A G Davis, BSc, MSc, PhD, and S A Robertson, BSc, CEng, MICE, MIHE. This paper was first published in GE’s May 1975 edition.
Until a few years ago pile testing was automatically assumed to mean a form of static load test in which the pile was loaded to near or beyond its ultimate load, and the corresponding load/settlement curve established. However, for large diameter piles with ultimate loads of up to 1 000tonnes and more the cost is becoming prohibitive at present day prices of £10-15 per tonne of applied load.
This has led to the development of more economic methods for testing the structural integrity of piles, as described by Whittaker. Amongst these are the sonic coring and vibration methods developed by CEBTP, of Paris, and now operated commercially in the UK and overseas by Testconsult Ltd.
Sonic coring is essentially a tool for measuring the integrity or homogeneity of the concrete. The vibration test, on the other hand, gives a two-fold result by testing the concrete at high frequencies for structural integrity and by vibrating the soil-pile system together at low frequencies to give a measurement of stiffness which may be related to load/settlement test results.
These two test methods have already been described in some detail by Levy, Gardner and Moses, Briard, Paquet, and Davis and Dunns but it may prove of interest to briefly review the methods, to refer to some developments in the techniques and to enlarge on practical applications and recent findings.