New construction projects: Choose backfill material to suit the permeability characteristics of the surrounding soil to ensure that the completed trench does not hold water nor obstruct existing drainage paths through the soil. Choose backfill material that will provide uniform support to match the adjoining subgrade material.
Under existing road carriageways:
Granular fill or “no fines” concrete in stormwater drainage trenches (Standard Drawing BSD-2042).
Stabilised sand, controlled low strength cementitious material or lean mix concrete in trenches as shown on Standard Drawing BSD-2042.
Lean mix concrete in isolated patches less than 2 m2 in size or where the minimum specified cover to service cannot be achieved.
Under footpaths and bikeways: Excavated material, provided adequate compaction can be obtained (Standard Drawing BSD-2043). Alternatively use Class 3 material, stabilised sand, controlled low strength material or lean mix concrete in trenches where free drainage points are not available or trenches in impermeable soils. Use granular fill or sand in trenches where free drainage points are available or where trenches are located in permeable soils.
