The Wugu-Yangmei Overpass, where cracks were found last week, poses no immediate danger to drivers, the National Expressway Engineering Bureau said yesterday, following an investigation over the weekend.
The 40km-overpass, which opened four months ago, was built alongside the Sun Yat-Sen Freeway (National Freeway No. 1) to divert the traffic between Wugu (五股) in New Taipei City (新北市) and Yangmei (楊梅) in Taoyuan County.
Its safety came under scrutiny after three cracks were found in the road by the 45km-marker last week.
As the damaged road surface was discovered after the nation was struck by heavy rainfall brought by Tropical Storm Trami, many have begun to question the quality of the overpass’s construction and whether it is able to withstand the impact of natural disasters.
The bureau said that it launched a two-day on-site investigation to determine the cause of the cracks.
It excavated section of the road in which the cracks were found, as well as those nearby, and compared the data with results of the geological surveys previously done on National Freeway No. 1.
The investigation showed that the draining of the overflowing groundwater caused by heavy rainfall was not quick enough, which forced some groundwater to flow in the direction of the road surface, the bureau said.
Some media reports compared what happened on the overpass last week with the massive landslide on the Formosa Freeway (National Freeway No. 3) three years ago that killed four people. However, the comparison was wrong, the bureau said.
The 2010 landslide at the 3.1km-marker of National Freeway No. 3 happened because the road has a dip slop, formed by sandstone and shale, which was softened due to continuous infiltration of the ground water. The ground anchors lost their grip on the dip slope due to corrosion. Both factors together had caused the massive landslide, the bureau said.
According to the bureau, construction personnel would continue monitoring the overpass. The bureau said it would work on measures that would help drain the excessive groundwater, or obstruct the refill of groundwater.
Taiwan Geotechnical Society civil engineering experts would be invited to conduct a separate safety assessment and offer suggestions, which the bureau would follow to reinforce the structure of the overpass.
The bureau said the problem will not affect the safety of the overpass.