While Network Rail have not responded to the Post's request for information, plenty of theories have been put forward on social media about the work.
Some people think the work is connected to the tram line being proposed by Preston Trampower.
>>>Click here to read how we reported the tram plans in 2020.
James Taylor said: “What’s going on there? Is this for trams? When are they running?”
Karen Lee said: “I think I’d read that they were reopening it for tram use?”
Tony Singleton said: “Is this work anything to do with reinstating the Longridge route, or is it being filled in?”
Matt Adam Cartwright said: “Looks like they’re doing structural works nothing more.”
Vicky Crowe replied and said: “Loading bay on the scaffolding so not structural ... wonder what they're doing?”
Karen Robinson wrote: “Think they making walls on either side of wind tunnel safer or higher because it's a long drop over walls that are already there.”
Jennifer Clements said: “I love Miley I hope they don’t change it. Used to go in there as its supposed to be haunted.”
John Gill said: “Miley tunnel scary – rats scurrying around as you was walking through.”
Charlotte Holden said: “Used to go down there with my mates and be afraid of man holes”.
Many people shared their childhood experiences of walking through Miley Tunnel.
Marie Fitzsimon said: “Went through the tunnel a few times when we were kids. It is kind of creepy especially in the middle were it bends slightly.
"Very silent and cold in that area.”
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Mandy Britton said: “This place is haunted I went down there with my brothers when i was about eight and we heard a train.
"We felt the vibrations of the train so much so we ran to the nearest place to get away from the train – pinned against a wall I think we were, only to find the train didn’t come.”