Recommendations for Statnamic use and interpretation of piles installed in clay

The following presents guidance for the effective use and analysis of Statnamic testing, based upon five years of research undertaken at the University of Sheffield and Dundee. The major focus of this research has been the development of non-linear strain dependant analysis techniques for piles installed in clay. This has lead to the development of simple analysis that requires soil specific damping parameters as input. This technique has been found to perform well for skin friction piles in both glacial till and London Clay.

Undertaking both laboratory and field studies has given insights into potential improvements in both testing techniques and equipment. The most important of these is the need for users to apply loads significant enough to achieve maximum pile settlements equivalent to 10% pile diameter. Thus, tests should not be terminated on maximum load criteria but more appropriately on maximum and permanent settlement achieved. This is to improve both analysis and to avoid selection of Statnamic devices incapable of applying adequate loads. As a rough guide, in clay soils the Statnamic device should be capable of applying loads twice the predicted ultimate static capacity. This should preferably be applied as a single loading event rather than cycling load pulses.

Accuracy of the Statnamic test would be verified through the use of high-precision optical levelling before and after all loading events. Both analysis and settlement measurement would benefit from the incorporation of an accelerometer at the head of the pile. This installation should be standardised with minimum logging rates stated. In addition, non-contact settlement measurement should be undertaken with respect to the underlying soil conditions with the pile-measurement device separation being selected as appropriate.