Wong Cheuk Kwan comments

The Yen is still too high at around 100. Depreciation of the Yen is necessary but the enterprises have to work smarter and harder to produce products/services that the world (not just Japan) will need (look at the Samsung products). The complicated economic system has to be trimmed for hgiher efficiency and effectiveness. The immigration policies have to be adjusted to deal with the aging society. Every person from the Prime Minister (who takes the correct move to depreciate the Yen) to an ordinary person on the streets has to work harder and smarter for reforming the economy. Learn from Iceland as to how to save its collapsed economy - http://www.youtube.com/watch?v=_idQjW4ZWak

Japan has built a lot of infrastructure in the past 30-40 years. The quantity Such infrastructure built by the Government and the Private Operators now must amount to immense figures. The recent tunnel disaster reveals that the operator has not maintained the flat slabs and the anchoring systems for 35 years after commissioning. This is only the tip of an iceberg. Does the Japanese Government implement a system for the so-called "Infrastructure asset management (IAM)" (ref. Wikipedia on http://en.wikipedia.org/wiki/Infrastructure_asset_management)?

From a seminar I attended 4 to 5 years ago organized by the Instution of Civil Engineers in Hong Kong, the speaker introduced the IAM already implemented in UK. IAM is the integrated, multi-disciplinary set of strategies in sustaining public infrastructure assets such as water treatment facilities, sewer lines, roads, utility grids, bridges, and railways. With this system in place, the government officers can easily manage the infrastructure built and the degree of maintenance needed. This is just like the inventory control in a company or warehouse or banks. If a private company does not know what inventory it posseses, how can it order new goods and make money with little wastage.?

A simple working definition of asset management would be: first, assess what you have; then, assess what condition it is in; and lastly, assess the financial burden to maintain it at a targeted condition. It is understood that Japan has built a lot of valuable infrastructure but what are the conditions at the moment, how safe they are and what is the priority of maintenance to achieve a reliable degree of safety for the public to use within the contraints of finance, technology and human resources needed??

Please install additional supports for the flat slabs in other tunnels using the same design, while the investigations are going on. This is to prevent another disaster from occurring. Time is running out!

The flat slabs supported by means of ordinary steel rods inside the tunnel are expected to fail within 20-30 years after use. Failure after 3 decades of use is not surprising. Therefore, it is dangerous to use tension rods whether they are made of stainless steel or ordinary steel.

According to the Murphy's Law, "Anything that can go wrong will go wrong". The original design using tension rods to support the flat slabs has a limited design life of say 20-30 years. If there exist stress corrosion cracks inside the grains of the metal bars, visual inspections cannot detect them. Failure is expected to occur within 20-30 years of construction. It is better now to figure out a permanent solution like installation of arch-shape steel beams to support the existing flat slabs. This solution may be more cost effective and quicker than reconstruction of the overhead air-ducts using curved slabs resting on the tunnel walls by means of arch action.

After talking to an experienced engineer in Hong Kong yesterday, I now became aware that in the 1960-70s, engineers installed overhead ventilation air ducts above the flat-slabs, which were in turn supported by tension bars anchored into the roof of tunnels. Such a design relies on the use of tension bars anchored into the roof of tunnel to support the flat slabs but the bars would corrode in 10 to 20 years and with stress corrosion cracks in the metal, the bars might fail. Competent structural engineers should not have adopted such a design. Later in 1980s-90s, engineers started using curved (with the crown pointing upwards) instead of using flat slabs. The curved slabs are resting on the sides of the tunnel and by means of arch action, transfer the loads from the curved slabs to the tunnels walls. Like arch bridges that do not need columns, curved slabs do not need using central supports by means of tension bars. Thus, the least maintenance is needed for the curved slabs..

If the flat-slab design was already formally approved in the 1960s-70s, it cannot be said that there was negligence on the engineers of the old time. The design life of the metal tension bars has reached its design life limit so we should not blame the maintenance staff. But the problems now are how to provide new supports to the flat slabs. Of course, these slabls can be reconstructed but the costs are prohibitive. I suggest that engineers should think of using hot-dip galvanized arch-shaped steel beams to support the flat slabs. Hot-dip galvanization can provide steel with a design life of 25 years at least and these beams can be replaced later easily. The beams can be resting on hot-dip galvanized steel frames placed against the tunnel design walls if the walls do not have enough strength. As long as there is still enough headroom inside the tunnel, the curved beams can be placed beneath the flat slabs. Otherwise, the steel beams can be installed above the flat slabs but hangers are then needed to support the slabs.

It is far better to think of remedial actions now for the many tunnels than to pursue why the old design now becomes ineffective and which engineers should be blamed.

I am a retired civil and structural engineer in Hong Kong. It is very shocking for me to note that the roof of the tunnel failed, not because of the rock at the roof, but because of the heavy concrete panels suspended from the roof. These heavy concrete panels might have been used to act as false ceilings. I have not yet seen the use of heavy concrete panels here (too dangerous). Why not use light-weight alumimium panels as false ceilings (or no ceilings)? It must be understood that any steel supports (if not made of high-grade stainless steel) can corrode in 10-20 years. This is common sense, and I don't believe that the conservative Japanese engineers could have made such low-level mistakes.