scratch, dig up, crawl, crouch
扒 centers on using the hands to scrape or pull at something: scratching, digging up, or moving in a low, scrabbling way like crawling or crouching.
扒 combines the hand radical 扌 with 八, which may have contributed a sound element. The exact historical development is uncertain, but the hand component fits the scratching and digging meanings.
A hand 扌 beside the shape 八, which looks like two claw marks. Picture a hand scratching or digging into the ground, leaving two parallel grooves.
For ハイ, imagine a hand scratching a high wall: high -> ハイ, and the scratching sound echoes as you dig upward.