The Da Nang Department of Construction recently reported on a proposal for construction of an east-west traffic connection route through the Da Nang International Airport. According to the Department’s proposal, to build a tunnel through the airport, the section outside the operating runway will be constructed with closed and open tunnels using the open excavation method; the section under the operating runway has two options: using the Pipe Roof method and the TBM method.

A scene of the Da Nang Airport. Photo: THANH LAN

The municipal Department of Construction proposed applying the Pipe Roof method to the section under the runway, because the tunnel section is shallow, easily connecting to outside traffic and there have been many similar projects in the world applying this method. This method is conveniently applied to underpasses, construction in areas with heavy traffic or limited interruptions or where settlement needs to be minimized during construction.

This method involves the construction of temporary structures using interlocking steel pipes, installed by micro-tunnel or underground jacking, to form a temporary ground support system, and then the permanent structure can be built inside. The advantage of the Pipe Roof method is that the diameter of the steel pipe from 318.4~1219.2 is used. The small diameter can make shallow tunneling feasible; the variety of pipe roof arrangements allows for the construction of many different excavation sections; at the same time, it is cheaper and faster than the TBM tunneling method.

The highlight of the two proposed technologies is that the tunnel is built through the road, the ground (airport) while the above is still operating normally. The Pipe Roof side uses pipes to penetrate around the perimeter of the tunnel, then digs and uses a frame system to support the pipes and build the tunnel lining, then continues in that cycle moving forward (it can also be divided into sections to do if the route is long).

For the East-West traffic connection project through the Da Nang airport, the Department of Construction proposed a tunnel route with a length of more than 2.9km, including 2 open tunnel sections with a total length of 570m, 3 box tunnel sections with a total length of 1,450m and a tunnel through the existing runway of 900m. There are 2 proposed options. Option 1 is a metro line (MRT) running with the road; option 2 is an MRT line not running with the road.

According to the analysis, option 1 has a high level of technical difficulty, a cost of about VND10,000 billion, an average safety/operation level, difficulty in expanding the MRT, and a high level of suitability for the infrastructure of the Da Nang International Airport. Meanwhile, option 2 has a lower level of technical difficulty, a cost of about VND7,500 billion, a high level of safety/operation, ease of expanding the MRT, and a level of suitability for the infrastructure of Da Nang International Airport.

With the MRT system combined with the road tunnel, integrating the MRT and the road tunnel into the same tunnel structure helps reduce the occupied area, especially in the airport area where land is often limited. The cost of tunnel excavation and infrastructure construction is also reduced because only one construction is required; at the same time, only one tunnel is needed instead of two, which helps limit the impact on airport operations on the ground such as runways and terminals. In addition, passengers from the airport can easily switch between the MRT and road vehicles in the same area, improving the travel experience.

For the MRT system combined with the road tunnel, the MRT and the road tunnel operate separately, so a problem in one system does not directly affect the other, ensuring continuity and stability. Repairs, expansions or renovations to one system can be carried out without interfering with the other system, minimising disruptions. In addition, each tunnel only serves one type of vehicle, so the technical requirements (ventilation, load, safety) are optimised separately, reducing the complexity of construction. The location or route of each tunnel can be adjusted to suit the specific needs of the airport without being constrained by the other system.

The Department of Construction recommends that for the tunnel route through the airport, it is not advisable to combine the arrangement of the MRT line and the road to go together. The reason is that the technical standards of the MRT and the road are different. At the same time, the investment progress of the MRT line has not been determined, so with rapid changes in technology, the determination of the route and technology will be selected at the time of investment. However, with actual conditions such as the Da Nang airport being planned for expansion, the MRT route option also needs to be studied soon.

Reporting by THANH LAN - Translating by ANH THU