Valorization Potential of a Greek Coal Spoil Heap by Civil Linear Infrastructure

Coal surface excavations create wastes, typically dumped in nearby areas forming massive spoil heaps. Several reclamation options have been proposed, including constructing linear civil infrastructure. Evaluations on this reclamation type have not been presented in the literature as the necessary geotechnical characterization of the spoil material is generally lacking, and various literature, design standards, and regulations are included. In this work, the potential of constructing a railroad or a highway on a massive spoil heap in Greece is assessed based on the geotechnical characterization of the spoil material. The soil body is highly heterogeneous due to the extraction and deposition processes related to the heap’s construction. Thus, the soil mass was considered one unified spoil material with significant uncertainty for a preliminary assessment. The representative material of the spoil heap is high plasticity silt (MH for USCS). The mean values of the constraint modulus (Es) for 100–200 kPa, the compression (cc), and recompression (cr) indices were determined through 1D consolidation tests as 2.7, 0.216, and 0.37 MPa, respectively. The most significant property of the subgrade’s suitability for road or railroad construction is stiffness, quantified through an elastic modulus (e.g., the resilient modulus). Each country’s regulations specify the minimum subgrade stiffness requirements for railroads; spoil stiffness is significantly smaller than the minimum requirements. Moreover, based on soil classification, worldwide standards qualitatively characterize the highway subgrade and its potential; high plasticity silt—the representative spoil material—is generally unwanted as a subgrade material for highways. Additionally, considering the resilient modulus and the CBR, the spoil results are far below the minimum requirements. Overall, the spoil material is too soft to withstand linear infrastructure without ground improvement.