to an impact hammer over the lower 10 m (33 ft) to ensure adequate bearing capacity. This study aims to compile new data for existing projects to identify the main differences induced in the soil by the pile installation method and its influence on bearing capacity. These results analyse whether the current design methods used in pile design are adequate. The final results will provide recommendations to facilitate the design of vibratory driven piles. Impact for Industry Vibratory driving is a cost-effective solution to drive load-bearing piles and sheet piles, especially in granular soils. The technique allows for a quicker driving process with fewer noise issues, lower energy consumption and less fatigue in the driven element compared with the impact driving technique. These advantages make vibratory driven piles potentially competitive in a wide range of markets, particularly where noise is a critical problem. Vibratory driven foundations are an opportunity for the deep foundations industry to add environmental value to projects and improve the competitiveness of deep foundations. However, to take advantage of this opportunity, we need improved design methods and research into vibratory driven pile performance. State of the Art In general, technical regulations do not consider any difference between impact driven and vibratory driven piles; this is primarily because the industry lacks comparative evidence. The U.S. Army Corps of Engineers’ Design of Pile Foundations (1991) notes that the use of vibratory driven piles needs special attention, but does not propose any design recommendations. In Europe, the technical regulations do not consider any difference between impact and vibratory driven piles, e.g., the Eurocode 7 (2004) or the Fascicule 62 (1993) in France. The exceptions are Russian (SNiP 2.02.03-85) and Polish regulations (PN-83/B-02482), which provide different design factors for tip and shaft resistance, depending on whether the pile is driven by impact or vibratory hammer, as reported by Rocher-Lacoste (2008). When working with driven pile foundations, it is important to assess the driveability, or particularly the vibro-driveability, and in the case of load-bearing structures, to estimate the installed pile capacity. To date, research on vibratory driven piles has primarily focused on the driveability of such piles, which is especially oriented to hammer selection to optimize the penetration rate. This topic involves studying the different aspects that influence the pile penetration, such as the vibration frequency, the displacement amplitude or the relative density. Driveability research has produced some different models and methods to predict the penetration process (Viking 2008). Other related disciplines include the fields of vibrocompaction and earthquake engineering, from which some interesting results can be used in vibratory driven piles. The vibratory pile resistance to axial and lateral loads is also a critical subject, but has been studied less than the driveability process. There are a few different estimation methods based on energy-balance concepts that aim to predict the axial capacity of the Impact driving a test pile for the New NY Bridge (courtesy of New York State Thruway Authority) installed pile directly from the hammer parameters. There are also a limited number of case studies that compare the axial capacity of impact and vibrodriven piles. However, model tests in the laboratory do not properly simulate the soil boundary conditions and do not offer reliable results. By comparison, full-scale field tests can provide reliable information, but very few have been performed. Using field tests to extract conclusions for a particular case is difficult, because of the differences between soil profiles, hammers and pile shapes used in each test. A National Vibrodriving Project was completed in France, where the results suggested applying reduction factors to the pile resistance to account for the vibratory installation process. Based on these results, Borel et al. (2006) recommended applying a reduction of 50% on the axial toe capacity and 30% on the axial shaft capacity when the capacity is calculated following impact driven design rules. For laterally loaded vibrodriven piles, the information available is even scarcer, with no full scale field tests reported in the published literature. This lack of knowledge limits the use of vibratory installation techniques. 64 • DEEP FOUNDATIONS • JAN/FEB 2015
