This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
垸 combines 土 (earth) with 完, which likely contributes sound. The exact historical development is uncertain.
The left side is earth 土, and the right side is 完 (complete). Picture a completed earthwork, but its exact meaning is unclear.
For カン, imagine a can of earth sitting beside a completed mound: can -> カン.