raft foundation vs substructure

raft foundation and substructure both are nouns.

Word	Noun	Adjective	Verb	Adverb
raft foundation	Yes	No	No	No
substructure	Yes	No	No	No

As nouns, substructure is a hypernym of raft foundation; that is, substructure is a word with a broader meaning than raft foundation:

raft foundation: a foundation (usually on soft ground) consisting of an extended layer of reinforced concrete
substructure: lowest support of a structure

Other hypernyms of raft foundation include base, foot, foundation, fundament, groundwork, understructure.

raft foundation (noun)	substructure (noun)
a foundation (usually on soft ground) consisting of an extended layer of reinforced concrete	lowest support of a structure
	the basic structure or features of a system or organization