プログレッシブ和英中辞典(第4版)の解説
つみかさね【積み重ね】
〔蓄積〕accumulation;〔積んで高くなった山〕a pile, a heap(▼pileは積み上げたもの,heapは雑然とした山)
経験の積み重ね
the accumulation of experience
それは彼の努力の積み重ねのお陰だ
It is due to his constant [unremitting] efforts.
この仕事は経験を積み重ねないとできない
You'll be able to do this work only after 「you accumulate [you've had] years of experience.