Dynamic Methods in Pile Testing: Developments in Measurement and Analysis

In a current research project funded by the German Research Society (DFG) the low-strain integrity method is investigated to gain improved results in terms of localisation and identification of structural defects in piles. Variations of measurement gauges and impact hammers are examined especially to cover the high frequency content of the impact vibrations. To widen the limits of application the development of analysis algorithms is a central part of the research. The up to date analysis consists solely of the visual interpretation of the velocity signal gained from the acceleration signal measured. To increase the objectivity of the results analysis algorithms are necessary. Those algorithms based on the physical behaviour of the stress wave propagation also include additional information from site investigation and pile installation. The performance of pile tests of static or dynamic nature is standardised in Germany in the Recommendations for Static and Dynamic Pile Tests of the German Society for Geotechniques, Working Group 2.1. Moreover the IGB-TUBS uses high-strain measurements during driving and as a restrike for the continuous quality assurance on several construction sites in Germany. Depending on the local conditions a flexible testing programme consisting of three process-phases was developed. Due to the critical nature of a soft boulder clay at a site in the harbour of Hamburg, Germany extensive use of dynamic pile test was made to optimise the piled foundation of a quay wall structure. Finally finite element computations were used to analyse the influence of nearby excavation on the load-settlement behaviour of the piles.