Chennai: Soil underneath the road became loose and gave way to the road caving in due to tunnel boring work that is underway on the 2-km stretch between Thousand Lights and DMS, Metro officials said on Sunday.

Minutes after 2 pm, a crater around 5m wide, 10m long and about 2m deep was formed on the arterial Mount Road, which witnessed a lean traffic, as it was a Sunday. “Two tunnel boring machines (TBM) are being used to make a tunnel underneath. A solution is poured in front of the TBMs to hold the tunnel intact as the boring work goes on. A strong pressure is exerted on the TBMs so that it can move forward while making a tunnel,” said a senior CMRL official to Deccan Chronicle.

A similar incident happened in the last week of March, when a small portion of the road in the same area had caved in and foaming water had gushed in. When asked about how such risky incidents can be avoided in future, the official said that with the current technology involving TBMs it is not possible to know beforehand if the work is causing any impact to the soil underneath the road and above the TBM work.

“We can try reducing the pressure imparted by the TBM while making the tunnel, else such incidents creep in at places where there is some looseness in the structure of the soil,” the official added.

As the incident came to light senior CMRL officials, in-cluding the Managing Director, rushed to the site for inspection. “A monitoring point has been installed throughout the tunnel alignment at 10m intervals. A continuous reading is taken every six hours to cross check any development due to the ongoing tunneling works,” an official statement from CMRL said. “The recent reading was taken around 2 pm just before the incident and there was no settlement recorded while taking the reading.”