The cause of subsidence in Vinh city has been identified.

(Baonghean.vn) -At the meeting with the functional agencies of Vinh City People's Committee on the afternoon of September 14, the cause of the subsidence of the North Canal was determined.

According to the report of the Vinh Urban Development Sub-project Management Board, the location of the incident is the GT9 separation station, at KM 1+115 on the left bank of the canal, at the corner of Phung Chi Kien Street and Le Nin Avenue, part of the Northern Canal Construction and Upgrade Package - Section 2, constructed by Tan An Construction Joint Stock Company.

After the rain that lasted for many hours, from 2:00 p.m. to 4:00 p.m. on September 13, on Phung Chi Kien Street (connected to Lenin Avenue), there was a phenomenon of subsidence of manholes, sidewalks and part of the roadway. The mouth of the sinkhole at 3:00 p.m. was about 30 square meters, the discharge gate sank 25 cm deep, the telecommunication manhole tilted 30 degrees; there was a frog-jaw phenomenon, part of the road surface collapsed.

This subsidence phenomenon happened very quickly, after only about half an hour the sinkhole had reached nearly 30 square meters, the manhole had sunk 25 cm deep, at this time observation showed that the D1000 sewer joint at the first and second sewer segments, between the second and third segments was broken open, water gushed strongly from inside the sewer.

After reviewing and evaluating, AYCC Consultant - the project supervisor, found that running along the sidewalk of Le Nin Street, there are D1200 BT drainage pipes and D150 fiber optic cable bundles; at a location about 15m from the outlet, there are two technical stations of the two above pipes. Within 100m from Le Nin Avenue to the location of these two stations, there have been many times when the Le Nin Avenue sewer pipes have leaked and localized subsidence, in which typical subsidence holes have appeared before (the first time in January 2016, the second time in mid-August 2016 and the third time on September 12, 2016). People have filled and restored these sinkholes themselves.

When repairing the sinkhole of the D1.200 pipe and fiber optic cable, sand was found flowing along the outside of these pipes towards the GT9 separation station. From August 18th to now, there has been continuous heavy rain; of which, on September 10th, 11th, 12th and 13th, there was heavy rain that lasted all day and night.

On the morning of September 14, the construction unit temporarily fixed the problem by inserting sandbags into the sinkhole. When the rain stops, the unit will study solutions to completely fix the problem.

Based on the above factors, the functional sectors of Vinh city have determined that the cause of the subsidence is due to water flowing for a long time along the outer wall of the existing sewer D1200 due to escaping from the damaged joints of this pipeline along Le Nin Avenue, leading to erosion of sand to the embankment to the location of the GT 09 separation station.

New landslides appeared around the mouth of the culvert that empties into the main canal.

In recent days, due to heavy rain, the overloaded sewers could not drain in time, the flow was very strong. The stronger the flow, the sand flowed around and under the circular sewer of Lenin Avenue near the GT09 separation station, including the joints between D1200 segments No. 1 and 2, No. 2 and 3, which were loosened. This loosening caused more water in the D1200 sewer to overflow outside the separation station and the discharge gate, leading to a sharp increase in the subsidence rate in just under 2 hours.

On the morning of September 14, workers actively filled sandbags into the sinkhole despite heavy rain.

Previously, on the morning of September 14, authorities continued to work to minimize the subsidence because there was continued landslides around the drainage outlet to the main canal.

Regarding the solution to this problem, Mr. Nguyen Quoc Thang - Head of Vinh City Urban Management Department said that currently, Tan An Company is coordinating with Vinh Urban Infrastructure Management and Development Joint Stock Company to implement measures to maintain and repair the above subsidence point.

Vinh City Urban Management Board also directed that in the immediate future, it will limit subsidence points with sandbags, prevent new landslides from appearing, and ensure traffic for people.

After the rain stops, the relevant authorities and construction units will assess the extent of the incident's impact and come up with a thorough solution./.

Ha Chi - Hoai Thu