Collapse settlement of dump soils revealed by studies on soil samples of modelled lithology and lump-size distribution

The paper deals with the collapse settlement of dump soils i.e., made grounds composed of the overburden soils of mineral deposits, which were worked out with the open-pit method, transported and deposited as a dumped fill. The principal aim of the studies was the analysis of factors controlling the collapse settlement process, mostly the structural model of dump soil and external determinants: initial compaction, initial water content and history of its changes in time as well as the history of loading of studied soil before saturation. In order to reflect the natural structure of dump soils, experiments were carried out on samples of specially modelled lithology and structure. Hence, the samples represented three basic structural models of such soils: non-cohesive, cohesive and transitional, partly cohesive/partly non-cohesive. Attention was paid to diversified dynamics of collapse settlement, which results from two clearly different processes: rebuilding of soil structure and additional consolidation settlement. It was found that from the physical point of view the collapse settlement results from the release of elastic energy delivered to the sample by loading before inundation and accumulated at the contact surfaces of soil lumps.