Dorset County Council said they are now checking the structure of Beaminster Tunnel in Dorset.
It's parapet was destroyed in a landslide caused by heavy rain.
The Council said they will need to tackle the drainage before they address the stonework.
Beaminster Tunnel is expected to remain closed until the 22nd July.
More top news
Bristol City manager has moved to reassure club supporters and detractors. Lee Johnson remains defiant about the severity of the situation.
The latest forecast for Bristol, Somerset, Wiltshire, Gloucestershire and Dorset.
Here's the forecast for Devon, Cornwall, Somerset and Dorset.