Merely advancing the drill by rotary action and flushing with drill mud causes a core to be extracted inside the barrel. However, at a depth of perhaps 300 m, there must be a way to retrieve the core and take it to the surface.
Constantly withdrawing the entire drilling rod string is impractical, so methods were developed to pull up the core inside the barrel. If the rock would always be solid granite, and the core would always break at the drill bit, then it would be a simple matter to stop the drilling and lower a simple grabbing device by a wire and pull up the core.
Unfortunately, many applications require an undisturbed core in fractured rock, which calls for elaborate wire-line devices.
Using a triple-tube wire-line system, capable of extracting core under the worst conditions. This is very important with cost and time saving when exploring fault zones or difficult ground conditions to stop overburden material falling back in the drill hole.