Pulse Echo Integrity Testing
Ultrasonic Integrity Testing
Pulse echo integrity testing (also called low strain dynamic test, sonic echo test, or low strain integrity test) can be carried out on any type of concrete foundation-piles (e.g drilled piles, auger cast piles, mixed in place vibro concrete columns, bored diaphragm walls, etc.)
The test is not only suitable for quality assurance of new deep foundations but also to inspect the serviceability and length of existing piles under pile head beams or other constructions.
An impact wave is induced into the pile trough a blow of a light, hand-held hammer. The echo of the pile toe and thus the pile length can be determined by the measurement of the movements at the pile top. The wave speed c, a measure of the concrete quality arises from pile length L and travel time T.
Changes in pile properties - such as a reduction in diameter or material properties, voids in concrete, soil inclusion and cracks - produce wave reflections. The depth of the defect arises from the measured travel time of the wave the strength of the defect from the intensity of the reflected signal.
GSP uses the powerful measuring instrument Pile Integrity TesterTM (PIT) by Pile Dynamics, Inc. for pile integrity testing. You can receive more information about the measuring instrument directly at www.pile.com. Please click here:
Special Case: Impact Echo Analysis
With the impact echo analysis components and building materials can be tested by impulse initiation. Due to the vibrational behaviour of the components their integrity can be determined. Loading a structure by a hammer blow in general is well known. The use of advanced measuring technology allows a refined analysis in frequency or time domain. From such measurements grade registers for concrete components, masonry, wooden beams or also steel frameworks can be generated. With the impact echo analysis in particular the thickness of only unilaterally accessible concrete slabs (raft foundations) can be determined.
The ultrasonic integrity testing (also: cross hole sonic logging - CSL, ultrasonic testing or “carottage sonique”) is a method to inspect the homogeneity of materials of solid bodies. A standard use of this measuring method is testing of in-situ piles. Divergences in homogeneity of the material are ascertained by sudden changes of the travel time of ultrasonic waves. These divergences are called anomalies.
Measuring Method (CSL)
In ultrasonic integrity testing the wave speed as well as the signal strength of an ultrasonic wave are measured. The emitted ultrasonic wave travels horizontally from transmitter to receiver. Both probes are placed in separate parallel access tubes. For transmission of the ultrasonic signal the access tubes are filled with water. Depending on the number of tubes the number of distances per measuring level (ring measurements and cross measurements) is defined. As a rule one access tube is installed per 25 cm of pile diameter (e.g. for a 90 cm diameter pile 4 tubes) with a minimum of 3 tubes per pile. The measuring tubes are fixed to the reinforcement cage.
For Ultrasonic integrity testing the „Cross Hole Analyzer“ (CHA) by Pile Dynamics, Inc. (PDI) is used. You can receive information about the measuring equipment here:
Information about the "Cross Hole Analyzer" CHA
Evaluation of Measuring Results
Codes (e.g., USA-ASTM D6760-02 or France-NF P94-160-1) define the technical conditions for the execution of the tests as well as the requirements for the measuring equipment. A recommendation of GSP for the evaluation of measurements can be found in the German "Recommendations on Piling (EA-Pfähle)" or downloaded here:
Recommendations for the evaluation of ultrasonic measuring signals (in German)
Cross sections or 3D-views can be generated from the measured values using the program "Tomosonic" by Pile Dynamics, Inc. and thus the size of defects can be visualized.
Thermal Integrity Profiling (TIP)
Thermal Integrity Profiling is a new development which assesses the homogeneity of the concrete column of a cast-in-place pile by the time history of the curing heat.
Temperature sensors embedded into cables are installed together with the reinforcement cage. It is also possible to use a probe system in tubes, similar to CSL.
After the pile concrete has been poured the measurement starts and temperature is recorded at regular intervals until the temperature goes back to a residual value.
For Thermal Integrity Profiling the sensor cables and the processing units of Pile Dynamics, Inc. (PDI) are used by GSP. You can receive information about the measuring equipment here:
Information about the "TIP"
Evaluation of Measuring Results
Codes (e.g., USA-ASTM D7949 - Standard Test Methods for Thermal Integrity Profiling of Concrete Deep Foundations) define the technical conditions for the realization of these tests and provide specifications for the measuring equipment.