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SPECIFICATION FOR THE REINSTATEMENT OF OPENINGS IN ROADS

NG2 Performance Requirements

NG2.1 There are no Notes for Guidance

NG2.2 Surface Profile

NG2.2.1 There are no Notes for Guidance

NG2.2.2 Edge Depression - Intervention

Freedom from excessive edge depressions, or 'trips', for all pedestrians and two wheeled vehicles, is considered to be one of the most important performance requirements. Given that pedestrians and various two wheeled vehicles are likely to use or cross any roads, footways and cycletracks, it is considered necessary to set a single limit for all edge depressions.

NG2.2.3 Surface Depression - Intervention

Excessive surface depressions will reduce ride quality and give rise to noise and vibration. The maximum depth of surface depression within the area of a reinstatement is limited to approximately 2.5% of the width of reinstatement, which represents a mean slope of 1 in 20 (5% gradient). In order to prevent excessive areas of standing water, it is considered necessary to limit the maximum depth of a surface depression to 25 mm, regardless of the reinstatement width.

NG2.2.4 Surface Crowning - Intervention

Excessive surface crowning will reduce ride quality and give rise to noise and vibration. The maximum height of crowning within the area of a reinstatement is limited to approximately 2.5% of the width of the reinstatement, which represents a mean slope of 1 in 20 (5% gradient). In order to prevent excessive surface irregularity, it is considered necessary to limit the maximum height of crowning to 25 mm, regardless of the reinstatement width.

NG2.2.5 Combined Defect - Intervention

The intervention limits specified for surface depressions and surface crowning include a reduction in the intervention limit, to 80% of the tabulated value, subject to a minimum of 10 mm, where surface depressions and/or crowning and/or edge depressions abut. The individual features shall be measured, and the reduction applied, as follows:

1) Combination Depressions

Where an edge depression abuts an area of surface depression, then the area of abutting depression should be measured as shown in Figure NG2.2. Any surface crowning also abutting the area of combined depressions should be measured separately, as shown in Figure NG2.3. The permitted depth of a combination depression is further limited if the depression results in standing water.

Figure NG2.2 - Combination Depression

E = Edge Depression Contribution = 10 mm
S = Surface Depression Contribution = 10 mm or 80% ) whichever is of tabulated value ) the greater

2) Combination Crowning

Where an area of surface crowning abuts an edge depression, or a surface depression, or any combination thereof, then the area of abutting crowning should be measured as shown in Figure NG2.3. The area of abutting depression should be measured separately, as shown in Figure NG2.2. The maximum height of combination crowning is further limited if the crowning results in standing water.

Figure NG2.3 - Combination Crowning

C = Surface crowning contribution = 10 mm or 80% ) whichever is of tabulated value ) the greater

NG2.2.6 There are no Notes for Guidance

NG2.3 Fixed Features

Fixed features, e.g. kerbstones and related precast concrete products, channel blocks and drainage fixtures, surface boxes and ironware, should be bedded on a sound foundation, in accordance with the owner's requirements. In order to prevent excessive areas of standing water, it is considered necessary to set separate intervention limits for channel blocks, drainage fixtures, surface boxes and ironware.

NG2.4 Surface Regularity

Where the use of a rolling straightedge is not permitted, the surface regularity shall be assessed on an agreed basis. One method could be the use of a two metre or three metre straightedge.

NG2.5 Structural Integrity

1) Reinstatement materials and compaction requirements have been specified in order to safeguard the pavement structure, both within and adjacent to the reinstatement. Any substantial or rapid settlement within a reinstatement may therefore indicate a potential reduction in the stability of the adjacent pavement structure, as well as potential defects within the reinstatement.

2) There will be cases, in adverse circumstances, where the correct application of this Specification, in all respects, will still result in levels of settlement within the reinstatement that do not meet the requirements of Section S2.5, Structural Integrity. For example, the type and condition of the adjacent ground and/or pavement structure may limit the degree of compaction that can be achieved, so influencing the amount of settlement that could occur.

3) Any engineering investigation is intended only to determine the likelihood and extent of any further settlement, and the most cost-effective and convenient method of restoring the structural stability and surface performance of failed sections of a reinstatement, to a satisfactory condition.

4) In the case of large or deep excavations, it may be appropriate for the Authority and the Undertaker to agree an extended interim guarantee period, with additional interim surfacing materials laid to restore the running surface. When no further consolidation or settlement is considered likely, a permanent binder course and surface course may be laid, and the permanent guarantee period initiated. In any event, the location and extent of any re-excavation should be mutually agreed, taking full advantage of any bound materials already in place.

5) The depth of unbound materials is the difference in vertical height between the underside of the base of the trench and the top of the surround to the apparatus.

NG2.6 Skid Resistance

1) An adequate skid resistance of the reinstated running surface must be maintained, by selection of the polished stone value (PSV), aggregate abrasion value (AAV) and texture depth of the aggregate exposed at the road surface. The exposed aggregate may be precoated chippings rolled into the surface (HRA), coarse aggregate within the surface course, coated material to BS 4987 or any chippings or other aggregate applied in any form of surface dressing or slurry sealing treatment.

2) Smaller reinstatements constitute a much lower degree of skidding risk, but the measurement of skid resistance, texture depth and surface regularity become progressively more difficult as the reinstatement width reduces. However, material requirements and laying conditions remain unchanged and it is expected that the skid resistance of smaller reinstatements will not be significantly different.

3) For the purposes of identifying reinstatement sites where the risk of skidding is potentially high (Site A), sections of carriageway of greater than 10% gradient should be identified from existing steep hill warning signs or by notification from the Authority. Similarly, bends of less than 100 metres radius in roads where the speed limit is greater than 40 mph (65 kph) should be identified from existing bend, double bend or chevron warning signs or by notification from the Authority.

4) Given good site conditions, it is possible to obtain reasonably representative measurements of skid resistance and surface regularity on narrower reinstatements but amended test procedures and/or extra care are required. The TRL Mini Texture Meter and TRL Rolling Straightedge should always be fully contained within the limits of the reinstatement. The actual minimum practicable width for these instruments will depend on the trench alignment and radius of curvature. Measurements can be particularly difficult when testing on tight radius bends.

NG2.7 There are no Notes for Guidance

NG3 Excavation

NG3.1 There are no Notes for Guidance

NG3.2 Excavation

1) HSG 185 "Health and Safety in Excavations" gives guidance to those carrying out excavations.

2) Where possible, all excavations should be planned before commencement of works on site.

3) Work must be undertaken and supervised by properly qualified personnel.

NG3.3 There are no Notes for Guidance

NG3.4 Side Support

1) Where required, there must be sufficient quantities of appropriate materials available to provide safe trench support.

NG3.5 - NG3.7 There are no Notes for Guidance

NG4 Surround to Apparatus

NG4.1 General

1) It is often necessary for an Undertaker to require a specific type or quality of material, and/or special protective components, to be laid within the immediate vicinity of certain types of underground apparatus. This material is usually referred to as the surround to the apparatus, and may include fine unbound granular materials (usually termed 'finefill'), bound materials, tiles, covers, tubular shields, etc., or any combination thereof. The resulting surround may be required for a variety of reasons, including structural support, low corrosion potential, protection for non-metallic materials or special coatings, etc.

2) The nature of the Undertakers apparatus, and/or the protective features of the surround, especially any fine unbound granular materials used within the surround, may impose additional restrictions on the type of compaction equipment that can be used and the necessary operating procedures. However, the entire surround will effectively form a foundation structure for the remainder of the reinstatement and must be capable of providing adequate support for all loading imposed on the reinstatement surface, as well as the weight of the reinstatement structure.

3) In selecting a material for the surround to apparatus, Undertakers should be mindful of the potential for the migration of fines from the adjacent ground, and/or the overlying backfill, into any surround material that is open-textured. Such migration will normally result in settlement of the adjacent ground, and/or the backfill. Migration of fines can be prevented by using a close textured surround or, if this is undesirable, by enclosing the surround within a suitable filter membrane.

NG5 Backfill

NG5.1 Backfill Material Classification

The assumed limiting performance of the five classes of backfill material defined in Appendix A1 is shown in Table NG5.1.

Table NG 5.1 - Backfill Material Performance

NG5.2 There are no Notes for Guidance

NG5.3 Additional Requirements

1) Frost Heave Susceptibility

The frost heave test described in BS 812: Part 124 is costly and time consuming and is not suitable for routine on-site control checks. The test is primarily intended as a method to establish whether an aggregate from a particular source is likely to be frost susceptible when used in road pavement construction. Material for the frost heave test must be representative of the source or sub-grade encountered. Authorities usually maintain a list of "Approved Suppliers of Non-frost Susceptible Materials" and should have knowledge of frost susceptible sub-grades in their locality.

The following notes on identification of potentially frost heave susceptible material are for guidance but are not, in themselves, exhaustive:

a) Clay materials can be regarded as non-frost susceptible, particularly when the plasticity index is greater than 15%. Clay/silt mixtures are more difficult to assess and are likely to be of marginal frost susceptibility.

b) Silts, particularly those with more than 10% passing a 75 micron (m) BS sieve size, are likely to be frost susceptible.

c) Cohesive/granular materials will often be frost susceptible; the quantity and type of granular aggregate and, to a lesser degree the silt fraction are the controlling factors. If the aggregate is a frost susceptible type, then it is very probable that the mixture will also be frost susceptible.

d) Granular materials with more than 10% passing a 75 micron (m) BS sieve size have a high potential for frost susceptibility and granular materials with more than 12% passing 75 micron (m) are likely to be frost susceptible.

e) All crushed chalks are frost susceptible and the magnitude of the frost heave will increase with the saturation moisture content of the chalk.

f) Oolitic and magnesium limestones are likely to be frost susceptible, particularly those where the aggregate saturation moisture content exceeds 3.5%.

g) Hard carboniferous limestones are unlikely to be frost susceptible unless they have been contaminated with clay or have more than 12% passing 75 micron (m).

h) Crushed granites will only be frost susceptible if the percentage passing 75 micron (m) exceeds 12% and is partially plastic.

i) 'As dug' sands and gravels are frequently frost susceptible especially if the percentage passing 75 micron (m) BS sieve size is greater than 12% or if it is plastic. Sands and gravels won by "wet working" techniques are unlikely to be frost susceptible unless contaminated by a clay or a high silt fraction.

j) Burnt colliery shales, slags, PFAs, etc. are secondary materials, and it is not possible to give general guidance to their potential for frost heave resistance. Each source is different and will need to be assessed by the frost heave test. The exception to this is graded bottom furnace ash produced by modern power stations, which has been found to be non-frost susceptible.

k) Foamed concretes can generally be regarded as non-frost susceptible.

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