How Aurecon’s innovative engineering approach brought an expanded interchange to life at one of Hong Kong’s best-known MRT stations

Hong Kong’s MRT system is one of the busiest in Asia, and few places encapsulate this better than Admiralty Station, an interchange that is regularly bustling with commuters and tourists. To improve network connectivity, MTR Corporation commissioned ‘Contract 901’, a highly complex project to expand the existing station into a four-line interchange, integrating the existing Island Line and Tsuen Wan Line with the South Island Line and the future Shatin to Central Link.

In December 2016, MTR Corporation’s South Island Line completed construction and began operations, providing additional public transport options from the Southern District of Hong Kong Island to the existing MTR network at Admiralty Station. The expectation is this new line will transport approximately 170,000 passengers per day.

The HK$16.5 billion line, operated with driverless three-carriage trains, will run from South Horizons in Ap Lei Chau to Admiralty via the other three new stations at Lei Tung, Wong Chuk Hang and Ocean Park. With the new railway line, passengers can travel from South Horizons to Admiralty in approximately nine minutes, as compared with the 25 to 45 minutes taken by using road transport during rush hours.

Contract 901 delivered an extension to the existing Admiralty station, providing a convenient interchange between the existing network and the new interchange concourse, plus four new platforms; two for the SIL (E), and two for the future Shatin-to-Central Link. A large-span cavern and two platform tunnels were excavated immediately below the existing Island Line platform, which was successfully underpinned while trains ran continually above.

Global engineering and infrastructure advisory company, Aurecon, provided geotechnical, civil and tunnel engineering services on the project for the main contractor, a Kier-Laing O’Rourke-Kaden joint venture.

Heart of the congested city
The site, in the heart of Hong Kong Island with its high-density built environment, presented numerous constraints and challenges from surrounding high-rise buildings, major roads, and significant underground infrastructure.

Scott Smith, Project Director & Client Director of Infrastructure – Asia at Aurecon, said integrating work with existing infrastructure at the station was one of the most important considerations on the project.

“A key aspect was interfacing with the operating railway at one of MTR Corporation’s busiest interchange stations,” he said. “Underpinning the existing SIL finger platform was a highly complex task that required innovative engineering. Both Admiralty Station and the Island Line remained fully operational during the entire construction period.”

The new station cavern has a large excavated span and is situated underneath a major traffic corridor carrying east-west traffic across Hong Kong Island. To further complicate matters it also has relatively low rock cover and lies close to the foundations of a nearby high-rise development.

Ground control — it’s all in the numbers
Aurecon carried out the detailed design of rock support for caverns, tunnels and station box including Island Line underpinning, as well as elements of the permanent concrete lining in the cavern and platform tunnels. Aurecon also undertook the blasting assessment reports for drill and blast excavation.

Understanding the in-situ ground conditions and controlling ground movement were vital. Aurecon developed a comprehensive and robust multi-staged methodology for the temporary ground support design with state-of-the-art numerical modelling. The design successfully considered the impact of construction on several structures near the excavation and loads from existing building foundations.

An innovative excavation and support sequence was developed for the underpinning, which provided enhanced stability while reducing temporary support requirements and minimising risk. It included a flexible system of rock support that accommodated construction sequence constraints and optimised as-found ground conditions, thereby significantly improving excavation rates.

Zero disruption
Excavation and support of the large-span cavern in a dense urban area posed unique challenges. Despite the scale and complexity of the works there was zero disruption to existing rail services and no impact on the safety of the Tsuen Wan Line or Island Line train service throughout the entire construction period.

Scott Smith said teamwork was a central factor in ensuring that rail operations continued to run smoothly. “This was explicitly a result of the remarkable levels of collaboration between all the parties involved, with innovative design, excellent construction supervision, rigorous planning and attention to detail on work permits and safety procedures,” he said. “The safe completion of the work marks an outstanding achievement in finalising work to customer satisfaction, maintaining railway performance, and operating in the safest possible environment.”

Aurecon is an engineering and infrastructure advisory company, working alongside clients to co-create clever, innovative solutions to some of the world’s most complex challenges, adding value across the project lifecycle through deep technical and advisory expertise.,
www.aurecongroup.com