What should I include in a scope for a geotechnical engineer (soil test)?

Summary: Tests the soil and classifies the site so the engineer can design the slab and footings.

Why it matters: Reactive or poor soils are a common cause of cracking and major structural defects. A site classification is normally required before slab and footing design.

Minimum scope by stage

• Design: boreholes at the building footprint (number based on house size); site classification to AS 2870; report with bore logs, soil profile, founding depth, fill, rock, groundwater, trees and excavation conditions
• Planning (if required): slope stability or landslip assessment where an overlay applies
• Building approval: design parameters for the engineer (bearing capacity, retaining wall and pier design inputs); acid sulfate soil management plan if triggered
• Construction: founding inspection to confirm pier or footing depth; compaction testing and supervision where structural fill is placed
• Completion: inspection and compaction certificates issued to the certifier

Options

• Wind classification (sometimes bundled)
• Effluent disposal or percolation testing (unsewered sites)
• Rock or groundwater investigation for basements or deep cuts
• Dilapidation report on neighbouring structures before excavation

Meetings and site visits: One visit for testing; extra visits for founding inspections and compaction testing, priced per visit.

Watch-out: The house position and finished levels must be known before testing. If the footprint moves or cut and fill changes, re-testing or a revised classification may be needed.