Parallel seismic test

Parallel Seismic Test

Parallel seismic test is a NDT to determine the pile length when the foundation info is no longer exist or doubt on the constructed pile length. Test equipment consists of accelerometers, impact hammer, and data acquisition system (DAQ). Hammer is used to create an impact by hitting on top of the structure that is connected to the pile or foundation (more preferable to hit on top of the pile itself). A wave will be firstly collected by accelerometer and shown by DAQ, next, wave is transferred down along the pile and a shear waves will be propagating through soil to receiver locations by other accelerometer located in a PVC hole 1.5 m away from the pile cap, which will be put down every 50 cm to maximum 1.0 m.
The diffraction, or change in slope, that occurs in the data as a result of the pile tip acting as a point diffractor and a reflector indicates the end of the pile. Thus, pile length can be determine.
Illustration from RE past project is given as follows.

Pile depth vs wave travelling time