West Rail Tai Lam Tunnel (Contract DB-350) Introduction

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1 Introduction General Scope of the Contract Tai Lam Tunnel (TLT) was awarded as a Design and Build Contract on 22 September 1998 to a Nishimatsu-Dragages Joint Venture by the Kowloon Canton Railway Corporation (KCRC) as Contract DB350 for HK$1.79 billion. At 5.5 km long, TLT is the longest transportation tunnel in Hong Kong and has been constructed using the drill and blast method with computer controlled drilling jumbos and laser guidance to ensure an accurate alignment. The conforming design was to provide two single-track tube bored tunnels with interconnecting cross passage adits every 250m for escape to the non-incident tunnel in the event of an emergency. The successful JV proposed an innovative alternative tender design scheme, which was to drive a twin-track, single tube bored tunnel constructed with a center partition wall to separate the mainline up-track and down-track. Nishimatsu drove the southern half of the drill and blast tunnel. The package also included the construction of the 0.35km section of twin-cell cut-and-cover tunnel linking between the Southern Portal and the new Tsuen Wan West Station, as well as the ancillary ventilation building at Chai Wan Kok. In paralled with these works Dragage drove the northern half of the tunnel along with 0.33km of at grade site formation and slope works and the northern ancillary ventilation building.

2 Introduction Southern Portal and the Cut-and-Cover Tunnel at Chai Wan Kok, Tsuen Wan The works were complicated at the southern portal due to a number of physical factors. First of all, the tunnel alignment was directly obstructed by a group of piled foundations to a pier of the existing Chai Wan Kok Bridge at the entrance of the Tuen Mun Highway. Before any tunneling works could commence, the existing foundation needed to be underpinned, which was done by the introduction of a 27m long, 3.5m deep and 5.6m wide transfer beam. To facilitate this, two new groups of 1200mm diameter bored piles, 3 on each side, were driven to support the transfer beam, which spanned across the tunnel alignment. To account for deflection of the transfer beam and any initial settlement to the foundation under loading, the bridge was jacked up by 5mm using six 200-tonne single acting hydraulic ram jacks providing a design vertical uplift of 1000 tonnes. A secondary jacking system, consisting of two 90-tonne jacks provided horizontal restraint to the bridge deck. The vertical jacks maintained the bridge deck in a constant position throughout the whole operation to ensure the total safety of road users at all times. A simplified sequence of enabling works at the Southern Portal location is shown in the flow chart below.

3 Introduction The provision of the Southern Portal at Chai Wan Kok was a difficult job. A 250m trench, measured 40m wide x 25m deep, needed to be formed. The trench initially acted as a service shaft to provide room for the assembly of the required tunnel equipments and alter as access for the tunneling work during construction. The Southern Portal was formed in slightly to moderately decomposed medium-grained dacite with occasional localized highly decomposed bands. At this location, 1.2m thick diaphragm wall panels formed the vertical support for the sides of the trench being locally restrained by ground anchors. When reaching the formation level, a temporary ramp with up-track and down-track provision, was erected with supports onto a steel frame. This temporary access was maintained for about 15 months as the main route for spoil removal until the tunnel excavation was completed. This was followed by the dismantling of the access ramp and the construction of the approach tunnel section within the trench using a traditional cut-and-cover arrangement. The remaining 350m long cut-and-cover tunnel linking between the approach section and the Tsuen Wan West Station portion. The cut-and-cover tunnel was constructed in residual soils marine deposits, alluvium and reclamation fill. The construction of this section of tunnel was quite routine in term of tunneling work of this scale. However, the arrangement for the traffic diversion at the existing interchange at Chai Wan Kok was quite a challenge. A temporary deck supported on steel H-piles was erected in various phases in order to provide the necessary road surface for the diversion arrangement, which involved the maintenance of uninterrupted traffic to the dual 2-lane roadway in 3 directions at all time. There is a ventilation building located at both ends of the tunnel portals. The facility has a dual purpose, as well as providing ventilation to the tunnel in normal operating mode, they can also be used for smoke extraction from the tunnel in the event of a fire.

4 Introduction The Construction of the Tunnel The bored tunnel is essentially a twin-track (14m span) tunnel with the exception of the first 518m of tunnel from the Northern Portal, which is constructed as a triple-track (19m span) tunnel to accommodate a siding track. The tunnel was driven through granitic and volcanic rocks. As the tunnel advanced, the Grimstad and Barton Norwegian Method of Tunneling support methodology was used as the guide to assessing the tunnel support requirements. The face of the tunnel was advanced between 1m and 5m per blast depending on geotechnical conditions as well as the charge weights used. The anticipated monthly production for usual twin-track tunnel was 170m but for TLT the contractor managed to achieve and maintain a production rate between 200m to 210m per month. As a result, despite the additional time required for the enabling works at the tunnel portal, the tunnel breakthrough was achieved exactly on programme. For the southern section, mucking out was carried out by loading tunnel spoil into vehicles at the face of the excavation. While for the northern portal, a full-range extensible conveyor system was employed for the purpose. The tunnel has been constructed with a permanent concrete lining in order to achieve the required 120-year design life. For the southern section of the tunnel an in-situ reinforced concrete lining was only required at the portal zone, the majority of the lining being un-reinforced. All of the tunnel lining was cast in 12.5m lengths using a steel shutter and lining construction was carried out concurrently with the excavation works.

5 Introduction Tunnel Interior Arrangement A 300mm thick reinforced concrete center partition wall was constructed separating the up-track and down-track tunnel. As a safety requirement to provide access to a non-incident tunnel in the event of an emergency, openings are formed every 60m along the full length of the partition wall for passenger access between the up-track and the down-track tunnel. Each opening has a sliding cross passage door with an FRP of 4 hours. A track cross-over opening in the partition wall 52m long and 8m high in the center of the tunnel (at the location of a diamond cross-over section of track) was also provided to facilitate the diversion of trains within the tunnel. This was achieved by installing a large pair of sliding doors, each leaf measuring 27m long by 6m high (162 sq m surface area) and weighing 30 tonnes which will provide 4 hour FRP separation between tracks. The cross-over door installed will be one of only two systems of its kind in the world, the other being in the Channel Tunnel, between the UK and France. The cross-over door is normally closed during usual operation hours, but in the unlikely event of an emergency or for routine maintenance, it can be remotely controlled from Tsuen Wan West Station which is located approximately 3.5km to the south of the crossover. The cross-over door operation is inter-locked with the automatic train operation systems to provide maximum safety, such that the door can only be in motion when the point device is locked and there are no trains on the track.

6 Introduction Combined services niches perpendicular to the line of the tunnel were also required. With respect to the rock mechanics for the temporary support and the permanent lining, the perpendicular niches were relatively straightforward with the niches designed with an arched roof, (typically of 7.5m span, up to 19m long). The major civil works, E & M works and tracklaying works are now substantially completed with overhead line energisation anticipated shortly. Schedule With the overcoming of all these challenges as well as the compliance of stringent requirements imposed in the job both technically and contractually, the contract is on schedule to be completed in line with KCRC's original programme of October 2003.

7 Drilling Jumpos working inside the tunnel.

8 The tunnel breaking-through in March 2001.

9 An interior view showing the completed tunnel lining and a service niches.

10 A ventilation gantry mounted with axial fans to provide fresh air supply for the tunnel interior.

11 A diamond cross-over track provided in the middle of the tunnel for emergency or routine maintenance of the train operation.

12 The 4-hour FRP (Fire Resistant Period) fire door located at the tunnel cross-over.

13 Forming the Southern Portal at Chai Wan Kok in early Note the highway flyover at the background, which was located within the alignment of the Tai Lam Tunnel where underpinning work was required.

14 Another view of the tunnel portal near the Chai Wan Kok interchange. The cut-and-cover tunnel in the background was also part of the contract packages for DB350.

15 Overview of the works at Chai Wan Kok with the portal provision and the trench for the cut-andcover tunnel in place.

16 The temporary ramp erected in the Southern Portal provided a two-way traffic for access into the tunnel during its construction.

17 Close up of the temporary access ramp leading into the portal.

18 The transfer beam that supported the pier of the highway bridge at the entrance of Tuen Mun Highway.

19 The portal arrangement at location where the tunnel cut underneath the Tuen Mun Highway.

20 A ventilation gantry being assembled inside the Southern Portal before launching into the tunnel interior.

21 Diversion and protection of the existing underground services at the Southern Portal at the early stage.

22 The ventilation building as seen in mid 2002 with the basic structure being completed.

23 An overall view of the cut-and-cover tunnel linking between the Southern Portal and the Tsuen Wan West Station.

24 An overall view of the traffic diversion arrangement for interchange at Chai Wan Kok. The road surface spanning over the cut-and-cover tunnel was a temporary deck supported on steel H-piles.

25 An aerial view of the DB350 cut-and-cover tunnel linking the Southern Portal and the Tsuen Wan West Station. On the left hand side of the photo there is another 300m section of approach tunnel (Contract CC-300 for Tsuen Wan West) to be constructed by another contractor.

26 Photo showing the work arrangement for the cut-and-cover tunnel for DB350. Far at the background of the photo was the work site for the Tsuen Wan West Station.

27 Overview of the cut-and-cover tunnel as seen from the Tsuen Wan By-pass.

28 Constructing of the tunnel cell at the formation level within the tunnel trench.

29 Detail of the formwork being used for the construction of the tunnel cell.

30 Typical cross-section of the twin-track and triple-track tunnel.

31 Flow Chart showing the underpinning operation for the pier support for Tuen Mun Highway at Chai Wan Kok

32 Animated photo showing the arrangement for the underpinning work and the layout of the transfer beam at the Southern Portal.