Chennai metro collects soil samples from Adyar bed from next week

Starting next week, a team of engineers of Chennai metro will collect samples from the Adyar river bed ahead of tunnel construction to operate driverless trains. The test will be finished before tunnelling starts in October.

Twin for about 400 m lengths will be built under the river up to 29 m depth to connect Greenways Road metro station with Adyar junction station. For the three corridors 118.9 km phase-2 project, the deadline is 2025.

A metro rail official told the media that the samples would be collected at 12 m to 18 m depth for every 25 m to 50 m distance. Two drilling rigs will be deployed in specially designed boats measuring 10 m X 6 m.

It will take at least three to four months to finish the soil sample collection and investigation. Now, the water flowing in the river is at 6 m depth, so we require boats to take the rigs for sample collection.

While Chennai Metro Rail Limited (CMRL) had conducted soil tests before awarding construction contracts, the contractors were offered an option to do their tests. Thick sturdy tunnels will be constructed through rocky soil strata under the river, with heavily reinforced concrete slabs and additional grouting to seal the surface to ensure no water seepage.

In phase-1, tunnels were constructed under Buckingham Canal at about 30 m depth. Special tunnel rings with heavy reinforcement were created and established to counter the load from the top overburdened crust and the canal water. Under the Adyar river, the top of the tunnel will be at 18.75 m to 22.35 m depth from the river bed, while the bottom of the tunnel will be 25.05 m to 28.65 m depths.

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