Identify the Cause of Wall Failure

What happens here

Closely examine any exposed sections of the wall and the material directly behind the failed timbers. The video explicitly identifies the root cause of failure, stating that the wall collapsed "not just because of the fact that it is timber, but the fact that there's just soil behind this," specifically pointing out "sand right up against the back of this wall." Understand that the absence of proper drainage and an appropriate granular backfill material (such as gravel) directly led to excessive hydrostatic pressure, which ultimately caused the wall's structural failure and collapse.

Goal: Understand the structural reasons behind the wall's collapse.