Modeling the Leo Slope Failure with PFC

Industry:

Mining, Open Pit

Client:

Rio Tinto Kennecott Copper

PFC3D

Project Background

In May 2021, a slope failure called the “Leo Failure” occurred at Bingham Canyon Mine, one of the world’s deepest open pit mines, for a total runout mass estimated at 21 million tons. Comprehensive monitoring systems were in place, which allowed mine staff to anticipate and record the event and prevent harm to personnel or equipment.

In this analysis, a PFC3D model was used to simulate the failure runout to better understand ore grade distributions within the runout material and to inform plans to mine through the landslide mass. The model aimed to reproduce the failure runout and provide understanding of the failed material characteristics, including lithology, ore grades, and the trajectory and landing position of rock blocks.

ITASCA’s Role

A 3D Discrete Element Method (DEM) model of the failure event was built, with both a coarse resolution (275,000 particles with diameters between 2 to 4 meters) and a fine resolution (2,200,000 particles with diameters between 1 to 2 meters).

To reproduce the complex, two-stage failure, model parameters were adjusted by trial and error to match site measurements of the post-failure runout surface, the positions of the failure zones and benches, and the trajectories and final positions of the recorded markers.

Then, the ore control block model that included results from drilling and sampling was compared to a geology block model output from the PFC model.

Copper grade distribution of the Leo Failure before the collapse based on data extracted from a site kriged geology block model.

After failure. Transparent surface indicates post-failure surface measured on site. Balls contoured by fragment number.

PFC3D model of the failure colored by bench level.

Results & Impact

The PFC model and the ore control block model show no significant difference in tonnage, and the distribution of rock types in the PFC model is very similar to the actual rock types in the ore control block model. The PFC model is closer to the actual grade of the mined material because it is based on exploration drilling, which has wider spacing that the blast holes used in the ore control model.

This project demonstrates the accuracy of PFC for failure runout analysis, which can provide more data for back-analysis of slope failure dynamics and significantly influence plans for mine operations and the management of large instabilities and associated risks.

Plan view comparison of post-failure grade distribution.

References

Ergun, S., et al. (2022). Particle Flow Code modeling of slope failure and runout at Bingham Canyon Mine. In Proceedings, Slope Stability 2022 (Tucson, Arizona, October 2022).