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Drilling in confined galleries in Angostura dam

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When complete, the Angostura Hydroelectric Plant will deliver power to around 300 000 households. The bedrock needed water-proofing, this was done by drilling 64 mm holes and then grouting with cement. The Wassara system was also used for drainage drilling with 100 mm diameter holes.

The allowed borehole deviation was set to 2% at full length. Wassara managed to meet the requirement by far. The drilling environment was healthy, friendly and comfortable as it was dust-free and held a low noise level.

A 320 MW hydropower plant under construction

The Angostura Hydroelectric Plant is located some 600 km south of Santiago, being the largest hydropower plant built in Chile since 2004.

A total of 200 000 m3 concrete will be used in the construction. When completed, the plant will have a generation capacity of 320 MW, enough to power around 300 000 households. The total production will be 1 542 GWh a year.

Waterproofing the bedrock

The dam is a RCC (Roller-Compacted Concrete) dam. Although the bedrock was in good condition for placing a dam on, it was stipulated that it should be made water-proof by drilling and grouting with cement. The drilling would also detect any weak or permeable zones along the dam body.

Drilling in cramped galleries

Part of the drilling took place in 2.5 meter high galleries. This made drilling of the 64 mm holes a bit particular as there was only 1.2 meter free space to operate on above the drill rig. The drill tubes were as short as 1 meter, not optimal for straight drilling. Despite this, Wassara managed to meet the accuracy requirement.

Drainage drilling

The Wassara system was also used for drainage drilling with 102 mm diameter holes. One site drilled for drain curtain along the dam,
3 200 meters downwards and 1 100 meters upwards. The other site drilled along the gallery around the principal machine cavern (comprising 3 turbines and generators), 1 000 meters downwards and 800 meters upwards.

 

Borehole accuracy

The allowed borehole deviation was set to 2% at full length. Wassara managed to meet the requirement by far.


Drawing of the drilling plan

A pleased customer:

The Wassara system was very satisfactory along this project. We were able to meet the target for minimum drilling deviation and we improved the production ratios with no tool cost increase. The dust-free drilling and low noise emission from the equipment gave us a healthy, friendly and comfortable work environment inside the working gallery.
Alberto Mukden

Production Manager at the drilling contractor Pilotes Terratest

Equipment used

DTH hammer

Wassara W50
Wassara W80

Drill bit Ø 64 mm (2.5")
Ø 102 mm (4")
Pump Hammelmann HDP -127 
Drilling fluid Clean water from the dam 
Rig Commacchio MC 235 with a 1.2 m free stroke length 
Drill rods Wassara 1 000 mm, OD 48mm 
Bore hole length 5-60 meters 
Scope of drilling 4 000 meters (W50)
6 100 meters (W80)
Drilling formation Sedimentary rock