Simile? Metaphor? Mixed metaphor? <confused>

[fuzzpig]

Wasn't sure where to put this post sorry.

Reading to DD earlier and she's keen to point out similes/metaphors lately.

Then we came to this:
"Lower down there were great pillared arches, yawning blackly like the mouths of railway tunnels."

We couldn't decide what it was. DD first noticed 'like the...' so that would make it a simile. But then the yawning bit on its own would be a metaphor since the arches can't actually yawn. But then neither can tunnels.

I googled mixed metaphors (don't remember doing that in school myself) but not sure that fits.

Can anyone help please? :)

A simile with personification, imagery can have more than one type in a sentence.

Aha! I didn't know about personification, so I googled it. That's great, thank you :) will tell DD tomorrow.