The collapse potential of loess is a distinctive geotechnical property influenced by moisture variation. In southern Vietnam, the collapse potential and geotechnical characteristics of a sandy loess-like deposit (SLD) have not been fully investigated. This study addresses this gap through in situ and laboratory testing. The SLD is classified as silty sand, comprising well-sorted fine sand with silt and clay. Coarse grains are sub-angular to sub-rounded, coated with clay, forming a metastable open structure characteristic of aeolian deposits. Plate load testing at the natural moisture content and saturation level ( \( w = \) 5.6%, \( S = \) 32.3%) under 70 kPa stress showed no collapse, but immediate collapse occurred after saturation. Laboratory oedometer testing under saturated conditions ( \( w = \) 17.3%, \( S = \) 99.8%) and 200 kPa stress revealed moderate collapse (collapse potential index \( \delta = \) 4.4%), consistent with in situ testing ( \( \delta = \) 5.1%). Cone penetration resistance ( \( q_{c} = \) 4.2–9.8 MPa) decreases with increasing moisture content ( \( w = \) 2.3–10.0%), dropping to 2.0–4.3 MPa under saturated conditions ( \( w = \) 15.1–17.3%, \( S = \) 87.1–99.8%). The undrained shear strength is 76 kPa with a sensitivity of 3.8. Compacted soil yields a maximum dry unit weight of 18.3 kN/m3 at 10.6% moisture. Cohesion strongly affects compacted soil shear strength. At 50 kPa normal stress, shear strength and cohesion decrease by 24.2% and 67.9%, respectively. Over four weeks at optimum moisture, shear strength rises by 28.9% as cohesion improves. The SLD has lower collapse potential than the sandy yellow loess in northeastern Thailand, but still requires careful foundation assessment as a soft soil.
