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Tailings Dam Management & 3D LEM Risk Assessment

Tailings Dam Failures & Regulations

With a number of catastrophic tailing dam failures in recent years, the mining industry is now under a microscope to implement safer methods for storing tailings. Following the 2019 Brumadinho tailings dam collapse in Brazil, the Agência Nacional de Mineração (ANM) published “Resolution No. 13,” to strengthen and better regulate the construction of tailings storage facilities (TSF). One method to achieve safer TSF’s is by using filtered iron ore tailings dry stacking (FTDS), which bypasses the need for a tailings impoundment, mitigating the risk for dam failure.

This paper by Freire et al., presented at the Rocscience International Conference 2021, analyzed the stability of a proposed filtered, dry-stacked, iron ore tailings storage facility in Brazil using the 3D limit equilibrium software, Slide3.


3D Stability Analysis

The model was created in Slide3 using geological data from Leapfrog Geo and a design constructed in Autodesk’s Civil3D. The FTDS was designed to have a height of 115m with a capacity of 6265 Mm3. The final geometry of the stack includes a bench height of 10m, width of 8m, and a bench face angle of 18 degrees. The general view can be seen in Figure 1.

General View of a Tailings Storage Facility in Brazil
Figure 1: General view of the FTDS

The model was analysed using Slide3’s 3D limit equilibrium method using the Cuckoo search algorithm with ellipsoidal asymmetric surfaces and using the Bishop analysis method. Different scenarios were analysed to consider both the peak and residual parameters of the filtered tailings. Results from 3D analysis were compared with a 2D cross-section of the model, analysed in Slide2. These analyses were conducted based on the new standards set by the ANM as well as the international guidelines recommended by the Canadian Dam Association (CDA).

Results

The critical factor of safety (FOS) at residual material strength was found to be 1.85 and the area of the critical slip surface can be seen in Figure 2.

3D Stability results of the Filtered Dry Stacked Tailings Storage Facility at Residual Material Strength
Figure 2: Perspective and plan view of the results obtained from 3D stability analysis at Residual material strengths.


The critical FOS at peak material strength was 2.04 (Figure 3.)

3D Stability results of the Filtered Dry Stacked Tailings Storage Facility at Peak Material Strength
Figure3: Perspective and plan view of the results obtained from 3D stability analysis at Peak material strengths


The safety maps of the 3D stability analysis are shown for residual material strengths (left) and peak material strengths (right) in Figure 4.

3D Safety Map from Slide 3 of Tailings Storage Facility
Figure 4: Safety Map view of the results obtained from 3D stability analysis at Residual (left) and Peak material strengths (right).

2D Section View in Slide3

In addition to the 3D results meeting the FOS criteria set by the ANM and CDA, a cut from the Slide3 model using the section creator tool was used to better visualize and evaluate the depth of the critical slip surface and its characteristics.

Slide3 2D Section Creator tool for Tailings Storage Facility
Figure 5: 2D section view of the results obtained from 3D stability analysis at Residual (left) and Peak material strength (right).

Future Tailing Dam Design

In this research paper, 3D slope analysis plays an important role of verifying the design of the tailings storage facility, to ensure it will meet the acceptance criteria. Slide3’s interoperability with other software programs provides you a streamlined process of using your data to build models efficiently, and its 2D section creator tool is an added tool for validating 3D results with the 2D results.

See for yourself how Slide3 can benefit your everyday analysis by getting a free two-week trial today or watching one of the many Slide3 tutorials on the Rocscience YouTube channel.

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