Explicit discontinuum simulation for probabilistic forecasting of fault slip and rock mass seismic potential

Abstract

With increasing depth, there will always be situations where stress, strength and structure combine to store energy in unstable ways around mining work areas. Some mining induced seismicity is unavoidable. The job of the planning team is to balance the compromises between production demands and rock mechanics driven sequencing principles so that all essential constraints-safety, economy and recovery-are met. Achieving a sufficient and defendable balance requires quantitative tools: tools that can differentiate various courses of action, as well as assess the underlying risks for each method. It is not good enough to simply rank possible scenarios or reduce the forecast performance to a single economic value, without actually determining if the bottom line risk is below acceptable levels. In this paper, a numerical modelling technique for simulating seismic effects of mining is described. The approach estimates the energy released throughout the mine at each stope extraction step, and has been validated for its intended purpose using data from Xstrata's Nickel Rim South (NRS) Mine.

Solving rock mechanics issues through modelling: then, now, and in the future?

“…Examples of discontinuum modelling with explicit representation of shear slip are found in Jarufe Troncoso et al (2012), and Beck et al (2012). Often, the seismic moment is often used to compare results from a numerical model with actual observed behaviour (Figure 15).…”

Rock mechanics tools for mining in high stress ground conditions at Nickel Rim South Mine

“…Drill hole notching or raisebore breakouts often show stress directions parallel to the local faults. The mine wide modelling (see following sections) takes this into account by including the fault surfaces and calibrating the model results with the observed seismicity (Beck et al 2012). The seismic response to stoping is often asymmetric, and can only be 'mimicked' by the model if fault movement is considered.…”

“…Small magnitude seismicity in itself rarely poses a safety risk, however, the cumulative effect of seismicity is an excellent record of rock mass damage. This has proven to be a very useful tool for numerical modelling calibration, and general rock mechanics understanding (Beck et al 2012;Simser 2013). Several examples are included in the following sections to show how the high resolution data is used to track overall rock mass response to mining (Figure 3).…”

“…3D non-linear models are out sourced to Beck Engineering who provides some interpretation of the results as well as the results files for local mine site engineers to assess. The main calibration tool has been clustered seismicity which is related to commutative plastic strain in the model (Beck et al 2012). The output is used in short term and long-term planning, prioritising enhanced support installation, location of non-entry zones after stope blasting, and to focus efforts where alternate sequencing may alleviate some potential ground control problems.…”

The statistical presentation of seismicity for appreciating seismic hazard

“…The use in block caving is presented as an example in Figure 3. In this case, simulated energy release (displayed as a volume rendered cloud) is correlated to the actual seismic response (displayed as a wireframe) for the corresponding period to define the seismogenic zone in a cave (Beck & Putzar 2011). Such analysis can be undertaken for all events, or for events exceeding particular magnitude.…”