New measurement methods detect flaws in foundation piles
Published: 24 April 2015
Doubts about the quality of approximately 1,000 piles a year
About 100,000 foundation piles of this kind are produced annually. The standard approach to checking them is acoustic ‘tapping’ to see whether the pile conforms with the requirements. This technique is used on construction projects in soft soil in built-up areas, preventing vibration and possible damage to buildings and infrastructure in the vicinity. This fails to generate adequate information in 5 to 10% of the measurements. On those occasions, it is impossible to decide whether there are any anomalies that weaken the pile. In turn, that leads to construction delays and pushes up costs. To cut delays and costs, a number of new measurement techniques have been tested with a number of other measurement organisations. The new measurement techniques are expected to provide more precise information about whether a foundation pile complies with all requirements.
Testing field with defective piles
To test the new measurement techniques, twenty piles with flaws such as cracks and shape deviations have been installed at the Deltares testing field. To ‘look’ at the piles below the ground, a range of measurement techniques were used drawing on sound, heat or electrical data. The new measurement techniques are expected to provide more precise information about whether a foundation pile complies with all requirements. Six piles were taken out of the ground recently to see what the flaws actually look like and to compare them with the measurement data.
Initial test results promising
The initial results have shown that variations in the diameter of piles can be determined to a large extent by including glass-fibre cables in the concrete. This is a simple and cheap approach that uses the temperature to determine the thickness of the concrete. The Seismic Tube, an acoustic method developed by Deltares, is very promising but more research is still required to improve the data analysis. Steps are being taken with market parties who worked on this study to produce a follow-up research plan. The aim is to further develop the Seismic Tube so that it can actually be used in practice. All the test results will be published in mid-2015.
Practical answers about the right technology for specific situations
Ultimately, the research looking at the quality of the piles will have to produce a practical answer to the question of which technologies should be used in which situations. Here, it is vital to know how reliable a particular technology is in field conditions. A reliable measurement method will make it possible to reduce uncertainty and therefore to minimise discussions about pile quality. And fewer extra piles will be installed unnecessarily. The tests are part of the Geo-impuls research programme, which aims to reduce failure costs by 50%.