Figure 2 - uploaded by Georgia Efthymiou
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Vertical transfer function of a single pile compared to that of a pile in the centre of the front and back row of a 3x3 pile group with s/d=3; vertical harmonic point load; v = 0.4 (Efthymiou & Vrettos, 2022).
Source publication
The potential reduction of vibrations caused by moving loads in the vicinity of pile group foundations is investigated for different layout geometries by means of finite-element analyses in the time-domain. First, the piles are indirectly excited by the wave field induced by a distant, stationary harmonic load. For given soil properties, the effect...
Context in source publication
Context 1
... These two piles are selected as reference piles to monitor the attenuation effects. These are quantified herein by the frequency-dependent transfer function w p (0)/w ff (0), where w p (0) is the vertical displacement amplitude of the pile head, and w ff (0) is the respective value of the free-field at the same location. Results are presented in Fig. 2. The response of the reference pile as an isolated single pile, namely after removal of all its neighbours, is also given. As part of the pile group without cap, the reference pile at x 0 = 12 m can have a greater amplitude in comparison with the corresponding single pile, depending on the excitation frequency. This increase can be ...
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Citations
The present numerical study focuses on the problem of dynamic interaction of piled foundations under harmonic excitation at high frequencies relevant for the vibration protection practice. The finite-element programs Plaxis (2D & 3D) and Abaqus are employed for time- and frequency-domain analyses, respectively.
As a first step, dynamic impedances of pile groups, piled rafts and embedded footings are derived for all oscillation modes in order to gain insight into the problem of inertial loading.
Emphasis is placed on the kinematic response of single piles, pile groups and piled rafts to a wave field emanating from a distant stationary or moving harmonic vertical point load acting on the surface of the soil. Transfer functions, which are ratios relating the response of the foundation to that of the free-field, quantify the kinematic interaction. Only the vertical component of the response is assessed as mostly critical in the frame of the selected excitation. It is shown that a stationary harmonic load is a good approximation for a moving harmonic load; this is true for a travelling speed of the load that is relatively low in comparison with the Rayleigh wave velocity in the soil, which is quite common in engineering practice. Analogously, a static load is a good approximation of a moving load of constant magnitude. Moreover, analytical solutions are presented for single pile and pile group response under Rayleigh wave excitation, which can be also employed in the near-field, as shown herein.
The extension of piled foundations by additional rows against the wave propagation direction is examined under the scope of vibration protection. Indeed, for a considerable frequency range, the further addition of pile rows to a piled foundation has a favorable effect on the reduction of the vibration level calculated at the furthest-back pile row or at the free-field behind the foundation. This is, however, not valid, as the excitation frequency increases further, and the interplay between the piles becomes more complex. On the other hand, the extension of the piled foundation by additional pile columns parallel to the wave propagation direction has a positive effect at high frequencies.
The accuracy of the results is assessed by verification against rigorous solutions. The importance of key aspects in finite-element modelling is also highlighted.
