Bringing the MTR to Ho Man Tin and Whampoa
By Angela TAM
Expanding an existing railway network is no easy task, the more so in a densely populated city like Hong Kong. When a decision was made to extend the Kwun Tong Line to Whampoa at the eastern edge of the Kowloon Peninsula, two key challenges immediately presented themselves: where to find the space to accommodate the two stations in Ho Man Tin and Whampoa respectively; and how to integrate it with the future Shatin to Central Link (SCL), which will offer residents an alternative route to the New Territories in the north and the northern shores of Hong Kong Island in the south.
The Kwun Tong Line Extension (KTE), for which Arup and Hyder are lead consultants, is a 2.6 km long extension to the existing Kwun Tong Line that runs from the existing Yau Ma Tei Station to Ho Man Tin Station and Whampoa Station, the new terminus station.
Finding sites for the two new stations proved challenging for different reasons. Ho Man Tin has a hilly terrain where a combination of public and private residential developments and trunk roads drove the selection of a hillside location that involved extensive site formation works in order to develop what will become the largest interchange station in the existing MTR network. Ho Man Tin Station is an eight-level station located on a site with a height difference of 70 m, from +45 mPD at the highest point on Chung Hau Street to -25 mPD at the lowest platform level. Creating it required the excavation of about 750,000 cu m of soft and hard material.
The search for a site for Whampoa Station within the densely built-up private residential estate in the area ended with a practical split of the station into an east and a west concourse on a narrow strip of private land. Because that narrow strip is a main road, constructing the underground station without disrupting surface traffic necessitated the implementation of constantly changing temporary traffic management schemes (TTMS) as well as liaison with the community over the use of heavy construction equipment in close proximity to homes and offices.
Ho Man Tin Station
Ho Man Tin Station has eight levels with a total floor area of 58,000 sq m. The top three levels are entrance structures connecting the residential areas uphill as well as Chatham Road North. Below the station entrances are the station concourse, a mezzanine floor accommodating all the plant rooms, and two platform levels and a transfer lobby. The KTE platform comes in at the lowest level with the SCL platforms two levels above. As a result of KTE's and SCL's alignment, they will intersect at a sharp angle at Ho Man Tin Station, thereby generating a cruciform-shaped interchange station.
"This is the first cruciform-shaped interchange station on the MTR network. It reflects the constraints imposed by the alignment of KTE and SCL. The transfer lobby was created between the KTE and SCL platform levels to make passenger distribution more efficient," said MTR KTE general manager Ir James Chow.
A number of existing structures were demolished prior to the construction of Ho Man Tin Station, notably disused air raid tunnels which were built during the Second World War.
Excavation for Ho Man Tin Station involved the removal of a top layer of soft material and the excavation of the rock underneath by drill and blast. To protect residential buildings and trunk roads in the area, the excavation was carried out with extensive blast protection in the form of a blast cage within another protection cage until the site had been sufficiently enlarged for a protective roof to be erected. Mechanical excavation was carried out in areas designated as no blast zones predominantly due to proximity to sensitive structures and major trunk roads.
A combination of soil nails and rock bolts was used to support steep temporary cut slopes up to 70 deg with a total of 2,900 soil nails up to 28 m long being installed. Using this tie-back lateral support, instead of the conventional waling and strut system, enabled the contractor, Nishimatsu Construction Co Ltd, to make full use of the excavated space for material delivery and construction logistics. Structural work for the station was thus supported by the setting up of six tower cranes and four material hoists. Areas were also set aside for steel bending and a temporary rock spoil stockpile.
Ho Man Tin Station is served by five entrances located at Chung Hau Street, Chung Yee Street, Yan Fung Street, Chatham Road North and Fat Kwong Street respectively. A system of pedestrian links totalling 1.2 km in length will provide convenient, all-weather access to and from the housing estates in uphill Ho Man Tin as well as the urban areas of Hung Hom. The Essential Public Infrastructure Works (EPIW) includes a pedestrian subway, footbridge and covered walkway connecting Oi Man Estate and Ho Ma Tin Estate and a footbridge to Chatham Road North.
Whampoa Station is located underneath an existing road and is bounded on all sides by multi-storey private developments. The majority of the station structure is underground except for ventilation shafts and entrances at an east concourse and a west concourse serving residents from both sides of Whampoa Garden. The concourses and the platform structures were constructed by the cut-and-cover method. Steel pipe piles were installed to support the excavation using 12 m high piling rigs that were less than 3 m from some adjacent buildings.
A number of measures were adopted to address the community's concerns over noise and safety. Instead of drill-and-blast excavation, mechanical splitting was adopted for excavation of the 100 m long platform tunnel at a depth of -20 mPD. The average progress rate of the drill-and-split method was approximately 300 mm/day but did not involve the use of explosives, the source of stakeholders' concerns. Where the piling work in sensitive areas could disrupt normal office operations, the project contractor, Chun Wo-Hip Hing Joint Venture, agreed to curtail the work to within the lunch hour and between 5:00pm and 6:00pm to minimise the disruption. Community liaison group meetings were also held regularly to keep stakeholders informed of project progress and forthcoming works.
Temporary road decks were placed over the excavation footprint and various TTMS were implemented as construction progressed, both to maintain normal vehicular traffic flow and to facilitate utility diversion works. More than 100 temporary traffic management schemes were implemented to enable the piling and decking installation.
To provide access to the underground site, a small delivery opening was incorporated into the road deck to allow the transport of materials. The construction logistics had to be carefully planned and coordinated due to the need of multiple parties to make use of limited access, which was compounded by the lack of space for holding and storage of delivered equipment and materials. The situation was improved following the completion of the KTE tunnels and track work, which facilitated the use of works trains to deliver equipment such as cable drums, transformers and compressors to site.
The running tunnels for KTE were mostly within rock with sections of tunnels under shallow rock cover. The drill-and-blast method was adopted for the excavation. According to Ir Chow, the Corporation considered the option of using tunnel boring machines for the excavation but the lack of space for the staging works in both Yau Ma Tei and Whampoa drove the decision to adopt drill-and-blast excavation.
"Most parts of the tunnels were in rock. Since the drill-and-blast is a proven excavation method within Hong Kong and contractors are very familiar with and have accumulated years of experience and expertise using this tunnelling method, we decided to take up this option," Ir Chow said.
In view of the fact that many buildings along the tunnel alignment underneath Wu Hu Street are more than 40 years old and have few or no building records, the 'pilot-and-strip' method was used for the excavation of critical sections of the tunnels. The method involved blasting a small, pilot section with further separation from residential buildings using a higher charge weight, then enlarging the tunnel to its full size.
To delink the tunnel excavation from the station work, two access shafts were excavated at Wylie Road and Fat Kwong Street playground respectively to allow the tunnel excavation to start concurrently with the station work. To connect the new KTE tunnels with the existing Kwun Tong Line, the overrun tunnel at Yau Ma Tei Station was enlarged and modified using mechanical means, with access via a narrow shaft within an operational substation building.
Two types of travelling formwork, for twin-track sections and single-track tunnel, were used for construction of the tunnel lining.
KTE was commissioned in two stages. The tunnel section was first commissioned for the overhead line energisation and train tests with standard commuter trains deployed from the Kowloon Bay depot. The stations were commissioned in the second stage where testing and commissioning were witnessed by the regulatory departments. To meet a tight programme, the works carried out by different contractors were closely coordinated to ensure statutory inspections could proceed as scheduled while other work continued.
Trial running and stress tests on railway systems and station facilities such as platform screen doors, ticket machines and gates were conducted for about one month prior to the extension's opening in October. The platform screen doors at the two new stations, for example, were taken through more than 550,000 cycles of tests.
The construction of KTE began in mid-2011. After a five-year wait, residents of Ho Man Tin and Whampoa can finally enjoy the convenience of a quick train ride to Kowloon via the Kwun Tong Line. Train service to the New Territories and Hong Kong Island via the Shatin-Central Link is planned for 2019 and 2021 respectively.
The alignment of Kwun Tong Line Extension. Images: MTR
The hilly site picked for Ho Man Tin Station
Cross section of Ho Man Tin Station
Congested site in Whampoa
Standard commuter trains were deployed for train tests