A study to assess and understand what causes sinkholes on roads across the city will help prevent such incidents to some extent, experts say.
After the incident where a sinkhole developed near the Chennai Metro Rail site on Sunday, civil engineering and road transport experts say a host of issues could cause this problem and a study will aid in getting to the roots of the issue.
K.N. Krishnamurthy of Indian Roads and Transport Development Association, says, “Civil engineering experts from IIT-Madras or any other reputable institute can be used to do the study. Since such sinkholes have occurred in the past too, if a study is done, it will help in assessing a pattern, understand what caused it and find solutions.”
Civil engineering experts from IIT-Madras say such studies will be very expensive but they will determine what led to formation of sinkholes in different areas. Officials of the CMRL say tunnelling work didn’t cause the sinkhole as it was over years ago.
Civil engineering experts from IIT-Madras say the after-effect of the Chennai Metro Rail tunnelling work or even air pockets in the soil due to various other reasons, however, may have caused it.
“Tunnelling work may cause settlement of soil even after years after it is complete. That apart, even if there is an old sewerage line nearby and has given way, sinkholes can occur,” an expert from IIT-Madras, who didn’t wish to be named says. Even if there is construction work happening in the nearby area, the vibration may force soil to settle, he adds.
If grouting is carried out well and soil is strengthened, sinkholes caused by the Chennai Metro Rail work can be avoided, another expert from IIT-Madras adds.
Sources in the Highways Department say land on which the sinkhole appeared originally belonged to the Directorate of Medical Services.
“We had taken it over through alienation way back in 2002-03 and formed a bus bay. From that time till now, we have not had any problem. This hole could have been caused only as a result of excavation — either for the D wall or for the tunnel itself,” the official explains.
Highways engineers, who were at the spot during the repairs, said that they could see a block of tar of about 2 feet thickness and had to use an earthmover to cut the road. “The soil in that area is not clayey, but lose. Measures are usually taken to control soil sliding. This seems to be a problem that happened during construction and it is nobody’s fault. We can expect soil sinking to happen for another year or so even after completion of the works,” another official said.
