Positioning of an underground river in cave


Context

Our client, a ski resort, wanted to make a drilling to access an underground river in a karst environment.
He had drilled several unsuccessfull boreholes on the recommendation of a hydrogeologist based on the survey of a group of local cavers.

Our solution

The underground river (or rather the drain) is accessible by a sump after over a kilometer of underground galleries located at a depth of 380m (1250ft) .
The drillings had been made on the basis of topographies made by amateur cavers. In difficult conditions (cold, mud, humidity, verticality) and combined measurement uncertainties, a subterranean topography, even with great care, remains accurate to a few percents or, in other words, in a one-kilometer-long cave, tens of meters of final X-Y positioning error.

Pascal Orchampt and his "underground GPS"
The detector is coupled with an advanced receiver that automatically detect the EM waves from the surface (or vice versa)

Pascal Orchampt, electronics engineers at NOT Engineers, has developed a specific magnetic beacon for this positioning, ultra precise and tailored to great depths. The radiolocation beacon that exist elsewhere are designed according to a widely described principle, precise to depths of less than 50m, but where electromagnetic interference and construction defects make the use unreliable beyond 150m.

The 50W NOT Engineers beacon can emit during 60 hours in a row ...
As a result of our intervention and combining the data (topography and electro-magnetic positioning), NOT Engineers was able, with good confidence interval, readjust the position of underground galleries over the surface.

Positioning a cave with radiolocation
This shows both the previous topography (pale colors) and the new, repositioned with reference to the ground surface. It is clear why the previous drilling, based on the speleological topography, was a failure: it was realized 40m from the siphon. Note: data has been slightly modified to comply with confidentiality.

Read more: Underwater Positioning a sump