GIA debut on Hong Kong drainage tunnel project
Published 2010-03-15 00:00:00 | Updated 2010-03-19 13:36:43
Two GIA Häggloaders and three GIA locomotives, each pulling three shuttle cars, have been delivered to Hong Kong’s West Drainage Tunnel Scheme for ‘spoil’ removal from 29 adits, totalling 8 km. Making their debut in Hong Kong, the GIA units were ordered specifically by Joint Venture contractors Dragages-Nishimatsu for their ability to work in small diameter tunnels. A complete ‘line-up’ of GIA tunnelling equipment comprising locomotives, shuttle cars and Häggloaders have been delivered to the Dragages-Nishimatsu JV for work on the Hong Kong Drainage Tunnel Scheme.
In a bid to alleviate the flooding problems in northern Hong Kong Island, work has begun on the Hong Kong West Drainage Tunnel (HKWDT) Scheme; awarded by the Drainage Services Department to the Dragages-Nishimatsu Joint Venture.
Whilst the Drainage Services Department has made improvements and extensions to the aged systems, the improved drainage systems still fall short of current flood protection standards. They remain inadequate to deal with the flooding caused by heavy rainfall or typhoons.
Hong Kong experiences an annual average rainfall of some 2200 mm, one of the highest among cities in the Pacific Rim. It is located in a sub-tropical region and has an oceanic climate making it vulnerable to heavy downpours and tropical cyclones.
With continuous urban development making the northern district of the island one of the most densely built areas of Hong Kong, the surface water run off has considerably increased in recent years; reducing the flood carrying capacity of the existing drainage systems and aggravating the flooding problems.
Affecting low lying areas including Sheung Wan, Central, Admiralty, Wan Chai and Causeway – the financial and business districts of Hong Kong – this therefore disrupts the economic activities and business operations leading to huge economic loses.
HKWDT Project
The scope for the new HKWDT project involves construction of a new 11 km long drainage tunnel, deep in the ground in the mid-levels of the island from Tai Hong to Pokfulam. The scheme will intercept and convey the storm water from the upper catchment areas directly into the sea near Cyberport.
The Dragages-Nishimatsu JV is responsible for constructing the tunnel in two sections. The first, 4.5 km long and 6.25 m in diameter, will run from Tai Hong and under the Aberdeen tunnel. The second, 6 km long and 7.25 m diameter, is from the Aberdeen tunnel to Cyberport.
Adit construction
Using two tbm:s for the main tunnel, construction excavation by mid-October had reached 1.1 km from the Western Portal at Cyberport and 400 m from the Eastern Portal. Breakthrough is anticipated some 6.5 km from the Western adit.
The GIA fleet of two 8 HR2-B Häggloaders and three sets of GIA locomotives and nine shuttle cars will be used throughout excavation of the adits and ‘spoil’ removal at the Western Portal for off-site clearance.
With 27 of the adits measuring 2.59 m width x 2.25m height and a single adit measuring 3.5 m width and 3.435 m height, the GIA equipment was purpose-chosen for its ability to operate in such compact tunnel construction.
A key factor in the Joint Venture ordering the GIA equipment was a visit made by representatives to the Gemerska Polona project in Slokavia, where an identical GIA configuration was being used to excavate a 4.2 km long tunnel, with a cross sectional area of just 11.5 m2; highlighting the advantages of the system in small dimensional tunnels.
The 8 HR2-B Häggloaders, generally fitted with two digging arms to speed the ‘mucking out’ process at the face, has been modified to include just one ‘arm’ due to space constraints. The ‘arm’ is also used for ‘scaling’ the blasted profile.
When used in conjunction with its built-in conveyor, the Häggloader is able to continuously load the blasted ‘spoil’ from the face into the GIA shuttle cars in an uninterrupted, spill-free loading operation; offering loading capacities of up to 3 m3/h.
For the first 5-6 m of the adits from the main tunnel junction, the JV contractor will use ‘rock splitting’ techniques to open the adit, preventing possible damage to the high voltage supply and conveyor belt systems in the main tunnel.
Thereafter drill and blast methods will be introduced. Blasting is carried out once a day working on, according to JV Plant Manager, Masanori Ishii, up to 12 faces simultaneously. This includes initially, for example, two faces of the first adit, three faces of the second adit and three of the third. Spoil is removed from the face after blasting by the Häggloader and loaded directly into the GIA shuttle cars.
Shuttle car operation
Utilizing three GIA 115 CE shuttle cars allows loading from car to car using internal conveyors to ensure the fastest loading system possible.
With each 1700 mm car featuring an 11.5 m³ (22,000 kg) capacity along its 11.2 m length, use of the three cars connected together allows Dragages-Nishimatsu JV to transport up to 34.5 m³ (66,000 kg) of ‘spoil’ in a single trip without time consuming car switching.
Up to eight cars can be coupled to suit different size construction sites and, by matching the number of cars to the volume of blasted rock, it is possible to transport up to100 m³ of spoil in a single trip.
The shuttle car floor is lined with Hardox 500 wear parts to ensure long life and low service requirements.
At the discharge point outside the tunnel at the Western Portal all three shuttle cars, utilizing the internal conveyor system, discharge the ‘spoil’ from the front car, in an operation taking less than 5 minutes.
The shuttle cars feature specially designed boogies, with centre suspension and rubber springs which contribute to a smooth and safe running of each car. By that, the risk of derailing is minimised, even when running on uneven tracks.
The centre suspension features a well protected Teflon bearing, which requires virtually no maintenance.
The ’cars’ are ‘hitched’ to a GIA DHD25 hydrodynamic diesel locomotive which offers high productivity, easy operation and service. It has a maximum speed of up to 30km/h, but the system allows 12 km/h.
The 25,000 kg class locomotive is powered by a 144kW engine.
For the shorter adits – four in the Eastern and seven in the Western – the Dragages-Nishimatsu JV is utilising a skid loader to remove the spoil directly, loading the GIA shuttle cars in the main tunnel instead of installing rails for the Häggloader.
Currently the contractor is achieving tbm advance rates of 450 m/month in the main tunnel, although this recently slowed to around 200 m when water was ‘hit’.
Rock conditions are however generally good, although a number of ‘faults’ have been identified. Two types of rock are predominant – granite at both portals with a toughness factor of 200 MP – 300 MP and up to 400 MP Tuff in the central section.
Drop shafts
A total of 34 intake shafts are to be excavated to intercept water flow from existing drains or streams along the 11 km route.
Most will be constructed using the ‘raise boring method’, initially using a small diameter pilot drill down to the adit. At the bottom a larger reamer, brought in along the adit, is installed to the drill rod.
The reamer then bores upwards to the ground, excavating the shaft along the way. All excavated material falls to the bottom, for retrieval by the GIA equipment and removed to the portal.
The finished drop shafts feature a mix of three diameter sizes, 1.5 m, 1.8 m, and 2.3 m, and a variety of depths varying from 17 m to 170 m at Tregunter Path.
In a 49 month contract, completion of construction is scheduled for December 2011. Consultant engineers for the project, responsible for planning and design is Ove Arup & Partners Hong Kong Ltd.
Tags: scaling and mucking, transportation, conveying and hoisting
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