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Stationary harmonic loading: (a) 3D FE-model; (b) top view of the pile group with the reference piles highlighted in grey.
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...
Contexts in source publication
Context 1
... the wave field emanating from a vertical harmonic point load acting on the soil surface. Emphasis is placed on the vertical component of the response. The FEM software PLAXIS 3D is used for the analyses, which are performed in the time-domain. Taking advantage of symmetry, only half of the problem is modelled. The finite element model is shown in Fig. 1(a). The vertical boundary is set at 20 m depth from the soil surface. In order to simulate a half-space, appropriate build-in viscous boundaries are placed along the periphery and at the base of the model. For the simulation of a soil stratum, the base of the model is fixed in all three directions. The soil is assumed linear-elastic with ...
Context 2
... top view of the 3 x 3 pile group is given in Fig. 1(b). The centre-to-centre pile spacing is s = 3d = 2 m. The distance of the central pile in the front row (in relation to the direction of the wave propagation) from the point load is equal to 12 m, while from the central pile in the back row the distance is 16 m. The piles are either freeheaded or connected to a rigid, massless ...
Context 3
... shielding efficiency of a 3x3 pile group in a half-space has been subsequently investigated. The distance of the central pile in each row from the vibrating source is denoted with x 0 , and equals 12 and 16 m with respect to the front and back row, respectively (recall Fig. 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 ...
Context 4
... response of the previously presented 3 x 3 pile group with s/d = 3 (recall Fig. 1(b)) is investigated under the excitation of a moving point load on a soil stratum. The load path axis is parallel to the front pile row, which is located at a distance of x 0 = 12 m. A further system of 2 x 3 is also considered. It is created by replacing the front row of piles in the 3 x 3 configuration by soil. The vibration reduction ...
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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.
