expression, na-adjective
mountain of; piles of; a lot of
Figurative expression comparing a large amount of something to a mountain. Used with nouns to indicate abundance.
机の上に山のような書類がある。
There is a mountain of documents on the desk.
彼は山のように仕事を抱えている。
He has piles of work to do.
たくさん is a general quantifier meaning 'many' or 'a lot', while 山のよう emphasizes a visually or figuratively large pile or amount, like a mountain.
山ほど is a more casual, adverbial expression meaning 'loads of' or 'tons of', often used in speech. 山のよう is slightly more descriptive and can be used attributively with な.
Compound of 山 (mountain) + の (possessive particle) + よう (appearance, likeness). Literally 'like a mountain', used figuratively to describe a large quantity.