Vol 20 No 5 (04-2011)
Sai Ying Pun and Hong Kong University Stations Sai Ying Pun to Kennedy Town Tunnel Construction (MTRC Contract 704)


Construction of Sai Ying Pun Station, Hong Kong University Station and Sai Ying Pun to Kennedy Town underground tunnels (MTR Contract 704)

Background

The 3km long MTR West Island Line (WIL) which extends from Sheung Wan to Kennedy Town, will provide convenient transportation service to passengers. The construction of the WIL project began in July 2009 and is expected to be completed in 2014.

MTR Contract 704

The MTR contract 704 was awarded in March 2010 to Gammon Nishimatsu WIL Joint Venture. The scope of construction includes the construction of Sai Ying Pun Station, Hong Kong University Station and Sai Ying Pun to Kennedy Town underground tunnels. In order to empty up required space for the stations in the space limited Western District, some old government facilities, including David Trench Rehabilitation Centre, Center Street Market West Block and the public toilet at Whitty Street were demolished and reprovisioned at nearby vicinity. Also, the contract involves construction of station entrances and backfilling constructions for associated works. The contractor also needs to install and operate a Temporary Barging Point which will be demolished upon the completion of the construction.

On the other hand, the contractor needs to establish as well an enclosed conveyor system to link the Barging Points and Kennedy Town Praya. It is also the responsibility of the contractor to backfilling and reinstating the shafts that located in Kennedy Town Praya and the ones constructed in advanced works at the King George V memorial park of Hong Kong. Apart from these, the contractor also constructs, operates and maintains the explosives magazine constructed at Victoria Road as well as decommissioning and reinstating the magazine after completion of the works. Lastly, there are entrustment works arranged from the Government, including the construction of two footbridges under the same contract.

Information

Sai Ying Pun Station
Sai Ying Pun Station is located 93m below Bonham Road, with a shape of a huge box of 225m in length and divided into upper and bottom levels. The bottom level houses an Island Platform with plant rooms at the western end and certain areas between the two platforms. The upper level is the concourse with plant rooms, operational rooms and staff rooms at the west end. There are totally six entrances in the station.

Hong Kong University Station
Hong Kong University Station is located 70m below Pok Fu Lam Road and it consists of a 250m long box shape station structure with two levels. There are totally five entrances in the station.

Construction method of stations

Both Sai Ying Pun Station and Hong Kong University Station are built in doom-shaped rock caverns produced from Drill and Blast Method excavating from top to bottom progressively on the underground bedrock. Since most of the pedestrian tunnels linking station and entrances are lying deep within rock layer, the Drill and Blast Method is also applied in these parts as it is the preferable method for the hard rock excavation and can shorten construction period since it allows the contractor to construct 24-hours a day at multiple ends concurrently. The nuisance caused to the community, including traffic and environmental, is relatively small. With also a shorter lead-in time than the Tunnel Boring Machine (TBM), it can effectively speed up the progress.

Types of entrances:

1. Conventional station entrance using travellators/escalators connected to the station by adits.

2. Entrance using passenger express lifts connected to the station from ground level to underground. These express lifts are also to be used for evacuation in case of emergency.

Most of the station entrances and passages are constructed by Cut and Cover Method with different types of cofferdam walls.

Only the adits of Sai Ying Pun Station (from B3 Exit at Ki Ling Lane to B1/B2 Exit at Second Street and B1/B2 to Station) will be constructed by Ground Freezing Method due to adverse ground condition envisaged.

Cavern Design

The rock caverns formed for the stations are located wholly in the rock layer, and the entire weight of the station will be transferred to the rock layer which allows at least 5000kPa bearing pressure. The concourse slab is supported by beam-column systems and walls and the design loads from the concourse slab will eventually be transmitted through the supporting columns and walls to the strip and pad footings above rock.

Construction of the Tunnel

The tunnels of Sai Ying Pun Station to Hong Kong University Station and Hong Kong University Station to Kennedy Town Station will be constructed by Drill and Blast Method. The drill and blast method for the single track tunnels and twin tracks / bifurcation sections located in Kennedy Town Station to Hong Kong University Station will be carried out in full-face.

Materials excavated from construction work of the tunnel between Kennedy Town Station and Hong Kong University Station, and 60% of spoil removal from the tunnel between Hong Kong University Station and Sai Ying Pun Station will be transmitted via an enclosed conveyor system. It will eventually be collected in the temporary barging point at the Public Cargo Works Area and shipped away.

Underground Magazine

An underground magazine was built in Victoria Road, with eight explosives storage chambers for storing explosive which are used for the West Island Line Project. A Hazard to Life Assessment Report was done to select the current location for the underground magazine. Its key advantages are being far away from densely populated area and good accessibility to the magazine and all explosive delivery points.

Challenge

The two underground stations are to be built deep in underground rock layer across the densely populated Western District. There is limited space and time for construction work to be carried out. Besides, impacts towards the community and the environment have to be minimized.

Environmental-friendly

Trains are powered electrically and attain the emission free purpose. Once the rail comes into service, road traffic can be reduced and hence improve noise pollution, air quality and living condition of citizens.

Since the West Island Line is a community railway, various measures have been adopted in an attempt to minimize the impacts to the community during construction works.

The dust and noise problem is of most concerned. In an attempt to effectively control dust, construction access are paved with regular water spraying in place; vehicles must be wheel-washed before leaving the sites; dump trucks are equipped with covers; dusty activities are well-covered. An enclosed conveyor belt will be used to deliver most of the excavated rocks from Sai Ying Pun Station and Hong Kong University Station.

For noise control, most excavation processes are to be conducted with acoustic deck / quiet plant. The contractor has also kept constant attention on monitoring the blast vibration to minimize the effect to the vicinity areas. For those processes which cannot be conducted under noise enclosure, such as the demolition and piling of buildings, other corresponding measures are to be adopted, for example, building noise barrier, laying acoustic fabrics and quiet plants etc. Contractors regularly monitor noise and dust generated from construction sites to ensure that requirements from the Environmental Protection Department are fulfilled. "Reusing" excavated materials on site is another environmental practice to reduce most burden from landfills and save natural resources.

Progress and Conclusion

Demolition of Centre Street Market West Block and Whitty Street Public Toilet etc have been completed, and ancillary foundation construction has started. Excavation works has commenced as well. Upon completion of the West Island Line project in 2014, the transportation network in Western District will be more efficient and convenient, thereby alleviating the current problem of serious traffic congestion.


Courtesy acknowledgement :
MTR Corporation Limited
for providing the abovce information and photos