NDTnet - April 1997, Vol.2 No.04

Ultrasonic crosshole testing on large concrete piles

H. Gross, W. Brameshuber Bilfinger + Berger Bauaktiengesellschaft, Mannheim (D)

Keywords: Ultrasound, Crosshole Sonic Logging, Piles
This paper was presented at the International Symposium Non-DestructiveTesting in Civil Engineering (NDT-CE) 26.-28.09.1995 in Berlin. NDT-CE, Full Program or the Ultrasound Part

1. Introduction

    Large concrete piles are one of the important elements of modern constructions. They serve as high-loaded foundations of various buildings. To dismantle the burdens of buildings, piles often have to carry up to 8 MN into very deep layers of good bearing soils. To avoid the slightest settlements which may effect enormous damages on buildings, great demands have been made to the quality of piles.

    Buildings like the ,,Pont de Normandie" which has recently been built up and the multi-storey building ,,Commerzbank II" in Frankfurt which is still under construction have foundations consisting of large concrete piles. They were executed by foundation engineers of the BILFINGER + BERGER Bauaktiengesellschaft. These two projects are an evidence that despite of difficult marginal conditions a length up to 60 m and 2.10 m in diameter are practicable to be concreted. The piles of both buildings were examined by ultrasonic technology to check the quality of concrete.

    The ultrasonic crosshole testings of an institute in France taken at the piles of the largest cable-stayed bridge all over the world induced BILFINGER + BERGER Bauaktiengesellschaft to develop the methods of testing further which was used for the first time as a criterion of testing at the piles of the multi-storey building Commerzbank II. The principle of testing is shown in figure 1.

Figure 1+2:

Figure 1: principle of ultrasonic testing ,
Figure 2: sonic speed with pile length

2. Defect of concrete

3. Reinforcement and ultrasonic pipes

    Along with concrete, reinforcement is an essential element of the pile foundation for carrying bending moments. The reinforcing cage in the weight of tons is installed in several sections according to the special length of pile before concreting. Steel pipes (see figure 3) fastened to the reinforcement make an access possible with transmitter and receiver in the marginal zone of the pile about the whole length.

Figure 3:
Pile reinforcement with ultrasonic pipes

4. Ultrasonic crosshole testings Commerzbank II

    111 piles about 180 cm in diameter, reduced to 150 cm at half of the total length, with telescope casing mean a length of 45 m, were established by the foundation of the highest office-center in Frankfurt. The cross-hole-sonic-testing was carried out with four steel pipes integrated into the reinforcement. BILFINGER + BERGER Bauaktiengesellschaft carried out the ultrasonic tests with the help of efficient equipments of the state-of-the-art technology world-wide. In addition to the construction of the probe a matter of the principle of Gemini-systems of BILFINGER + BERGER Bauaktiengesellschaft is the computer-measurement-technology which is based on a modern equipment The probes are shown in figure 4. Compared with conventional analyses of systems of signals, evaluations and documentations could be carried out more effectively. A special evaluation software facilitates a lead-in up to a single sound-impulse in the time of analysing a measuring. The measuring chain of this system mainly consists of transmitter and receiver-probe, impulse control mechanism, step control mechanism, computer measuring unit and software.

Figure 4:
Probes for ultrasonic testing

5. Course of measuring

6. Conclusion

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    © Copyright 1. April 1997 Rolf Diederichs, info@ndt.net
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