Forensic analysis of the instability of a large-scale slope in a coal mining operation

In this study we present the results of the forensic analysis of the slide in the large southern slope of an open-pit coal mine located in northeast Spain. The slopes have a total height from 100 m to 350 m. The mine’s benches are 10 m in height and the berms have a width of 5–6 m. Along the entire length of the southern slope there is a fault of significant size which is close to the Romera seam. This seam is mined via underground mining operations. The entire Southern slope presents a series of significant strains and even some examples of subsidence on its head. It is believed, in principle, that these are a result of interaction between the Romera seam operations and the above mentioned fault. The northern, eastern, and western slopes do not, however, show any signs of failure. In order to analyse the above hypothesis we have created and calculated, using numerical methods, a two-dimensional model that represents a cut parallel to the path of the analysed slope. This modelling technique has been used to analyse the degree of alteration to which the rock mass formed by the slope has suffered. An analysis of results during the different phases of mining operations indicates that underground operations carried out in the small seams to the left of the fault only cause minor alterations to occur. Something similar occurs during the first phase of operations performed using sub-level caving of the Romera seam. Nevertheless, the second phase of operations in that seam results in significant changes to the slope. The fault is affected, and blocks are displaced by distances of up to 13 m. This phenomenon also causes considerable surface-level subsidence. terest of this study resides in combining the experimental results obtained from field tests and strains registered in the galleries using a numerical model that allows us to evaluate the state of stress and strain in a highly detailed manner for the area under study.