Engineering-Compliant Foundation Excavation You Can Trust
We’ve been doing foundation excavation work across Greater Hobart for years now, and honestly, there’s no two sites that are exactly the same. You’ve got clay soils in some suburbs that need wider footings than you’d expect, rock showing up in places where the engineer didn’t predict it, and drainage that needs sorting before you even think about pouring concrete. Add in Hobart’s rainfall patterns and the fact that half the city seems to be built on a slope, and you start to see why proper foundation excavation takes someone who knows what they’re doing.
Whether you’re building a new home in Mount Nelson, putting an extension on your place in Battery Point, or sorting out commercial foundation work anywhere from Kingston to Glenorchy, the excavation work is where everything starts. Get it wrong here, and you’re paying for it later. Get it right, and your concrete contractor’s going to have a perfect base to work with.
Types of Foundation Excavation We Handle
Site Assessment and Investigation
What Happens Before We Start Digging
Before any excavator rolls onto your site, there’s assessment work that needs doing. We’re looking at soil test results, checking the engineering drawings, and working out exactly what equipment we need and how we’re going to access the site.
Soil Testing and Classification Reports
Your geotechnical report tells us what we’re digging into. Is it stable sand that’s easy to work with? Reactive clay that needs special attention? Rock that’s going to slow everything down? The soil classification determines our approach and equipment selection.
Determining Excavation Depth
The engineer specifies minimum depths based on soil type, but we also need to account for frost protection (300mm minimum in Hobart), drainage requirements, and any rock or hard layers that might affect the design. We verify depths as we go with laser levels.
Identifying Rock and Soil Layers
Some Hobart sites have rock close to the surface. Others have layers of different soil types as you go down. We need to know what we’re dealing with before we quote the job, because rock excavation is a whole different story time-wise and cost-wise.
Water Table Assessment
If your site has groundwater close to the surface, we need to manage it during excavation. This might mean dewatering pumps, timing the dig for drier months, or adjusting the foundation design. Hobart’s 600mm+ annual rainfall means water management is always on our radar.
Underground Service Location
Dial Before You Dig is mandatory before we start. We need to know where every water main, electrical cable, gas pipe, NBN line, and stormwater drain is located. Hit a service and you’re looking at expensive repairs, delays, and safety risks.
Strip Footing Trench Excavation
Strip footings are continuous concrete beams under external and load-bearing internal walls. Excavation follows the foundation plan precisely:
Continuous Trenches Under Walls: Trenches follow the building perimeter and internal load-bearing walls.
Typical Width: 450–600mm: Width depends on soil type and loading; clay soils usually require wider trenches.
Typical Depth: 300–600mm Below Ground: Depth varies for frost protection, soil conditions, and load requirements.
Stepped Footings on Sloping Sites: Trenches step down slopes, maintaining proper depth and width for each level.
Straight, Clean Trench Edges: Vertical, tidy sides provide solid support for formwork and prevent soil contamination.
Level Base Preparation: Bases of each section are leveled using laser levels and hand trimming.
Hand Trimming for Precision: Final edge and base adjustments ensure accuracy and engineering compliance.
Ready for Formwork and Reinforcement: Trenches are prepared for formwork setup and steel reinforcement placement.
Pad Footing Excavation
Pad footings support individual columns, posts, or concentrated loads, with excavation following the structural plan precisely:
Individual Holes for Columns and Posts: Separate holes are dug under each post or column location.
Square or Rectangular Excavation: Most pads are square (e.g., 600mm x 600mm, 800mm x 800mm), rectangular if engineered for specific loads.
Typical Dimensions: 600mm x 600mm: Standard for residential posts; larger pads for heavier loads or poor soil.
Depth Based on Soil Type and Loading: Depth varies from ~400mm for light loads on good soil to 800mm+ for heavy loads on reactive clay.
Clean, Vertical Sides: Vertical, stable sides hold concrete shape; loose soil may require over-excavation and compacted backfill.
Level Base Compaction: Base is leveled, compacted, and firm to support the concrete.
Multiple Pads Aligned to Design: Rows of pads are aligned and leveled using string lines or laser guides.
Service Location and Protection
Before any excavation, identifying and protecting underground services is critical:
Dial Before You Dig is Mandatory: We run a search to locate water, gas, electricity, and telecommunications lines before digging.
Electrical Cables (Overhead and Underground): Located and hand-exposed to avoid electrocution, outages, and costly repairs.
Gas Pipes and Infrastructure: Confirmed and hand-dug due to safety risks; relocation handled by licensed gas fitters if required.
NBN and Telecommunications: Located and protected to prevent service disruptions and repair costs.
Stormwater Drains: Temporarily supported or relocated as needed to avoid damage and site issues.
Hand Digging Within 500mm of Services: Standard practice to verify exact position and depth before continuing mechanical excavation safely.
Equipment and Machinery
Selecting the right equipment ensures efficient and precise excavation:
Large Excavators (20 Ton): For full house sites with good access, move large volumes of soil quickly.
Medium Excavators (8–12 Ton): Standard residential blocks; balance productivity and maneuverability.
Mini Excavators (3–5 Ton): Tight access areas and precise footing work; fit through narrow gates.
Bobcats: Material handling, leveling, and site cleanup.
Tip Trucks: Transport excavated soil to approved disposal facilities; multiple loads may be required.
Laser Levels: Ensure precise excavation depths relative to engineering designs.
Compactors: Plate compactors and jumping jacks stabilize the base and fill for concrete.
Right Equipment for Accuracy and Efficiency: Equipment selection depends on access, volume, and precision needs.
Rock Excavation Challenges
Rock can create significant challenges during excavation in Hobart:
Rock Presence: Dolerite, sandstone, or mudstone can appear anywhere, slowing excavation compared to soil.
Time and Cost Implications: Rock excavation can take 3–4 times longer than soil, impacting budgets and schedules.
Engineering Assessment: Determines whether shallow rock can support foundations or requires design changes.
Alternative Foundation Solutions: Extensive rock may require piers, raft foundations, or other methods instead of strip footings.
Pier and Beam Options: Useful for sites with near-surface rock, drilling piers into rock for floor support.
Specialized Equipment Needs: Heavier breakers, more powerful excavators, or drilling rigs may be required.
Impact on Timeline: Rock can add days or weeks; early geotechnical testing helps anticipate delays.
Soil Removal and Disposal
Excavated soil must be managed carefully for safety, compliance, and efficiency:
Calculating Excess Soil Volume: Measure length × width × depth to determine how much soil needs removal and how many truck loads are required.
Tip Truck Transportation: Load excess soil into 10–12 m³ tip trucks and coordinate transport to keep excavation moving.
Approved Disposal Facilities: Soil must go to council-approved sites; clean fill may be reused on other projects.
Clean Fill Separation: Separate clean soil from contaminated material; clean soil can be reused, contaminated soil requires proper disposal.
Reuse On-Site if Suitable: Stockpile good-quality soil for landscaping or other uses to reduce costs.
Cost Per Cubic Meter: Disposal typically costs $30–60/m³ plus trucking; full house excavations may cost $1,500–$2,500 or more.
Access Limitations in Hobart
Excavation in Hobart can be challenging due to site access constraints:
Limited Access in Older Suburbs: Narrow streets and tight driveways restrict machinery size and site entry.
Narrow Side Passages: Many backyards are only 1–1.2 m wide, requiring mini excavators or hand digging for inaccessible areas.
Sloping Driveways: Steep hillside driveways may prevent safe entry for standard excavators, requiring alternate access or smaller machines.
Equipment Size Considerations: Excavator choice depends on what can physically reach the site, balancing efficiency with accessibility.
Mini Excavators for Restricted Access: Small machines (1.5–3 ton) fit through gates and tight areas but are slower than larger machines
FAQs About Foundation Excavation in Hobart
When's the best time of year to schedule foundation excavation in Hobart?
Summer through early autumn (December to April) is your best window for foundation excavation work around Hobart. We get less rainfall during these months, the ground’s drier and easier to work with, and you’re less likely to have excavations filling with water or work stopping due to weather. That said, we do excavation year-round – winter jobs just need more weather watching and sometimes take a bit longer if we’re dealing with wet conditions between the rain breaks.
What happens if you hit unexpected rock during our excavation?
We stop, assess how much rock there is, and contact your engineer to work out the best approach. Sometimes shallow rock means we can reduce excavation depth and found directly on the rock, which actually saves you money. Other times we need to bring in rock breaking equipment, which adds time and cost but we talk through the options with you before proceeding. Most Hobart geotechnical reports identify rock risk beforehand, but occasionally it shows up where testing didn’t pick it up.
Do we need council permits for foundation excavation on our property?
The excavation itself doesn’t usually need a separate permit – it’s covered under your building permit for the house or extension you’re constructing. Your builder or architect sorts out the building permit before we start excavating. The main thing we handle separately is the Dial Before You Dig searches for service locations, and making sure the engineer inspects and approves everything before concrete goes down.
How do we know if a foundation excavation quote is fair?
Get quotes from 2-3 excavation contractors and compare what’s included – are they quoting per cubic meter or a fixed price for the job, does it include soil disposal, are inspection coordination and base preparation included? In Hobart you’re generally looking at $50-150+ per cubic meter depending on soil type, access, and site conditions. The cheapest quote isn’t always the best – look for contractors who understand Hobart’s soil conditions, have proper insurance, and communicate clearly about what might add to the cost like rock or difficult access.
Can we stay living in our house while foundation excavation happens for an extension?
Yeah, most families stay put during excavation work for extensions or additions. It’s noisy when the excavator’s running and you’ll have machinery and workers around, but it’s manageable for a few days. We coordinate access so you can still get in and out, we protect your existing landscaping where possible, and we clean up at the end of each day. The main disruptions are noise during work hours and potentially limited access to parts of your yard while equipment’s on site.
What if soil testing shows contaminated soil on our Hobart property?
Contaminated soil needs special handling and disposal at approved facilities, which costs more than clean fill disposal. We separate any contaminated material during excavation and arrange proper disposal with EPA-compliant facilities. Depending on what the contamination is and how much there is, it might affect your foundation design or mean additional excavation to remove it all and replace with clean fill. Your engineer and environmental consultant guide this process – it’s not common in most Hobart residential areas, but older industrial sites or properties with underground tanks sometimes have contamination issues.
