An onomatopoeic/mimetic word describing a squelching, squashing, or splatting sound — the noise or feeling when something is crushed or soggy.
庭の泥を踏んでグチャリと音がした。
I stepped on the mud in the yard and it made a squelching sound.
パンが古くて中身が柔らかく、噛んだらグチャリとしてしまった。
The bread was stale and soggy inside; when I bit it, it went squishy.
雨で濡れたチラシを踏んでグチャリと潰れてしまった。
I stepped on a rain-soaked flyer and it got squashed with a splat.