A pile is a slender element cast in the ground or driven into it. Since pile construction as well as the final product are mostly invisible, engineers have often questioned their integrity, i.e. their compliance with project drawings and specifications. In fact, experience  has shown that in piles, of all kinds flaws may occur. The purpose of integrity testing is to discover such flaws before they can cause any damage.
Historically, pile integrity was investigated by direct methods. These included external methods such as excavation around the pile and internal or intrusive methods, such as core-drilling . While excavation may be effective in exposing flaws in the outer part of the pile, it is usually limited to a depth of a few meters. Core drilling, on the other hand, can be carried out to a large depth provides full information, but only for a very small fraction of the pile volume.