Optimizing Slope Stability in Complex Sedimentary Domains With Slide3 and RS3
Managing stability at the 430-meter-deep open-pit copper mine at Bozshakol is no small feat — especially when the mine’s south wall contains altered and anisotropic sedimentary materials prone to complex failures. Weak bedding planes, anisotropic materials, and intense deformation all contributed to early instabilities, and to accurately model these complex failure mechanisms, advanced analyses were needed.
Researchers from KAZ Minerals combined laboratory tests and field investigations and conducted 3D back-analyses using Slide3 to refine shear strength parameters for the sedimentary materials, optimize slope designs for future pushbacks, and improve depressurization strategies.
Here, we’ll cover how Slide3 and RS3 were used at Bozshakol. For the full story, read the original conference paper by Bayuprima Adiyansyah, Danila Gorokhov, Bekzad Rakhmetov, Jamie Caratti, and Neil Bar.
The Geological Setting
The Bozshakol mine is located within the Central Asian Orogenic Belt and features a south wall dominated by sedimentary rock masses intruded by granodiorites and crosscut by structural faults. Two key sedimentary domains were identified:
- Sedimentary-Class 1 (Sector 6): Characterized by intense hematite alteration, weak anisotropic bedding planes, and friable rock mass, this domain exhibits ductile behavior in some cases. The materials can behave more like soil in certain areas of the domain and are prone to rotational failure.
- Sedimentary-Class 2 (Sector 5): These less altered anisotropic rocks included major shear zones and exhibited feature deformation along bedding planes.
The altered and anisotropic nature of these sedimentary domains directly influences slope stability. Sedimentary-Class 1 demonstrates reduced shear strength and ductile ground behavior, which are key factors in slope failures observed during early mining phases.
The Challenge
During early mining, the south wall experienced multi-bench instabilities in the altered sedimentary domain. These failures required immediate geotechnical attention because they posed safety risks to operations, particularly near the main haulage ramp.
The slope geometry during this period included a 55° bench face angle and a 34.6° inter-ramp angle, typical for mining at this scale. This design proved inadequate under the conditions of the south wall, where the altered, weak, and friable Sedimentary-Class 1 materials were particularly vulnerable to rotational and composite failure mechanisms.
Groundwater conditions complicated stability further, as the high water table and seasonal snowmelt led to increased pore pressures. The observed instabilities highlighted the need for a more robust understanding of material behavior and failure mechanisms to ensure safe operations and guide future pushbacks.
The Solution
The team conducted rigorous geotechnical analyses using Slide3 (for limit equilibrium modelling) and RS3 (for finite element validation). The activity consisted of both back and forward analysis as outlined below:
Back-Analysis
To replicate observed failures and refine material strength parameters for Sedimentary-Class 1, back-analysis was conducted. Laboratory tests provided baseline cohesion and friction values, but adjustments during modelling produced the following final parameters:
- Rock mass cohesion: 25 kPa
- Rock mass friction angle: 34°
- Bedding plane cohesion: 5 kPa
- Bedding plane friction angle: 16°
Back Analysis Results: Rock Mass Cohesion and Friction Angle Correlations
Anisotropic strength modelling was applied to bedding planes, with variability parameters A=15° and B=30°. Geological faults, modeled as weak planar surfaces, had limited influence on stability.
Three groundwater scenarios were assessed using Hu coefficients:
- Fully saturated (Hu = 1.0): Representing pessimistic conditions.
- Partially saturated (Hu = 0.75): Reflecting available WPP data.
- Fully depressurized (Hu = 0.50): Representing optimistic conditions.
The sensitivity analyses demonstrated that pore pressures played a significant role on slope stability, as they significantly impacted the FoS. These findings emphasized the necessity of depressurization strategies, including horizontal drilling, and the installation of VWP networks to monitor pore pressures effectively and achieve stable operating conditions.
Forward Analysis
Forward analysis optimized the slope design for the Stage 3 pushback by evaluating various configurations and groundwater scenarios (Hu = 0.75, 0.60, and 0.50). Using Slide3, the team determined that achieving a FoS > 1.2 required both geometry adjustments and effective groundwater management.
RS3 validated these findings, confirming that the proposed configurations met design acceptance criteria and excluded additional failure mechanisms. Based on the results, the team recommended reducing the inter-ramp angle to 29.7° and the bench face angle to 45°, with 10 m bench heights and 7.5 m berm widths for slopes in Sedimentary-Class 1.
The analysis also highlighted the importance of horizontal drilling and piezometer networks to reduce and monitor pore pressures, especially during snowmelt when risks are highest.
The Results
By utilizing Slide3 and RS3 together, geotechnical engineers found actionable insights and achieved measurable improvements. The back-analysis successfully replicated observed deformation patterns that validated the refined strength parameters for Sedimentary-Class 1. Forward analysis demonstrated enhanced stability through proposed geometry changes, with the FoS increasing to 1.26 under partially depressurized conditions (Hu = 0.60) and reaching 1.33 under fully depressurized conditions (Hu = 0.50).
These results provided the following key recommendations for the Stage 3 pushback:
- Decrease the inter-ramp angle from 34.6° to 29.7°, with 45° bench face angles, 10 m bench heights, and 7.5 m berm widths to achieve long-term stability for the highly altered Sedimentary-Class 1 domain.
- Implement horizontal drilling and a dense network of vibrating wire piezometers to reduce and monitor pore pressures, particularly during snowmelt, to ensure FoS > 1.2.
- Conducting additional diamond drilling and borehole geophysics to refine material property data and improve modeling accuracy for the altered sedimentary domain.
The Verdict
With Slide3 and RS3, engineers at Bozshakol were able to better manage slope stability in the south wall’s complex sedimentary domain. By combining 3D back-analysis, forward analysis, and validation, the team addressed geotechnical challenges with accurate and practical solutions.
For mining operations facing similar complexities, our advanced modelling software provides a proven workflow for safe and efficient slope designs.
Beyond Bozshakol: How Slide3 and RS3 Can Aid Your Geotechnical Projects
This case study highlighted how Slide3 and RS3 improved slope stability methods for Bozshakol’s strongly altered sedimentary domain. However, these programs have broad applications across various engineering and geological areas:
Slide3:
- Open Pit Mines: Evaluate and optimize slope designs for safety and cost-effectiveness under diverse geological and groundwater conditions.
- Landslide Remediation: Model potential slip surfaces and identify critical factors contributing to instability in natural slopes.
- Retaining Structures: Analyze the stability of complex retaining systems, accounting for soil-structure interaction and variable loading conditions.
- Dams: Assess slope stability in dam embankments under static and dynamic loading, ensuring compliance with safety standards.
RS3:
- Tunnelling: Simulate stresses, displacements, and failure mechanisms around tunnels in complex geological environments.
- Excavations: Model deep excavation behavior and support systems, including retaining walls and anchors.
- Rock Mass Behavior: Analyze stresses and deformations in fractured or anisotropic rock masses, including fault-affected zones.
- Dynamic Loading: Investigate the effects of seismic or blasting loads on slopes, retaining structures, and other geotechnical features.
Slide3 and RS3 can be essential components of your modern, reliable engineering workflow. Whether you’re optimizing slopes in a copper mine or designing safe excavation projects in urban areas, they can help you to confidently and efficiently tackle geotechnical challenges.
