Field tests of vibro-driven piles under lateral impact loading

ABSTRACT This paper presents lateral impact load tests carried out on three steel pipe piles vibro-driven into marine soft clay at the tourist port “Mirabello” in La Spezia. Piles are displaced with a L-shape plane layout and kept free at the head. The instrumentation system of piles, unconventional for field test in marine environment, includes accelerometers, strain gauges and pore pressure gauges, with the relevant chemical and mechanical protections. The impact load tests were carried out in two different campaigns, the first 1 week and the second 10 weeks after the pile vibro-driving. Some of the results collected are presented, i.e. time histories of strains and accelerations. The response of the single pile and the dynamic behaviour of the pile group, at very small strain, are investigated: the dynamic behaviour of soil-water-pile system is discussed in terms of natural frequencies, damping and mode shapes; the pile-soil-pile interaction is studied by analyzing the different types of wave propagating from loaded pile to the receivers and estimating the shear wave velocity. Furthermore, the variation in time (for the two experimental campaigns) due to the re-consolidation of the soil close to the pile subsequent to the vibro-driving is observed.