Α comprehensive geotechnical characterisation of overburden material from lignite mine excavations

Abstract

For the sustainability of lignite and coal mining, engineers need the soils' appropriate geotechnical characterisation of the excavations. This characterisation relates to the slope stability, the overall area stability, and the sustainable exploitation of mining areas during operational and post-closure eras. This work presents a novel perspective on the soil characterisation of lignite mine excavations. Rather than focusing on one particular mine, a comprehensive geotechnical characterisation provides insights about the soils of related mining areas. Additionally, slope stability representative cases guide soil characterisation and analysis rather than following it. The Greek lignite mines are used as a representative example for the illustration of this framework. Initially, the two typical slope stability scenarios for Greek lignite mines are established: a slope in the presence of a weak zone and a homogeneous slope. The crucial geotechnical parameters are then statistically examined based on an extensive database established from laboratory results of various mines. Focus is on shear strength (friction angle and cohesion), the key to slope stability, and physical properties that can provide the strength through empirical correlations. Many soil layers exhibit a low residual friction angle from 5° to 15°, corresponding to the weak zone. Peak friction angle presents a mean value of 28.4°, and a characteristic value of 25.0°; cohesion presents a wide range with a mean value of 111 kPa and a characteristic value of 84 kPa. Finally, cross-correlations between geotechnical parameters present large scatter, but relations for estimating the residual and the peak friction angle reveal general trends.