Back analysis of static load tests of CFA piles in chalk

A number of static pile load tests, undertaken in the last ten years in the south of England have been analysed in order to assess the ultimate geotechnical capacity of the pile. This includes approximately twenty cases, distributed over six different construction sites and comprising both preliminary and working piles, tested in compression or in tension. The piles were tested in accordance with accepted practice in the UK regarding test procedures and related standards. All cases refer to bored piles, constructed using continuous flight augers, with diameters between 300 mm and 600 mm. Since the pile load tests have not been taken to the point of failure, estimates of the ultimate load have been established based on the Fleming method. As a comparison, the failure load has been assessed for each pile from design methods according to CIRIA Report PG6 and PR86, taking into account the relevant information from ground investigation at each site. The major conclusions that can be drawn from this study are the satisfactory performance of all the pile tests reviewed, and the overall conservatism of the current design methods.