Pile integrity tests using crosshole sonic logging
A total of 79 bored piles with lengths between 15 m and 35 m were used for the foundation of the Prime Tower (126 m high). Solexperts AG was commissioned to test all these piles for pile integrity using the crosshole sonic logging method.
The Crosshole Sonic Logging (CSL) method measures the transit time and energy strength of an ultrasonic signal through the concrete body. For this purpose, ultrasonic transmitters and receivers are lowered into parallel, water-filled tubes in the bored pile. At regular intervals, the concrete body between the transmitter and receiver is examined for flaws. If the transit time (propagation speed of sound in healthy concrete between 3000 and 4500 m/s) and the amplitude of the signal decrease markedly in an area of the pile, this indicates a defect or weak point in the concrete.
Test evaluation / criteria of the measurement
According to the recommendations of the working group "Piles" (EA-Piles) of the German Society for Geotechnics e.V., deviations in the propagation velocity of more than 20% from the average velocity with simultaneously significantly reduced energy transfer are marked as anomaly or defect. The quality indicator ηQ can be applied as an adjustment factor for the concrete quality in the considered cross-section and used, for example, for the reduction of the internal load-bearing capacity at this location, if this procedure is covered by the verification concept (DGGT, 2007). Comparable assessment criteria can also be found in the American (ASTM D6760-08) or French standard (AFNOR NF P94-160-1) for the assessment of piles using CSL.