Assessment of induced seismic hazard and excavation damage in deep underground mines

Abstract: Mining is a continuous process of extracting valuable minerals from the earth. It is an important part of human society and development that we cannot live without.  Although, it requires an extensive amount of resources, underground mining is comparatively faster and more environmental feasible over surface mining.However, there are some major challenges involved when mining underground. As underground mining advances to greater depths, the stresses in the rock mass increase, and consequently the level of induced seismicity and damage to excavations usually increases as well. This poses a hazard to the mine personnel and infrastructure that in worst-case scenarios could lead to fatality, revocation of mining rights and temporally or permanent closure of the mine. Therefore, mining at greater depths has become a major operational issue and a challenging planning factor for most underground mines worldwide, especially at depths greater than 900–1000 m.As a result, there is a great need to explore and gain an understanding of excavation damage associated with seismic events phenomenon in deep underground mines. The occurrence, mechanisms and magnitude at a given site could provide great insights of associated influencing factors and design parameters significant for rock mechanics seismic hazard assessment.The performed study incorporates four components: firstly, seismic hazard tools (evaluation of seismic hazard tools currently used in deep underground mines), secondly, seismic source (which focuses on an evaluation of seismic event sources associated with excavation damage), thirdly, excavation damage resulting from seismic loading (detailed study of the characteristics of the damage, and correlation with the local geological structures, rock mechanical parameters and local stresses) and fourth, correlation between the seismic event source and excavation damage parameters.Methods of data collection such as forensic investigation of excavation damage associated with seismic events and a study of old mine damage reports were used to gather required detailed information. Qualitatively and quantitatively analysis was done on gathered information to: evaluate the nature and parameters  of seismic event  sources that potentially caused excavation damage, assess the merit and performance rate of short-term seismic hazards in mines, evaluate excavation damage characteristics, mechanisms as well as severity parameters and finally deduce the relationships between sources of seismic event and excavation damage.A rock mechanic seismic damage hazard methodology was developed to serve as a main guideline for forensic investigation of excavation damage in seismically active mines, ensure a consistent collection of important data/information by different project team members in mines and to provide guidelines of different types analyses that can be applied on data collected. This is important information that can be obtained and serve as initial stage of integrating different areas of expertise to find complex relationships between seismic sources and excavation damage.   Detailed outcome of the study is presented further in the thesis.