Performance of vertical and batter pile groups under vertical vibrations: a comparative assessment using model-scale field testing and numerical study

This paper presents the field test results of 2 x 2 vertical and batter pile groups having batter angle of 20 degrees for four different eccentric moment magnitudes of 0.225, 0.885, 1.454, and 1.944 N m, respectively, under the static load (Ws) of 12 and 14 kN subjected to vertical vibrations. The piles used are 3.3-m-long driven steel pipe with an outer diameter (d) of 0.114 m with 3d spacing between the piles. The field test results include the determination of frequency-amplitude response, distribution of dynamic axial load and dynamic bending moment, and soil-pile separation length. The test result shows that the batter pile groups may be more susceptible to resonance amplification compared to vertical pile group. Resonance amplification results in significantly larger amplitudes of vibrations. The test results also show that the inclined configuration of batter pile groups contribute to the potential for pile-soil separation and lowering the overall load-bearing capacity under vertical vibrations. The frequency-amplitude responses from the field tests were compared with the numerical prediction based on the continuum approach with the superposition method. Furthermore, the study highlights the normalized plots on the comparative performance of batter and vertical pile groups based on the numerical and experimental study. From the present study, it is affirmed that the batter pile groups when compared to vertical pile group offers less resistance when subjected to vertical vibrations. This is due to resonance amplifications, uneven contact pressure distribution, increased potential for soil-pile separation, increased risk of overturning, and inadequate load transfer.