Having piled all the wood outside, slump on the ground (8)
I believe the answer is:
collapse
'slump on the ground' is the definition.
'collapse' can be an answer for 'slump' (I've seen this before). I'm not sure about the 'on the ground' bit.
'having piled all the wood outside' is the wordplay.
I cannot really see how this works, but
an anagram of 'all' is 'lla' which is within the answer.
'wood' could be 'copse' (I've seen this before) and 'copse' is found within the leftover letters.
This accounts for all the letters.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for collapse that I've seen before include "Faint and fall" , "Abrupt failure of function" , "Founder" , "Break down - fall" , "Disintegration" .)