A Porosity-Height Relationship for Soil-Rock Mixtures of Unsaturated Dumps Based on Field and Laboratory Investigations

The stripping ratio increases as the surface mine gets deeper, causing an increase in the height of waste dump slopes. This poses a threat to stability since dumps are composed of soil-rock mixtures, mostly in an unsaturated state. In this research work, field and laboratory-based studies were conducted on soil-rock mixtures to propose an analytical relationship between in situ porosity and dump height. Sand replacement method in the field and standard Proctor test and consolidated drained triaxial shear tests in the lab were performed to establish the porosity-height relationship curves. It was found that the porosity decreases with height, as described by a negative exponential distribution with an exponent termed ‘mechanical pseudo pore compaction coefficient,’ which determines the shape of the curve. The proposed relationship was then utilized to evaluate the compaction of soil-rock mixtures at a pre-residual state. The parameters of the porosity-height relationship were also assessed for lightly, partially, and fully compacted dump slopes.