Time-Dependent Settlements’ Analysis of a Spoil Heap

Surface coal mining involves excavating the overburden material, typically dumped in massive spoil heaps; appropriately managing and reclaiming these areas is a global priority. Time-dependent settlements are a crucial challenge to any efficient reclamation, such as renewable energy systems or civil infrastructure. Several studies examined the geotechnical stability of spoil heaps, but very few include characterization of the spoil material, and none a time-dependent settlements’ analysis. This work simulated time-dependent settlements as self-load 1D consolidation settlements to model the spoil response and predict their completion time and magnitude. The Finite Element Method was used for the consolidation analysis implementing the Hardening Soil model for the spoil. The calibration of the model parameters was based on a multipoint settlement gauge with two-year measurements from a massive spoil heap of 136 m in Northern Greece. Validation of results has been primarily based on secondary in situ measurements of surface markers spanning a larger period and on in situ and laboratory geotechnical testing. The numerical simulation fitted the multipoint settlement gauge measurements well, while the parameters were within the range of the geotechnical testing results. The simulation results agreed well with the validation measurements, further supporting the model’s parameters. The settlement completion time was calculated at 22 years, denoting the heap’s massive nature and the material’s fine-grained nature. Overall, the consolidation analysis of the spoil heap’s time-dependent settlements, serving as a paradigm for similar cases, provides valid lessons and results according to the available measurements and can serve as a design basis, at least on a preliminary evaluation.