The Sonic Echo data is used to determine the depth of the foundation based on the time of arrival of the impact signal and an echo signal returning from the pile base.
A reflector can be the bottom of the foundation or any discontinuity along the embedded part of the foundation, this enable SE to be used for defect location.
In the SE data below reflections in the data are used to calculate the depth of the first pile and the depth of the break in the second. Finally SE testing can be used to determine the existence of a bulb, a neck, or the bedding of the pile base.
Sonic Echo data for undamaged pile
Sonic Echo Data for pile with damage close to surface
The SE method works best for columnar foundations such as piles and drilled shafts. Reflection events are clearest if there is nothing on top of the foundations (such as a column or pile cap)
Typically, SE tests are performed on shafts or piles of length to diameter ratio no more than 20:1.Higher ratios (30:1 or greater) are possible in softer soils.
Where a simple element such as a slab or footing rests on the pile, the thickness of the element must not exceed 1.7 times the diameter of the pile for the SE analysis to be interpretable.
Sonic Echo tests are accurate to within 5% in the determination of the depth of the foundation provided an independent measurement of the sonic wave velocity used in the depth calculation is made. This may be done using an Ultrasonic Pulse Velocity measurement.
In case the wave velocity is assumed based on the material type, SE tests are normally accurate to within about 10%.
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