Minage Valade

Underground location and drilling for water supply : 130 m deep


Map of part of the cave
where the river is
Goal :

Extract water from the 4m diameter room, 130 m deep.


Constraints :

  • very small target, its size is only 3% of the height to drill
  • drilling deviation because of the slope of limestone strata
  • drilling deviation because of geological faults
  • avoiding karstic void during the drilling because it would cancel it
  • Numerous magnetic interferences from high voltage overhead cables and electrified railway


Under-earth situation of the river room


Section of the cave and the river.





Method

The speleologist team progresses from the cave to the river cavern, then they activate the transmitter.
Above ground, the antenna receives the signal. For a better accuracy, several points are localised.




Matching between surface area points
and underground points and topography.



Considering these positions and the geological dip*, the first drilling point was determinated : point A.
We thought the drilling deviation would follow the dip (north-east/south-west), so we placed point A at the north-east of the targeted area. This first drilling came in a karstic void less than 20 m deep, so we had to withdraw it.
Point B : we attempted a second drilling 3 m further, again at north-east at the plumb of the river room. We drilled 160 m without finding the place. To understand why, we put a transmitter in the drilling (localisation of point C).
We learnt that, surprisingly, the drilling deviation was affected by the geological fault and not by the dip.

With this new element, we were able to determine a new drilling point (point D). This drilling, despite of the deviation (point E) arrived in the river room ceiling, at - 130 meters.
*The dip (incline of stratas) cans modify the drilling axis.

Result

Drilling hole in the ceiling of the river cavern when water level is low.