Parallel seismic

This technique is commonly applied for the determination of the depth of foundation elements of whose tops are no longer directly accessible (e.g. the foundation elements are already interacting with the superstructure) or to test piles which cannot be fully tested by other indirect methods, such as the Pile Echo Test / Pile Integrity Test.

For this method, a borehole must be drilled as close as possible to the foundation edge and must extend 5 to 10 m deeper than the estimated foundation depth. The borehole must be cased with PVC, firmly grouted in the hole and filled with water prior to testing.

The test consists in lowering a hydrophone or geophone probe in the borehole at regular intervals recording the arrival of compressional waves generated by hitting the exposed top of the foundation. Finally, the depth of the foundation is estimated by tracking the arrival times of the waves and observing the depth where a change of slope occurs.

Typical setup scheme and example of acquired record showing the estimated length of a pile (15m)