Shatin-Central Link progress in Hong Kong 17 Feb 2016

The engineered products division of Trelleborg is selected to seal the 11 concrete elements that will make up the immersed tube tunnel crossing of Victoria Harbour Shatin-Central metro rail link in Hong Kong.

The contract is awarded by the Penta-Ocean/China State JV, which is building the cross-harbour tunnels of the 17km-long Shatin to Central Link (SCL) on behalf of project owner MTR Corporation of Hong Kong. The tunnels, once completed, will span 1,300m and carry twin rail tracks to connect Kowloon to Hong Kong Island.

Ramping up for construction of Victoria Harbour immersed tunnel

The crossing consists of 11 concrete elements of approximately 160m in length each. These are currently in production at a dock-based casting yard and will be towed to the construction site by sea, and connected using Trelleborg’s Gina gaskets, which are supplied as closed rectangular frames to seal each sectional element; along with Omega seals to connect each segment together. Both are designed to withstand seismic activity and to absorb movement.

Andre de Graaf, Sales Manager Infrastructure for Trelleborg’s engineered products division, said: “Our tunnel seals enable installers to deploy a lighter force jack to seal the deeper joints, as the Gina gasket is softer and able to close more easily upon initial compression. These solutions therefore help clients to reduce costs and to reduce the time it takes to close the seals.”

The Gina gasket serves as the primary sealing mechanism for preventing water ingress resulting from external water pressure. It has an outer dimension of 370mm x 370mm and comprises different rubber hardnesses for optimised sealing performance. The Omega seal serves as the secondary safety seal that can withstand extreme movement. It is designed with two cross-weaved reinforcement layers made of nylon for durability and strength. The seals are designed to perform to 3.6 bar of pressure at a depth of 28m, but have the ability to withstand up to 5 bar.

The combination of the two seals enables the transfer of hydrostatic loads and movement between the tunnel elements that can be caused by soil settlement, concrete creep, temperature effects and earthquakes.

Site works have been initiated on the Victoria Harbour and Trelleborg has started production of gaskets for the project.

17km Shatin-Central Link, with excavation methods

Progress so far

Contract rollout for the underground sections of the Shatin-Central Link began in 2012, with award in July of that year of the station and tunnels contract for the Kowloon City section to the Samsung/Hsin Chong JV.

The Victoria Harbour immersed tunnel contract was among the last to be awarded – in December 2014 – of a complex project that incorporates all of the major excavation techniques. In total there are 10.2km of TBM headings (ten drives for a total twin bored length of 5.1km), a number of cut and cover and hand-mined sections, and two major drill+blast headings (Fig 2).

Last year (March 2015) the first tunnel breakthrough on the project was recorded after a TBM operated by the Chun Wo/Seli JV completed the upline of the 750m-long Kai Tak–Diamond Hill underground section. After being removed and transported back to the launch shaft, the machine is now excavating the downline.

Meanwhile, both TBMs for the 1.6km section of running tunnels between the launch shaft at To Kwa Wan Station and Ho Man Tin are in the ground, the first launched in April 2015 and the second later in the year.

The 5km-long tunnels between Hin Keng and Kai Tak, a stretch that features challenging mixed ground conditions and necessitates a mix of excavation methods, are now connected following completion of drill+blast operations 35m below Lion Rock in November (2015).

Breakthrough celebrations for Chun Wo/Seli JV

For the tunnel from Hin Keng, beneath Lion Rock, to Ma Chai Hang, drill+blast was adopted, with more than 500 blasts carried out since the works commenced in January 2014, and approximately 360,000m3 of rock removed. The tunnel section between Ma Chai Hang and Kai Tak via Diamond Hill was constructed by two TBMs – the first machine completing the running tunnel between Diamond Hill and Kai Tak in October (2015), and the second machine completing the upline between Ma Chai Hang and Diamond Hill in June (2015). The second TBM Is now excavating the downline, having launched on the return drive in September (2015).

“The Hin Keng to Kai Tak Section is one of the most critical tunnelling works of the SCL project, and will allow us to run new train services directly from the New Territories to urban Kowloon,” said Dr Philco Wong, MTR Corp Projects Director. “On top of the difficult geological conditions at Lion Rock, tunnelling underneath the existing railway tunnels of the Kwun Tong Line and various busy traffic arteries required great precision engineering,” he added.

The SCL is a territory-wide strategic railway project comprising the Phase I Tai Wai–Hung Hom section, due to be commissioned in 2019, and the Phase II Hung Hom–Admiralty section, due for completion in 2021.