DNJV are also relying on a Sandvik DC 300 compact rig for drilling duties on the projects 28m deep Stubbs Road shaft. The DNJV contract includes a total of 32 shafts; with the Stubbs Road shaft being the only one to be excavated using the Sandvik DC 300 rig.
Four Sandvik SR530 reaming heads will be used by the raise - drilling division of Australia's mining and construction contractor Macmohan for 23 shafts on the Hong Kong West drainage Tunnel (HKWDT) scheme in Hong Kong's largest raise boring application.
Main contractor, the Dragages-Nishimatsu JV (DNJV) appointed Macmohans Raisedrilling Division to use raise boring techniques for 2.4m and 3.154m diameter shafts to a variety of depths ranging between 40-181m.
The raise boring method was selected due the isolated shaft intakes on the hill sides across mid-levels with difficult access and the restricted weight loadings of the adjacent pathways.
It was also considered to be the safest shaft option- with no people required in the shaft during boring - and ensured the least environmental disturbance. The technique will also ensure the fastest construction time over known methods.
Raise boring is widely used for shaft excavation on construction and mining projects around the world.
Macmahon will start each shaft with a 13¾ inch pilot hole using Sandvik Pilot bits and 11¼ inch drill pipes and, together with a number of Macmahon controls, will contribute towards critical hole straightness.
The pilot hole will then be reamed to the final shaft diameter from the tunnel below using a Sandvik SR530 extendable reaming head. This particular head used in the Hong Kong project is a CRH8E which is extendable from Ø 2.4 - 3.5 m by using different types of segments fitted to the base head.
The raise boring technique was also felt to be the best option for fast mobilisation and penetration rates.