Crews sample soil beneath Big Dig tunnel

BOSTON -- Drilling crews are searching for clues near a Big Dig tunnel.

Contractors are looking at the frozen soil around the I-90 tunnel to investigate a possible sinkhole.

During construction of the tunnels, crews chemically froze the soil so they could drill into the ground.

That soil is now thawing and causing the ground to sink.

Engineers say the tunnels -- and drivers -- are not in any danger.

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