New drill rigs to provide 4.5 million m3 of rock for Turkey’s Gökçebel hydropower dam
Turkey’s Kolín Construction has taken delivery of a purpose-ordered DX800 drill rig, bringing its fleet of Sandvik rigs on Akköy hydropower project to five units – producing almost 4.5 million m3 of rock fill for the schemes Gökçebel dam.
Five drill rigs are producing almost 4.5 million m3 of rock fill for the Gökçebel dam on Turkey’s Akköy II hydropower (HEPP) project.
The HEPP scheme is located some 150 km from Trabzon and close to Gümüshane in the Eastern Black Sea region of Turkey.
It encompasses the Aladereçam regulator, the Gökçebel and Yasmaki dams and an electric power plant close to the Akköy 1 scheme also under construction, to produce a total of 890 GWh.
The Aladereçam regulator is being constructed at a ‘thalweg’ elevation of 1797 m directing water to the Gòkçebel dam lake through a 4.5 km long link tunnel with an inner diameter of 3.20 m.
The dam has been designed as a rock fill construction with a concrete coated front and a height of 140 m.
Served by the Gelaver stream in the Gumushane and Giresun Province borders, Gòkçebel lake will hold an estimated 65.07m m3.
The dam is in turn linked to the Yasmaki dam lake area at a ‘thalweg’ elevation of 1527 m via a 6.65 km long tunnel.
Yasmakli dam is a 100 m high concrete gravity dam on the Gavraz scheme in Giresun Province. The dam has a water holding capacity of 15.51 million cm3 to channel water into a 4km surge tank and tunnel.
Virtual quarry
In a ‘virtual’ quarry style application the five Sandvik drill rigs will be used to produce almost 4.5 million m3 of rock for the Gòkçebel dam plus further rock for access roads and eventually the concrete production equipment.
Kolín Construction is currently using two new machines to prepare access roads at an elevation of around 1860 m.
They will also be used, together with two rigs in drill and blast operations to provide infill material for the rock fill dam; producing 300-450 drill metres every 10 hour shift.
Featuring a base of 140 m x 340 m rising to 6 m X 250 m at 140 m height, the dam will require almost 4.5 million m3 of rock.
Rock conditions feature a mix of very hard and abrasive volcanic basalt, granites, granite diorite and quartz with a hardness factor of between 5 – 7.5.
Blasting is carried out twice daily at shift change and lunch.
All five hydraulic rigs are fitted with the Sandvik T51 3.6 m long mf drill rods.
Depending on the rock conditions three different bits are used. Retrac ‘normal face’ 89 mm diameter bits are predominantly used, particularly in the harder rock.
Retrac ‘drop center’ and ‘flat face’ bits are also used when the rock conditions dictate. If the contractor is drilling less than 10 m in soft ground, standard drop center 89’s are used.
Kolín is also shortly to introduce guide tubes for poor ground conditions to also achieve much straighter holes.
Abrasive rock
But it is the abrasiveness of the rock which is the prime consideration where the drill bit life can be as low as 100 drill metres.
The rig operators confirmed however that the bits are frequently lasting each 10 hour shift with around 400 drill metres.
“This performance is very high and quite exceptional considering the abrasiveness and inconsistencies of the rock,” said Mehmet Tuncay, adding, “Another challenge is being able to meet the speed of the drill and blast cycles.”
“The MF rods are also providing high performances and exceptional long life.”
Each drill rig is producing 200 m3/h per rig to ensure the specified 2000 m3/rig is produced each 10 hour shift.
Drilling to 15 m depths, each hole takes an average 20 minutes depending on the rock conditions.
On completion the project, which features a 1219 m high penstock makes it the highest head on an hydro-power plant scheme in Turkey to date.