The workers used a rammer to pack the foundation tight.
Tips
usage
夯 is the everyday reading: the heavy tool that pounds earth, or the action of pounding. Common in 夯实 ('to ram solid'), now also used figuratively for 'to consolidate (a foundation, skills)'.
memory
Picture the parts: a 大 (big) person putting 力 (force) into slamming a heavy block down. Big effort, downward force, that is 夯.
大 on top pictures a big person. Combined with the force element below, it gives the meaning idea of a person putting their whole weight into pounding the ground.
