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The parallel seismic method for foundation length measurement: useful also to check pile integrity?
(2012)
Modern geophysical methods might be either directly applied to foundations or integrated into existing testing schemes to assist in quality assurance and inspections. This paper gives an overview on available ideas and some more detailed examples from the author `s work including:
- Vibrator technologies to improve pile integrity testing.
- Ideas from vertical seismic profiling used in multichannel pile inspection
- Cross- and downhole seismics to check the diameter of jet grouting columns
- Improving the parallel seismic methods for precise length measurement of piles and foundation walls
- Seismic migration methods to improve ultrasonic imaging of foundation slabs
- Seismological tools to monitor subtle changes in concrete constructions
The author strongly believes that the cooperation between geophysics and civil engineering, which is obviously becoming stronger and stronger, will lead to a large number of innovative approaches for investigations tasks currently still unresolved. A lot of challenges and chances for science and technology are right here.
Parallel Seismic was introduced about four decades ago for foundation length estimation. As the borehole required by this test is in most cases more expensive than the test itself, the usage is limited so far. In addition the graphical Interpretation technique which is still state of the art tends to overestimate the length and neglects several geometrical Parameters. New Interpretation algorithms have been recently introduced rely on model based travel time curve Utting. They improve the accuracy and extend the maximum ränge (distance pile to borehole) of the method. Borehole or pile inclination as well as soil layering can be considered. If the location is properly chosen, several piles can be tested using a single borehole.
The capabilities and limitations of the methods have been tested using simulations and measurements at the BAM-TTS test site in Horstwalde south of Berlin and several commercial projects involving piles, pile secant walls and sheet piles. To improve the accuracy of the method as well as to provide additional Parameters to the geotechnical engineer it is recommended to use the borehole for Downhole Seismic measurements. Determination of compressional and shear wave velocities can be used to determine the dynamic elastic properties of the subsoil. The approach is evaluated again on the BAM-TTS test site. The affectivity of this kind of combiuation can be further enhanced by using a seismic cone.