Known un-knowns at Hong Kong Mass Transit Railway
Getting to grips with Hong Kong's known unknowns
The use of digital engineering on three major rail infrastructure projects in Hong Kong is key to the successful execution and management of some extremely complex engineering works.
The Hong Kong Government’s announcement in 2009 of major investment in rail infrastructure prompted Laing O’Rourke to set up a local office with the capabilities and resources to bid for the work. Although the business had worked in the region for many years on rail maintenance projects, it hadn’t up to this point undertaken large-scale civil engineering schemes.
Major projects in Hong Kong are notoriously complicated. It is one of the world’s most densely populated urban environments, with buildings and infrastructure jockeying for space both above and below the ground. Even the ground itself is a challenge, the mountainous terrain is varied and site conditions often encompass a combination of reclaimed land on the coastal fringes on top of very hard granite. These factors as well as maintaining pedestrian / traffic movements and coordinating site deliveries mean it is perhaps technically and logistically one of the hardest places on earth to build.
"Early on it became apparent that experience with DE in Hong Kong is behind the curve compared to other regions we operate in," says Laing O’Rourke’s Digital Engineering Lead John Myhill. "Using DE enables the project team to demonstrate their understanding of the project during a tender which can give us a competitive advantage."
Fast forward to 2014 and the team is well advanced on three major rail infrastructure contracts all involving complicated engineering. Two of these, 811A and 810B, in which Laing O’Rourke is working in joint venture with Bachy Soletanche and Hsin Chong-Paul Y respectively, are associated with the West Kowloon Terminus for the Express Rail Link providing a high-speed connection to mainland China. The third, 901, which is being undertaken in joint venture with Kier and Kaden, involves the extension of Admiralty mass transit system (MTR) station on Hong Kong Island.
Because DE is not well established in Hong Kong, we had to help initiate and drive the process. John MyhillDigital Engineering Lead (Hong Kong) Laing O'Rourke
DE has been used across all three projects, providing new levels of information. From quantifying topography to de-risking complex construction procedures, the common theme in its use is DE as an enabler for making critical decisions and demonstrating the design and construction process to the project team.
"Getting to this point, however, is a significant undertaking on our part," says Myhill. "Because DE is not well established in Hong Kong, the project team had to help initiate and drive the process." Most notably, he adds, the client’s design consultants are only contracted to deliver the design in 2D form. "Because of this we painstakingly create 3D information models from their 2D drawings. This is an inefficient process, however, a very worthwhile one. We identify missing and inconsistent information as well as interrogate the design before it becomes an issue onsite."
With this added requirement, Myhill explains, "we knew we couldn’t keep all elements of the model up to date, so we focused our efforts on particular tasks as the engineering and construction teams required them."
All three projects involve a substantial amount of excavation, and a good understanding of the ground conditions is critical. Given the variable nature of the local terrain, there is rarely full confidence that actual conditions will be as the site investigation predicts.
"We created a model from the initial site investigations which we compared with a second surface model which was created as the rock head was revealed during excavation," says Myhill. "This gave our construction and commercial teams a much more detailed understanding of the conditions, helping them better manage their respective risks.
"At Admiralty, we employed drill and blast techniques to tunnel through rock. We surveyed the tunnel profile following the smoothing process, which we then fed back into the model. This provided an accurate volume for each concrete pour, helping the team increase the accuracy of material deliveries to site and ultimately reducing waste.
"We also helped the team identify potential areas of under-break using the model. This was done using heat mapping visual indicators to identify where and how much more excavation was required. This has been done at particularly complex blast areas to verify the works. This lets the team check that the blasting has successfully removed the rock to the profile we require.
"We used this technique when investigating a design change to thicken an escape shaft’s wall lining. The initial study showed that a reasonable amount of rock would have to be excavated. However, we were able to see the results instantly, if the shaft was repositioned slightly. This reduces the amount of hard rock to be removed if this option is taken, greatly simplifying this part of the project."
De-risking the construction process
De-risking the construction process
DE has also helped manage risk, again most notably at Admiralty. The work involves supporting two live passenger platforms and a vent structure while the underlying rock is removed, leaving them supported at a height in excess of 20m, while the new station is built around them.
The complex operation called for a series of load transfer beams and sophisticated jacking system supported by temporary steel columns – around half of which would then have been encapsulated in reinforced concrete to form the permanent support whilst the others are removed.
As the digital model developed, the team was able to test both the design and the buildability. This highlighted the enormity and complexity of the task, putting a spotlight on the exact step-by-step process needed to carry out the work safely.
"Because of the number of stakeholders involved, we commissioned our digital visualisation team Symmetry to create a video to demonstrate how the work was to be done and various risks controlled along the way," Myhill explains. "After the video was produced the design developed into production stages and the detail in the model increased. The process flushed out many coordination problems, particularly with respect to the setting out, reinforcement detailing and the installation of the steel box beams and jacking anchors."
"Addressing these from a position of foresight allowed us to identify and analyse the practicalities of potential solutions. For instance we used an ergonomics tool within the DE software to investigate the potential of installing dowels into the soffit of the existing tunnel."
On the 810B West Kowloon terminus structure project the works include lowering the junction of Lin Cheung Road and Austin Road, which will lead into a new underpass within the new station structure. The works must be carried out while maintaining the busy traffic flow at all times. The resulting 17m-deep excavation requires an extensive amount of excavation lateral support (ELS) steelwork, in excess of 3,000 tons, a portion of which must be woven between the neighbouring contractor’s temporary traffic deck structure.
Our team was able to compare the ELS design against the temporary road bridge design and as-built information, as it was discovered, to assess the impact upon the ELS. The construction team was able to hone the excavation and construction sequencing taking place within a limited working space, before the works began.
Visualisation and communicating to stakeholders
In its most basic form DE allows people to visualise the job-in-hand. This has taken a few forms in Hong Kong, from adding 3D images into project documents, facilitating meetings and using the images to illustrate the work being undertaken to employees and project stakeholders.
Of particular note, Laing O’Rourke used the model on the 810B project to demonstrate to the ports authority an alternative scheme to limit the effect of the work on the adjacent sea wall. The authority had no adverse comments to the new proposal, a positive outcome that will ensure the works go ahead.
Similarly, the 901 team satisfied the blasting authority that the drill and blast activity at Admiralty would not impact on the live rail tunnel by representing the imposed blast exclusion zone in 3D, which was not clear using 2D information. This allowed the team to advance with the blasts, as opposed to using less effective breaking methods.
The 811A project team is using its model to demonstrate to the client the complex, irregular nature of the project, which is helping aid clearer understanding of the challenges.
On 901, Symmetry went one step further by converting its project video to run in a virtual reality environment. Using this tool has allowed the team to be immersed into the work environment before setting foot on the site. The task is then demonstrated in front of their eyes as they navigate through the environment against the programme timings.
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