Rama IV sinkhole is not threat to subway, official says

The Bangkok Metropolitan Administration (BMA)’s Public Works Department will check the rest of the tunnel under Rama IV Road as well as Henri Dunant Road and Sena Niwes Road, while conducting an ultrasound check of all BMA roads. 

The sinkhole, which was five metres in diameter, or two lanes across, and about 2 metres deep, opened up at the Rama IV intersection at 7.45pm on Sunday. By 5am yesterday, the BMA had filled the hole and paved the road with asphalt before reopening it to traffic. 

Although the sinkhole was near a subway station and waterworks tunnel, Metropolitan Water Authority (MWA) and MRTA officials initially checked and couldn’t find any flaw or damage to either system, Jumpol said. 

The Mass Rapid Transit Authority of Thailand (MRT) said in a press statement the sinkhole had no effect on the subway station at Lumpini Park because the station was about 20m underground.

Following a meeting yesterday with MRT and other agencies, Jumpol said the sinkhole resulted from the seeping of 40-50 cubic metres of sand from underneath the road, which had been used heavily for a long time. He said the sand might have seeped through a nearby drainage tunnel under the Rama IV Road, as the tunnel, built in 1972, had been in service for 40 years without any maintenance. 

Jumpol said the oval-shaped 3m x 3.5m tunnel was used to drain water at 220 cubic metres per second. The BMA would check if seepage occurred at the front of the tunnel. If it had, the tunnel might be shut down for repairs, he said. 

Besides the tunnel under Rama IV, Jumpol said the BMA would also check two similar tunnels under Henri Dunant Road and Sena Nikhom Road. The BMA drainage office would study and hire a consultant company to prepare for the major repair of these three old tunnels, he said. 

Retrospect checking found two similar incidents occurred in 1972 and 1979, and the BMA has urged Pathumwan and Sathorn districts to examine roads for any sinkholes and report back to the BMA urgently, he added. 

BMA Deputy Bangkok Governor Thirachon Manomaipibul said the BMA’s Public Works Department was instructed to survey all BMA roads to check for possible sinkholes, using ultrasound equipment. 

Thirachon said the BMA had found 20 risky spots along the Rama III road to Chong Nonsi Road during the construction of the Bus Rapid Transit system where soil had seeped to the side into a roadside canal. They had already been repaired. 

He said road sinkholes could occur because of the city’s expansion with building, subway and pipe-laying construction.