small hill, mound, bury, dam
陻 centers on a small earthen rise or mound, and by extension the act of burying or blocking with earth, as in a dam.
陻 combines ⻖ (mound, hill) with 垔, which likely contributes the sound and the idea of earth or blocking. The exact historical development is uncertain.
The left side ⻖ is a mound or hill, and the right side 垔 looks like earth piled up. Picture a small hill made of packed earth, used to bury something or block water like a dam.
For シュ, imagine a shoe buried in a small mound of earth: shoe -> シュ, and the mound covers it completely.