Why Dry Soil Collapses When Wetted | Collapse Potential Derivation and Example

Some loose unsaturated soils appear stable while dry but suffer sudden volume loss when wetted under load. This lesson uses 2D and 3D animation to explain the open metastable fabric, capillary suction and weak bonds that support it—and the particle rearrangement that produces collapse settlement. The video derives collapse potential in height, volume and void-ratio forms, explains the one-dimensional inundation test, and emphasizes that severity tables are valid only with their referenced procedure and inundation stress. A worked example calculates 6% laboratory collapse potential and an idealized 120 mm field-scale screening estimate, followed by practical control options: removal or densification, water control and load transfer. This is Video 10 in the Soil Index Properties and Advanced Soil Behaviour series. 00:00 — Stable while dry, settlement after wetting 00:44 — 3D collapse mechanism 01:24 — Deriving collapse potential in three forms 02:07 — One-dimensional inundation test 02:51 — Checked numerical example and field estimate 03:34 — Engineering control measures 04:17 — End #SoilMechanics #GeotechnicalEngineering #CollapsibleSoil #CollapsePotential #Loess #InundationTest #Settlement #FoundationEngineering #CivilEngineering #GATECivil