Martinez, M & Hull, A 2019, 'Toward a common practice in the selection of earthquake ground motion criteria for the design of critical mining facilities at closure and post-closure', in AB Fourie & M Tibbett (eds), Proceedings of the 13th International Conference on Mine Closure
, Australian Centre for Geomechanics, Perth, pp. 249-262.
The lack of a uniform engineering practice for earthquake design of critical mining facilities at the closure and post-closure stages can result in confusion for designers. Although local, international and company guidelines for critical mine facilities (e.g. tailings dam embankments, heap leach pads, rock waste dumps) are widely cited by designers, the selection of earthquake design levels for dynamic stability analyses are often arbitrary and can be inconsistent from site to site. Much of the inconsistency centres around how to use the earthquake ground motions developed from probabilistic seismic hazard analysis (PSHA) and deterministic seismic hazard analysis (DSHA).
At earlier stages of the mine planning, important elements in earthquake design of critical facilities at closure, post-closure and abandon are the site-specific earthquake hazard, the selection of the probabilistic and/or deterministic approach, and the seismic performance expectations.
The seismic hazard approach used in low hazard regions in stable continental regions differs significantly from that used for sites at high to very high seismic hazard regions like tectonic plate boundaries at subduction zones, or where seismogenic crustal faults have been mapped within about 100 km of the mine site. Adopting a combination of both PSHA and DSHA is generally recommended when seismic sources can be identified and characterised with confidence. At sites located in stable continental regions, PSHA is the best method to develop earthquake ground motions.
Modern international guidelines for seismic design of critical facilities typically recommended earthquake performance for an operating basis earthquake (OBE), and the safety evaluation earthquake (SEE). The SEE performance level defines the maximum earthquake ground motion to be resisted by the critical facility with acceptable damage but without a fatal collapse, or an uncontrolled release of materials in the case of dams. The SEE is usually proposed for closure, post-closure and abandonment.
The SEE performance level is typically based on the facility failure consequence and selected as the lesser of either the deterministic maximum credible earthquake (MCE), or the probabilistic spectral accelerations at low annual exceedance probabilities (AEP) of up to 1 in 10,000 (or 1:10,000). The median or 84th-percentile maximum credible earthquake ground motions have no return periods associated.
This paper suggests criteria for a consistent engineering guideline for the seismic analysis and design of critical mine facilities. It describes how current probabilistic and deterministic approaches complement earthquake performance assessment of critical mining facilities located in different seismic hazard regions.
Keywords: earthquake, seismic hazard, performance, probabilistic, deterministic, failure consequence