General Description
The 12.5km-long MTR Tseung Kwan O Extension is a HK$18 billion project which provides an extension line from the existing station of Lam Tin in Kwun Tong to the new town of Tseung Kwan O serving a population of about 180,000 in the district.

The new line comprises of 5 stations, namely the Yau Tong, Tiu Keng Leng, Tseung Kwan O, Hang Hau and Po Lam Stations. In addition, a further extension will be provided in a few years' time from the Tseung Kwan O Station to a new station at the eastern end of the new town which serves also as the depot of the Tseung Kwan O Line. Residential development with more than 20000 housing units will be provided around this depot area.

The civil work of the project subdivided into 13 main contracts with the first contract commenced in November 1998. The line was put into full operaion in August 2002.

The alignment
The alignment of the line starts immediately from the existing station of Yau Tong eastward through a 1.2km-long drill-and-blast tunnel and another 300m cut-and-cover tunnel before reaching the Yau Tong Station. Immediately leaving the Station, the rail cuts into another 2.2km-long drill-and-blast tunnel (Black Hill Tunnel), the outlet of which joins almost to the station structure of the Tiu Keng Leng Station. Further to the eastern direction, a section of 0.9km long cut-and-cover tunnel links between the station of Tiu Keng Leng and the adjoining Tseung Kwan O Station on the newly reclaimed land of Tseung Kwan O Bay. Leaving the Station, the alignment continued in another 1.8km-long section of cut-and-cover tunnel which heads slightly northwestward into the Hang Hau Station. Finally, through the final section of 1.4km-long cut-and-cover tunnel, the line reaches its terminal station at Po Lam.

The extension to the depot comprises of a section of 0.8km cut-and-cover tunnel which branches off from the approach tunnel about 0.6km eastward from the Tseung Kwan O Station. The alignment of this extension then cuts into the Pak Shing Kok hill through a 2.0km-long drill-and-blast tunnel and reaches its eastern portal, which serves also as the entrance to the depot facilities.

Construction Features of the Major Work Portions

1. Tunnel between Lam Tin and Yau Tong Station

   The existing Kwun Tong Line links to the Tseung Kwan O Extension Line directly through a 1.2km-long drill-and-blast tunnel cutting from the eastern end of the station structure of Lam Tin towards Yau Tong. The tunnel is in twin-tube design with one track slightly located on top of the other to convenient the interchanging arrangement provided in the Yau Tong Staion. Tunnel portal is situated in the western end with access ramp for the handling of equipment and excavated spoil (Photo 1).
   

2. Yau Tong Station

   The station situates in a shallow trough which is formed by cutting into a solid rock terrace averaged 12m above the nearby level (Photo 2 and 3). Since the contract involved the formation of the undulating ground around Yau Tong Road and Cha Kwo Ling Road with area more than 12 hectares (Photo 4 and 5) a temporary pier facility (Photo 6) was set up in the nearby Kwun Tong Tsai Bay for the dumping of the excavated spoil. The box-shaped station structure measures about 450m x 50m (Photo 7, 7a, 8 and 9), with the track and passenger platform built on the formation level (about 12mPD) and the entrance concourse at an elevated podium structure 25m above. Besides serving as an interchanging station to the Island Line, there are also provisions of pedestrian footbridges leading to the nearby Yau Tong Estate (Photo 10).
   

3. Approach tunnel linking Yau Tong Station and the Eastern Harbour Crossing
   
   The Tseung Kwan O Line connects into the Island Line through the existing track within the Eastern Harbour Crossing (EHC). The 0.8km-long approach tunnel is slightly curved in a 600m radius, linking the Yau Tong Station to the tunnel approach of the EHC. This section of tunnel comprises of three major sub-sections, including the approach section leading to the Yau Tong Station (Photo 11), a cut-and-cover tunnel section formed in the rocky sub-soil of the nearby ground (Photo 12 and 13), and a merging section joining into the existing tube of the EHC (Photo 14). Provision of ventilation facility is located on top of the approach tunnel near the merging section (Photo 15). Complicated phasing requirement is introduced in the construction process, especially when doing the section approaching EHC where traffic diversion is required in order to allow the tunnel to cut into the side of the EHC vehicular approach (Photo 16).
   
   
4. Black Hill Tunnel (located between Yau Tong and Tiu Keng Leng Station)
   
   Due to spatial constraint, this 2.0km-long tunnel fits almost the entire alignment between the Yau Tong and Tiu Keng Leng Station, leaving less than 300m on each side (Photo 17 and 18) as approach before joining the station structures. In addition, the track arrangement in the stations in particular to cater for the interchanging requirement merging to various Lines, further complicates the tunnel configuration and alignments. As a result, the provision of the tunnel portals and the teething arrangement with the station contracts became very difficult.

   The tunnel alignment is arranged in a four-tube configuration at the two ends abutting the approach section. It then converts into two-tube arrangement in the centre section (Photo 19). A 20m diameter service shaft (Photo 20) was also provided in the southeastern end of Lei Yue Mun Road for emergency, ventilation and material access purposes.
   

5. Tiu Keng Leng Station
   
   The Station situated partly on the previous Tiu Keng Leng village and partly on the formed land by cutting into the rocky slope in the neighborhood around (Photo 21 and 22). The station formation process involved the cutting and removal of more than 1600000m3 of spoil mainly in solid rock, which includes the forming of a 480m x 55m x 20m deep rock trough (Photo 23) to house the underground portion of the station structure. The four-level underground structure was directly seated on raft on the formed trough and constructed using bottom-up method (Photo 24). The lower 2 levels are used as the passenger platform in double-deck arrangement for interchanging purpose for the Kwun Tong Line and Tseung Kwan O Line. The contract also included the construction of a ground transportation and passenger interchanging facility (Photo 25) and a 600m section of cut-and-cover tunnel heading to the Tseung Kwan O Station direction.
   
   
6. Tseung Kwan O Station
   
   The Station situated in a newly reclaimed land with provision for a ground transportation and passenger interchanging facility that covered an area about 5 hectares in size (Photo 26). Except for the entrance concourse, majority of the station structure is buried underground. The Station was constructed using bottom-up arrangement (Photo 27, 27a and 28) within a gigantic trench lined with diaphragm wall on both sides and supported with truss-form standard strut members. The contract also included the construction of the ground transportation facilities (Photo 29) and two sections of approach tunnel on both ends of the station. The approach tunnel was constructed using bottom-up arrangement similar to the station, but with several locations at existing road junctions using top-down arrangement in order to provide undisturbed traffic at the ground level.
   
   
7. Hang Hau Station
   
   The Station situated in a reserved land within the center of a cluster of densely populated private housing estates (Photo 30). Majority of the station structure, including the 120,000 m2 ground transportation facility, was constructed underground (Photo 31). The 16m-deep main station structure was constructed using top-down arrangement (Photo 32) for this method could assure the least disturbance caused to the surroundings during the excavation process. While the 9m-deep transportation facility was built in bottom-up manner (Photo 33) due to the reason of minimizing cost. The approach tunnel at both ends of the station cut across two existing roadways at the ground level, which was thus constructed using top-down arrangement with the minimal disturbance caused to the surface traffic.
   
   
8. Po Lam Station
   
   This Station is the terminal station of the Tseung Kwan O Line (Photo 34). The box-sectioned tunnel (Photo 34a) for the rail track ascends slowly after leaving the Hang Hau Station and levels to ground surface before reaching the station of Po Lam (Photo 35). The station structure is built at grade with bored piles as foundation, (Photo 36). The superstructure measures about 380m x 40m, with the passenger platforms located on the ground level (Photo 37).
   
   
9. The Depot
   
   The Depot, including the nearby areas for future development, is located on a 26 hectares reclaimed land (Photo 38) in the southeastern corner of the new town of Tseung Kwan O. Besides serving as the maintenance depot of the line, the depot is provisioned to accommodate residential development to house about 20000 residential units at its final stage. The depot structure is a one-level podium deck, about 25m above ground, with minor structures scattered underneath to provide logistics, services and support for the maintenance of the train (Photo 39). The layout of the depot structure is basically in column and transfer beams (Photo 40) arrangement with span ranging from 12m to 30m. Method of construction is rather traditional, all structures are cast-in-situ (Photo 41), with foundation using bored piles on isolated rafts and stiffened with tie beams (Photo 42), rectangular-sectioned steel form for columns (Photo 43), panel form for transfer beams, and plywood soffit supported on I-beam joist and propped for the deck structure. Majority of the transfer beams were post-tensioned, and with some built-in services trough decked with precast panels. Starter bars were provided over the podium deck for linking to the superstructures of the future residential development.
   
   
10. Pak Shing Kok Tunnel (located between half way of Tseung Kwan O Station and Hang Hau Station, and the Depot)
    
    This is a drill-and-blast tunnel excavated in extremely hard volcanic rock. The tunnel is in twin-tube design with branching-off into four at the eastern portal when approaching to the depot entrance. After blasting and treatment to the exposed rock surfaces, a smoothing layer of shotcrete was applied as the underlay (Photo 44), before the installation of the waterproofing membrane (Photo 45 and 46), and the placing of the 250mm thick lining using Grade 40 mass concrete. A 12m long shutter form was used to construct the tunnel lining (Photo 47). The shutter was set up on short length of rails in order to move the form easily to the onward work position. The final finishing of the tunnel interior can be seen in Photo 48 and 49.
    
    
11. Cut-and-cover tunnel in general
    
    Cut-and-cover tunnel forms a major part of the rail alignment in the Tseung Kwan O Line. Majority of the cut-and-cover tunnel was constructed in the newly reclaimed land in the previous Junk Bay (Photo 50). The tunnel was basically in standard box-section, measure 14m x 8m in average, with structural partition wall in the center to form two separated tubes. Some tunnel sections are double-decked for platform interchanging purpose (Photo 50a), as in the approaches to the Yau Tong, Tiu Keng Leng and Tseung Kwan O Station.

    Excavation of the tunnel was done in bottom-up manner, with side support using diaphragm wall, or for some shallow or non-typical sections, using sheet pile or pipe pile wall (Photo 50b, 50c and 51). Ground water control is a crucial problem in most situations for a large portion of the sections are located in made ground with some laid less than 20m from the seawall (Photo 52 and 53). For the tunnel structure, a travel-type tunnel formwork system was used in the construction (Photo 54 and 55), with some non-typical sections employing usual large-panel type shutter form (Photo 56 and 57).

Summary

1. Composition of work along the alignment:
   
   

   Drill-and-blast tunnel	5.4 km
   Cut-and-cover tunnel	4.2 km
   Stations, junctioning and approach sections	2.9 km

   
   
2. Ground/sub-soil condition and earthwork involved in the major work portions
   
   

   Major work segment	Ground/Sub-soil condition	Work involvement	Approximate quantity
   Formation of the Cha Kwo Ling and Yau Tong area	Mainly volcanic rock	Formation of the nearby undulating foothill into terraced ground for the station structure of Yau Tong and to provide land for future residential developments.	Land area involve: 12 hectaresExcavation: 1400000 cube metre
   Yau Tong Station	Volcanic rock	Forming a shallow trough for the housing of the station structure	Excavation: 120000 cube metre
   Black Hill Tunnel	Volcanic rock	Forming of the drill-and-blast tunnel and a service portal	Excavation: 150000 cube metre
   Formation of land for Tiu Keng Leng and Tsung Kwan O Station	Mainly volcanic rock	Formation of the previous Tiu Keng Leng Village to provide leveled land for the Tiu Keng Leng Station, as well as to form new land by reclamation for the Tseung Kwan O Station. The works also included the provision of land nearby the stations for residential or related development purposes.	Total areas of land formed: 28 hectaresExcavation (by rock cutting): 1600000 cube metre
   Tiu Keng Leng Station	Volcanic rock	Forming a rock trough for the housing of the station structure	Excavation : 550000 cube metre
   Tiu Keng Leng Station	Volcanic rock	Forming a rock trough for the housing of the station structure	Excavation : 550000 cube metre
   Tseung Kwan O Station	Made ground	Forming of the station structure using bottom-up method	Excavation: 280000 cube metre
   Hang Hau Station	Made ground	Forming of the underground station and ground transportation facility structure	Excavation: 800000 cube metre
   Po Lam Station	Made ground	Cutting down of the surface soil to form the rafts of the station structure	Excavation: 20000 cube metre
   Pat Shing Kok Tunnel	Volcanic rock	Forming of the drill-and-blast tunnel and portal facilities at both ends	Excavation: 130000 cube metre
   The Depot and the related development	Made ground and partly decomposed rock	Formation of land for depot and related residential development purpose. General excavation by cutting down of the surface soil to form the rafts for the construction of the depot structure	Total newly formed land: 26 hectaresGeneral excavation: 100000 cube metre