Damage of Entryway Stairs due to Settlement of Gravel Backfill

It is commonly assumed that open-graded gravel dumped behind gravel walls will not settle. This paper presents a case history where open-graded gravel was dumped behind garage walls; stairs were then built atop the gravel; and the gravel and the stairs settled with time. The stairs were initially constructed to slant away from the buildings, but in some cases they settled so much that they now tilt toward the buildings. The typical amount of settlement of the entryway stairs was about 1–2 in. (2.5–5.1 cm). The settlement of the gravel backfill could have been triggered by light vibration or perhaps even the flow of water down through the gravel backfill. The potential for settlement can be reduced by placing the gravel in thin layers and densifying the gravel using vibratory compaction equipment on each layer.