- A single pass of any compaction plant is deemed to be completed when the foot, roll or plate of the compactor has impacted the entire surface area of the layer.
- Where the excavation is more than 50 mm wider than the foot, roll or plate, two or more traverses of the compaction device will be required to ensure coverage of the entire surface and all will be deemed to constitute a single pass.
- Compaction plant should be steered along a line offset from that steered on the previous pass so that alternate passes are run close in to each side wall of the excavation.
- Small items of compaction plant will frequently be required and additional provisions must be considered for use in trenches within restricted areas. In general, lightweight vibrotampers and mechanical pole tampers are capable of achieving the same degree of compaction as the heavier items of plant specified in A8, However, small plant is usually not self-advancing and therefore more difficult to operate effectively.
Hand rammers
- Hand rammers may be used for initial tamping of fine fill material or immediately adjacent to street furniture, reinstatement edges etc.
- Full machine compaction complying with A8, will normally be applied immediately after the required thickness of material has been built-up. However, hand ramming alone may be necessary in small openings, narrow trenches, around access chamber covers, around standpipes and other isolated fixed features.
Percussive rammer
- A percussive rammer is deemed to be a hand-held or pedestrian guided machine in which an electric, pneumatic or hydraulically operated reciprocating mechanism acts on a plate or ‘foot’.
- Percussive rammers may only be used to provide full machine compaction in restricted areas.
Vibrotamper
- A vibrotamper is deemed to be a free-standing, pedestrian guided machine in which a reciprocating mechanism, driven by an integral engine or motor, acts on a spring system through which oscillations are set up in a base plate or ‘foot’.
- Vibrotampers may be operated at reduced speed, for the first pass only, with cohesive materials.
- Vibrotampers are not preferred for any permanent surface course application or any other application involving a layer thickness of less than 50 mm.
Vibrating rollers
- A vibrating roller is deemed to be a self-propelled pedestrian steered machine with a means of applying mechanical vibration to one or more rolls.
- Vibrating rollers should be operated in the lowest available gear, except for the first pass which should be at maximum forward speed.
- All compaction passes should be carried out with full vibration, except for the first pass which should be carried out without vibration to nip in the material adjacent to the reinstatement edges and to prevent uneven displacement of material within the remainder of the reinstatement area.
- Vibrating rollers are the preferred method of compaction for all permanent surface courses.
- The use of twin drum rollers is preferred to single drum for compacting bituminous mixtures and will improve the quality of the permanent surface course. However, single drum vibrating rollers are permitted, as detailed in A8.
Vibrating plate compactors
- A vibrating plate compactor is deemed to be a pedestrian guided plate equipped with a source of vibration consisting of one or more rotating, eccentrically weighted shafts.
- Vibrating plate compactors should be operated in the lowest available gear, except for the first pass which should be at maximum forward speed.
Other compaction equipment
Compaction plant not referenced in A8, including machine-mounted, modified and other alternative compaction equipment, may be permitted for compacting reinstatement materials in accordance with the following relevant requirements:
- Machine-mounted compactors
A machine-mounted compactor is deemed to be any compaction equipment that is mounted as an attachment to the chassis or front or rear booms of an excavator, tractor, skid-steer vehicle or other proprietary vehicle.
All machine-mounted compactors, whether integral to the vehicle design or on special attachments, should be operated in accordance with the recommendations of the compactor or attachment manufacturer, to the relevant compaction procedure required by A8, However, other operational variables should also be considered before operating such plant as follows:- Compactor downforce
The downforce will vary depending upon the weight of the vehicle chassis or compactor frame, and any additional force applied by hydraulic rams etc. However, changes in the configuration of any vehicle by adding or removing accessories etc, changes in the width of the vibrating foot, roll or plate etc, movement of any boom resulting in a significant change of loading geometry or outreach etc, attaching of the compactor to other vehicles of differing types or weights etc, can all result in a significant reduction of compactive performance that is seldom apparent. All operators should be aware of the potential reduction in compactive performance resulting from such changes in configuration. - Applied downforce
The mounting of compaction equipment to the front loader arms of an excavator, where the downforce is sensibly limited by the lifting of the front wheels, is preferred. All compactors mounted to the backhoe of an excavator should be fitted with a downforce-limiting device, correctly set, or with a simple indicating device allowing the amplitude to be estimated. - Compactor set-up
Where vibration frequency or amplitude, or any other parameter affecting the dynamic output of a compactor is expected to be adjusted on a routine basis, all parameters should be set in accordance with the manufacturer’s recommendations unless specific testing meeting the requirements of NG1.6 (4) has shown other settings to be at least as effective.
- Compactor downforce
- Modified compaction equipment
Modified compaction equipment includes any proprietary vibrotamper, vibrating roller, vibrating plate compactor, percussive rammer or other compaction plant that has been adapted, converted, revised or otherwise changed from the original manufacturer’s specification, resulting in a significant change to the original configuration, dimensions, operational weight or power output.
Modified compaction equipment is acceptable provided it is operated in accordance with compaction procedures meeting the following requirements:- The original manufacturer must provide written confirmation that the modified compaction equipment, operated in accordance with the original compaction procedure, is capable of achieving the same degree of compaction as any other option permitted in A8, or
- A revised compaction procedure is developed in accordance with the requirements of NG1.6. (4)
- Alternative compaction equipment
Alternative compaction equipment includes all other compaction devices not specifically permitted within NG10.3. Alternative compaction equipment may be permitted, provided it is operated in accordance with compaction procedures developed in accordance with the requirements of NG1.6 (4).
