Table of Contents
2.4 Consideration
of Different Alignment Options and Built-forms
2.5 Justifications
and Consideration of Alternative Built-forms
2.6 Consideration
of Alternative Construction Methods and Sequences of Works
2.7 Description
of the Selected Alignment and Proposed Engineering Works
2. description of the project
2.1 Introduction
2.2 Scope of
the Project
2.3 Need of
the Project
2.4 Consideration
of Different Alignment Options and Built-forms
2.5 Justifications
and Consideration of Alternative Built-forms
2.6 Consideration
of Alternative Construction Methods and Sequences of Works 2-
2.7 Description
of the Selected Alignment and Proposed Engineering Works
2.8 Construction
Programme
2.9 Concurrent
Projects
Table 2‑1 Evaluation of Conformed and Alternative
alignment for Tsuen Wan Road
Table 2‑2 Anticipated
Development Schedule of Concurrent Projects
Table 2‑1 Evaluation of Conformed and Alternative
alignment for Tsuen Wan Road
Table 2‑2 Anticipated Development Completion Dates of
Concurrent Projects
Figure 2-1 General Layout of
the Project
Figure 2-2 Typical Sections
of Tsuen Wan Road in the Project
Figure 2-3 Project Construction ProgrammeTsuen Wan Rd
Upgrading-Investigation Construction
Programme for Tsuen Wan Road UpgradingConstruction Programme for
Tsuen Wan Bypass, Widening of Tsuen Wan Road between Tsuen Tsing Interchange
and Kwai Tsing Interchange and Associated Junction Improvement Works
Figure 2-4 Project Works
Areas
Figure 2-5 Typical Construction
Sequence
Figure 2-6 Alignment Options
2.1.1
This Chapter presents a description of the proposed engineering scheme,
and describes the process by which the preferred engineering approach has been
developed.
2.2.1
The Project is mainly to upgrade and widen the existing 2.8km Tsuen Wan
Road (TWR) between Tuen Mun Road (TMR) and Kwai Tsing Interchange. Major scope of the Project are as follows:
a)
construction of dual one-lane viaducts
parallel to the existing TWR between Tuen Mun Road and Hoi Kok Street;
b)
construction of dual 2-lane viaducts
parallel to the existing TWR between Hoi Kok Street and Tsuen Tsing
Interchange;
c)
widening of the existing at-grade section
of TWR from dual 3-lane to dual 5-lane between Tsuen Tsing Interchange and Kwai
Tsing Interchange;
d)
modification of the associated existing
junctions;
e)
provision of noise mitigation measures;
f)
reprovision/ modification to existing
crossing affected; and
g)
provision/ reprovision of associated
civil, structural, geotechnical, landscaping and associated drainage, traffic
installation and lighting works.
2.2.2
Figure 2-1 shows the general layout of the Project. Figure
2-2 shows the typical sections of TWR in the Project.
2.3.1
TWR is part of the strategic road network carrying out a significant
volume of long distance traffic through Tsuen Wan area, between the north-west
New Territories, Kowloon and Hong Kong Island. It also functions as a
collector-distributor road in Tsuen Wan.
2.3.2
Future development of north-west New Territories, operation of MTRC
west rail and corresponding residential and commercial development, as well as
the planned MTR residential development TW5, TW6 and TW7 would definitely lead
to an increase of traffic demand of the region. Currently, peak V/C ratio has already reached 1.0, which leads to
very often traffic congestion. It is
anticipated that the V/C ratio on TWR will be further increased up to 1.2 by
2016, and leading to even more serious traffic congestion problem.
2.3.3
In order to relieve the foreseeable traffic congestion problem,
implementation of the Project is considered necessary.
2.4.1
Detailed investigation on the possibilities of different alignment
options and built-forms have been conducted in December 2002, as presented in the report “Working
Paper on Preferred Alignment” (the Report) prepared by
Scott Wilson Ltd. Summary of the major findings and conclusions are listed in the
following paragraphs.
2.4.2
The widening of TWR can essentially be split into 3 geographic areas (Figure 2-1):
·
Area 1 – The section between Kwai Tsing
Interchange and Tsuen Tsing Interchange
·
Area 2 – Under Bridge 38/2 (where Wing
Kei Road crosses the TWR)
·
Area 3 –Section between Tsuen Tsing
Interchange and TMR
2.4.3
The reasons for considering the widening in the 3 geographic sections
are as follows:
a)
Area 1
– Between Kwai Tsing Interchange and Tsuen Tsing Interchange: This area
is the subject of a separate Report in which economic factors are also
considered, and the normal provision of adequate capacity for traffic is not
the prime criterion for the evaluation of the dual 5-lane and 4/5-lane
carriageways proposed over this section.
b)
Area
2 – Under Bridge 38/2: As TWR will be D4
lane under the bridge, the selection of either a D5 or a 4/5 lane configuration
upstream does not affect the layout through the bridge because:
i)
If it is 5-lane upstream, the junctions
with Texaco roundabout will be configured as lane drops/gains;
ii) If
it is 4-lane upstream, the junctions will be conventional merges or diverges;
and
iii) Furthermore
either configuration for Bridge 38/2 can be selected for either the conforming
or monolithic widening option. The
Bridge widening can therefore be considered as an independent area.
c)
Area 3 –
Section between Tsuen Tsing Interchange and TMR: There are two
sub-sections in this section:
i)
Tsuen Tsing Interchange to Tai Chung Road
Interchange. This is a weaving section and any attempt to use a monolithic
approach past Clague Garden Estate and to then diverge and use separate
viaducts closer to Tsuen Tsing interchange will significantly exacerbate
weaving as it entails reducing the distance between the Tai Chung Road on-ramp
merge and the diverge to Tsuen Tsing Interchange.
ii) Tai
Chung Road Interchange to the junction with TMR. This is not a weaving section
but the interchange with Tai Chung Road necessitates either a scheme with
independent viaducts or a wholly different arrangement assuming monolithic
widening.
As a result, the widening of these two
sub-sections (i.e. (c)(i) and (c)(ii) are considered together
as either monolithic or independent options.
2.4.4
Five options have been considered for this Project (Figure 2-6). The first three options are for the section
between TMR and Wing Kee Road (Bridge 38/2) and the other two options are for
the section under Bridge 38/2. The
options are:
·
Option
1: To widen TWR [North of Wing Kee Road]
by the provision of new viaducts on either side of the existing bridges. The
structural elements are separate, which simplify the bridge design and have
important implications on the operation of the scheme. This is referred to as
the “Conforming Option”.
·
Option
2: To widen TWR [North of Wing Kee Road]
by the provision of new viaducts generally on either side of the existing
bridges by stitching together the various structural elements to form a
monolithic mainline, which allows the realigning of the centreline to suite
constrained areas. This is called the “Monolithic Option”.
·
Option
3: Modification of the up-ramp at Clague Garden
Estate to allow the mainline widening to fully overlap the up-ramp and reduce
land resumption.
Section B – Section of Tsuen Wan Road [South of
Wing Kee Road (Bridge 38/2)]
·
Option
4: At Bridge 38/2 the mainline can be widened
from 2 to 4 lanes by demolition of the narrow centrespan and
reconstructing/widening it to allow 4 contiguous lanes. This is referred to as
the “Contiguous Scheme”.
·
Option
5: At Bridge 38/2 the mainline can be split so
that the existing lanes pass under the centrespan, and the additional lanes
pass under the side-spans. This is called the “Split Scheme”.
2.4.5
Furthermore, the environmental impact of preferred and alternative
alignments has been listed as below.
Table
2‑1 Evaluation of Conformed and Alternative
alignment for Tsuen Wan Road
Scheme |
Environmental Benefit |
Environmental Dis-benefit |
Option 1 |
·
less waste generated due to the
retaining of existing ramps and bridge parapet ·
avoid night-time construction works ·
reduce construction period and staging |
·
tall piers or portal frames above
ground level across Castle Peak Road and Hoi Shing Road to cause the
intrusive visual impact ·
more land take required at Clague
Garden Estate |
Option 2 |
·
less intrusive visual impact ·
no land take required at Clague Garden
Estate due to symmetrical widening of existing bridge |
·
more waste generated due to the
demolition of existing ramps and bridge parapet ·
extensive temporary traffic management
and sequence of construction required due to demolition of existing ramps and
construction of new ramps ·
complex widening of monolithic
structure required ·
night-time construction works may be
required ·
longer construction period and
associated impact |
Option 3 |
·
less intrusive visual impact ·
less land take required at Clague
Garden Estate due to symmetrical widening of existing bridge |
·
more waste generated due to the
demolition of bridge parapet ·
complex widening of monolithic
structure required ·
night-time construction works may be
required ·
longer construction period and
associated impact |
Option 4 |
·
less impact on existing
slopes and minimize the rock excavation |
·
more waste generated due to
the demolition of existing bridge |
Option 5 |
·
less waste generated due to
the retaining of existing bridge |
·
more impacts on existing
rock slope and required rock excavation ·
long construction period and
associated impact |
2.4.6
Having reviewed the benefits of the above Options, it was
suggested that the assessment of the “Monolithic Option” (Option 2) was
brief, as the major reason for its consideration was based on preliminary
traffic figures, which indicated acceptable weaving along the route would seem
possible. Final traffic flows investigation, however, demonstrated that this
was no longer the case, with unacceptable weaving occurring between the Kowloon
bound on-ramp at Tai Chung Road Interchange and the off-ramp to Tsuen Tsing
Interchange. In other words, it has
been concluded in the Report that a full comparison
between Monolithic and Independent viaducts is not warranted and hence the
“Monolithic Option” is not feasible. Details of the investigation of the “Monolithic
Option” could be referred to Appendix
B of the Report. With similar reason, it
was concluded in the Report that Modifications to
Slip Road (Option 3) were not feasible. Details of the investigation
of this option could be referred to Appendix
C of the Report. In consideration of the above
engineering issues and environmental impacts, Option 1 was recommended as the “preferred alignment option” of the Project.
2.4.7
The “Contiguous Scheme” (Option 4) and “Split Scheme” (Option
5) for Section B of the Project have been rated for comparison
against the following criteria:
·
Topographical;
·
Alignment;
·
Structural and Bridges;
·
Gazettal Concerns;
·
Land Matters and Land Usage;
·
Transport Planning and Operation;
·
Landscaping and Visual Impact;
·
Drainage;
·
Environmental; and
·
Cost and Construction Time.
2.4.8
Referring to the findings in the Reportabove, the “Contiguous
Scheme” (Option 4) has less
topographical impacts, while the widening of the rock slopes in the “Split
Scheme” (Option 5) would require some improvements to
landscaping. In addition, the “Contiguous Scheme” layout is preferable for
operation compared with the “Split Scheme”, even structural
difficulty/cost/time related to reconstruction of the bridge would seem
slightly more onerous. As a result, the
“Contiguous Scheme” was recommended as the “preferred alignment option” for Section
B of the Project.
2.4.9
To conclude, considering all the above factors, the “Conforming Scheme”
(Option 1) and the “Contiguous
Scheme” (Option 4) were recommended
as “preferred alignment option” for the Project.
2.5.1
The following is the assessment if a tunnel is used instead of bridge
structures. A tunnel option may have
many impacts and in particular the vertical gradients of main lines and slip
roads are restricted. The gradients for
main lines must be below desirable maximum 4% and the absolute maximum for slip
road is 8%. Ventilation shafts are also
required.
2.5.2
The engineering analysis for providing a tunnel is as follows:
·
Most of areas are constrained by existing
West Rail tunnel, building & highway structures, extensive underground
services and at-grade interchanges.
·
A bored tunnel has to be excavated at
nearby sea and existing structures, this will induce the high construction risk
due to the large quantity of water ingress into the tunnel. This will require a very substantial
drainage system to divert the seawater, which will make this option infeasible.
·
A tunnel has to be bored parallel the MTR
West Rail tunnel or underneath the foundation of existing bridges, it is also
rather risky.
·
Bifurcation in bored tunnel is extremely
difficult and is not practical in this arrangement.
·
Open cut tunnel will involve the
extensive temporary traffic management scheme.
·
The cutting may be extremely deep and
requires extensive and expensive shoring.
·
The recurrent cost of operation and
maintenance of tunnel is much higher than the viaduct option.
·
There is no suitable space to accommodate
the ventilation shaft(s), since exhaust gas will be dispersed through
ventilation shafts and the air of the entire tunnel will be concentrated to at
one spot or two spots, which might results severe local air quality
impacts.
·
Longer construction period and derived
construction impacts.
2.5.3
It is concluded that the viaduct option is preferred to the tunnel
option in terms of both engineering and environmental.
2.6.1
Regarding the cumulative effects of the construction period and the
severity of the construction impacts to the adjacent sensitive receivers along
the Project area, a preliminary construction programme and sequences of works
have been worked out, which will allow, whenever possible, the application of
quiet powered mechanical equipment (PME) and to avoid parallel construction
works in nearby locations.
2.6.2
The three construction methods of viaduct are:
·
Conventional cast-insitu method;
·
Balanced-cantilever precast segmental
method; and
·
Balanced-cantilever in-situ segmental
method.
2.6.3
The construction of substructures including piers and pile cap will be
carried out by the conventional cast-insitu method. Suitable temporary traffic arrangements are required. Large number of piles on each pile cap will
prolong the construction time of piling and its associated impacts. Reconstruction of Road Bridge 38/2 will be
used by cast in-situ method. The span
lengths of the bridge vary form 23m to 33m over the existing and widening of
Tsuen Wan Road.
2.6.4
The Balanced-Cantilever precast segmental launching is proposed for the
use in this project since it can offer various advantages. One of the advantages is that false work is
not required which might need extensive road closures. An other significant advantage is that the
construction time is short and the operation is quiet compared with any other
method. A gantry girder is initially
set up between two columns. Segments
are delivered within at deck or ground level to the appropriate location and
construction cantilevering from both sides of the front column. When the segment reach the mid span, this
cantilever is completed and the gantry can shift to the next pier and construct
the other half span. When the two half
spans meet at the middle, prestressed cables will be stressed and stitch the
span.
2.6.5
For bridge span length of around 40m long, there will be around 16 precast
segments (2.5m long each) in one span.
Two pairs of segments can be lifted and erected during a dayworks, and
in general, including preparation and positioning works, a 8-day cycle for a
span can be achieved. It is noted that
an in-situ method will take around 80 days for each span including the false
work supported from ground. The
advantage of this method is fast and not labor-intensive. Most of the works can be achieved
off-site. The disadvantage is that the
gantry girder cannot be very long thus restricting the span length to a maximum
of around 60m currently in Hong Kong.
2.6.6
The Balanced-Cantilever in-situ segmental launching is another method
use in this project which is an in-situ concreting method using a traveling
formwork. A pair of traveling formwork
is initially set up at the two sides of a pier; the segment length will be
3m. The reinforcement will be fixed
within this formwork and concreted in-situ.
The formwork will travel forward for the next segment once the concrete
had gained enough strength. This
process will continue until the traveling form reaches the mid span and join
with the other form and segment. The
two half span will then be stitched using prestressed cables. No false work i.e. ground supports is
required for this system, however a working platform which should also be used
as protective platform is required. The
disadvantage of this method is that the speed for fixing steel and concreting a
segment is time consuming. It will take
at least 1 week per pair of segment.
The advantage is that it can be used for span length exceeding 60m. More concrete trucks will be stationed
temporarily on the site during concreting works, additional fuel and emission
and concrete debris generation is expected.
2.6.7
More detailed descriptions on the sequences of work stages are
presented in Section 2.7.
2.7.1
Two single lane viaducts with connections to TMR will be provided on
the two sides of the existing elevated section of TWR. The proposed viaducts
will be separated from the existing structure. Near Hoi Kok Street, these two
single lane viaducts will be linked with the up and down ramps from/to Hoi On
Road and become two 2-lane viaducts. The proposed 2-lane viaducts will also be
separated from the existing structure and located on the two sides of the
existing elevated section of TWR.
2.7.2
A down ramp branching off from the Kowloon bound 2-lane viaduct would
be provided near Tsuen Tsing Interchange for the traffic to Texaco Road. The
proposed 2-lane viaducts will terminate after joining the at-grade TWR near
Tsuen Tsing Interchange, where the existing at-grade TWR would be widened from
dual-3 to dual-5 until the Project limit near Kwai Tsing Interchange.
2.7.3
Under the former project scope, a tunnel providing a bypass to the
Castle Peak Road traffic would be constructed near Hoi On Road as part of the
Tsuen Wan Bay Further Reclamation (TWBFR) to join new viaducts parallel to
existing TWR. With the absence of TWBFR, this bypass will no longer be
provided. As such, the project scope has been revised.
2.8.1
The proposed works are due to be undertaken over a period of 48 months
commencing in June 2011, with completion scheduled in May 2015. The
construction programme and works areas are shown in Figures 2-3 and 2-4,
respectively.
The main activities are:
·
Establishment including casting yards
off-site;
·
Road and Utility Diversions;
·
13 No. Kowloon-bound sections of
multi-span viaducts – Tsuen Wan section;
·
10 No. Tuen Mun-bound sections of
multi-span viaducts – Tsuen Wan section;
·
Reconstruction of Bridge 38/2 (Wing Kee
Road);
·
Kwai Hei Street Bridge Widening;
·
At-grade dual 5-lane expressway - Kwai
Tsing section;
·
Footbridge TW36/85 Reprovision;
·
Noise enclosure (mixed with fully &
semi-enclosed types) built on new viaducts;
·
Traffic Control and Surveillance System;
and
·
Finishing.
2.8.2
Construction of the viaducts is expected to use the precast segmental
construction method. This will require initial set-up of a casting yard for
match-casting of segments and shipping to Hong Kong if they are cast in other
places (i.e. the Pearl River Delta area). A diagram of the typical construction
sequence is shown in Figure 2-5.
2.8.3
Before viaducts construction can commence, extensive utility diversions
will be required at many pier locations.
The various utility undertakers will generally execute diversions
sequentially. At critical sections such as Texaco Road and Hoi Shing Road there
are up to 5 utility providers. Material supply can require extensive lead-times.
Where this occurs, diversion of these utilities should be scheduled after the
diversion of others in the sequence. Generally 12 months has been allowed for
the diversions for each viaduct. For critical areas up to 24 months is
available. This is considered adequate.
2.8.4
Construction of the Kowloon-bound and Tuen Mun-bound viaducts should
commence by Q2, 2011, and must take place concurrently, necessitating separate
gantries and a concurrent precasting schedule. The portion between Tai Ho Road
and Tai Chung Road shall be lated possessed upon the completion of temporary
car park and Public Transport Interchange by MTR adjacent to MTR’s TW5
development. The construction of the
viaduct within this portion will commence by Q3, 2012. For each section of viaduct a nominal
duration of about 3 months was allowed for piling, 3 months for pier
construction and 1 month for deck erection. Based on these durations, works
will be required on two fronts in each of the Kowloon-bound and Tuen Mun-bound
directions.
2.8.5
Works in the Kwai Tsing section must take place concurrently with works
in Tsuen Wan section. The critical task is the reconstruction of Bridge 38/2
over Wing Kee Road. The two decks for the opposing carriageways must be
reconstructed sequentially, during which time traffic diversions are required
to maintain two-way traffic flow on a single 2-lane deck.
2.8.6
The five major retaining walls in the area of Bridge 38/2 are
constructed concurrently with the reconstruction of Bridge 38/2, providing the
additional width for the dual 5-lane section. Reconstruction of existing
drainage is also required. The drainage works must be done after the widening
of TWR (including construction of the retaining walls, provision of new
drainage and new pavement), and diversion of traffic. Most of the central
median barriers will also have to be realigned and/or replaced along the
at-grade section.
2.8.7
Landscaping has not been shown as a discreet activity as it is not
critical. However the seasonality of plantings and also the long establishment
period for plantings should be considered when programming for this activity at
the Detailed Design stage.
2.8.8
About 18 months has been allowed for Traffic Control and Surveillance
System and Electrical and Mechanical works, which can either be included under
the main contract, as a separate contract, or as a Nominated Subcontract.
2.8.9
Noise enclosure (mixed with fully enclosed & semi-enclosed types)
would be built on new viaduct section, mainly on south-bound structures No. S4,
S5 and S6, and north-bound structures No. N3, N4, N5, N6 and N9. The structure No. are shown on works areas in Figure 2-4.
2.8.10
9 months has been allowed for the noise enclosure construction after
completing the structural decks of the aforesaid structures.
2.8.11
As to the noise barriers to be constructed on other viaduct structures,
it is deemed that the viaduct construction period could absorb the noise
barrier construction.
2.9.1
The Project may have interaction with the projects Residential
Development at TW5, Residential Development at TW6, Residential Development at
TW7, and Reconstruction and Improvement of Tuen Mun Road as their boundaries
are located within 500m study area of this Project and their construction
periods would overlap with this Project.
2.9.2
Table 2-12 shows the anticipated
development schedulecompletion
dates of the concurrent projects. Figure 4-3 shows the
locations of these concurrent projects.
Table 2‑22 Anticipated Development Completion DatesSchedule of Concurrent
Projects
Concurrent Project |
Anticipated
Development Commencement Date |
Anticipated Development Completion Date |
Residential Development at TW5 |
2011 |
2015 – 2016 [1] |
Residential Development at TW6 |
2008 |
2011 – 2012 [1] |
Residential Development at TW7 |
2011 |
2012 – 2014 [1] |
Reconstruction and Improvement of Tuen Mun Road |
2009 |
2011 |
Notes:
1.
Latest completion programme for Residential Development at TW5, TW6 and and
TW7 are shown in Appendix 3-P.