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Technical paper: Frequency response problems to instrumented pile tests

T J Poskitt, Queen Mary & Westfield College and K L Yip-Wong, G Maunsell and Partners. This paper was first published in GE’s May 1991 issue.

Synopsis

The paper reports data obtained from a series of tests on two fully instrumented large diameter test piles. Critical aspects of the design and selection of transducers are discussed. The discussion considers initial laboratory testing under simulated field conditions and field performance. For driven piles, it is shown that the driving is often the most severe condition which the instruments and their fixings must survive. Data is given which shows that the passage of a stress wave down a pile can produce extremely vigorous motion in transducers and their fixings. The natural frequency and damping are shown to be critical in these circumstances, if damage is to be avoided. Under hard driving conditions, major problems occur with accelerometers. During re-drive, signal: noise ratio dropped to 1:5 This is of special significance for commercial dynamic pile-testing systems. For these, the authors recommend that the raw data be plotted in the frequency domain. This ensures that the true extent of the problem is not masked by the signal conditioning. 

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