hankyoreh

By Nam Jong-young　

The Waegwan Railroad Bridge in Yangmok Township, Chilgok County, North Gyeongsang Province (also known as the “Bridge of National Defense”), after standing solidly for the last hundred years, has collapsed in light monsoon rain. The bridge, which, after being built across the Nakdong River in 1905, had withstood not only major typhoons such as “Maemi” and “Sara” but also the greatest Korean flood in the 20th century, in 1925, is a registered modern cultural property.

The bridge collapsed at around 5:15 a.m. on June 25. The Nakdong River had swollen due to rain that had been falling since June 22, when the bridge’s second pier suddenly collapsed, leaving a 100m stretch of the bridge stuck in the water. Several thousand people cross the bridge, now used by pedestrians only, every day, but the fact that the collapse occurred in the early hours of the morning meant that there were, luckily, no injuries.

“It appears that this occurred because of heavy rainfall, which led to higher water levels and a higher rate of flow,” the Ministry of Land, Transport and Maritime Affairs (MLTM) said on June 25 regarding the cause of the accident. But barely 13.5mm (0.5 inches) of rain fell in the Chilgok area on June 24, the day before the collapse, while rainfall in Sangju and Andong, upstream from the bridge, were no higher than normal monsoon levels at 128.5mm and 147mm respectively. The bridge, moreover, was deemed “satisfactory” by a safety examination conducted immediately prior to the start of the Four Major Rivers Restoration Project. A bridge that stood for 100 years during which rainfall levels reached 100mm two or three times every year, has collapsed.

At the time of the collapse, dredging as part of construction for the Four Major Rivers Restoration Project was in full swing. The swollen water was forming eddies above the riverbed, into which dredgers had dug deep. The rapid currents hit the piers supporting the bridge hard. It appears that the pier had been weakened. This is because dredging for Four Major Rivers Restoration Project had taken place around the pier, just like everywhere else. If the riverbed is excavated to a significant depth around a pier, the base of the pier is exposed and begins to be eroded by the flowing water.

Because of this, dredging around the area of the bridge was limited to a depth of 4m (13.1 feet), but this was not strictly observed.

“Because we have to dredge large amounts at a time if we are going finish our work quickly, we used excavators with specially lengthened digging tools on the Nakdong River,” said Song Chan-heup, head of the Daegu Construction and Mechanical Workers’ branch of the Korean Confederation of Trade Unions (KCTU). “Digging tools that could go down to a depth of 6-7m were also used near the Waegwan Railroad Bridge.”

Protective work to reduce erosion had not taken place, moreover, on the second pier. An environmental impact assessment and reinforcement plan for Waegwan Railroad Bridge submitted by Busan Regional Construction Management Administration (BRCMA) stipulate that construction work to shore up all seven piers of the bridge must take place. This is necessary in order to at least allow the pier to withstand the water pressure once the ground around it has been worn away.

“Last year, when we ran out of places to process the huge amounts of dredged matter, we reduced dredging volumes and the plans for dredging around Waegwan Railroad Bridge were also changed,” said an official at BRCMA. “We made the judgment that there was no need to shore up the second pier because the plans to dredge around it were canceled.”

Despite the changed plans, BRCMA did not notify the local environment office at Daegu. The work went forcibly ahead with no assessment of safety and the river brought down the second, and weakest, pier.

Park Chang-kun, professor of civil engineering at Kwandong University, said, “The construction work went forcibly ahead in order to meet the deadline, with no alternative sought despite an important change in plans.”

Experts have specifically noted the fact that a bridge that had showed no signs of damage collapsed after barely 100mm (3.9 inches) of rain. Their opinion is that the accident was provoked by a combination of globally unprecedented excessive dredging and sub-standard construction work.

Park Jae-hyeon, professor of civil engineering at Inje University, said, “If Waegwan Railroad Bridge collapsed after this amount of rain, there is a high probability that accidents will also occur at other places in future.”

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