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Straight survey holes at Mitholz, Switzerland

Project Description:

The 38 km-long Mitholz Tunnel in Switzerland is one of the most important elements in the construction of the new Lötschberg Line. The railroad joins Frutigen in Kanderdalen with Raron in the Rhône Valley. Boart Longyear's Morissette Division was commissioned to drill a 250 m-long exploration hole. The rock conditions were to be studied by analyzing the mud from, and filming inside the hole. Morissette chose Wassara's W80 Drilling System to do the job.

One of the main reasons was the high risk of encountering sections of high hydrostatic pressure, which ruled out drilling with an air hammer. The Wassara systems' stabilized pipe also guaranteed a straight hole, which was one of the project requirements.


Choosing Wassara gave Morissette a significantly faster and more cost-effective method compared with traditional core drilling, and the average penetration rate was 2-3 times higher than for traditional core drilling.

Equipment used

DTH hammer

Wassara W80

Drill bit Wassara 95 mm
Pump 2 Cat pumps, 184 litre/minute at 200 bar 
Drilling fluid Clean water 
Rig Longyear LM 150 
Drill rods Wassara 93 mm, stabilized 
Bore hole length 250 meters 
Drilling formation

Hard limestone, quartz, schist