According to Oriental Consultants’ Director R. MaNai, the three solutions consist of: making the best of self-healing mechanisms of concrete, relying on ventilation or using specialized glues like polyurethane or epoxy. He explained that the first method is very useful for cracks of less than 0.2mm wide. The second solution can alleviate moisture up to the designed level. The last measure is effective for larger cracks.

Oriental Consultants will present its detailed repair plan in July and will begin working in the same month once all segments of the tunnel are joined.

“The repair will be completed before the tunnel is handed over to the equipment contractor,” R. MaNai predicted.

He added that repairs can’t be carried out immediately because of the water tanks used to hold segments from rising to the surface. Once these tanks are dismantled, the repairs will be performed.

East-West Avenue Project Management Unit Director Luong Minh Phuc explained that the two first solutions are auxiliary measures. The major one is using specialized glue to fill the cracks. “Many underwater works in the world have used this method, such as the tunnel at Australia’s Sydney Port. It work has been used for 20 years,” Phuc noted.

According to Oriental Consultants, there are three levels of leakage. The first is called moistness if the surface of concrete is discoloured. The second is soaking if someone touches concrete and feels water on the surface. The third is leaking if concrete changing its color and water is dripping along the wall. The 130 spots in Thu Thiem tunnel belong to the first and second levels.

The consultants agree that the leaks are not serious and that they don’t affect the tunnel’s structure.

MaNai confirmed that the standard of leakage applied for Thu Thiem tunnel (less than 5cc/hour/one square meter or 0.12l/day/one square meter) is applied for many other submerged works in the world.

According to Oriental Consultants’ report, the space between the concrete and bolts and sand-blowing pipes is among the reasons for the wet and soaked spots.

Thu Thiem tunnel is the longest river tunnel in Southeast Asia. It has four segments, 93m long, 33m wide, 9m high each, nearly 27,000 tons in weight.

From March 7-10, the first segment were in place. The second segment was connected on April 5-6 and by April 28. On May 5-6, the third segment was set in place and connected to the other segments. The last segment will be joined to the third on June 4-5. The tunnel is scheduled for completion this August and the entire East-West avenue will open for traffic at the 2011 Tet festival.