Our firm was approached in 2022 following extreme rainfall events that destabilised a 10-meter sandstone slope near Manly, endangering residential properties and a popular public walkway. The slope was composed of weathered sandstone and residual clay. Environmental constraints further complicated the project, as the area was home to native coastal vegetation protected under local regulations.

The Challenge

• Slope Instability: Severe rainfall had caused significant erosion, compromising the slope’s stability.
• Environmental Constraints: Native coastal vegetation required protection under local regulations.
• Limited Access: Tight access conditions necessitated specialised equipment for slope reinforcement.

Our Approach

BHM Geotechnical employed a structured, multi-phased strategy to address these challenges:

1. Stability Analysis

Conducted comprehensive stability analysis using commercial software and on-site field assessments.

2. Anchor System Design

Developed a tailored anchor system with strategically placed soil nails to reinforce unstable soil masses.

3. Drainage Management

Installed a subsurface drainage network to redirect groundwater and mitigate slope saturation.

The Solution

The team redesigned the foundation using improved soil analysis, cutting down on footing depth and saving costs.

1. Slope Reinforcement

Soil nails were installed at precise angles, anchoring unstable soil to deeper, stable strata.

2. Groundwater Management

Integrated drainage systems reduced pore pressure, enhancing slope stability.

3. Eco-Conscious Execution

Utilised a tight access rig to limit excavation and protect native vegetation.

Results and Impact

• Enhanced Safety: Secured the slope, protecting nearby residential properties and public walkways.
• Environmental Preservation: Minimized disturbance to native vegetation while ensuring ecological compliance.
• Community Benefits: Restored access to the popular walkway, enhancing community safety and recreation.

Conclusion

This project highlights our capability to deliver innovative geotechnical solutions while respecting environmental concerns. By combining engineering excellence with ecological preservation, we successfully stabilised the Northern Beaches slope, safeguarding both infrastructure and natural habitats.

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