Wall failure after a typhoon

This photo shows wall failure during a heavy rainfall caused by a typhoon.

There was no adequate internal drainage in the fine-grained backfill although water in front of the wall was collected by a concrete-paved ditch. Redundancy due to apparent cohesion disguised the lack of proper drainage for four years, holding the wall system stable. When heavy rainfall occurred—as should have been expected during the life span of this wall—the apparent cohesion vanished resulting in failure.