The use of cohesive soils in geogrid‐reinforced backfills requires consideration of the performance of these materials under both as‐compacted and long‐term conditions. Depending on the as‐compacted conditions, the long‐term performance, as a result of in service saturation, can lead to strength loss and failure of such structures. This paper documents the case history of a geogrid reinforced retaining wall, constructed with cohesive backfill, that failed. Several different failure modes were observed along the wall. The results of extensive field and laboratory testing programs and engineering analyses to investigate the causes of failure are presented. These studies permit the different observed failure modes to be explained. Deficiencies in design and construction quality control are identified. The need for site‐specific design considerations rather than generic design procedures for such structures is demonstrated.