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Central Kowloon Route: Linking east with west

Central Kowloon Route: Linking east with west

Content provided by the Highways Department with the coordination of the HKIE Civil Division


Central Kowloon Route (CKR) holds the key to relieve congestion on existing east-west corridors in Central Kowloon by providing a high capacity segregated trunk road to connect East and West Kowloon. The dual three-lane carriageway with a total length of 4.7 km links the West Kowloon Cultural District (WKCD) and Kai Tak Development Area to support the development of the world-class integrated arts and cultural destination at WKCD and the evolvement of Kowloon East into a vibrant premier business district.


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Figure 1: The alignment of Central Kowloon Route


Enhancing connectivity and environment

The CKR is an alternative express route bypassing the congested Central Kowloon area. It is expected to shorten the journey time between Yau Ma Tei and Kowloon Bay during peak hour from 30 minutes to about 5 minutes upon its anticipated commissioning in 2025.


On the western side, the Yau Ma Tei Interchange of the CKR will provide comprehensive slip roads connecting to the West Kowloon Development, Western Harbour Crossing and Hong Kong Island in the south, to Kwai Tsing Container Terminal and Hong Kong International Airport in the west, as well as to the northwest New Territories in the north, that largely enhance linkages between districts across the territory.


In a broader regional perspective, the CKR will further connect with Trunk Road T2, which is currently under construction, forming part of the Hong Kong’s strategic road Route 6, providing an important road link from West Kowloon to Tseung Kwan O (TKO) New Town with intermediate interchanges at Kai Tak and Lam Tin. It will bring the Kowloon East and TKO New Town closer to the western portion of Hong Kong and other Greater Bay Area cities through the Hong Kong-Zhuhai-Macao Bridge and thus will help drive the economic development of South East Kowloon and South East New Territories through improved connectivity.


This underground artery through the heart of Kowloon will divert the traffic away from the existing at-grade district distributors and local distributors in Central Kowloon road network. With the reduced traffic, the noise and air pollutant levels will decrease with an improvement to the environment of nearby neighbourhoods such as Yau Ma Tei, Ho Man Tin, Wong Tai Sin and Kowloon City.


Sustainable road design – Routing selection strategy

In the alignment design, the Highways Department of the HKSAR Government adopted a 3-level approach to achieve sustainability. The three levels are:


  • Level 1: Minimising social and cultural impact
  • Level 2: If demolition is unavoidable, temporary/permanent relocation will be provided
  • Level 3: Besides avoiding impact, improving the environment


Since the planning of CKR in the 1990s, over 40 alignment options, including tunnel and flyover options, were considered for the CKR. Eventually the tunnel option was chosen. The CKR will be mainly built in rock stratum deep underground, thus avoiding resumption and demolition of private properties and the associated rehousing issues, minimising traffic disruption, and avoiding construction in proximity to sensitive receivers.


At the eastern end of the CKR in the Kai Tak Development Area, the optimised routing between Ma Tau Kok and the Kai Tak Development will run through a 370 m long underwater tunnel, which will be constructed in the seabed of Kowloon Bay using temporary reclamation and cut-and-cover method. The curved tunnel is adopted to achieve the shortest connecting route with minimised impact to the existing structures and future development as well as the waters of Kowloon Bay.


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Figure 2: CKR routing in waters of Kowloon Bay


At the western end of the CKR at Yau Ma Tei, preservation of the historical heritages of the Grade 2 historic building of the former Yau Ma Tei Police Station is one of the biggest challenges in alignment selection. The alignment of the CKR was carefully selected to run pass the old wing of Yau Ma Tei Police Station at the south side to avoid causing impact to the old building during construction.


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Figure 3: Grade 2 historic building of the former Yau Ma Tei Police Station


With best endeavours in selecting an alignment to avoid affecting the private properties and historical heritage, clearance and demolition of some existing public facilities are yet inevitable since a section of the CKR tunnel of about 500 m long will be constructed at the section of Kansu Street between Yau Cheung Road and Nathan Road and will pass through the underground stratum of the foundation of Kansu Street section of Gascoigne Road Flyover (GRF) and the Yau Ma Tei Multi-storey Car Park (YMTMCP) Building. To facilitate the construction, a section of about 290 m long of the GRF has to be shifted northward and the YMTMCP is to be demolished. Several public facilities along the tunnel alignment were re-provisioned, such as Yau Ma Tei Jade Hawker Bazaar, Yau Ma Tei Public Library and Yaumatei Specialist Clinic Extension.


Underwater tunnel at Kowloon Bay

A section of 370 m long underwater tunnel, which is the deepest at Ma Tau Kok and the shallowest at Kai Tak, is being constructed at Kowloon Bay connecting Ma Tau Kok and the Kai Tak Development Area. Besides the careful alignment selection to avoid land resumption and demolition of private buildings and to minimise the extent of affected marine area, the CKR team had also explored various options on underwater tunnel construction methods which are commonly used in Hong Kong, such as immersed tube tunnel, bored tunnel and cut-and-cover tunnel. With due considerations of the site constraints, environmental impacts and disturbance to the public, it is considered that the cut-and-cover method inside a temporary cofferdam is the most suitable, practicable and safest method for construction of the CKR underwater tunnel at Kowloon Bay.


Marine pipe piles and sheet piles were installed to form the outline boundary of the temporary reclamation and the working platform for the cut-and-cover tunnel. A patented clutch pipe pile system was then installed within the temporary reclamation to form the temporary cofferdam. The clutch pipe pile system contains two major parts, namely the pipe pile casing which provides structural stiffness for the lateral support system and a tailor-made clutch welded on two sides of the pipe pile providing an effective water cut-off.


To further enhance the safety in underwater works, the team has explored alternatives to carry out the removal of temporary works underwater. Traditionally, the temporary steel works would be removed by manual underwater flame cutting by commercial divers which have always been considered a high risk activity with low productivity. With joint efforts from the contractor, the team looks into the feasibility of the use of mechanical cutting of the pipe piles by hydraulic driven disc cutting and high pressure water jet cutting (HPWJC). Upon trial on site, the team concludes that the HPWJC is a sustainable method to carry out the works with minimal safety risk and low material consumption during the course of the works.


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Figure 4: Stage 1 underwater tunnel construction at Kowloon Bay


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Figure 5: Excavation and lateral support system for cut-and-cover underwater tunnel


Bridge works at Kai Tak River

Kai Tak River, previously named as Kai Tak Nullah, is one of the major drainage channels in East Kowloon. The CKR Kai Tak Interchange consisting of a bridge system is to be constructed across the Kai Tak River. During construction, the temporary occupancy of the Kai Tak River would have impact on the flow capacity of the River. In this connection, temporary steel platforms with streamlined features are being used in order to minimise the impact. Apart from submitting the Construction Drainage Impact Assessment, the CKR team has to maintain close communication with the Drainage Services Department of the HKSAR Government during the construction stage.


Given the large catchment area of Kai Tak River, a considerable amount of discharge is anticipated during the wet season, which may result in a rapid surge of water level and a high flow velocity in Kai Tak River during the occurrence of a heavy rainfall event. To closely monitor the water level during construction, water level sensors are installed at both upstream and downstream of Kai Tak River for real-time monitoring of the water level. Furthermore, in collaboration with the Hong Kong Observatory and the Drainage Services Department, the CKR team initiates the development of an Early Rainstorm and Tidal Alert System in order to provide a real-time safety monitoring for extreme weather conditions and issue alert messages to allow sufficient time for the workers to evacuate from the temporary working platform erected in the Kai Tak River during extreme weather.


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Figure 6: Temporary platform at Kai Tak River for construction of bridges at Kai Tak Interchange


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Figure 7: Early rainstorm and tidal alert system


Rock tunnel in the heart of Central Kowloon

The main alignment of CKR tunnel section from Shanghai Street to Kowloon City Ferry Pier Public Transport Interchange is located at deep rock stratum of about 30 m to 140 m below ground, which runs underneath several railway lines, water services reservoirs and over a hundred existing buildings as well as in close proximity to Ma Tau Kok Gas Works. Construction methodology for tunnel excavation in adjacent to these sensitive structures has to be carefully planned to meet the stringent requirement on vibration and ground movement control. The tunnel alignment also passes through a number of fault zones or geological weak zones, posing additional challenge to ground water control and temporary support arrangement during excavation.


Given that it is difficult to source a tunnel boring machine (TBM) for constructing the CKR tunnel with a width of over 19 m in rock, drill-and-blast method is adopted for most of the tunnel excavation with logistic support from three vertical access shafts located at Yau Ma Tei, Ho Man Tin and Ma Tau Kok, ranging from 34 m to 107 m deep. On the other hand, taking into account the geological conditions, an earth pressure balance (EPB) TBM is deployed to construct a 722 m long pilot tunnel with a smaller diameter connecting the access shafts at Ho Man Tin and Ma Tau Kok in advance so as to allow greater flexibility to site logistic.


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Figure 8: Tunnel boring machine


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Figure 9: Bottom of Ho Man Tin Access Shaft


With the stringent vibration limits and the limited site access available, various measures are being deployed to enhance the productivity of tunnel excavation and spoil disposal, including the application of double deck blasting and advance external grouting. To support the extensive mucking out demand, large scale semi-automatic control gantry cranes have been installed at the three access shafts. For the gantry crane at Ho Man Tin Access Shaft of 107 m deep, the maximum travelling speed of the gantry crane is up to 50 m per minute, which is currently one of the fastest in Hong Kong, enabling a mucking out capacity of over 5,000 tonnes per day.


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Figure 10: 40 tonnes semi-automatic control gantry crane installed for Ho Man Tin Access Shaft


To minimise the noise and air quality impacts resulted from blasting works to the neighbouring area, a series of mitigation measures are being implemented, including installation of filter inside the ventilation system and construction of temporary noise enclosures above the access shafts. Close communication with the nearby stakeholders is also important so as to earn their understanding and support to the construction works.


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Figure 11: Drilling blast holes on blasting face


Cut-and-cover tunnel at congested Yau Ma Tei

The section of CKR tunnel connecting to Yau Ma Tei interchange is located between Shanghai Street and Yau Cheung Road at Yau Ma Tei, which is one of the busiest and densely-populated districts in Kowloon. Since this section was constructed using cut-and-cover method, the project team faced various challenges including highly complex site constraints in the urban areas as well as limited site areas, which made the construction even more challenging.


During the construction of diaphragm walls, the traffic at Kansu Street would be unavoidably affected. Hence, the project team closely liaised with relevant government departments as well as the key stakeholders for well-planned temporary traffic schemes so as to maintain the traffic at Kansu Street and to minimise the impact to the traffic in this busy area.


Furthermore, in addition to the traditional bottom-up method, top-down method was adopted in the selected tunnel section to minimise the impacts on the environment and existing traffic adjacent to the construction. Following the completion of the construction of diaphragm walls and cross walls, the ground will be excavated to the tunnel roof level for the construction of the tunnel roof slab. In order to maintain the pedestrian access and road traffic above ground, the first stage of excavation and roof slab works will be undertaken beneath temporary decking, which also serves to contain the noise and dust produced by the works being carried out beneath as well as enabling traffic to be maintained on the temporary decking. The remaining tunnel construction will then be continued beneath the tunnel roof slab. This top-down approach has the advantage of maintaining the traffic above and therefore reducing the disturbance to the public.


The western side of Yau Ma Tei is a well-developed area with substantial existing underground developments. These underground features including MTRC rail tracks, pipe lines, drainage box culverts and various types of cables and service ducts, etc, have been fully taken into account during the design stage in order to avoid clashing between these existing features and the CKR permanent structures. However, the challenges remain during the construction stage to construct the CKR permanent structures under such a constrained site condition which meticulous method and logistic planning is required. The various layers of structures which have to be constructed in sequence, including the CKR ventilation adit at the bottom, the diverted drainage box culverts, the CKR depressed road, the elevated Hoi Wang Road and the landscaped deck structures, introduce great challenge to the construction programme planning. In this area, stage-by-stage traditional bottom-up excavation and lateral support construction method with temporary support systems is adopted to overcome the construction challenges.


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Figure 12: Longitudinal section showing the CKR work at Western Tunnel Portal at Yau Ma Tei


Underpinning for Yau Ma Tei Police Station

The project team also faces challenges of working in close proximity to historical heritage. The CKR tunnel runs beneath the existing new wing building of Yau Ma Tei Police Station and provides around 2.3 m clearance only with the old wing building. In respect of the existing new wing building, it is a four-storey building supported by concrete friction piles. Construction of the CKR tunnel beneath this building requires the removal of those affected piles. A comprehensive underpinning scheme is proposed to transfer the existing column loadings to a deeper rock stratum. Polyurethane grout and bentonite cement grout were first applied adjacent to the existing pile caps for ground stabilisation. Temporary micro-piles of 114 mm diameter with stitching to the existing pile cap were then installed to enhance the short-term stability during construction. New socketed H-piles and steel beams with jacking system were then installed to support the existing foundation in the area within the cut-and-cover tunnel footprint. With the installed micro-piles as an interim stabilising measures and the adopting of ring bit drilling method, the settlement due to installation of socketed H-piles could be well controlled. Upon successful transfer of loadings to the new pile system, the existing piles can be removed accordingly. In respect of the old wing of the Police Station, in order to strengthen the ground, Tube-a-Manchette (TAM) grouting was carried out for the area before the construction works of CKR so as to minimise the adverse effect from the adjacent excavation during construction stage. To date, the effect on the buildings has been well-controlled.


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Figure 13: Construction of diaphragm walls in close proximity to the former Yau Ma Tei Police Station


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Figure 14: Strengthening of pile caps of the new wing of the former Yau Ma Tei Police Station


Re-provisioning of Gascoigne Road Flyover

The section of Gascoigne Road Flyer (GRF) between Temple Street and Ferry Street will be re-provisioned for the construction of CKR. To allow adequate working space in the congested site and to minimise the construction impact to the traffic and social-economic activities in the vicinity of the Temple Street, the project team adopts in-situ balanced cantilever form travellers method using for the construction of the re-provisioned section of GRF. Opposite directions of span construction are proceeded by using the top of the pier as the initial anchor point for a pair of separate form travellers, which operates as a balanced unit. Cantilevered construction is allowed by moving each pair of form travellers farther away from a pier in tandem. This construction method could free up the at-grade area at footprint of the bridge which provides extra working space for other concurrent construction activities at ground level and maintains the existing traffic and social-economic activities on at ground level.


Self Photos / Files - 15Figure 15: Installation of form traveller for bridge deck construction of Gascoigne Road Flyover


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Figure 16: Launching of form traveller after casting of bridge deck segment for re-provisioning of Gascoigne Road Flyover


Demolition of Yau Ma Tei Carpark Building

Yau Ma Tei Multi-storey Car Park (YMTMCP) Building is well-known with a feature of the flyover passing through the building. To facilitate the construction of the CKR tunnel, the YMTMCP is demolished under two phases. In order to maintain the traffic at GRF, the whole northern part and the 7th to 12th floor of the southern part of the building are firstly demolished to make room for the construction of the eastbound of the re-provisioned GRF. The existing section of GRF passing through the building remained in operation during Phase 1 demolition works. Precautionary measures including covered hoardings and walkways in different phases along the exterior wall of the YMTMCP, scaffoldings with catch-fan and steel canopy, crisis management plan etc, were implemented to ensure the safety of the public and the traffic on the existing GRF. To monitor the internal structural safety of the YMTMCP under demolition, deflection monitoring at the external walls of the east and west sides facing Shanghai Street and Temple Street was implemented. To preserve the Temple Street Night Market and to minimise the construction impact to the social-economic activities of the Temple Street during the demolition of the YMTMCP, cantilever hoarding was specially designed to retain the night market stalls and to protect the existing street activity. Upon the commissioning of the newly-constructed eastbound of the re-provisioned GRF, the remaining southern part of the building and a section of the existing GRF passing through the YMTMCP will be demolished to facilitate the construction of the CKR tunnel and westbound of the re-provisioned GRF.


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Figure 17: Yau Ma Tei Multi-storey Car Park Building under demolition


BIM for complex construction

Building Information Modelling (BIM) is widely adopted in the delivery of the CKR project. The advanced 3D modelling software can simulate the construction sequence of complex engineering issues. BIM is also used for asset and facility management at the operations and maintenance (O&M) stage of the project to enhance the efficiency in sustainability evaluation, management of as-constructed records, scheduling of maintenance, space utilisation management, and facility energy analysis on system equipment performance data. The information and modelling provided by BIM help the O&M parties communicate with contractors and craftspeople and facilitate total management of the CKR across teams of different needs and expectations.


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Figure 18: BIM simulation of phased demolition of the Yau Ma Tei Multi-storey Car Park Building (L) and site utilisation for Gascoigne Road Flyover construction (R)


Integrated digital works supervision system

To further enhance the performance on construction management and supervision of the CKR, the Highways Department of the HKSAR Government initiated the use of the Integrated Digital Works Supervision System (iDWSS) and enhanced BIM management tools with integrations on quality supervision platform (ie eRISC) of Digital Works Supervision System (DWSS). The CKR is the first public works project developed with iDWSS to transform the data from six individual contract-wide DWSS into a single project-wide management platform providing data analysis with various Key Performance Indicators (KPIs) to facilitate management decision on key aspects for the improvement of quality, safety and environmental performance in project implementation. The collected data is centralised, processed and securely stored in the cloud platform. The big data transformation to the project-wide useful information in iDWSS with support of real-time monitoring on site activities and automatic generation of KPIs enhances efficiency of overall construction process with reduction of on-site supervisory manpower. 


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Figure 19: The use of integrated digital works supervision system by top management


Benefit the environment – the enhancement work

An air purification system (APS) is introduced in the CKR during the operation stage to treat the air discharged by the tunnel ventilation system, aiming at reducing the air quality impacts on nearby air sensitive receivers and thus achieving the air quality objectives. The proposed APS for the CKR schematically comprises of two main processes. The first main process involves the use of Electro-static Precipitators (ESP) to remove portion of particulates including PM10 and PM2.5 from the air extracted from the tunnel. After passing through the ESP, the air would be fed into a Nitrogen Dioxide (NO2) removal system under the second main process to reduce the NO2 concentration before the extracted air is eventually discharged to the atmosphere. Tunnel operators will 24-hourly station in the CKR Administration Building to control and monitor the tunnel systems as well as the operation of the APS.


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Figure 20: Air purification system


A step is further taken to enhance the surrounding environment in the vicinity of CKR by incorporating a greening initiative in the design of CKR. At the western side of the CKR, a landscaped deck of about 250m-long from east to west and 270m-long from south to north will be constructed above the western tunnel portal of CKR, covering the CKR depressed road and the section of Hoi Wang Road between Yan Cheung Road and Lai Cheung Road providing with additional greenery. It will also be connected to the landscaped deck of the West Kowloon Station of Guangzhou-Shenzhen-Hong Kong Express Rail Link (Hong Kong Section) to form a grade-separated pedestrian route between Yau Ma Tei and the station, serving as a sitting-out area for public enjoyment.


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Figure 21: Conceptual design of the landscape deck at Yau Ma Tei


At the eastern side of the CKR, re-provisioning works of the existing Kowloon City Ferry Pier Public Transport Interchange (PTI) are required after the construction of the cut-and-cover tunnel underneath the PTI. In conjunction with the development of the Ma Tau Kok waterfront area as part of the Vision Statement for Victoria Harbour, the re-provisioning works will be incorporated into the development of the waterfront promenade which acts as key green connectors linking up individual open spaces, residential areas and surrounding areas.


Conclusion and way forward

The CKR is an impressive feat of engineering that involves interfaces of multi-disciplinary engineering works and multi-parties interfaces. The CKR project team, following the initiatives in the Construction 2.0 initiated by the Government, strives for engineering excellence to implement various innovations in design, construction and asset management in overcoming the challenges in the project. Enhancement in productivity, control of budget and working cycle has been observed with the implementation of BIM under the complex multi-interface environment. The winning of Merit Award in the Project Category of the CIC Construction Digitalisation Award 2021 has encouraged the project team to continue striving for new innovative technologies and to make prompt adjustments to tackle upcoming challenges. The Highways Department will consolidate the valuable experiences gained from this mega-scale multidisciplinary project for future sharing with the industry and for nurturing the young engineers.


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Figure 22: Ir Tsui Wai, Principal Project Coordinator of CKR, Highways Department conducted a presentation in the opening ceremony of Construction Safety Week 2021


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Figure 23: Permanent Secretary for Development (Works), Ir Ricky Lau, presented the Merit Award to CKR project team



Special thanks to project consultants Arup-Mott MacDonald Joint Venture, all the contractors and their subcontractors for their efforts in delivering this challenging and complex project. Tributes are also paid to the stakeholders and counterparts of the project for their advice and contribution to the works.

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