This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
墱 combines 土 (earth) with 登, which likely contributes sound. The exact historical development is uncertain.
The left side is earth 土, and the right side is 登 (climb). Imagine earth piled up to form a steep path or steps for climbing.
For トウ, picture climbing a tall earthen mound: toe by toe, you ascend. Toe -> トウ.