Drilling roosts in HK

Three-lane tunnel goes under Hong Kong’s eagle nest

  • E-Mail
By  Colin Foreman Published  November 20, 2004

Technology|~|Eagles-nest-Big.jpg|~|Digging away|~|Hong Kong’s roads have one of the highest vehicle densities in the world. In September 2003, there was more than 522 745 licensed vehicles and only 1932 km of roads. The high vehicle density combined with difficult terrain and dense building development, imposes a constant challenge to road builders to cope with the ever increasing transport demands. A new highway and tunnel, the Eagle Nest Tunnel, in the New Territories will help alleviate some of the motoring ‘bottlenecks’. Leighton Contractors (Asia)-Kumagai Gumi Co Joint Venture have the contract to build the tunnel. It will be relying on the winning combination of five purpose-ordered Tamrock Axera computerised jumbo drilling rigs, all fitted with Sandvik rock tools to meet a contract of just 42 months for the 2.1 km dual three lane Eagle Nest Tunnel. The JV will drill out more than 500 000 m3 of granite to get the job done on time. The tunnel is a key element of the Route 8 highway passing under the Lion Rock Country Park close to Shatin in the New Territories. The HK$1.8 billion (Euro192.5 million) contract forms part of a strategic route between Cheung Sha Wan and Shatin. It is the Government’s plan to improve the road capacity between Shatin and Kowloon so as to cope with the future traffic demand; generated by developments in the North West New Territories and an increase in cross border traffic. Together with the new Stonecutters Bridge, which will be the world’s longest cable-stayed bridge when it is completed in 2008, the new Route 8 will cut the time to drive from Shatin to Chek Lap Kok Airport from 1 h to just 30 min. Four Tamrock Axera T12 3-boom fully computerised jumbo’s and an Axera T08 2-boom jumbo were specifically ordered for the project with an older 2-boom jumbo providing standby back-up. Once tunnelling gets underway, two 3-boom rigs will operate side-by-side in the 11.8 x 16.3 m high tunnel in each twin tunnel; anticipating a breakthrough in the middle. The new two-boom jumbo will be used to drill a 400 m long ventilation adit. Currently, as plant mobilisation gets underway, one of the three-boom jumbos is standing in preparing the ventilation adit portal and slope stabilisation around the portal. While awaiting delivery of the new jumbo’s the JV relied on its older two-boom jumbo to drill three probe holes around each portal. Using a Sandvik Retrac drill bit and a total of eleven T38 3.7 m long extension rods, each 64 mm diameter hole was drilled to a depth of 40 m to determine the extent of any water ingress and rock conditions.||**||Core Holes|~||~||~|The Retrac drill bit design ensured that any deviation was retained at an absolute minimum over the 40 m length. On completion of the probe holes, a total of 40 casing holes around each portal were drilled. Using a Tubex XL90 drill bit fitted with Sandvik T45 extension rods, each hole was drilled 12 m into the rock. Completing more than 1000 m in preparing the core holes, each bit was reground just twice, despite the manufacturers recommended 50 drill metres for regrinding. Once drilled the core holes were inserted with grout to offer improved stability at the portal for the start of tunnelling. With a profile of 16.3 m wide x 11.9 m high, the JV will initially drill a top 8 m heading with an estimated 227 holes. Using Sandvik R35 drilling tools for drifting with a mix of 48 mm and 51 mm bits will drill 1.5 m deep holes close to the entrance so as to allow steel arches to be installed and offer additional support from the portal. Hole depths will then be increased to 5.5 m using a type TF500X20 feed and 6.1 m rod. In common with all tunnel construction in Hong Kong, strict environmental legislation must be complied with including blasting certification. On Eagle Nest the problem is further compounded by the North Portals close proximity to the Kowloon reservoir. This has resulted in strict restrictions being implemented involving blasting and constant inspections checking for water ingress with grouting being undertaken before blasting can continue. In a subcontract to main contractor China State-China Railway JV, Him Sum Contractor is using a CHA1100 Powertrack drill rig and Sandvik rock tools to stabilise rock slopes around the toll plaza area of the Eagle Nest Tunnel. Holes are being drilled at an angle of 10o with two different diameter holes. A Sandvik Retrac T51 rod and bit fitted for 102 mm diameter holes and a combination of Sandvik 60 rod and ST68 bit ensures a 152 mm diameter hole.||**||

Add a Comment

Your display name This field is mandatory

Your e-mail address This field is mandatory (Your e-mail address won't be published)

Security code