Reference Specifications for Civil Engineering Work 2001

Table 7.3 – Maximum thickness of uncompacted layers

Static module weighty or vibrating drum equivalent (tonnes)	Maximum thickness of uncompacted layer (mm)
	Voids not filled	Voids filled*
5	400	300
10	600	400
15	900	600
20	1200	800

* Proportion of finer grained materials to completely fill the voids between rocks

Asphalt supply and placement

Asphalt manufacture: In accordance with Reference Specification S310 Supply of Dense Graded Asphalt.

Asphalt transportation and placement: In accordance with Reference Specification S320 Laying of Asphalt. Place and compact hot mix asphalt so that the edges (saw cut or edge planed) are flush with the existing pavement. A slight crown (maximum camber above the existing pavement of 5 mm for trench  0.5 m wide or 10 mm for trench  0.5 m wide) may be formed to allow for subsequent consolidation of the trench.

Surface Preparation: The top surface of the backfill and the remaining sides of the trench shall be thoroughly broomed to remove any loose material before placing the tack coat.

Tack coat: Tack coat the top surface of the backfill and the remaining sides of the trench with a light sprayed application of a liquid bituminous material (0.2 l/m² residual bitumen) prior to placing the asphalt layers.

Asphalt spreading: Use hand spreading method for trenches less than 1 m wide and machine spreading method (use a tamper spreader) for trenches more than 1 m wide.

Hand spreading: Take asphalt directly from the receiving hopper (or other approved location), distribute immediately into place using shovels, spread to the required loose depth using metal rake or board rakes (lutes), and compact immediately.

Cold planing: If required, prepare for resurfacing by cold planing the existing asphalt surface. Take out ruts, bumps depressions or other uneven areas of pavement to allow a uniform thickness of new asphalt to be placed.

Compaction: Select rollers or plates (such as vibrating plate compactor, vibrating rammer, pedestrian roller, small tandem vibrating roller) to suit the size of the job. Keep the drum or plate moist to prevent the adherence of asphalt. Complete rolling while the mix temperature is above 95C. The relative compaction (ratio of the in situ density or the compacted asphalt and the representative maximum density of the asphalt) must not be less than 94%.

Cemented materials

Place material by discharging directly from a concrete agitator truck. Alternatively use a concrete pump where access is restricted.

Controlled low-strength material (Flowable fill): Use freely flowing material capable of completely filling horizontal trenches, over lengths of up to 100 metres, without the aid of pumping, vibration, rodding or other mechanical action.

Dry lean mix concrete: Use compacted layer method of construction.

No fines concrete: Rod sufficiently only to ensure the trench is completely filled. Screed to the required levels without tamping or vibrating.

Wet lean mix concrete: Deposit concrete in horizontal layers not exceeding 400 mm thick. Commence compaction of concrete immediately after deposition. Use high frequency immersion vibrators to achieve compaction.

Puddling and jetting

This construction method applies to sand and is NOT to be used for trenches under existing pavements and footpaths. Compact by flooding and the use of immersion vibrators. Do not use puddling or jetting of material, unless prior approval is obtained from the Superintendent. Flooding will only be permitted where the process does not cause damage to adjacent works. Where puddling and jetting is not approved, use the compacted layer method of construction.