fall into, cave in, fall (castle), slide into
陷 centers on a sudden downward collapse: falling into a pit, a cave-in, a castle falling to siege, or sliding into a bad situation. All meanings share the idea of being trapped or overwhelmed by a downward force.
陷 combines ⻖ (mound, hill) with 臽, which likely contributes both sound and the idea of a pit or trap. The character originally depicted falling into a pit or being trapped in a depression.
The left side ⻖ suggests a steep slope or mound, and the right side 臽 looks like a person falling into a pit with a cover closing over them. Together, they show a sudden collapse or trap.
For カン, imagine a can falling into a deep pit: can -> カン, and the can clatters down as the ground caves in.