How 3GSM Software Completed a Mine Slope Stability Review in Under a Week

Geology at Pueblo Viejo

The Pueblo Viejo mine is located 80 km north of Santo Domingo in a tropical climate. Gold mineralization is hosted in the Los Ranchos Formation, consisting primarily of andesite overlain by Hatillo Limestone. Near-surface materials include highly weathered saprolitic soils up to 20 meters thick, which influence slope stability.

The Cumba pit failure occurred within andesitic rock masses characterized by:

Hoek-Brown failure criteria parameters: Uniaxial Compressive Strength (UCS) = 42 megapascals (MPa), Geological Strength Index (GSI) = 60-80, and material constant for intact rock (mi) = 16.
Fully saturated slopes during wet seasons with a relative pore pressure coefficient (Hu) of 0.88.
Presence of three dominant fault planes (blue, red, and yellow faults in the below image), which were retrospectively identified using ShapeMetriX photogrammetry.

The Constraints of Traditional Tools

The Cumba slope failure required detailed analysis, and traditional investigation methods were limited. Ongoing instability made in-person inspections dangerous, and ground control measures further limited access and close-up geological assessments.

Conventional mapping and geotechnical modelling were also time-consuming and inefficient. Field-based mapping could take 30 to 180 minutes per 10-meter section, while developing a numerical model often required days. Even then, discrepancies between predicted and observed failure mechanisms can create analysis uncertainty.

A final challenge was the need for multi-source data integration. The failure’s complex, non-daylighting kinematics meant no single method could fully capture its behavior. Engineers needed to combine UAV photogrammetry, radar displacement data, and numerical modelling for an accurate and reliable assessment.

Figure 1. A high-resolution 3D photogrammetric reconstruction of the Cumba slope failure on the left, illustrating the extent of deformation and key structural features contributing to instability. On the right is a photograph of the failure, taken a month after the model was created.

A Smarter, Safer Approach

To overcome these challenges, engineers used 3GSM’s ShapeMetriX software alongside 2D and 3D geotechnical modelling and radar validation to create a comprehensive failure analysis.

UAV Photogrammetry and Geological Mapping

Using ShapeMetriX, engineers processed 224 high-resolution drone images to create a detailed 3D model of the failure site. This way, mapping time was reduced, and engineers could more quickly and accurately identify key fault structures.

Figure 2. A UAV-derived 3D model of the Cumba pit, processed in ShapeMetriX, which covered a surface area of around 1.7 million m2. On the right is a dense 3D model, made up of more than 15 million points and 25 million mesh elements.

Engineers mapped five key geological structures linked to the Cumba slope failure. Three fault planes (red, blue, and yellow seen in Figure 3 below) were modelled and projected as 3D wireframe meshes, which were then integrated into the limit equilibrium and finite element analyses to replicate the failure mechanism with greater accuracy.

Unlike traditional window and traverse mapping, which can take hours or days in hazardous conditions, ShapeMetriX makes it safer and faster to collect accurate geological data. The software’s geologic mapping capabilities used in the research include automatic and semi-automatic mapping features, which enhance the efficiency of geological surveys and mapping processes.

Figure 3. Cumba Pit at 300 mRL (north is up); Left: Mapped geological features across multiple bench levels, showing red and blue traces associated with the slope failure. Right: 3D projection of the discontinuity model, illustrating red, blue, and yellow fault surfaces contributing to the failure mechanism.

Figure 4. Example of a linear fault trace (blue) identified using ShapeMetriX’s semi-automatic mapping, generated by selecting two surface points.

3D Limit Equilibrium and Finite Element Modelling

Slide3 (3D LE) confirmed shear displacement along mapped faults.
RS3 (3D FE) simulated stress redistribution and failure mechanics.
2D cross-sections showed up to 10% variation in Factor of Safety.

With a detailed geological model in place, engineers used Slide3 for 3D limit equilibrium (LE) analysis, which confirmed that shear displacement occurred primarily along the blue and red fault planes. The failure was driven by progressive instability as mining advanced from 310 to 300 mRL, a mechanism that had not been fully captured in earlier 2D analyses.

To further validate the failure mechanism, 3D finite element (FE) analysis in RS3 simulated stress redistribution and displacement patterns. Concentrated shear strain was revealed at the base of the slope, confirming that the failure was structurally controlled by pre-existing fault planes.

A comparison with 2D LE cross-sections (Slide2) showed that Factor of Safety (FoS) values could vary by more than 10% depending on the chosen section, highlighting the limitations of traditional 2D slope stability assessments. This underscored the importance of 3D modelling in complex failure scenarios.

Figure 5. Top: 3D Limit Equilibrium model of the Cumba pit at the 310 mRL level, viewed from the northwest. Bottom: Sequential bench progression from 310 mRL (left) to 300 mRL (right), illustrating the gradual daylighting of the Blue Fault on the eastern side and the resulting large-scale deformations.

Figure 6. Plan view (left) and north-west perspective (right) of the 3D Limit Equilibrium (LE) analysis at the 310 mRL level, highlighting the minimum Factor of Safety (FoS = 0.95) and the placement of 2D cross-sections used for further analysis.

Figure 7. Results of the unconstrained 2D Limit Equilibrium (LE) analysis at 310 mRL created in Slide2, searching for the lowest Factor of Safety (FoS). Cross-sections 1 to 6 are displayed in a clockwise arrangement from the top-left (see Figure 6 for the slice locations).

Radar Monitoring Validation

ArcSAR radar displacement data confirmed failure locations
Up to 9 meters of measured displacement aligned with models
Integration of real-time monitoring with geotechnical analysis

To further strengthen the analysis, engineers compared their numerical modelling results with real-world radar monitoring data. The ArcSAR synthetic aperture radar (SAR) system provided real-time displacement measurements, capturing up to 9 meters of movement within the failure zone.

When overlaid onto the 3D FE model, the radar displacement patterns closely matched predicted deformation trends, reinforcing confidence in the accuracy of the geotechnical simulations. This integration of remote sensing with numerical analysis allowed engineers to validate their findings in a way that was previously impossible with modelling alone.

By combining 3GSM’s ShapeMetriX, Slide3, RS3, and ArcSAR radar data, engineers achieved a faster, more reliable, and highly detailed slope failure analysis, reducing uncertainty in future mine slope stability assessments.

Figure 8. A side-by-side comparison of predicted displacements from 3D Finite Element modelling and real-world displacement measurements captured using synthetic aperture radar (ArcSAR).

Results Overview

The entire failure analysis was completed in under one week, marking a significant improvement in traditional assessment timelines. The ability to rapidly integrate UAV photogrammetry, numerical modelling, and radar monitoring data provided a highly detailed and accurate reconstruction of the failure mechanism.

The key findings include:

Validated failure mechanism: The non-daylighting failure was accurately modelled and showed shear displacement along pre-existing fault planes.
3D analysis outperformed 2D models: Comparisons between 3D LE and 2D cross-sectional analyses in Slide2 showed that 2D FoS values could vary by more than 10%.
Technology integration accelerated the process: The combination of ShapeMetriX, Slide3, RS3, and ArcSAR data allowed engineers to complete the full geotechnical review in a fraction of the time required by traditional methods.

The Verdict

This case study highlights how 3GSM’s ShapeMetriX software significantly improved the speed and accuracy of a mine slope stability assessment. By automating geological mapping, enabling rapid 3D analysis, and integrating real-world monitoring data, engineers were able to reconstruct a complex slope failure in record time.

Key Takeaways:

3GSM’s ShapeMetriX reduced geological mapping time from hours to minutes.
3D geotechnical modelling provided a more reliable failure interpretation than 2D methods.
Radar validation ensured numerical models aligned with real-world deformation.
The full mine slope stability review was completed in under one week.

Looking to Speed Up Your Geotechnical Analysis?

This case study is just one example of how photogrammetry-driven geotechnical analysis is reshaping the mining industry, and your project could be next. Start your free trial of 3GSM and Rocscience software here.

Source: N. Bar, B. Mojica, J. C. Cobián, M. Bautista R. Hammah, A. McQuillan, T. Yacoub, A. Gaich, M. Pötsch, N. Coli, C. Preston. Cumba Slope Failure: A Technical Review. Slope Stability 2022, Tucson, AZ.