Hydrostatic pressure builds behind walls when drainage is poor, pushing even strong structures out of plumb

https://rylannncg173.lucialpiazzale.com/why-atlanta-hillside-lots-need-engineered-retaining-walls-not-stacked-block

Hydrostatic pressure builds behind walls when drainage is poor, pushing even strong structures out of plumb. Gravel backfill, perforated drains, weep holes, and geotextiles are critical to stop water from toppling walls.