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SPECIFICATION FOR THE REINSTATEMENT OF OPENINGS IN ROADS
NG6 Flexible and Composite Roads
NG6.1 There are no Notes for Guidance
NG6.2 Sub-base Reinstatement
1) It may be reasonable to expect that an adequately compacted sub-base should achieve an in-situ CBR value in excess of 30%.
2) It is expected that a bituminous sub-base will only be selected where the base (roadbase) is also bituminous.
3) When placing bituminous material directly on to the backfill it is important to ensure that the exposed surface of the backfill has been compacted. This operation is essential to minimise the risk of a build up of pore water pressure causing the subgrade to become spongy. It is also imperative that construction is phased such that excavated areas are covered, on the same day, with the first layer of bituminous material, to prevent the ingress of water. Care should be taken in the compaction of this first layer. If pore water pressure builds up in the backfill at this stage, then rolling should cease and the material left overnight, or longer if necessary, prior to the placement of any further layers.
NG6.3 Base (Roadbase) Reinstatement
Overlaid Modular Layers
1) This Specification permits the re-use of cobbles and setts for the reinstatement of the relevant layer. However, it is often extremely difficult to achieve a performance from such reinstatements that is similar to that of the original, well interlocked and 'stress hardened' layer. Failure to achieve this structural stiffness could result in failure of the reinstatement and particularly any surfacing materials laid thereon.
2) The Specification does not permit the re-use of penning, in which the layer of modules is laid upright, in an interlocking manner, exhibiting a greater stiffness than an equivalent layer of cobbles/setts.
NG6.4 Surface Reinstatement
NG6.4.1 Hot Rolled Asphalt Surfaces
1) HRA design mixtures give better resistance to deformation where queuing of heavy traffic is likely to occur and may be more economical to lay.
2) Type C mixtures use fine aggregates of a coarser grading than Type F mixtures, usually associated with the use of crushed rock fines. Such mixtures tend to be stiffer and less well suited to the reinstatement of small excavations.
3) Type R mixtures have better fatigue and durability characteristics than type F or Type C mixtures but can be expected to have less resistance to deformation.
NG6.4.2 - NG6.4.5 There are no Notes for Guidance
NG6.4.5.2 High Friction Surfacings
Special friction surfacings are likely to be bauxite epoxy resin systems, special textured slurry seals or premium surface dressing applications. They will usually have been laid for safety reasons and their early reinstatement will be important.
NG6.4.5.3 Porous Asphalt
Edge sealing requirements specified in Section S6.5.2.2 may not be appropriate with porous asphalts.
NG6.4.5.4 Coloured Surfacings
1) Coloured surfacings are sometimes used for marking bus lanes, accident prevention measures, traffic prioritisation schemes, etc. The use of warning signs, e.g. "Temporary Road Surface", should be considered until the special surface can be restored.
2) It may not be possible to obtain coloured surfacings in a wide selection of colours and Authorities may have to accept limitations in colour matching. In addition, all coloured surfacings fade or undergo other changes in colour as the materials age.
NG6.4.5.5 Other Specialist Surfacing Materials
Texture depth requirements specified in Section S2.6.2 may not be appropriate for the increasing number of specialist surfacing materials currently being used by some Authorities.
NG6.4.6 Surface Treatments
In all roads, where the overall quality of existing surface dressings or surface treatments are to a high standard, it may be difficult to produce small excavations or narrow trenches with surface dressings or other surface treatments that closely and uniformly match the existing adjacent surfaces. Under such circumstances, some localised variation in surface quality may be acceptable to the Authority.
NG6.4.7 - NG6.4.10 There are no Notes for Guidance
NG6.5 Base and Edge Preparation
NG6.5.1 Base Preparation
Tack coating materials are generally based on rapid curing anionic or cationic bitumen emulsions to BS 434, with approximately 40% bitumen content. New tack coating materials are becoming available, and the trial use of more modern variants is recommended.
NG6.5.2 Edge Preparation
1) Edge regularity requirements are intended to provide a shape that will not hinder the compaction of material adjacent to the reinstatement edge. The final shape, when viewed from above, should be governed by the following general principles rather than by aesthetic considerations:
a) There is no requirement to trim the sides of trench excavations solely to provide a uniform width, provided that individual projections are not less than 250 mm length, measured parallel to the nominal centreline of the trench.
b) There is no requirement to trim a small excavation solely in order to provide a square or rectangular shape. Any shape, with included angles not less than 90° and with no projection less than 250 mm length, may be considered to be regular.
c) Where the existing surfacing material is sound at the corners of an excavation, there is no necessity to cut out to a corner; a regular chamfer may be preferable.
d) Where a 90° corner is to be cut out, overlapping cross cuts should be minimal and all cuts extending into the existing surface should be filled with sealant.
2) Edge sealant materials are generally based on rapid curing anionic or cationic bitumen emulsions to BS 434, typically 50 or 70 pen and approximately 70% bitumen content, or hot bitumens to BS 3690, typically 50 or 70 pen. An increasing number of high build and rubberised edge sealants are becoming available and, in general, are preferred. The use of high-build liquid sealants, sprays or solid sealing strips etc, is recommended, on a trial basis at least.
NG6.6 There are no Notes for Guidance
NG7 Rigid and Modular Roads
NG7.1 Reinstatement Methods
1) The requirements of this Specification shall apply to all rigid roads up to 125 msa traffic flow. All rigid roads with existing traffic flows exceeding 30 msa must be identified by the Authority, prior to the commencement of works, so that reinstatement requirements can be agreed.
2) Some modern concrete roads, constructed in accordance with current Government standards and specifications, may incorporate special design philosophies that are beyond the scope of this Specification. Similarly, there may be other existing rigid road designs that will also require the use of particular reinstatement methods. Such roads must also be identified by the Authority, prior to the commencement of works, so that reinstatement requirements can be agreed.
NG7.2 - NG7.6 There are no Notes for Guidance
NG7.7 Modular Roads
1) When excavating in modular roads, the existing modules shall be lifted carefully and stored for re-use.
2) It is particularly important to ensure that bedding and jointing sands should meet the performance demands in areas subject to heavy vehicular traffic.
NG7.8 There are no Notes for Guidance
NG8 Footways, Footpaths and Cycletracks
NG8.1 There are no Notes for Guidance
NG8.2 Sub-base and Binder Course Reinstatement
NG8.2.1 - NG8.2.3 There are no Notes for Guidance
NG8.2.4 Excavations Adjacent to Roads
The most heavily stressed area of a road is usually the inside wheel track adjacent to the road edge. Depending on ground conditions, it is often necessary to support the road edge by providing lateral restraint within the adjoining footway, footpath, cycletrack or verge. The most common form of edge support is a section of unbound or cement bound granular materials. This construction will most commonly be encountered when the horizontal distance, between the edge of the Undertakers' excavation and the edge of the road surface, is less than the expected depth of cover of the Undertakers' apparatus.
NG8.3 Surface Reinstatement
NG8.3.1 There are no Notes for Guidance
NG8.3.2 High Duty and High Amenity
1) In high duty footways, the durability of the wearing surface is of prime importance and simple cosmetic matching of materials may not be adequate. Specific grades of material such as York stone modules, or specific types of construction such as asphalt sand carpet/mastic, may have been laid in order to give an acceptable performance under extreme conditions. In these cases, similar or equivalent grades of materials will need to be reinstated.
2) In high amenity footways, the cosmetic matching of materials at the wearing surface may be of primary importance with durability of secondary importance.
NG8.3.3 Other Material to BS4987
A wide range of surface treatments exist and commonly these are less than 6 mm aggregate size. Where available, a similar surface finish will be reinstated. The surface course material may be reinstated using any of the allowed binder course or surface course materials, with a final surface treatment applied as soon as practicable following the laying of the permanent surface course.
NG8.3.4 There are no Notes for Guidance
NG8.3.5 Concrete Materials
1) In general, reinstatements in a concrete footway, footpath or cycletrack should match the existing surfacing as closely as is practicable.
2) Generally, the use of all flexible permanent reinstatements in overlaid concrete, mastic asphalt, asphalt carpet, sand carpet or other derivative surfaces etc., has proven to be entirely adequate in practice.
NG8.3.6 - NG8.3.8 There are no Notes for Guidance
NG8.4 - NG8.5 There are no Notes for Guidance
NG9 Verges and Unmade Ground
NG9.1 - NG9.4 There are no Notes for Guidance
NG10 Compaction Requirements
NG10.1 Introduction
1) Research has shown that failure to operate and maintain compaction equipment in accordance with manufacturer's schedules and recommended practices is likely to result in inadequate compaction with serious implications for the short term performance of individual structural layers and the long term integrity of the entire reinstatement.
2) All compaction equipment covered by this Specification must be frequently checked, adjusted and maintained, as necessary, in accordance with the manufacturer's recommended practices, in order to ensure that the manufacturer's recommended operating frequency is maintained throughout each compaction operation.
3) All compaction equipment covered by this Specification must be used in accordance with the manufacturer's recommended operating procedures.
NG10.2 Reinstatement Materials
NG10.2.1 Unbound Granular and Cohesive Materials
For granular or cohesive materials, a vibrating roller may be unsuitable in small excavations because of the restricted manoeuvrability of large heavy rollers required to achieve adequate levels of compaction with an acceptable number of passes.
NG10.2.2 There are no Notes for Guidance
NG10.2.3 Bituminous Materials
With some combinations of compaction plant and certain types of bituminous materials if compaction is continued as the material approaches its maximum density the following may result:
a) The migration of fines or binder to the surface.
b) The development of shear surfaces and or crushing of aggregates.
Provided that the material has been laid and compacted within the appropriate temperature range, fewer passes will be required if any signs of distress become apparent.
NG10.2.4 There are no Notes for Guidance
NG10.2.5 Modular Surfacing Materials
Depending on the size and type of paving module to be laid, and/or the extent of the area to be surfaced etc., the use of additional mechanical compaction may become necessary.
NG10.3 Equipment Operation and Restrictions
NG10.3.1 Hand Rammers
1) Hand rammers may be used for initial tamping of fine fill material or immediately adjacent to street furniture, reinstatement edges etc.
2) In all cases, full machine compaction complying with Appendix A8 will normally be applied immediately after the required thickness of material has been built-up. However, hand ramming alone may be necessary around standpipes and other isolated fixed features.
NG10.3.2 Percussive Rammer
1) A percussive rammer is deemed to be a hand-held and/or pedestrian guided machine in which an electric, pneumatic or hydraulically operated reciprocating mechanism acts on a plate or 'foot'.
2) Percussive rammers may only be used to provide full machine compaction in areas where restricted access prevents the effective use of conventional compaction equipment.
NG10.3.3 Vibrotamper
1) 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'.
2) Vibrotampers may be operated at reduced speed, for the first pass only, with cohesive materials.
3) Vibrotampers are not preferred for any permanent surface course application or any other application involving layer thicknesses of less than 50 mm.
NG10.3.4 Vibrating Roller
1) 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.
2) Vibrating rollers should be operated in the lowest available gear, except for the first pass, which should be at maximum forward speed.
3) All compaction passes should be carried out with full vibration, except for the first pass, which should be carried out without vibration in order to nip in the material adjacent to the reinstatement edges and to prevent uneven displacement of material within the remainder of the reinstatement area.
4) Vibrating rollers are the preferred method of compaction for all permanent surface courses.
5) The use of twin drum rollers is preferred to single drum for the compaction of bituminous materials and will improve the quality of the permanent surface course. However, single drum vibrating rollers are permitted, as detailed in Appendix A8.
NG10.3.5 Vibrating Plate Compactor
1) 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.
2) Vibrating plate compactors should be operated in the lowest available gear, except for the first pass, which should be at maximum forward speed.
NG10.3.6 Other Compaction Equipment
Compaction plant not referenced in Appendix A8, including machine-mounted, modified and other alternative compaction equipment, may be permitted for the compaction of reinstatement materials, in accordance with the following relevant requirements:
1) Machine-Mounted Compactors
A machine-mounted compactor is deemed to be any compaction equipment that is mounted, as an attachment or accessory, to the chassis or front or rear booms of an excavator, tractor, skid-steer vehicle or other proprietary vehicle, for the purposes of compaction.
All machine-mounted compactors, whether integral to the vehicle design or special attachments for front or rear mounting to the chassis or booms of any excavator, tractor or skid-steer vehicle etc. should be operated in accordance with the recommendations of the compactor or attachment manufacturer, to the relevant compaction procedure required by Appendix A 8. However, other operational variables should also be considered prior to the operation of such plant as follows:
a) Compactor Downforce
The total downforce will vary depending upon the weight of the vehicle chassis or compactor frame, and any additional downforce applied by hydraulic rams etc. However, changes in the configuration of any vehicle, by the addition or removal of other 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.
b) 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.
c) 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 Section NG1.6.3, has shown other settings to be at least as effective.
2) Modified Compaction Equipment
Modified compaction equipment shall include any proprietary vibrotamper, vibrating roller, vibrating plate compactor, percussive rammer or other compaction plant which 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 shall be permitted, provided it is operated in accordance with compaction procedures meeting the following requirements:
a) The original manufacturer shall 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 Appendix A8.
or b) A revised compaction procedure is developed in accordance with the requirements of Section NG1.6.
3) Alternative Compaction Equipment
Alternative compaction equipment shall include all other compaction devices not specifically permitted within Section NG10.3. Alternative compaction equipment may be permitted, provided it is operated in accordance with compaction procedures developed in accordance with the requirements of Section NG1.6 3).
NG10.3.7 Compaction Procedure (Note: There is no equivalent S10.3.7 for this section)
1) 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.
2) Where the excavation width is more than 50 mm greater than the foot, roll or plate width (i.e. side clearances between the compacting surface and the wall of the excavation exceed 25 mm per side), 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 compactive pass.
3) 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.
4) Small items of compaction plant will frequently be required and additional provisions must be considered for use in trenches of less than 200 mm width, small excavations and other areas of restricted access. In general, lightweight vibrotampers and poletampers are capable of achieving the same degree of compaction as the heavier items of plant specified in Appendix A8. However, small plant is usually not self-advancing and therefore more difficult to operate effectively. Currently there is no alternative equipment available for this application and the provisions included in Appendix A8 are proven in practice.
NG11 Ancillary Activities
NG11.1 Traffic Signs, Road Markings, Studs and Verge Markers
In the interests of safety generally and particularly in the interests of the disabled, all traffic signs, road markings, studs and verge markers removed during the course of the works should be replaced immediately following completion of works.
NG11.2 Street Furniture and Special Features
In the interests of safety generally, and particularly in the interests of the disabled, all street furniture, tactile paving and any other special features removed during the course of works should be replaced immediately following the completion of works.
NG11.3 Traffic Sensors
1) Examples of sensors include ice warning sensors, buried queue and traffic detectors, other electronic detectors and various data collection devices.
2) The replacement of some traffic sensors may require the use of specialist contractors.
NG11.4 - NG11.5 There are no Notes for Guidance
NG12 Remedial Works
NG12.1 - NG12.5 There are no Notes for Guidance
NGA2 Key to materials
NG A2.1
1) HRA design mixtures give better resistance to deformation where queuing of heavy traffic is likely to occur and may also be more economical to lay.
2) Type C mixtures use fine aggregate of a coarser grading than Type F mixtures - usually associated with the use of crushed rock fines. Such mixtures tend to be stiffer and are less well suited to the reinstatement of small excavations.
3) Type R mixtures have better fatigue and durability than Type F or Type C but can be expected to have less resistance to deformation.
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