Excavation has shifted by foot (5)
I believe the answer is:
shaft
'excavation' is the definition.
(I have seen 'Vertical excavation' mean 'shaft' so perhaps 'excavation' could also mean 'shaft')
'has shifted by foot' is the wordplay.
'shifted' indicates anagramming the letters.
'by' is a charade indicator (letters next to each other).
'foot' becomes 'ft' (synonyms).
'has' anagrammed gives 'sha'.
'sha'+'ft'='SHAFT'
(Other definitions for shaft that I've seen before include "Vertical mine access" , "Ray (of sunlight)" , "Beam - well" , "Long slender part or deep vertical opening" , "Beam of light" .)