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Soil Testing Begins Under Big Dig Tunnel In Sinkhole Probe

BOSTON (CBS) - The state Department of Transportation has started testing the soil near South Station to try to determine the size and cause of the sinkhole underneath the I-90 Connector Tunnel.

They are testing 140 feet below the ground and collecting samples every two feet. The samples are being sent to a lab to determine the extent and cause of the thawing.

When this section of the tunnel was built, the soil was frozen to keep it from collapsing. It was always expected to thaw, just not to this extent.

It was revealed in August that the soil ended up compressing twice as much as expected, creating a hole underneath the tunnel.

They will conduct the soil tests in four areas for the next three-to-four weeks.

Transportation Secretary Richard Davey said the tunnels are safe.

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