Excavation is more than digging a hole. The five main types of excavation work each have different equipment, different soil conditions to consider, and different price drivers. Melbourne's varied geology — heavy clay in the inner east, sandy soils to the west, basalt rock through pockets of the north — adds another variable. Here is what excavation actually involves and what to budget for in different scenarios.
The five main types of excavation
1. Site cut
Levelling a sloping or uneven block to a specific finished level before construction begins. Common for new builds on hillside lots. Excavated soil is either taken off-site or redistributed to fill low areas (cut-and-fill).
Equipment: Mid-size excavator (12–20 tonne), trucks for spoil removal.
Typical timing: 2–5 days for residential.
Typical cost: $5,000–$25,000 depending on volume.
2. Basement excavation
Digging out below the natural ground level to create a basement, lower-ground floor, or below-ground parking. The most complex residential excavation type because it involves shoring, water management, and engineered retention.
Equipment: Mid- to large excavator, sometimes mini for confined space, often supplemented by tippers.
Typical timing: 2–6 weeks depending on size and soil.
Typical cost: $40,000–$200,000+ depending on depth, area, retention required.
3. Bulk earthworks
Large-scale earth moving for commercial or development sites — multi-unit residential, factories, retail centres. Often involves multiple machines working in coordinated pattern, dedicated truck rotations, and sometimes blast or hammer work for rock.
Equipment: 20–35 tonne excavators, dump trucks, dozers, sometimes graders.
Typical timing: 2–8 weeks depending on volume.
Typical cost: Quoted per cubic metre or per project.
4. Trenching
Linear excavation for services — water, gas, sewer, stormwater, electrical conduits. Tight depth and width tolerances; the trench has to match the engineering specification exactly.
Equipment: Mini excavator, trenching bucket, sometimes specialised trenchers.
Typical timing: Minutes to hours per linear metre, depending on depth and conditions.
Typical cost: Quoted per linear metre.
5. Footing excavation
Specific dig-outs to engineer's specification for slab footings, beam pads, pier holes, or strip footings. Tight tolerances, no over-dig, soil disposal usually retained on site for backfill.
Equipment: Mini or 5-tonne excavator.
Typical timing: 1–3 days for residential.
Typical cost: Often included in builder's slab works rather than separately quoted.
Melbourne soil types — and why they matter
The major Melbourne soil types affect excavation differently:
Clay (most of the inner suburbs)
Heavy, sticky, holds water. Easy to excavate when dry; challenging when wet. Reactive — swells and shrinks with moisture, which has implications for slab and footing design. Sticks to bucket teeth and slows productivity in winter.
Sand and sandy loam (much of the west and bayside)
Easy to dig, but unstable on a vertical face. Trenches and basements need shoring earlier. Drains well, which helps in winter but creates dust in summer.
Basalt rock (pockets across the north and west)
Surface basalt or "bluestone" is common across northern and western Melbourne. Hard rock requires hammer attachments or, rarely, controlled blasting. Adds significant time and cost when encountered unexpectedly.
Made ground (everywhere)
Inner-city lots often have layers of fill from previous demolitions, road works, or unrecorded site changes. Excavating through made ground is unpredictable — you don't know what's under the surface until you find it. Tight site work detail.
For any project involving more than minor excavation, a geotechnical investigation report ($1,500–$5,000) tells you what's actually in the ground before quoting. It's standard practice for commercial work and increasingly common for premium residential. The report saves variations later.
Soil disposal
Excavated material has to go somewhere. Three options:
- On-site reuse — cheapest if the soil is suitable for fill on the same site. Requires the project design to incorporate the volume.
- Off-site disposal to clean fill site — most common. EPA-classified fees apply.
- Contaminated soil disposal — required for soil with hydrocarbon, heavy metal, or asbestos contamination. Significantly more expensive (sometimes 5–10x clean fill rates).
Inner-city sites with industrial history often have low-level contamination that triggers different disposal classification. A pre-excavation soil sampling assessment determines the classification before work begins.
Safety and shoring
Trench and basement excavation is high-risk work. The OHS Regulations require shoring or battering for excavations deeper than 1.5 metres. Practical implications:
- Vertical-walled basements require engineered retention systems — soldier piles, sheet piles, contiguous bored piles, soil nailing
- Battered excavations need lateral space, often impossible on tight urban sites
- Retention systems can cost as much as the excavation itself for deep basements
Water management
Melbourne's water table varies. Inner-suburban excavations near creeks and rivers often hit groundwater within 2–3 metres. Solutions:
- Sump pumps continuously running
- Wellpoint dewatering systems for larger projects
- Discharge permits from water authority for pumped water
Underestimating water management is the most common reason basement excavations run over budget.
Equipment matching to job
Choosing the right machine size matters more than people realise:
| Machine | Best for |
|---|---|
| Mini excavator (1.5–3 tonne) | Footing excavations, narrow trench work, tight access |
| Compact excavator (5 tonne) | Residential trenching, small site cuts, narrow lots |
| Mid-size (12–14 tonne) | Standard residential site work, basement digs |
| 20-tonne+ | Bulk earthworks, large basements, commercial |
Using a machine too small wastes time. Using a machine too large limits access and can damage neighbouring property. The right contractor brings the right machine.
What to expect from an excavation quote
A genuine excavation quote should specify:
- Volume to be excavated (cubic metres)
- Equipment to be used
- Disposal classification and destination
- Shoring or retention requirements
- Water management approach
- Geotechnical assumptions and what triggers a variation
- Programme in working days
The same principles as a demolition quote apply. Quote-reading detail here.
