Effect of Slag on Shear Parameters of Collapsible Soils Compacted to Proctor Optimum

Constructions on untreated collapsible soils requires special attention from geotechnical engineers and building owners. The collapse destroys intergranular soil bonds and decreases matrix suction, which mobilizes a reaction called shear resistance (tau). This experimental study was based on the contribution of slag (granulated slag (GS)) and natural pozzolan (NPz) on three fundamental parameters involved in the improvement of a laboratory reconstituted soil (S0), humidified to optimum water content (OWC): collapse potential (Cp), type of compaction and shear strength parameters (cohesion (c), internal friction angle (phi)). Compressibility tests by simple oedemeter, shear strength measurements using a Casagrande box, followed by scanning electron microscopy (SEM) analysis, were carried out on untreated and treated samples mixed with slag at different doses (1, 3, 5 and 7%) of the S0 dry weight. Samples were moistened to OWC and statically compacted. Test results showed that GS and NPz reduced the Cp by around 70%, improved c by 233.33%, 164.67% for GS and NPz respectively with slight decreases in phi for both additions. Scanning electron microscopy (SEM) analysis showed the formation of a compact structure due to the new rearrangement of particles in the granular matrix of treated samples.