Patrick Reynolds, Freelance Reporter

Main excavations are about to start on the varied tunnelling works on the long twin tubes of the Express Rail Link to connect Hong Kong with the rail network in mainland China. In a report by Patrick Reynolds, TunnelTalk looks at the packages and tunnelling methods planned for the largely underground route as preparations advance towards a start of drill+blast work this month and launch of the first TBM by mid-year.

One of the largest tunnelling challenges ever for Hong Kong - the Express Rail Link (XRL) - has been getting underway on site with a string of surface preparatory works ahead of the first blasting planned to take place this month to mark commencement of excavation on the almost 26km long main tunnels.

Express Rail Link (XRL) terminus in Hong Kong

The high-speed link will extend from Hong Kong to the border with mainland China as part of a larger high-speed scheme, which has already seen the connection built that will join the new railway to the growing cities of Shenzhen and Guangzhou. The large transport scheme will further tighten the economic and social bonds along this thriving axis, and tie-in to the Chinese national rail network beyond Guangdong Province.

MTR Corporation is developing the section of XRL on the Hong Kong side of the border. A dedicated, entirely underground corridor has been given over to the strategic transport link, which was approved 16 months ago by the Hong Kong Government to proceed towards completion by 2015.

Within Hong Kong, the underground route from central Kowloon to the border, is split into a chain of contract packages in which a variety of tunnelling methods are to be employed - predominantly drill+blast for single tube stretches, with TBM sections of twin tunnel, and some cut and cover excavations.

XRL tunnels
For XRL, the Hong Kong section will see approximately 51.4km of main line tunnelling, excluding ancillary and access works. Connecting two cities, the middle and northern sections of the link will run through hills and beneath villages, a wetland and the Shenzhen River.

In plan, the route is formed by two S-curves, the first on a relatively tight alignment out of downtown Kowloon for about 40% of the line, and the second on a more relaxed route up through the New Territories to the border and into Shenzhen.

Fig 1. Layout and contract packages for the XRL underground route through Hong Kong territory

The rail line passes below a low mountain range as the tight S-curve transits into the second S-curve with two other areas of high cover being short ranges of hills on either side. Cover is up to a little more than 600m in this stretch with the low, flat elevations, in built-up areas, ranging between 5m-55m below ground surface.

Geology along the alignment comprises varied rock strata, including volcanics and granites, as well as soft and mixed ground conditions.

The tunnels will be of varying internal diameter. The twin tube TBM sections range between 8.15m and 8.7m i.d. and linked by cross passages, whereas stretches of single tube, double track drill+blast excavation is about 15m wide.

In total, there is a series of nine principal underground packages. From the total tunnelling required, there will be approximately 14km of drill+blast, 17km (2 x 8.5km) of parallel TBM bores, 4km (2 x 2km) of cut and cover, and 2.4km (2 x 1.2km) of cut and cover for works near the terminus at West Kowloon.

Along the alignment there will be eight ventilation buildings and emergency access points, and at Shek Kong there will be an emergency rescue station (ERS) and stabling sidings (SSS) on a 2km long x 150m wide corridor.

Procurement
In October 2009, the Executive Council of Hong Kong's Government gave its approval for MTR Corp to proceed with its section of XRL. Trains will travel at up to 200km/h and will more than halve travelling time, from 100 minutes to 48 minutes, between Hong Kong and Guangzhou. To reach Shenzhen will take barely quarter of an hour. Journeys to Shanghai and Beijing will take eight and 10 hours, respectively.

Procurement quickly got underway with a staggered programme of bids and contract awards. The bulk of calls for pre-qualification to construct the main underground packages were issued in the second and third quarters of 2009 and awards of contracts were spread through 2010.

While preparatory works began in early 2010, the large lump sum contracts for the main underground works were issued over subsequent months up to late last year (Table 1).

Table 1. Award details of the main XRL construction contracts

Tunnelling schedule
Early and preparatory works began last year and main excavation is set to begin this month on the principal underground packages. Drill+blast and principal cut and cover works are about to get underway and the first TBM is expected to start about mid-year.

TBM launch and working site for XRL Contract 820

Commencing 2011 – First half
C811A
Tunnelling will start in March with Bachy Soletanche-Laing O'Rourke JV on the cut and cover works for the south approach tunnel at the terminus. The works involve construction of a 270m long tunnel, which includes a 170m long piled section, to run below the existing Kowloon Southern Link tunnel; and, 480m long diaphragm walls. Excavation is to be completed within 11 months, and the lining work is to take two years to finish in December 2013.

C811B
The first works near the terminus will be quickly followed, in April, by Gammon-Leighton JV commencing excavation in the adjacent area for the north tunnel.

Included in the package is construction of a 430m long cut and cover piled tunnel, and 710m of diaphragm wall. While starting just after the adjacent works, the excavation is scheduled to finish some seven months later. However, the lining work is scheduled to take less time and finish earlier, in October 2013.

C822
Also leading the first works to get underway, in March, is Leighton Contractors (Asia) with the planned start of drill and blast excavation on package C822, which runs through the main mountain range near the middle of the route. The main works are to blast a 7.7km long, single tube tunnel plus a 2.5km long ventilation tube, a 120m deep shaft and two adits of 400m and 700m long. Excavation is to advance on three headings and blasting is due to be completed in less than two years, by January 2013. Concurrent lining operations are to start by the end of this year for completion by mid-2013.

C825
Approaching mid-year, and scheduled for May, Penta-Ocean Construction Co is programmed to commence TBM boring on the C825Mai Po to Ngau Tam Mei section. The contractor will use a single EPB shield to excavate the 2.3km long x 8.15m i.d. parallel tubes, with about 300m in rock or mixed ground. Excavation is to be completed by Aug 2013 and tunnel civil works by December. The works also include a 35m deep shaft and cross passages to link the twin running tunnels.

XRL will connect Hong Kong to Shenzhen and Guangzhou

Commencing 2011 – Second half
C821 & C820
Dragages-Bouygues JV is undertaking the adjacent C821 and C820 TBM and drill+blast excavation contracts either side of the Mei Lai Road shaft.

The JV's first main excavation on adjacent packages will be on the Shek Yam to Mei Lai Road (C821) section, which is through the southernmost, short range of hills on the route, closest to Hong Kong. Geology is mainly grantitic rock though there are some fracture zones. Drill+blast on the 3.7km long section is to start in about July 2011. Two headings are planned and excavation is to be completed by January 2013 with concurrent lining work finishing about a month after. The tubes are to have twin track and single track sections.

The 3.4km twin tubes of the C820 Mei Lai Road to Hoi Ting Road package will be excavated using a slurry TBM in four separate drives either side of the Nam Cheong cut and cover station. The bores will pass below existing buildings and near pile foundations. The 8.15m i.d. tubes will be connected by 13 cross passagesexcavated mostly in soft ground. Boring is to commence on the longer Nam Cheong and Hoi Ting Road shaft section in Oct 2011 and finish two years later. Tunnel civil works are to be completed in the second quarter of 2014. Excavation of the tubes on the other side of Nam Cheong is to start in 2012.

C824
Kier-Kadan-OSSA JV is scheduled to commence drill+blast excavation on the Ngau Tam Mei to Tai Kong Po tunnel section in November 2011. The contractor will excavate a 2.6km long single bore, double track, a 400m long bifurcation cavern, stub tunnels, a 90m deep ventilation shaft and a 40m deep emergency access shaft. The geology comprises volcanic rock with fault zones anticipated and water ingress expected. The tunnels will cross below and within 22m of an existing 3.4m diameter water tunnel. There will be up to four faces and both excavation and lining works are to finish by February 2013. Tunnel civil works are to be completed by October 2013.

Curved route to the West Kowloon Terminus

Commencing 2012
C820: second section
The beginning of 2012 is to see the slurry TBM begin on the shorter of the two twin tubes sections between Mei Lai Road and Nam Cheong station on the Dragages-Bouygues JV contract C820. Tunnelling is to be completed in August 2013, shortly before the bores on the other section of the contract, which will have starter earlier. Tunnel civil works are to be completed in the first quarter of 2014.

823A (Tai Kong Po part) - Jan 2012
Contract 823A is another section of the route where TBM tunnelling is split into two sections with either side of the ERS site, which is a 650m long box structure built under a contract 823B. The contractor, Maeda-China State JV, will use an Hitachi 9.22m EPBM for the pair of short 1.2km and 800m twin tube drives.

On the section between Tai Kong Po shaft and ERS, boring is to start in January 2012 and be completed within a year.

Tunnel civil works are to be completed by August 2013. On the other side of ERS, the bores to Tse Uk Tsuem shaft are scheduled to be the last to commence on XRL, in March 2013. The tubes are to be completed by the end of 2013. Tunnel civil works, including eight cross passages are to be finished by March 2014.

C826
Main boring on the northernmost section on the route runs between Mai Po shaft in the New Territories and Huanggang in mainland China. The section is 3.3km long with slightly more than 40% of the 8.7m i.d. twin tubes in the New Territories. The contractor, CRCC/HC/CR15G JV, is to undertake the bores using a Herrenknecht Mixshield. The machine is to launch in October 2012 and progress for about a year towards completion of the tunnel civil works by April 2014.

From this month until the end of 2013, when all lining works are to be completed, the many and varied tunnelling packages on the Hong Kong section of the XRL will be an intense exercise in engineering and logistics.

References

Hitachi adds to overseas order book - TunnelTalk, January 2011

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