building vibration due to railway defects

Soil Non-Linearity on High Speed Railway Lines

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