Cut and fill | Chalkline

Cut and fill is the earthworks method that produces a level building pad by excavating high points of a site (cut) and placing the spoil into low points (fill). On most sloped residential sites it is cheaper than full cut-to-spoil or full bring-in fill because the haul stays on-site.

Balance ratio. The volume of cut should roughly match the volume of fill so the contractor minimises off-site cartage. Most contour surveys plot a “cut-fill balance” calculation alongside the design pad RL. A balanced site is the cheapest outcome; the further the design platform sits from the natural cut-fill balance line, the more spoil leaves site or new fill comes in.

Controlled vs uncontrolled fill. Any fill that ends up under a slab, footing, or driveway must be controlled fill: placed in layers, compacted to a target density, and supervised by a Geotechnical Inspection and Testing Authority under AS 3798:2007. The GITA issues a compliance report. Uncontrolled fill (or pre-existing fill from an earlier build with no documentation) pushes the site to Class P under AS 2870:2011 and triggers a fully engineered slab design.

Batter slopes. NCC 2022 Housing Provisions Part 3.2 sets maximum batter slopes by soil type. Steeper than the table allows, or higher than the unretained limit (commonly 1.0 m for cut, 2.0 m for fill), means a retaining wall is required. State exemption thresholds vary (NSW 600 mm, QLD 1.0 m).

Declare the scope before the slab. The geotech needs the final cut-fill volumes and depths before the site classification is locked in. Adjusting the pad RL after classification means re-running the soil report, not pouring on the old one.

Also known as: earthworks, site cut, earthmoving.

Category: Site preparation / earthworks.

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