S04 Service Trench Excavation and Filling


Note: The term contractor is used interchangeably to describe both subcontractors & suppliers

1. Service Trench Excavation

1.1.1.  Make trenches straight between manholes, inspection points and junctions.

1.1.2.  Provide trenches with vertical sides and uniform grades.

Trench widths

1.2.1. Keep trench widths to the minimum consistent with the laying and bedding of the relevant service and construction of manholes and pits.


1.3.1.  Backfill service trenches as soon as possible after laying the service. Place backfill in layers not exceeding 150mm compacted thickness. Compact each layer to a density sufficient to minimise settlement.

1.3.2.  Backfill material: Excavated spoil or well graded inorganic material with maximum particle size of 75mm.

1.3.3.  Next to services: Do not place any particles greater in size than 25mm within 150mm of services.

1.3.4.  Under paved areas and within 4m of structures: Coarse sand, controlled low strength material or fine crushed rock.

1.3.5.  In classified reactive clay sites: impervious material to current relevant Australian Code.

1.3.6.  Note: Inadequate backfilling can lead to differential settlement and damage to paving and landscaping. In reactive clay soils, it is important that service trenches do not act as a conduit to carry moisture into the ground next to the foundations, so impervious material should be used for backfill.

1.3.7.  Treatment and design for highly reactive soils should be as directed by the engineer.

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