Parallel seismic testing

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Parallel seismic testing is used when there are doubts concerning the integrity and length of piles and diaphragm walls after completion of a structure.  In such cases it is not usually possible to access the tops of the piles, and other non-destructive methods are hard to use.  The special characteristics of these tests mean that they are usually used in structural renovation work on buildings and civil engineering infrastructures.

sismica_paralela

For this test a shaft must be drilled parallel to the pile to be tested, as close to it as possible (0.5 mm).  This shaft must be at least 5 m deeper than the expected foundation depth.

A receiver probe is inserted into the PVC tube and raised in regular steps (usually of 0.5 m each).  At each step a signal is sent through the pile into the soil and from there to the receiver probe by striking with a hammer as close to the top of the pile as possible. The time taken for the wave train to reach the probe is recorded at each step.

A dromochronic (time/distance) graph is drawn up which is then used to calculate the length of the pile and the velocity of propagation of the waves in the concrete and in the soil.