Backfilling the excavation

​General 6.8.1

1. ​Backfill comprises the material above the embedment zone, in accordance with Drawing 7251/8/301 and AS 3725-2007.

2. Backfilling must be carried out in accordance with the relevant Drawings. Appropriate methods of compaction must be used to achieve the compaction requirements shown on the Drawings.

3. Impact loading of the pipeline must be avoided during placement of backfill material.

4. When backfilling the space between manholes and the sides of the excavations, the Contractor must ensure the manhole isn't displaced.

5. The Contractor must backfill any excavation to form a reliable, effectual and lasting support to the adjoining ground.

6. Over-excavation around structures where future works may be required must be backfilled in accordance with Excessive excavation.

7. Where the pipeline is supported on concrete, the Contractor mustn't place the overlay material until the concrete has obtained its initial set. The backfill material mustn't be placed within 24 hours of placing the concrete, or a longer period if shown on the Drawings.

8. In close-timbered tunnels, drives and shafts, the Contractor must fill the voids behind the timber ground support by pressure grouting or other approved means.

9. The Contractor must correct any deficiencies of backfilling exposed by settlement.

Backfilling materials 6.8.2

The materials used for backfilling for the purpose of this Specification must be as defined and designated in this clause.

Type A (crushed rock and sands)

1. Crushed rocks and sands permitted for backfilling:

   • Type A1 - 20 milllimetre VicRoads Class 2 crushed rock

   • Type A2 - 20 milllimetre VicRoads Class 3 crushed rock

   • Type A3 - 20 milllimetre Non Descript crushed rock

   • Type A5 - A Grade sand

2. A Grade sand must be in accordance with the specification for sand and rock.

1. The gradings for type A5 must be in accordance with circular pipes.

Type B (excavated material)

1. Excavated material permitted for backfilling is:

   • Type B1 - Select excavated

   • Type B2 - Ordinary excavated

   • Type B3 - Bulk excavated

2. Select excavated material must contain no rock fragments with dimensions greater than 20 milllimetres or hard clay fragments with dimensions greater than 40 milllimetres.

3. Ordinary excavated material must contain no more than 20 per cent of rock fragments with dimensions in the range of 40 milllimetres to 150 milllimetres, with no fragments greater than 150 milllimetres.

4. Bulk excavated material must contain no more than 60 per cent of rock fragments with dimensions in the range 40 milllimetres to 300 milllimetres, with no fragments greater than 300 milllimetres.

Type C (slurry)

1. Slurries permitted for backfilling are:

   • Type C1 - Sand-cement slurry

   • Type C2 - Clay slurry

2. Sand-cement slurry must be 20 parts sand to one part cement by volume, with sufficient water to permit the mix to flow under its own weight. If pumping or enhanced flow properties are required, any of the following may be added:

   • an approved wetting agent, at the rate recommended by the manufacturer

3. Clay slurry is soil removed from the excavation, consisting predominantly of clay mixed with water and worked on the surface to form a fluid mixture able to flow under its own weight.

4. Particles of rock or lumps of soil remaining after working must neither have dimensions greater than 20 milllimetre nor be in quantities sufficient to reduce the flow of the slurry.