Collapsible soils are often challenging from a geotechnical standpoint and are found in many parts of the world. As urban development rapidly extends into Egypt’s desert regions, construction projects increasingly encounter issues related to these problematic soils. In their natural dry state, collapsible soils tend to have relatively high strength. However, when inundated, they undergo major particle rearrangement and sudden volume reduction, which can cause serious structural issues like cracking, tilting, or even failure. In Egypt, sources of wetting might include irrigation of farmland, leaks from sewage systems, or occasional rainfall. This paper discusses a large-scale in-situ test that includes a deep infiltration system aimed at assessing the collapse potential and settlement behavior of collapsible soils at an arid site within Egypt’s New Administrative Capital. The location, with its uneven terrain, required extensive cut-and-fill earthworks, with excavated materials reused as engineered fill. After observing excessive settlements that impacted a structure, two in-situ tests were carried out: one on original native soil and another on compacted fill. The tests showed that the native soil settled approximately 2 cm under collapse conditions, while the compacted fill experienced about 9 cm of settlement, indicating the high vulnerability of reworked sand–gravel materials to collapse.
