2. description of the project

2.1 Introduction

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 Scope of the Project

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 Consideration of Different Alignment Options and Built-forms

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):

Tsuen Wan Road South of Bridge 38/2

· 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:

Section A – Section of Tsuen Wan Road [North of Wing Kee Road (Bridge 38/2)]

· 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
~~Referring to the Report~~ 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 Report~~above, 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 Justifications and Consideration of Alternative Built-forms

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 Consideration of Alternative Construction Methods and Sequences of Works

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 Description of the Selected Alignment and Proposed Engineering Works

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 Construction Programme

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 Concurrent Projects

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 schedule~~completion dates~~ of the concurrent projects. Figure 4-3 shows the locations of these concurrent projects.

Table 2‑22 Anticipated Development ~~Completion Dates~~Schedule 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.

List of Table

List of Figures