Uttarakhand tunnel collapse: What happened?

#Uttarakhand #India #BBCNews
Forty-one Indian workers rescued from a tunnel in Uttarakhand after being trapped inside for 17 days are safe and recuperating in hospital.

The workers got trapped inside the tunnel on 12 November after a portion of it collapsed due to a landslide.

They were freed on Tuesday evening after a mammoth rescue operation that overcame many obstacles.