Mount Martha Two Storey New Build: Precision Earthworks and Retaining Systems

Groundworks and Excavation: Setting the Foundation for Structural Integrity

Precise excavation ensures structural stability, prevents future drainage issues, and sets the foundation for every element above ground. For areas like Mount Martha, we faced several challenges before we began digging.

Site-specific challenges in Mount Martha

The Mornington Peninsula’s geology can vary dramatically within a single site. It can be sandy loam in one area and reactive clay or granite just metres away. These variations directly influence how the soil behaves under load and when exposed to seasonal moisture.

Without proper assessment, this can lead to:

• Differential settlement (uneven sinking of foundations)
• Slab cracking or movement
• Drainage inefficiencies and water pooling
• Accelerated erosion in sloped sections

Before the first bucket of soil was removed, we conducted geotechnical testing and moisture management to fully understand the conditions we were working on and the precautions we needed to take.

After the assessment, we carried out a significant site cut, removing over 800 cubic metres of spoil, using the process known as “cut and fill” to accommodate the home’s garage and lower level. 

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In this method, we cut into higher ground and used that material to fill lower areas. This allowed us to achieve a stable, balanced foundation while minimising the need for imported soil. The approach also ensures site stability, drainage, and overall structural integrity.

Retaining Wall Systems: Choosing the Right Support for the Site

Retaining walls define how a landscape performs over time. For the Mount Martha build, we opted for concrete sleeper retaining walls because of their structural strength and design flexibility.

Concrete sleepers are ideal for builds on sloped or excavated sites because:

• They provide high load-bearing capacity and resist soil pressure over time.
• They are durable against moisture and ground movement, which is essential in coastal environments.
• They offer a clean, engineered look that integrates seamlessly into both contemporary and natural landscapes.

We also incorporated batters, graded slopes that naturally stabilise the cut without requiring additional vertical walls. Compared to full-height retaining walls, batters reduce hydrostatic pressure and create a softer transition between the built form and the natural surroundings.

This hybrid approach balances engineering integrity with environmental sensitivity, allowing the landscape to breathe and reducing long-term maintenance.

Encountering Granite: Understanding and Overcoming Geological Challenges

Mount Martha is well known for its granite formations, which can make deep footing work complex. During excavation for the deepest retaining wall footings, which reached a total of 6 metres (2.5m cut plus 3.5m footing depth), our team encountered solid granite. 

This naturally occurring rock layer can significantly influence how foundations are prepared and constructed. Here’s why:

• High Density and Hardness: Granite is one of the toughest natural materials, making standard excavation tools ineffective.
• Specialised Equipment Required: Breaking through granite often needs heavy machinery such as rock breakers or core drills.
• Time and Cost Impact: Working through granite slows progress and increases labour and equipment costs.
• Structural Considerations: Proper drilling and footing depth are essential to maintain foundation stability in granite-heavy areas. 

Rather than compromise on footing depth, we adapted our approach using a 13-tonne excavator with a core drill attachment. This method allowed us to achieve the required footing depth while maintaining the integrity of the rock, preventing structural stress or cracking in the future. 

Looking Ahead: From Groundworks to Underground Services

With excavation, retaining systems, and site access complete, our focus is now shifting to the underground services phase, where plumbing, electrical, and drainage systems are laid with precision before the slab pour.

Each phase brings us closer to realising the client’s vision for a coastal-inspired, architecturally balanced home.