Assessment of failure mechanisms in deep longwall faces based on mining-induced seismicity

Failure mechanisms of the rock mass in the regions of maximum stress concentrations around a longwall face were assessed. In this respect, seismic events that result from changes in the stress field were analyzed to gain more knowledge about rock failure mechanisms in the proximity of the face area. A deep longwall mine developed at depths of about 3–3.5 km in South Africa was selected as a case study. Seismic moment tensor solutions were obtained for 32 seismic events with moment magnitudes in the range of 0.49 and 2.10. Through moment tensor decomposition, the dominant failure mechanisms were investigated by drawing focal mechanism plots. Further analysis was implemented by depicting the corresponding 3D radiation patterns of P-wave particle motions. Although the results cover various failure mechanisms, the dominant mechanisms are shear, implosional, and compressional failures. According to the results, most of the maximum principal stresses in the mine are compressive and oriented nearly vertical, which are in accordance with the gravitational collapses of the mined out areas. The results obtained from this research show that measuring and analyzing mining-induced seismicity can be a reliable measure to characterize the dominant failure mechanisms in a nondestructive manner and to provide a useful assessment of the stability of the longwall face in advance of extraction

A reliable computerized litho-morphometric model for development of 3D maps of Topographic Aggravation Factor (TAF): the cases of East Mountain (Utah, USA) and Port au Prince (Haiti)

A reliability analysis was performed of a model capable of computing Topographic Aggravation Factors (TAF) for real topographic features using a digital elevation model. This model is a module in the SiSeRHMap hybrid model that, by a metamodeling process, computes frequency depending maps (multispectral) of acceleration response taking into account the topographic effect. The model is described by a structure comparable to a series–parallel circuit problem that solves for the response of each given x, y, z map point by scaling the 1D seismic response by the TAF in the frequency domain (each a component of the series circuit). The TAF is dependent on two coupled factors (the parallel components): (1) the 3D shape of the surface and (2) the stiffness of an “equivalent uniform relief”. Reliability analyses were performed on two different areas each characterized by complex topographic features. The first case modelled the East Mountain area (Utah, USA), where a detailed topographic effects study was conducted. A comparison between the TAFs developed in this study and the estimated Median Reference Method and Standard Spectral Ratio results calculated from the recorded ground motions indicated good agreement between the numerical and experimental results. The second case performed a comparison-parametric analysis of two nearby topographic features located in Port-au-Prince, Haiti. For this case, the complete SiSeRHMap model was applied by utilizing stratigraphic and topographic modules. The results clearly confirm the role of the 3D-topographic surface in the seismic site response and the reliability of SiSeRHMap in predicting it