Korean tunnel success for new Sandvik rock tool
Aug 17, 2007
Korean contractor Sung Bo Development is achieving a 30% increased life span of its Sandvik Alpha tool system and eliminated rod 'gooseneck' breakages on highway tunnel drilling through difficult, fragmented rock on the Pyeoungtak-Eumsung Highway 40 section 7 contract.
Construction of the 2300 m long tunnel has been split equally between Sung Bo Development from the Western Portal and NanSun Construction Co working from the Eastern Portal. Breakthrough in the middle was anticipated by October 2005.
It is the tunnel that has presented both contractors with problems. Twin dual lane tunnels feature a 14 m wide x 8.5 m high profile. "Right from the start of excavation we recognised we would experience trouble with the rock," says Sung Bo Project Manager, Mr Lee. He adds, "The rock, black Biotite Gneiss is in very poor condition and is non-homogenous." As a result the contractor has opted to excavate the profile in two sections – the upper one across a 12 m base and 7 m high and the second, the lower section across the 14 m base and a height of 1.5 m.
Both contractors opted to use Tamrock drilling rigs; Sung Bo an Axera 3 boom computerised rig and NanSun a Titan 316 – 150 rig. Sung Bo, with experience of Sandvik’s recently introduced Alpha 330 tools system in Korea on a similar tunnel project again opted for the new system.
The Sandvik Alpha system was originally designed for the mining industry as contractors continue to exploit the power and speed of more powerful rock drills to increase production the standard for blast holes which continued to be 45 mm.
The new system has proved to be highly effective for Sung Bo providing an extended 30% life span compared with the previous R32 system. According to the rig operator, Mr Park, the R32 rods also experienced regular 'gooseneck' breakages. "These have now been eliminated with no breakages to date."
Using 4.9 m long rod type T38-H35 Alpha 330, the system quickly proved successful providing a higher quality and cleaner hole.
Since the start of tunnelling Sung Bo is regularly achieving 4000 m/rod. The contractor is drilling 120 face holes in the top profile using Sandvik spherical Alpha 330, 48 mm diameter bits to a depth of 2.2 m. These are completed in 80 minutes with each taking an average of 1.5 minutes. The contour holes around the outer perimeter are spaced at 600 mm distance with the second line 800 mm apart. Spacing between the lines is 740 mm.
On completion of the drilling, the full face is charged within an hour using Hinex for the contour holes and dynamite in other holes. Blasting is carried out twice a day in each tunnel with each blast producing 810 t, excavated and hauled by a fleet of 54 x 15 t dump truck movements. Once blown and cleared the roof is fragmented requiring immediate shotcreting.
He concludes, “Even though the rock is very soft, it is also extremely abrasive.” Despite this the contractor has been getting good service from the Sandvik drill bits grinding each bit three times on-site.By the end of May 2005, 800 m had been completed in the left portal and 700 m from its right portal.
During excavation of the West portals, Sung Bo used Sandvik 105 mm diameter bit to drill 34 holes to a depth of 22 m around the profile perimeter.
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