Experimental approach on the pile-to-pile interaction factors and impedance functions of inclined piles

Dynamic tests on model soil–pile systems under 1g (natural gravity) conditions are carried out to assess the effects of soil non-linearity on the horizontal pile-to-pile interaction factors of inclined piles. This paper examines 2 × 2 symmetric free-head floating inclined pile groups embedded in cohesionless soil and subjected to a low-to-high amplitude of lateral harmonic pile head loadings for a wide range of frequencies. Piles with head level centre-to-centre spacing of five times the pile diameter with three practical pile inclinations of 0° (vertical), 5° and 10° aligned parallel to the direction of loading are reported. Results from the experiments indicate a significant impact of soil non-linearity on the horizontal interaction factors. Moreover, utilising such experimentally measured interaction factors in conjunction with available experimental solutions for horizontal impedance functions of inclined single piles, the principle of superposition is assessed in obtaining the horizontal impedance functions of inclined pile groups. Comparison between the results based on the principle of superposition and experimentally available solutions shows a good agreement for the low-to-intermediate range of loading frequency. At higher frequencies, however, loading-direction-dependent soil–pile interface non-linearities developed for inclined piles cannot be captured in a straightforward way. To this end, a multiplication factor is proposed for the superposition method.