Seismic risk assessment
The yellow area in the flowchart represents the risk assessment (Figure 56) that forms an integral part of mine management and the management of occupational health and safety. The management of seismic risk is performed within a broader risk management framework.
Figure 56 Flowchart of the seismic risk management process emphasing the data collection activities
Gap#5; Seismic risk assessment: Most seismic risk assessments are currently qualitative.
How to fill the gap: Develop better methods to assess the likelihood of large events and rockbursts and quantify the financial loss associated with them.
Some level of risk assessment appears to be common practice on mines and is generally prescribed by national or state legislative bodies. The level of risk assessment varies from informal to formal and qualitative to quantitative.
Engineers typically perform experience-based, subjective evaluation of the consequences and probabilities associated with seismic hazards and evaluate its acceptance within the corporate risk matrix. Formal risk assessment techniques include the use of fault event trees with subjectively assigned component likelihoods. In our opinion, informal risk assessment should be limited to tactical decisions of limited consequence events and should not form the basis for strategic decisions.
Different levels of improvement are possible on the informal subjective risk assessment discussed the previous paragraph.
The individual formal subjective risk assessment
The geotechnical engineer performs a risk assessment employing formal risk assessment techniques like fault event trees and assign subjective probabilities to the components of such trees. This risk assessment is documented in a memorandum and the subjective probabilities listed. The documentation enables auditing and expert evaluation of the risk assessments. After the initial development of the fault event trees for a specific scenario, this process is not onerous.
Formal subjective risk assessment employing expert opinion
The employment of expert opinion to derive subjective probabilities in a formal risk assessment is well documented in geotechnical engineering context, for example, Vick (2002); and Baecher and Christian (2003). A panel of experts are selected and a facilitator manages the risk assessment according to well established processes. The risk assessment process is documented.
Quantitative risk assessment
Probabilistic calculations are performed to evaluate the probabilities required in the formal risk assessment employing fault- and event trees. The calculation process and the risk assessment process is documented.