Abstract: Collapsibility is a typical engineering characteristic of Angola red sand. It is of great significance to study its influencing factors for geotechnical investigation and evaluation in red sand area. Based on laboratory compression tests of undisturbed and remolded Angola red sand specimens, the effects of structure, pressure, moisture content, dry density and fine-grained soil content on the collapsibility of Angola red sand were examined. Test results show that when the pressure is larger than 100 kPa, the collapsibility of remolded red sand is 2.0 times that of the undisturbed red sand. The collapsibility coefficient of red sand has a positive correlation, i.e. to increase with increasing test pressure and fine-grained soil content, with peaking pressure and fine-grained soil content reaching 300 kPa and 60%-80%, respectively. Contrarily, the collapsibility coefficient of red sand is, in general, negatively correlated with dry density and water content. The critical moisture content for eliminating and completely losing the collapsibility of undisturbed red sand is 9% and 13%, respectively, and those of remolded soil 11% and 13% respectively. The critical dry density of remolded soil is 1.80 g/cm³ and 1.90 g/cm³ respectively, and the corresponding compaction coefficient is 0.92 and 0.97 respectively. For engineering construction, the collapsibility of red sand can be eliminated by increasing dry density.

Key words: red sand, collapsibility, influencing factors, physical indexes, Angola