Comparative behaviour and performances of impact and vibratory driven piles in stiff clay

This paper reports on the results of an extensive field test research carried out in the framework of the "French National Research project on vibratory driving", to investigate the comparative behaviour and performances of impact and vibratory driven piles. The test site is located in the airfield of Merville, North of France. The subsoil consists of dense Flanders clay. Various piles were driven using an ICE 815 vibratory driver and an IHC S70 impact hammer to the same depth. All these piles were instrumented with accelerometers and strain gauges positioned at the top and at the toe. Penetration rate, uplift load applied by the crane, vibrations transmitted to the ground, operating pressure and oil flow at the vibratory power-pack and energy per blow for the hammer were continuously recorded. The paper presents the main results obtained on double sheet piles (AU16 type) driven to 7 meters depth and steel open-ended tubes, 508 mm in diameter, which were installed to 9.4 meters depth. After a rest delay of 6 to 8 weeks, the piles were statically loaded to failure. The piles were instrumented using LCPC removable extensometers, which make it possible to measure the mobilization of shaft friction and toe resistance. The measured bearing capacity was significantly lower for the vibratory driven piles, which confirms the results obtained by the LCPC on other site.