stake, post, affair, matter
樁 centers on a wooden stake or post driven into the ground. The extended senses of affair or matter are rare and likely derive from the idea of a fixed point or marker, but this connection is uncertain.
樁 combines 木 (tree/wood) with 舂, which likely contributes the sound. The exact historical development is uncertain, but the character is associated with a wooden stake or post.
A wooden 木 stake is pounded into the ground with a heavy pestle-like 舂 action. Picture a large wooden post being driven deep into the earth.
For トウ, imagine a tall wooden stake marking the start of a long toe path: toe -> トウ, and the stake stands firmly at the beginning.