Central Kowloon Route, Hong Kong

Currently, more than 2M people are living in Kowloon, making it Hong Kong’s most populous area. Myriad roads and junctions criss-cross the peninsula, with many approaching or beyond capacity at peak times. The 320ha development at Kai Tak will attract more citizens to the north of Kowloon Bay with new homes and commercial space, putting further pressure on the transport network. Upon commissioning of CKR, it will shorten the journey time between Yau Ma Tei and Kowloon Bay during peak hours from 30 minutes to about five minutes and will improve the transport network and facilitate the commuting public.  

For communities in central Kowloon, less congested at-grade roads will reduce air and noise pollution, improving their health and quality of life. An air purification system (APS) will bring further health benefits: this will treat the air discharged by the CKR tunnel ventilation system and help Hong Kong achieve its air quality objectives for nitrogen dioxide and suspended particulates (PM2.5 and PM10).

Construction of CKR is also an opportunity to improve the surrounding environment with green space and landscaping in line with government policy for public works projects to deliver noticeable improvements in urban greenery. This includes landscaped decks in the west and east, a new green corridor and spaces for people to socialise and exercise.

The CKR project involves the design and construction of depressed and elevated carriageways, almost 4km of tunnels, access shafts, bridges, landscaped decks, ventilation adits and buildings, as well as temporary reclamation at Kowloon Bay for an underwater tunnel. We are providing design, engineering and construction supervision services across the eight contracts on CKR in a joint venture with Arup (AMMJV).  

The route and construction elements across Kowloon

A digital working environment

From building information modelling (BIM) to smart management systems, we are managing CKR as a digital project throughout.  

The use of BIM technology has been required in all capital works in Hong Kong since 2017. Our team and contractors are using it extensively on CKR to optimise planning and design, improve construction delivery, quality and safety, and for smoother interface co-ordination, as well as to reduce waste. We adopted advanced 3D modelling software to simulate the construction sequence for complex engineering elements, such as the excavation of sediment and dewatering required for the underwater tunnel in Kowloon Bay.  

We are also employing BIM to identify site safety risks and reduce them at the planning stage, as well as using it to facilitate design for manufacture and assembly (DfMA). One example is automatic canopy installation with an automatic drilling mast system, which have been introduced to install the brackets and canopy in the Central Tunnel – improving efficiency and reducing the risk of working at height.  

We developed a drive-through BIM model combining models from six separate construction contracts into one, to facilitate traffic management. CKR’s BIM model is also integrated with an eRISC system (a quality supervision platform) to identify, measure and manage the main risk factors on the project to help drive construction quality improvement. The six-in-one BIM model provides a holistic overview of site management too, accessed by the AMMJV team from one dedicated smart management hub. 

After commissioning of the expressway, the BIM models will support its management, maintenance and operation. They contain data on maintenance scheduling, space usage management, equipment performance and energy efficiency along with construction records. 

One integrated system

CKR is the first public works project in Hong Kong to have an integrated digital works supervision system, bringing together data from six separate contract operations into a single, project-wide management platform. A secure, cloud-based system, it supports real-time monitoring of onsite activities and automatically generates key performance indicators. This helps to improve quality, safety and environmental performance by informing management decisions on key aspects of the works.

Printing concrete

CKR has used 3D concrete printing to construct U-channels on site. The technology involves huge printers extruding concrete in layers from a nozzle to create a building element. The benefits include higher productivity and fabrication quality.

Eight contracts – from start to finish

Design and construction of CKR is spread over six main contracts. A seventh covers buildings, electrical and mechanical works (BEM), with an eighth focused on landscaping and environmental measures. We are consulting on all of these, in joint venture with Arup.

The main construction areas

4.7km three-lane, dual carriageway 

2.8km central tunnel 

550m of cut-and-cover tunnels 

350m underwater tunnel 

3 ventilation buildings 

3 access shafts, ranging from 34m to 107m deep 

1 administration building  

1km+ of noise enclosures and barriers

Contract 1: Yau Ma Tei West (YMTW)

Main contract elements

• Construction of 250m depressed road with western landscaped deck structure
• Underground ventilation adit and connection to ventilation building
• Landscaped deck and seven connection bridges to expand the road network

YMTW is where CKR connects with roads to the Western Harbour Crossing and Hong Kong Island in the south, the Kwai Tsing container terminals and Hong Kong international airport in the west, and the New Territories in the north. The district is one of the busiest and most densely populated areas in Kowloon, which brought the challenge of high traffic volume and complex site constraints. Our designers had to delicately navigate existing underground infrastructure, including rail tracks, pipes, cables, ducting and drainage box culverts.  

The site constraints also demanded careful planning and sequencing for the construction of the ventilation adit, depressed road and landscaped decking, and for the work to divert the existing drainage culverts. To minimise traffic disruption during the construction of the diaphragm walls for the tunnel, temporary traffic management schemes were introduced. Initial excavation and roof slab work was conducted beneath temporary decking for traffic. The decking also helped protect local communities by limiting the noise and dust escaping the site.  

Aerial view of the connecting bridges at Yau Ma Tei West

BIM highlight

An existing box culvert obstructed the construction of the ventilation adit and foundations for the landscaped deck. We used BIM to plan and model a diversion scheme, including the construction of a new box culvert, 5.05m high by 10.3m wide.

Contract 2: Yau Ma Tei East (YMTE)

Main contract elements

• Access shaft for Central Tunnel
• Construction of cut-and-cover tunnel
• Reprovisioning of a section of Gascoigne Road flyover and demolition work
• Reprovisioning of affected buildings (a clinic and library)
• Noise enclosures

This contract centred on construction of a 390m cut-and-cover tunnel with a 40m span, beneath the Yau Ma Tei district at the southern end of Kowloon, at a depth of between 20m and 35m. To minimise disruption from the construction works, a 290m section of the Gascoigne Road flyover was shifted northwards. This involved demolition of the Yau Ma Tei multistorey car park building, through which the original flyover passed.  

More than 50,000 vehicles use the flyover every day, so demolition of the car park building and the section of flyover passing through it was phased to maintain traffic flow. Floor 7 to 12 of the southern part of the car park and the whole of the northern section were demolished first, and the traffic was diverted onto a new section of flyover, located at the south of the car park and constructed using insitu balanced cantilever form travellers.  

Such a major demolition, alongside construction of the new flyover and simultaneous tunnel boring in the area, obviously caused disruption to the daily lives of Yau Ma residents. To counter this, enclosures were erected over two sections of the flyover to reduce noise pollution. A full noise enclosure, about 100m long, covers the section near Prosperous Garden, a residential area with more than 1500 flats, while a 40m long enclosure covers the part of the flyover fronting Yaumati Catholic Primary School. 

YMTE shaft

Construction of the YMTE access shaft to enable future ground investigation and excavation of the Central Tunnel to begin. Work on the shaft was beneath the two existing flyover piers, which required underpinning and removal. The loading on the piers was redistributed in stages from the existing piles to the ground beams of the shaft, which are supported by diaphragm walls on rock strata (see panel).
 
This section of CKR runs within 3 to 4m of the century old, grade two historic building – Yau Ma Tei Police Station. Since the new wing of the police station is on the footprint of the cut and cover tunnel, the team turned to an underpinning solution to transfer loads to a deeper rock stratum. Jade Hawker Bazaar, Maternal and Child Health Centre and the Methadone Clinic have all been moved temporarily to facilitate the construction. Our engineers had to be careful to avoid extensive subterranean utility infrastructure, including large twin box culverts and high voltage electric cables. Jet grouting and deep cement mixing were injected to stabilise the ground and improve its load bearing capacity, reducing the impact of excavation work on surrounding structures and utilities. 

Repositioning of Gascoigne Road flyover and demolition of Yau Ma Tei multistorey car park building

Transferring the load in three stages

1. Erect a temporary steel frame tower from the access shaft ground beams to the soffit of the flyover. Install hydraulic jacks on the tower and use a computer synchronised jacking system to steadily lift the flyover deck from the pier, transferring the load to the tower.
2. Excavate and install structural steel beams between the shaft ground beams, underneath the pile caps of existing piers. Install hydraulic jacks on the beams and connect them to the pile caps. Lock the hydraulic jacks under designated loads to transfer the pier and pile cap loads to the steel beams and ground beams.
3. Saw cut and remove the piles. Reconnect the pier to the soffit of the flyover using jacks, so the deck, pier and pile cap loads are transferred to the steel beams. Dismantle steel frame tower.

BIM highlight

An existing box culvert obstructed the construction of the ventilation adit and foundations for the landscaped deck. We used BIM to plan and model a diversion scheme, including the construction of a new box culvert, 5.05m high by 10.3m wide.

Contract 3: Central Tunnel (CT)

Main contract elements

• Construction of 2.8km dual three-lane tunnel 
• Foundations for Ho Man Tin ventilation building 

Most of the 2.8km Central Tunnel – spanning between 17m and 21m – is being constructed using the drill and blast method, which provides the flexibility required by the tunnel’s geometry and geology. Tunnelling by a tunnel boring machine was not an option for the main section because of the difficulties of finding one capable of cutting a 19m diameter tunnel through rock. However, to facilitate site logistics to benefit the construction programme and reduce the programme risk, an earth-pressure balance tunnel boring machine was used to cut a 722m long, 5m wide pilot tunnel west from the Ma Tau Kok access shaft before the main works of the Central Tunnel began.  

Tunnelling is through seven major fault zones, in geological strata that vary from hard rock to weak soils. The alignment also passes under or near four metro lines, six reservoirs and more than 100 buildings, as well as close to the Ma Tau Kok gasworks. An impact assessment was conducted to assess the structural integrity of public facilities and other structures along the route, and non-blasting zones are set to protect the most sensitive ones. Advanced double-deck explosives charging techniques are adopted near the metro tunnels and building piles to minimise disturbance to the surroundings. 

Keeping the tunnel dry

A waterproofing layer and geotextile membrane is being installed in each of the seven fault zones to avoid water seepage. It covers the entire perimeter of the tunnel lining, which is designed to take the full groundwater pressure. Sensors have been installed along the route, and vibration from drill and blast excavation is strictly controlled. To minimise noise and air quality impact from the blasting works, mitigation measures include installing filters inside the ventilation system and erecting temporary noise enclosures above the access shafts. 

While it normally takes at least a year to get a blasting permit from the Hong Kong authorities, we secured one in just five months to allow work to commence in 2019 – due to our impact assessments to test the structural integrity of public facilities and other structures along the route. The construction programme is tight – all work must be completed within four years. 

Tunnelling work along the 2.8km alignment

BIM highlight

We used BIM to model the assembly, launch and breakout of the tunnel boring machine that excavated the 722m pilot tunnel west from the Ma Tau Kok access shaft.

Contract 4: Ho Man Tin access shaft (HMTS)

Main contract elements

• Ho Man Tin access shaft for Central Tunnel
• Ground investigation
• Horizontal directional coring

The Ho Man Tin access shaft, which has a 21m internal diameter and is 107m deep, was completed in September 2019. Horizontal directional coring from the vertical shaft was used to gather continuous core samples over more than 3500m of the Central Tunnel alignment, and almost 40 boreholes were drilled to gather geological information of the site. Large semi-automatic control gantry cranes can remove more than 5000 tonnes of tunnel spoil each day through the shaft, which is the deepest of the three shafts along the CKR.

Underground at the Ho Man Tin access shaft

BIM highlight

To improve safety, we identified and marked up potential hazards in the 3D BIM model before construction. As well as the risk register, the model contained information on equipment, scheduling and delivery routes.

Contract 5: Kai Tak West (KTW)

Main contract elements

• Access shaft for Central Tunnel
• Construction of cut-and-cover tunnel
• Underwater tunnel and temporary reclamation at Kowloon Bay
• Depressed roads

A 370m long underwater tunnel at Kowloon Bay will connect Ma Tau Kok and the Kai Tak development area. Underwater tunnel construction is common in Hong Kong, and the cut-and-cover method inside a temporary cofferdam was selected for KTW with due consideration of the site constraints. We also considered the method better for environmental and site safety reasons, compared with alternatives such as an immersed tube tunnel or bored tunnel.  

The boundary for the dam to temporarily reclaim land from the sea was created with a combination of marine pipe and sheet piles. This area formed the working platform for construction of the cut-and-cover tunnel. To create the cofferdam, we installed a patented clutch pipe pile system. The advantages of using this system, rather than combining sheet piling with traditional pipe piles, include a casing that provides structural stiffness for the lateral support system and a bespoke clutch welded on two sides of the pipe pile for water cut-off.  

KTW also includes the construction of a section of the Kai Tak promenade. This includes an 11,500m² stepped terrace landscape deck which can be used for community events as well as casual exercise. The promenade will connect to a new sports park and public spaces, as well as major facilities such as the cruise terminal. 

Construction of the temporary marine platform and cofferdam at Kowloon Bay

BIM highlight

We developed 3D BIM models to plan the construction of the temporary cofferdam in Kowloon Bay.

Contract 6: Kai Tak East (KTE)

Main contract elements

• Interchange, including vehicular bridges, underpasses and link roads
• Construction of footbridge

A vehicle bridge is being constructed across the Kai Tak Nullah, a watercourse into which flow the lesser rivers and streams coming down from the hills in north Kowloon. Water level sensors upstream and downstream provide real-time monitoring during construction, and an early rainstorm and tidal alert system has been put in place so workers know when they must evacuate from the temporary steel working platform erected in the river, enhancing site safety.   

Construction work at Kai Tak East

BIM highlight

To optimise logistical planning, we used BIM to model the erection and removal of the temporary steel platform and subsequent construction of the bored piles, pier and bridge deck.

Contract 7: Buildings, electrical and mechanical works (BEM)

Main contract elements

• Three ventilation buildings
• An administration building
• Route-wide tunnel electrical and mechanical works
• Traffic control and surveillance systems
• Tunnel cladding
• Testing and commissioning

Three ventilation buildings will be constructed at Yau Ma Tei, Ho Man Tin and Kai Tak. These will be equipped with air purification systems to filter at least 80% of the nitrogen dioxide (NO2) and respirable suspended particulates from vehicle exhausts. The filter process has two stages: first, electrostatic precipitators remove PM10 and PM2.5 particulates, before the air passes through a system to reduce concentrations of NO2.  

An administration centre is also being constructed next to the Kai Tak ventilation building. Tunnel operators based there will monitor and control all the tunnel systems, including the APS, 24 hours a day. 

Yau Ma Tei ventilation building works

BIM highlight

We used BIM for site usage and logistics planning for the socketed steel H-piles to form the foundations for the Yau Ma Tei building (129 piles) and the Kai Tak ventilation and administration buildings (412 piles).

Contract 8: Remaining works

The remaining works contract includes landscaping in Yau Ma Tei (YMT) district. Above the western tunnel portal at YMT, a new 22,000m² landscaped deck, 250m-long from east to west and 270m-long from south to north, will connect with the existing green roofscape above West Kowloon rail station, which provides panoramic views across the peninsula. At the eastern end of CKR, the development of the Ma Tau Kok waterfront includes a new promenade and will form part of a green corridor, connecting open spaces and residential areas. Construction of CKR requires rest gardens and recreational facilities in YMT to be relocated.  Offsite compensatory planting for around 700 trees will also take place along the route. These remaining works are due to start in 2024 with completion in 2027.

Achieving Chartership underground

Geotechnical and tunnel engineer Calvin Yuen became a chartered professional in March 2022, and his work on CKR was pivotal to his success.

Calvin started with Mott MacDonald as a graduate engineer in 2018. In 2020, he was assigned to work on CKR as an assistant resident engineer helping to supervise drill-and-blast tunnelling works. He involved in site safety walks, risk reduction and site progress meetings, as well as checking and reviewing the contractors’ general and alternative design submissions. Lately, he has been an engineer and supervision-in-chief on three CKR contracts – Central Tunnel, Yau Ma Tei East and Yau Ma Tei West – and has been involved in resolving design conflicts, design changes and interface issues during the construction phase.

Construction of the Central Tunnel has been one of Calvin’s CKR career highlights: “Assessing the rock quality to determine if it is suitable for excavation was crucial to keeping site personnel safe. As tunnelling work progressed, I went underground daily with experienced geologists to identify the places where precautionary measures were required to keep everyone safe.”

Working and liaising with different stakeholders, including contractors, the Highways Department, the local transport corporation (Mass Transit Railway) and community representatives, has helped Calvin develop vital communication skills. “Building my soft skills, like communication and presentation with relevant parties and people at all levels, including non-technical stakeholders, was a big leap forward for achieving my Chartership,” he says.