3
Project Description and Construction
Methodology
The HHS will be located underneath the existing podium structure covering
the former Hung Hom Freight Yard at Hung Hom, except its shunt neck, launching/
retrieval and emergency tracks which will extend outside the podium as they
connect to the tracks to be constructed for the SCL (TAW to HUH) section. It is
also necessary to make appropriate changes in the design of Hung Hom, Kai Tak
and Diamond Hill Stations and its associated alignment and facilities proposed
in SCL (TAW-HUH) and SCL (MKK-HUH) EIA Reports to suit this operational
arrangement. This chapter presents the key design elements of the Project. The construction methodology for all the key
elements would also be discussed. The indicative location of the Project is
shown in Figure
1.1.
Minor updates to the
Project, such as locations and structures, could occur during further design
development and construction, and these would be updated through the monthly
EM&A reporting.
A summary of the general design of the key elements of the Project is
given in Table 3.1
below. The demarcation of permanent works for Hung Hom, Kai Tak and Diamond
Hill area considered under this Project is illustrated in Figure 3.1.1a to 3.1.3a.
Table 3.1: Summary of Key Elements of SCL
(HHS)
|
Key Elements |
Location |
Key Works
Required |
|
Stabling
Sidings |
HHS |
·
Construction of a train stabling sidings
under the existing deck of Hung Hom Station ·
Construction of a fan area to the north of
the train stabling sidings ·
Construction of tracks to the north and
south of the stabling sidings to enable manoeuvring of trains to and from the
stabling to the SCL (TAW-HUH) alignment ·
Construction of noise mitigation over the
fan area and near the shunt neck. |
|
Stations and its
associated alignment and facilities |
HUH
Modification |
·
Construction of underground platforms ·
Modification work of HUH podium ·
Construction of plant rooms underneath HUH
podium ·
Construction of ventilation shafts/plant
and CLP transformer plant ·
Others such as utility diversion |
|
|
KAT |
·
Construction of Kai Tak Station and
associated tunnels ·
Construction of underground refuge sidings
of about 300m in length as part of the Kai Tak
Station construction |
|
|
DIH |
·
Construction of the interchange station
with existing Kwun Tong Line at Diamond Hill ·
Site formation to connect station to
adjacent existing ground. ·
Construction of SCL (TAW-HUH) tunnel
section approaching to Diamond Hill Station to suit the DIH location without
DHS. ·
Others such as utility diversion in Diamond
Hill CDA site arising from the deletion of DHS |
3.2.2
Temporary At-Grade
Works Sites/Areas
Figure 3.1.1 to Figure 3.1.3 shows the
locations and demarcations of all the at-grade temporary works sites/areas. To
minimize the potential disturbance and impact to the public and environment,
the major works sites/areas are typically located at the site of the permanent
works. To support the construction of the Project, additional temporary works
areas would be required within SCL scheme / project boundary for the provision
of site office, storage of materials, utility, temporary traffic management scheme, temporary accesses
/ bridges, silos and ground treatment. The locations of works areas have been selected
with consideration of their accessibility and suitability for construction
works and future permanent facilities. The EIA report has included locations of
the works sites/areas for the Project and indicated the extent of SCL scheme /
project boundary (as indicated in Appendix
3.1) within which minor activities/ works for supporting
the construction of the Project may occur based on the latest information at
the time of writing. These are illustrated in Figure 3.1.1 to Figure 3.1.3. Subject
to actual site conditions and constraints, minor preparatory works could also
be required to be conducted in and around the boundary indicated in the EIA
report. However, these would only be short-term without inducing major
environmental implications to nearby sensitive receivers. With the
implementation of appropriate standard control measures and good site practices
for construction works, no adverse environmental impact would be anticipated.
3.3.1
Train Stabling
Sidings and Hung Hom Station
HHS and HUH are located
within the densely built up area in Hung Hom. The lack of space available at
the surface for locating HHS and HUH and the need of connecting to future SCL
(TAW-HUH) alignment poses constraint on the location and design of HHS and HUH
and thereby limited the options of construction methods available.
The tentative construction
methodologies for the HHS and HUH are summarized below.
Table 3.2: Tentative
Construction Methods for HHS and HUH
|
Key Design
Elements |
Tentative Construction
Methodologies |
|
HHS |
Train
stabling sidings under the existing deck of Hung Hom Station
Fan area to the
north of the train stabling sidings
Shunt neck to
the north of the train stabling sidings
Launching and
retrieval tracks to the south of the train stabling sidings
|
|
HUH
Modification |
Hung Hom
Station and Associated Plant Rooms
Ventilation shafts
and plant rooms
Others such as utility
diversion ·
Typical smaller scale excavation,
concreting etc |
Both the stabling sidings and HUH will be located underneath the existing podium. Two construction methods were considered appropriate for further investigation for the areas under the existing podium, which are:
·
Temporary Open Deck
Scheme; or
·
Underpinning Scheme.
Temporary Open Deck Scheme
This construction method is to “remove” the constraints imposed by the existing podium deck arrangements. The affected part of the existing podium deck would need to be demolished prior to the construction of SCL tunnels.
In order to minimize any potential implication to existing infrastructure (e.g. HKC, existing Hung Hom Station, Metropolis Tower, Metropolis Residence and Harbour Plaza Metropolis), a staged construction scheme must be developed to minimize the duration and extent of podium deck to be removed at any one time. The main tunnel works for SCL would be deferred until after each stage of podium deck reconstruction is completed, with only the temporary cofferdam walls being installed at each stage of the deck removal. Temporary reprovisioning of the affected HKC facilities would also be required.
Underpinning Scheme
This construction method is to construct new foundations and columns to underpin the existing podium deck structure. Once the loading is successfully transferred to the new supporting structure, those columns and foundations which are obstructing the SCL tunnel are able to be demolished.
The underpinning works are more complex than the open deck scheme as the mid-level walkway and plant room locations must be maintained throughout construction (as the facilities will remain open) and the headroom under these structures must be limited to 5m. The CLP substation and chiller plant room which serve the existing HUH will also be required to be maintained during all construction stages. In addition, no cofferdam wall could be undertaken within this area as maintenance access will be required. However, in order to avoid impact with existing foundation locations, the alignment of the cofferdam wall and temporary retaining wall will require precision engineering.
After the underpinning works, the connection between the column base and the pile cap can be cut. An excavation with layers of strut and waling can then commence in stages and a bottom up method could be used. Underpinning schemes have been modified to minimize the engineering difficulties as this is the scheme favoured by stakeholders such as HKC due to minimal interference with their activities.
The benefits and constraints of the two construction methods are compared in Table 3.3.
Table 3.3: Benefits and Constraints
of the Proposed Construction Methods
|
Station Works Construction Method |
Benefits |
Constraints |
|
Temporary Open Deck Scheme |
· Easier construction method and simple form of design. · No need for long term continuous inspection and maintenance of
permanent bearings. ·
Shorter construction
programme. |
· A staged construction scheme has to be developed to minimise as much
as possible the duration and extent of podium deck to be removed at any one
time. · Temporary reprovisioning of the affected HKC facilities would also be
required which will have concern from HKC due to the potential interference
on activities. · Since part of the deck needs to be demolished and some of the
construction activities will be exposed. Relatively higher construction noise
and dust will be anticipated. Additional mitigation measures would be
required to minimize the impact. |
|
Underpinning Scheme |
· This method in general is favoured by stakeholders, such as HKC due to
minimal interference with their activities. · Less environmental impacts, through reduction in construction noise,
dust and waste. · Less impacts on community through reduction in construction noise and
dust; · Existing evacuation route and emergency vehicular access for the HKC
would not be affected. · This method can be modified to minimize the engineering difficulties. |
· More difficult construction method and very complex in design. · Continuous inspection and maintenance of permanent left in place
bearing in future are required. · Longer programme is expected for underpinning due to the complexity of
works. |
Since the temporary open deck scheme
requires demolition of part of the deck and resulting exposure of major
construction activities, nearby sensitive receivers would experience adverse
construction noise and dust impact and require additional mitigation measures.
Furthermore, HKC operator, LCSD, raised objection to the use of temporary open
deck scheme. Therefore the underpinning option has been selected as the preferred
construction method for HHS and HUH.
As constrained by the geographical
and engineering constraint, the approach tracks in north fan area, shunt neck
and launching/retrieval and emergency tracks are located at grade level.
Therefore, it is considered appropriate to adopt traditional construction
methodology as described in Table 3.2
and it would be futile to seek out alternative construction methods.
3.3.2
DIH and KAT
Both DIH and
KAT would be underground. Their tentative construction methodologies and
associated entrances are summarized in Table 3.4.
Table 3.4: Tentative Construction
Methods for DIH and KAT
|
Key Design
Elements |
Tentative
Construction Methodologies |
|
KAT |
Underground Station
Underground
Refuge Sidings
KAT
Associated Tunnel
|
|
DIH |
Underground
Station
Others such as utility
diversion
|
A cavern station could be
constructed by drill-and-blast method to minimise disturbance to surrounding
areas, only if it situates within hard rock zone with sufficient rock cover to
the station crown. However, DIH and KAT
will situate in soft ground, drill-and-blast method would not be applicable and
DIH and KAT will adopt cut-&-cover and open cut method respectively.
According to the latest programme, the construction works for
the Project would commence in 2012 with completion in 2018.