DN Pav 03026 02 PDF
DN Pav 03026 02 PDF
DN Pav 03026 02 PDF
DN-PAV-03026
January 2005
DN Design
Standards
TRANSPORT INFRASTRUCTURE IRELAND (TII) PUBLICATIONS
About TII
Transport Infrastructure Ireland (TII) is responsible for managing and improving the country’s
national road and light rail networks.
TII maintains an online suite of technical publications, which is managed through the TII
Publications website. The contents of TII Publications is clearly split into ‘Standards’ and
‘Technical’ documentation. All documentation for implementation on TII schemes is collectively
referred to as TII Publications (Standards), and all other documentation within the system is
collectively referred to as TII Publications (Technical). This system replaces the NRA Design
Manual for Roads and Bridges (NRA DMRB) and the NRA Manual of Contract Documents for
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National Roads Authority Volume 7 Section 2
Design Manual for Roads and Bridges Part 5 HD 39/01
Addendum
NRA ADDENDUM TO
HD 39/01
FOOTWAY DESIGN
This Addendum supersedes the NRA Addendum dated June 2001 which implemented the revised Standard
HD 39/01 and incorporates changes related to the introduction of the revised Series 900.
Standard HD 39/01 – Footway Design – is applicable in Ireland with the following amendments:
GENERAL
1. At several locations:
For: “highway”
Read: “road”;
For: “Type 1”
Read: “Type A”;
For: “roadbase”
Read: “base”.
January 2005 1
National Roads Authority Volume 7 Section 2
Design Manual for Roads and Bridges Part 5 HD 39/01
Addendum
SPECIFIC
Chapter 1 – Introduction
2.1 Page 2/1, Section 2, Paragraph 2.2, line 9 and Page 2/3,
Section 2, Paragraph 2.15, line 14:
For: “or the NIRAUC Specification for the Reinstatement
of Openings in Roads (1995) in Northern Ireland”
Read: “or the Guidelines for the Opening, Backfilling and
Reinstatement of Trenches in Public Roads (published
by the Department of the Environment, Heritage and
Local Government)”.
January 2005 2
National Roads Authority Volume 7 Section 2
Design Manual for Roads and Bridges Part 5 HD 39/01
Addendum
Chapter 4 – Materials
January 2005 3
National Roads Authority Volume 7 Section 2
Design Manual for Roads and Bridges Part 5 HD 39/01
Addendum
Chapter 6 – Enquiries
……………………………………………………
E O’CONNOR
Head of Project Management and Engineering
January 2005 4
DESIGN MANUAL FOR ROADS AND BRIDGES
PART 5
HD 39/01
FOOTWAY DESIGN
SUMMARY
This part sets out the requirements and advice for new
footway construction. It covers footways constructed
from common materials that are subject to a range of
pedestrian traffic and some overrun by vehicular traffic.
May 2001
DESIGN MANUAL FOR ROADS AND BRIDGES HD 39/01
Footway Design
Summary: This part sets out the requirements and advice for new footway construction.
It covers footways constructed from common materials that are subject to a
range of pedestrian traffic and some overrun by vehicular traffic.
Volume 7 Section 2
Part 5 HD 39/01 Registration of Amendments
REGISTRATION OF AMENDMENTS
Amend Page No Signature & Date of Amend Page No Signature & Date of
No incorporation of No incorporation of
amendments amendments
May 2001
Volume 7 Section 2
Registration of Amendments Part 5 HD 39/01
REGISTRATION OF AMENDMENTS
Amend Page No Signature & Date of Amend Page No Signature & Date of
No incorporation of No incorporation of
amendments amendments
May 2001
DESIGN MANUAL FOR ROADS AND BRIDGES
PART 5
HD 39/01
FOOTWAY DESIGN
Contents
Chapter
1. Introduction
2. Design Considerations
3. Structural Design
4. Materials
6. Enquiries
C Compaction Specification
E Worked Examples
May 2001
Volume 7 Section 2 Chapter 1
Part 5 HD 39/01 Introduction
1. INTRODUCTION
General
Implementation
Mutual Recognition
2. DESIGN CONSIDERATIONS
Introduction Start
2.3 To choose the appropriate footway design it is 1. The footway is considered to be physically separated from
necessary to consider the pedestrian and vehicular the carriageway if there is a verge of width 3m or more,
traffic which the footway may have to support and the closely spaced trees or other physical obstructions such
characteristics of the ground on which the footway is to that vehicular traffic cannot mount the footway.
be constructed. Designs are given for three construction
categories, the appropriate category being chosen 2. Any footway in a residential area is likely to be used for
according to the risk and type of vehicle overrun and on parking private cars. However, if the footway is in a rural
the amount of pedestrian usage. area it may be sensible to adopt the pedestrian-only
design, even if vehicle overrun is not physically
The category required is selected by following the prevented. If there is little pedestrian traffic the risk of
flowchart in Figure 2.1. any damage by overrun causing inconvenience to
pedestrians is small.
3. There are many situations where light vehicle overrun is a default of 2 per cent should be assumed, unless the
common, but overrun by heavy vehicles would not be material is granular in which case the CBR can be
expected to occur more than very occasionally. This may assumed to be over 5 per cent.
apply to domestic crossings (access to private driveways);
situations where cars may park between obstructions that 2.8 For a footway subject to vehicle loading the
would prevent heavy vehicles parking; and footways estimate of CBR should normally relate to the moisture
adjacent to roads on housing estates. Some heavy vehicle content which is expected to be present in the subgrade
overrun is to be expected when footways are adjacent to under the completed footway, when any change in the
roads in areas where deliveries take place, such as outside water table due to construction and the installation of
local shops. Obstructions, such as broken down vehicles, drainage has taken place. However, if the in situ CBR at
will cause traffic to overrun the footway occasionally. the time of measurement is less than the expected
equilibrium CBR, then the in situ value should be used
4. ‘Pedestrian only’ footways are not designed to support for design, otherwise failure may occur before
any type of vehicle use, not even small cleaning and equilibrium is reached.
maintenance vehicles, except those that are pedestrian
controlled.
2.9 Tables 2.1 and 2.2 provide guidance on
estimating Design CBRs if testing is not
Site Investigation possible. They are more conservative than the
information presented for road pavements in
2.4 To perform satisfactorily, a footway must be HD 25 (DMRB 7.2.2.2), and should only be used
constructed on an adequate foundation. A soft subgrade in conjunction with the designs presented in this
provides insufficient support for compaction of the Part.
layers above, which may subsequently deteriorate
rapidly. For road pavement construction the subgrade is
conventionally assessed in terms of its California
Bearing Ratio (CBR) and as footways are associated Soil Type Plasticity Design
with road pavements it is convenient to use the same Index CBR%
measure.
Plastic Clay 50 or greater 2+
2.5 Methods for measuring CBR are described in
HD 25 (DMRB 7.2.2.4). If, because of site Silty Clay 40 2
investigations prior to constructing structures, the
Modulus of Subgrade Reaction (k) of the soil is known, Silty Clay 30 3
this can be related to the CBR by the relationship given
Sandy Clay 20 3
in HD 25 (DMRB 7.2.2).
Sandy Clay 10 2+
2.6 Tests should not be carried out on the soil near
the surface as the moisture content will not be
Silt - Less than 2
representative of the equilibrium condition at depth. It
is very important to remember that Design CBRs relate Sand (poorly graded) - 7*
to equilibrium conditions. A prolonged dry spell may
distort the results and lead to failure in wetter Sand (well graded) - 10*
conditions. If a cone penetrometer is used to assess
CBR, care must be taken in case services are present; Sandy Gravel (well graded) - 15*
the use of a Cable Avoidance Tool (CAT) is
recommended. Notes: + CBR may be less than 2 if construction
conditions are poor.
2.7 The CBR chosen for design purposes should be
the minimum measured value, not the average, * Indicates estimated values assuming some
otherwise local failure will occur at soft spots. probability of the material saturating in service.
Alternatively, soft spots can be removed and replaced
with better material to improve the subgrade CBR Table 2.1 Equilibrium CBR Values
value. If it is not possible to estimate the CBR because
the condition of the subgrade is extremely variable then
Soil Condition CBR 2.12 The direction of the crossfall should take surface
water away from buildings. However, if backfall
Very soft, exudes between fingers when Less than 1% towards buildings is unavoidable then covered drainage
squeezed channels can be used to remove the surface water.
Can be moulded by strong finger Between 2 and 3% 2.13 The strength of the construction and of the
pressure subgrade can vary considerably with moisture content,
so it is extremely important to keep the structure well
Can be indented by a thumbnail but More than 6% drained during its service life. Issues of drainage relate
not by a thumb to ensuring adequate longitudinal falls, grips/gullies and
level tolerances to prevent surface water ponding and to
Table 2.2 Rough Guide to CBR aid its disposal. The drainage system should be
designed to last the life of the footway and it should be
Geometry easy to maintain. Drainage should be kept away from
the centre of the footway because of the likelihood of
works by Statutory Undertakers. Any potential
2.10 When assigning geometric parameters to
problems which may be caused by tree and hedge roots
footways the comfort of the user is taken into account,
should be considered.
together with the necessity for providing adequate
surface drainage. Steep gradients or crossfalls make it 2.14 Generally footway drainage will be the same as
difficult for elderly or encumbered pedestrians to walk that of the adjacent highway, which should ensure a low
on the footway, while insufficient gradients would not water table and efficient disposal of surface water.
facilitate the removal of surface water. Where possible Where a footway is separated from the highway the
the footway width should be sufficient to allow two main consideration should be to ensure that surface
wheelchairs or double buggies to pass. The basic water drains away from the footway into the highway. If
geometrical parameters are set out in Table 2.3. a separate drainage system is required it should be
simple and robust; it should keep the water table below
formation level and deal satisfactorily with storm water.
Parameter Recommended Extreme
Regular maintenance of the drainage system will be
Limits Limits
necessary for long-term performance. Drainage is
Longitudinal gradient 1.25% to 5% 8% maximum*
especially important if there is any risk of vehicle
(normally the same as
overrun, as a sub-base can lose a considerable
adjacent highway)
proportion of its load spreading properties if it becomes
waterlogged.
Width 2m minimum 1.3m minimum
Statutory Undertakers
Crossfall 2% to 3.3% 1.5% minimum
to 7% maximum 2.15 Where possible, footways should be designed so
at crossings that services can run in the verge rather than under the
footway. If this is not possible the provision of service
Note: *In some cases it may be necessary to construct a ducts minimises any disruption during maintenance
footway with a gradient of more than 8 per cent. work. On new footways all Statutory Undertakers’
Provision of a handrail is recommended if site equipment must be placed before the footway is
constraints necessitate a gradient steeper than 10 formed. (Recommendations on positioning new services
per cent. are contained in NJUG Publication Number 7, 1997).
Any trenches excavated before construction of the
Table 2.3 Geometric Parameters for Footways
footway should be backfilled with suitable material and
fully compacted. Compaction of the backfill to any
2.11 Crossfall should be limited to that absolutely
trenches should be carried out according to Appendix
necessary to dispose of surface water. Crossfalls steeper
A8 in the HAUC Code of Practice Specification (DoT
than about 3 per cent are uncomfortable to walk on and
et al, 1992), or the NIRAUC Specification for the
if the slope runs towards a road it can be dangerous, as
Reinstatement of Openings in Roads (1995) for
wheeled users will tend to edge down the crossfall.
Northern Ireland, to ensure that the reinstatement will In Northern Ireland refer to “Roads Service’s Policy
have a bearing capacity at least as good as the natural and Procedures Guide, RSPPG_E010"). Pavers, even
subgrade. when well laid, may not provide ride quality as good as
bituminous or flag surfaces, which is a disadvantage for
Environmental Considerations users of small wheeled buggies and the like.
3. STRUCTURAL DESIGN
Introduction ice front. Well drained soils where the water table is
well below the construction are less likely to be
3.1 For most soils, other than silt, the CBR of the damaged by frost in any situation, because footways are
subgrade at the time of construction will be at least usually alongside road pavements and the road drainage
2 per cent, which should provide an adequate surface would tend to ensure a low water table. It is unlikely to
for compaction of the sub-base. If the CBR of the be cost effective to build the footway deep enough to
subgrade is lower than this, the soil can be stabilised, totally prevent frost damage. Modular footways are less
usually with lime (which should achieve a CBR of at susceptible to frost damage as they can move without
least 5%), or some soil can be removed and replaced cracking.
with extra granular sub-base/capping material.
Pedestrian-only Design
3.2 Alternatively, if construction is being carried out
in poor conditions, on a clay soil which is expected to 3.6 Construction thicknesses are as shown in Table
have an equilibrium CBR of at least 2 per cent, there 3.1, and construction materials are discussed further in
may be a case for using a geosynthetic separating layer Chapter 5 of this Part. The sub-base is a Type 1, see
as a construction expedient. The geosynthetic does not Specification Series 800 (MCHW 1) or equivalent
improve the CBR, but prevents soft ground material with a minimum compacted thickness of
contaminating the sub-base, which would weaken the 100mm to ensure a smooth and regular laying surface
structure and lead to inadequate support for compaction for the upper footway layers. The wearing course is
of the upper layers. Construction layers above the sub- usually bituminous, concrete or clay pavers or PCC
base would consequently not be properly compacted flags. If pavers are used the sub-base surface must be
and would deteriorate faster than would otherwise be sufficiently dense to prevent bedding sand leaking
the case, with subsequent increase in maintenance down into it.
costs. The subgrade should be levelled and compacted
before placing the geosynthetic or the sub-base. 3.7 Using a single 60mm thick combined basecourse
and wearing course avoids the problems associated with
3.3 If the sub-base is required to support the compaction of very thin layers. The material cools
construction traffic, then the sub-base thickness will down more slowly, allowing more time for compaction.
need to be designed accordingly, even if the footway is However, it can be more difficult to achieve a good ride
a pedestrian-only design. quality when a separate regulating layer is omitted.
More care needs to be taken with the surface finish of
3.4 For prevention of frost damage all material the sub-base if bituminous material is to be placed in a
within 450mm of the surface should be non frost- single layer.
susceptible, unless the mean annual frost index is less
than 50, in which case the requirement can be reduced
to 350mm. Advice on the frost index for any particular
area can be obtained from the Meteorological Advisory
Services. The frost index is defined as the product of
the number of days of continuous freezing and the
average amount of frost, in degrees Celsius, on those
days. If the subgrade is frost susceptible then it should
be protected by a blanket of suitable non-frost
susceptible materials.
Surface
Options
Bituminous Pavers Flags
Layer
Sub-base(2) 100mm
Subgrade(3) -
Surface
Options
Bituminous Pavers Flags Concrete
Layer
300mm x 300mm x 60mm
20mm wearing ≥50mm ≥60mm concrete blocks or 400mm x 400mm x 65mm 150mm
Surfacing(2) course clay pavers or 450mm x 450mm x 70mm unreinforced,
40mm basecourse (1) Grade C30P
30mm bedding sand (compacted) 25mm bedding sand (compacted) or
mortar
1. 60mm combined wearing/basecourse is an alternative, but may require a slurry surfacing if a close textured surface
cannot be achieved.
3. It may be necessary to stabilise subgrade or replace with granular capping, if CBR <2%.
3.8 Slurry surfacing can be used to provide a fine This does not include pedestrian areas that generally
textured surface if it is considered that the bituminous see a significant amount of delivery or maintenance
material used in a single 60mm layer would give a vehicles. For such areas a road pavement design, as
surface that is too open textured. However, this thin given in HD 26 (DMRB 7.2.3.2) is more appropriate.
surfacing has a short life span and will probably need
replacing every 4 years. 3.13 For this category of footway the design traffic is
assumed to be 50,000 standard axles. This allows for
Light-vehicle Design approximately one vehicle per working day over a
design life of 40 years, equal to the design life of
associated road pavements (assuming that one heavy
3.9 This design is used for cross-overs to private vehicle is, on average, equivalent to one standard axle).
driveways and wherever light vehicle overrun is likely. The number of standard axles has been multiplied by 3
Construction thicknesses are shown in Table 3.2. The to take channelisation into account and some allowance
designs for segmental footways are thicker than the has been made for dynamic loading due to the vehicle
equivalent designs for bituminous footways since mounting the footway.
experimental work has shown that segmental
constructions do not exhibit equivalent load spreading 3.14 Recommended design thicknesses are given in
ability to bituminous constructions. 50mm concrete Table 3.4, and are based on the performance of lightly
pavers are now available and there is no reason to trafficked roads (Road Note 29, Road Research
assume that their performance will be inferior to 50mm Laboratory, 1970), with a minimum sub-base thickness
clay pavers. However, 50mm concrete pavers are not of 150mm. This does not allow for the sub-base to be
included in current British Standards and so cannot be used as a platform for construction traffic. If the sub-
recommended at present. base is to be trafficked the thickness must be increased
to the values in HD 25 (DMRB 7.2.2.2). It is advisable
3.10 In situ concrete can be used for vehicle that all footways subject to possible trafficking by
crossovers. Kent County Council (1988) recommend heavy vehicles include a bound roadbase.
using an unreinforced concrete, class C30P, laid 150mm
thick over 75mm of sub-base, as illustrated in Table 3.2.
Heavy-vehicle Design
Surface
Options
Bituminous Pavers or Flags Concrete
Layer
Surface
Options
Bituminous Pavers or Flags
Layer
Subgrade(3) CBR ≤2% CBR ≤3% CBR ≤4% CBR ≤5% CBR >5%
1. 70mm combined wearing/basecourse is an alternative, but may require a slurry surfacing if a close textured surface
cannot be achieved.
2. Refer to Chapter 4 for material options.
3. It may be necessary to stabilise subgrade or replace with granular capping, if CBR <2%.
Edge Restraints
2.0m
50mm x 150mm
Edging
125mm x 255mm Basecourse
Kerb Wearing Course
150mm
Concrete Bed Type 1 Sub-base 100mm
and Haunch Concrete Bed
Type 1 Sub-base and Haunch
4. MATERIALS
Introduction
50/14 hot rolled asphalt basecourse; 0/3F or 15/10F hot BS594: Part 1 BS594: Part 2
rolled asphalt wearing course
45/6F or 45/10F hot rolled asphalt wearing course Annex A of this Part
Jointing sand
4.3 Type 1 was designed to be placed using large 4.5 A permeable sub-base may be useful under
plant, in relatively thick layers and rolled using 8-10 modular surfacing, which is, to some extent, porous. It
tonne dead-weight rollers. Footways are constructed may therefore be better to provide the drainage at a
using small plant and are often laid in thin layers lower level and have a more “free-draining” sub-base.
(100mm) for which the nominal size of Type 1 is too This material is often referred to as Type 1X and a
large. Alternative locally available materials may be grading is available in TRL Report PA/SCR243, “Road
suitable which fall into the category of secondary or Haunches: A guide to maintenance practice” (1994).
recycled aggregates; for example:- Use of a permeable sub-base will only be possible
where there are no services in the footway so that a
• Initial sweepings from 10mm and 14mm surface welded felt type geosynthetic can be used to prevent
dressing flow of bedding sand into the voids.
rather than minutes for handling and compaction. Early complying with BS 4987. The solution is to either use a
results suggest that these materials are as durable as 14mm close-graded wearing course as a basecourse or a
equivalent hot materials when laid on footways (TRL 50/14 hot rolled asphalt basecourse, the latter being
Report 134) but their long term performance remains to more expensive but more durable. Alternatively, the
be established. At the moment, unless NJUG basecourse and wearing course can be combined into a
accreditation has been gained, their use should be single layer, which could be a 45/10 hot rolled asphalt
restricted to the pedestrian-only category of footways. wearing course, as shown in Annex A of this Part.
4.9 The choice of basecourse may be limited 4.10 The binder penetration should be specified as
because of the thickness specified in the design. 100 pen or less where vehicle overrun occurs, otherwise
Pedestrian-only footways require 40mm of basecourse, 200 pen can be specified.
which is below the minimum thickness for basecourse
Material
6mm medium graded 6mm dense bitumen 45/6 hot rolled
bitumen macadam macadam asphalt
Property
4.11 The pavers or flags chosen will depend on the so that the two types of surfacing can be combined to
footway category and on aesthetic considerations. Large form attractive layouts. However, if these products are
flags can be difficult to lay, requiring mechanical to be used together the joint spacings for the flags need
handling, and will be damaged by any vehicle overrun. to be relaxed to allow wider joints. Tactile flags are
Flags for footways other than strictly pedestrian only, available in compatible sizes and are of the correct
should therefore be restricted to those of plan colour, and should be used at crossings.
dimension 450 x 450 mm or less – types E, F or G to
BS 7263: Part 1. Natural stone flags, where used, 4.13 It is possible to include clay pavers in schemes
should conform to the above maximum plan dimensions that also use flags and/or concrete blocks, but the
if they are to support any vehicular traffic, but tolerances on sizes of clay are different from and less
consideration should also be given to durability and onerous than the tolerances on concrete pavers and
abrasion resistance. flags, and therefore laying problems may occur. It is
possible to obtain clay pavers to the tighter tolerances
4.12 400 x 400 x 65mm flags are compatible with the of concrete, but they are likely to be more expensive.
standard 200 x 100 x 65mm rectangular concrete blocks
4.14 Difficulties may be caused if advantage is taken more difficult to compact it is recommended that they
of the larger variety of shapes, sizes and colours of are compacted to satisfy an end-product specification,
concrete blocks available. Stocks of each type and in terms of air voids (refer to Annex C of this Part).
colour would need to be kept for maintenance purposes.
It is therefore suggested that blocks are specified as 4.19 The durability of dense bituminous materials of
rectangular, with plan dimension 200 x 100mm. all types is heavily dependent on reducing the
Installation should follow the current British Standard permeability of the material to a level which will
and further guidance is available from the appropriate restrict weather and oxygen attack to the top surface.
trade association (Interpave for concrete blocks and The level of compaction is best characterised by air
Brick Development Association for clay pavers). void content which is generally recommended to be in
the region of 2-8%. Void contents less than 2% are not
Bedding Sand recommended for heavy-vehicle footways (Table 3.4),
else deformation may occur under trafficking.
4.15 The bedding sand and jointing material should
be in accordance with Annex B of this Part; Class II Skidding Resistance
bedding sand being used for footways designed to
support heavy-vehicle overrun, and Class III elsewhere. 4.20 The footway wearing course must not become
The moisture content of the bedding sand should be slippery and difficult for pedestrians to walk on when
within +/-1% of optimum determined in accordance wet. It is unlikely that this will be a problem with
with BS 1377: Part 4: 1990, Method 3.3. The quality of bituminous or concrete materials, but care should be
the bedding sand is critical to long life. The sand must taken when specifying clay pavers or natural stone. The
be free of deleterious salts or contaminants. Sand from skidding resistance of concrete products is always
quaternary geological series and sea dredged sands are adequate for use in footways, as the BS 6717
preferred. Sands from crushed rock sources and triassic requirement for acid soluble content precludes the use
geological series in the north-west are not advised of limestone for both coarse and fine aggregates. Some
particularly for Heavy-vehicle Footways. Gradings clay pavers in areas of heavy pedestrian use can become
should be checked by wet sieving. slippery when wet. The resistance to polishing of clay
pavers is expressed as a polished paver value (PPV). As
4.16 Jointing material should not be of a type which a first approximation PPV is equivalent to polished
could stain the surface, and should be supplied and stone value (PSV) for aggregates. A minimum polished
installed kiln dry and free flowing. The need to guard paver value (PPV) of 45 should be specified for general
against risk of failure due to removal of sand by suction use. Further guidance on skid resistance is available in
sweepers during early life should be recognised. There CSS publication ENG1-96. “The assessment of slip
are various proprietary sealing products available to resistance in paved areas for use by pedestrians and
prevent the loss of jointing sand, but they have yet to be horse riders”.
proven satisfactory in the long term.
Tolerances
Compaction
4.21 The tolerances given in Table 4.3 are intended to
4.17 The choice of compaction plant is limited by the apply generally and also take into account that a
small scale of the works, and obstructions such as street footway is usually hand laid. They are more stringent
furniture, but the use of appropriate plant is essential, than those in Table 7/1, Clause 702, of the Specification
together with an established testing scheme when (MCHW1). This is because the tolerances for road
required. The subgrade must be levelled and compacted pavements would allow too great a reduction in layer
adequately if the sub-base, when placed and compacted, thicknesses for thin footway construction layers. If
is to achieve the required density. The performance of kerbs and edging strips are properly laid it should be
both unbound and bound materials depends possible to achieve a high degree of compliance with
substantially on the degree of compaction achieved. design levels. Surface regularity is given in terms of
maximum deviation under a 1m straightedge, as the 3m
4.18 Compaction of asphalt materials can be carried straightedge used in road pavement measurement is too
out by a method specification (refer to Annex D of this large for footway use.
Part), but it is important that the work is adequately
supervised to ensure that the requirements are being
achieved. However, as dense bitumen macadams are
4.23 Testing should be carried out in accordance with 4.25 As the quality of workmanship will depend on
Table NG 1/1, Notes for Guidance (MCHW2). Where the operatives and their supervisor it is advisable that
possible the testing should be carried out by a the chosen contractor has a QA scheme which spells
laboratory which is NAMAS accredited for the out training for operatives. Each job should have a
particular test. Sampling is a very important part of any qualified supervisor and the checks that he will make
should be listed.
Parameter Tolerances
Horizontal alignment Horizontal alignments shall be correct to within 25mm, except for kerbs, channels and
accuracy edge strips which shall be correct to within ±13mm.
Formation level After completion of any drainage and immediately before laying sub-base the
subgrade surface shall be within + 10mm and –30mm of its design level.
Sub-base level If the footway is surfaced in bituminous material the compacted sub-base surface shall
be within +10mm and –20mm of its design level. If segmental surfacing is used the
sub-base must be within ± 10mm of its design level.
Sub-base thickness The thickness shall not be more than 10mm less than specified.
Bituminous basecourse The compacted basecourse level shall be within ± 10mm of the design level.
Wearing course The wearing course level shall be within + 5mm and –0mm of the adjacent kerb,
edging strip or any ironwork.
Bituminous thickness The total thickness of bituminous material shall not be more than 5mm less than
specified.
Bedding sand The compacted bedding sand level shall be within ± 5mm of the design level and not
less than 25mm thick.
Kerbs and edging strips The surface level shall be within ±6mm of the design level.
Joints between flags Joints should be not less than 2mm and not more than 5mm wide. For pedestrian-only
and pavers footways flags can be laid with wide (6-10mm) joints filled with compacted mortar.
Surface regularity The maximum deviation of the footway surface under a 1m straightedge shall not
exceed 3mm.
Precast concrete Transverse strength Minimum of 3 per 1000 units of each product (BS 7263: Part 1)
flags
Water absorption No frequency recommended
Concrete block Compressive strength 16 per 5000 blocks (BS 6717: Part 1)
paving
Clay pavers Transverse breaking Minimum of 10 per 10000 pavers (BS 6677: Part 3)
load
Skid resistance Minimum of 5 per 10000 pavers (BS 6677: Part 3)
Foundation CBR Visual, Mexe penetrometer for Visual over whole site, Mexe
vehicle overrun penetrometer on soft spots or every
50m.
Sub-base compaction Density. Compare with trial area Average of 3 per 500 linear m or part
thereof
All compacted bituminous Air voids or layer thickness Average of 3 per 500 linear m or
materials except medium (from cores or dips) part thereof
graded macadam
Medium graded macadam Layer thickness (from cores or Average of 3 per 500 linear m or part
dips) thereof
Surface regularity 1m straightedge and wedge Every 25 linear m and where doubt
exists
References 1995
1. Design Manual for Roads and Bridges Burtwell, M(Ed), “A Study of Footway Maintenance”.
Report 134. (Research Project Funded by TRL/CSS/
1994 HA).
1979 1993
Black, W.P.M. and Lister, N.W. “The Strength of Clay BS 6717: Part 1: Precast concrete paving blocks: Part 1:
Fill Subgrades: its Prediction in Relation to Road Specification for paving blocks.
Performance”, LR889.
BS 4987: Coated macadams for roads and other paved
1984 areas: Part 1: Specification for constituent materials and
for mixtures. Part 2: Specification for transport, laying
Powell, W.D., Potter, J.F., Mayhew, H.C., and Nunn, and compaction.
M.E., “The Structural Design of Bituminous Roads”,
LR1132. 1994
Bibliography
6. ENQUIRIES
All technical enquiries or comments on this Standard should be sent in writing as appropriate to:
Director of Engineering
Department for Regional Development
Roads Service
Clarence Court
10-18 Adelaide Street G W ALLISTER
Belfast BT2 8GB Director of Engineering
45/6F 45/10F
14mm 100
Notes:
Maximum % of aggregate passing 2.36mm sieve and retained on 600µm sieve is 11.0%.
The coarse aggregate shall be crushed rock with a polished stone value as described in the contract. For 45/6,
which is for footway use only, the aggregate shall be limestone.
The binder shall be 200 pen bitumen and the maximum temperature at any time for this binder shall be 160°C.
2.36mm 100
1.18mm 95-100
600µm 55-100
300µm 15-50
150µm 0-15
75µm 0-3
C.1 The adequacy of compaction of bituminous materials will be judged against the air void levels given in Table
C.1. The following procedure should be used.
C.2 Compliance should be judged from the determination of air voids for areas of 1000m² or from the area laid
in one day where the area is less than this. Where a number of small areas are laid in a day the client should
determine whether these are to be grouped into one site for testing purposes. Three 100mm nominal diameter
core pairs should be taken from each area in a random manner.
C.3 The density corresponding to zero air voids should be determined using ASTM method D2041-91. One core
from each set of six should be taken for the determination of the maximum density; where only one set is
taken then the determination should be carried on 2 cores from the set.
C.4 When the material contains applied chippings the void content should be calculated from the whole layer
including chippings.
C.5 The air void content should be calculated as 100(1-Dm/Do) per cent, where Dm is the measured density and Do
is the ASTM D2041-91 density, and should be calculated for the whole layer including chippings.
C.6 The Contractor should inform the Engineer of the sources of the constituents of the mixes at the start of the
contract and of any changes during the contract.
C.7 Where these requirements for the air voids are not met the Contractor should determine the full extent of the
area of the defective material to the satisfaction of the Engineer. The full depth and width, minimum 15m
long and the full width of the footway, of the defective material should be removed and replaced with fresh
material laid and compacted to this Specification.
C.8 The nuclear density gauge (NDG) may be used to reduce the amount of coring required but in case of dispute
the core density method should be used.
Over 1800Kg/m² 3 5 7 4 6 8
Vibrotampers are not the recommended plant for bituminous wearing courses.
EXAMPLE 1
A footway is to serve terraced dwellings on a new estate, linking them to a small garage court. Barriers prevent
children running straight out into the garage court, which is surfaced in concrete pavers. From the ground
investigation, prior to building the estate, the CBR is 2%. There are no services under the footway.
Footway is physically separated from the carriageway. Footway is not a cycleway, therefore category
is pedestrian-only.
Width and gradients should be within the limits of Table 2.3. Crossfall should run away from houses.
Adequate drainage should be provided. The plan shows that there are no services under the footway.
The footway surfacing should enhance the environment; concrete pavers would be chosen to match
the garage court.
There are no services in the footway so a geosynthetic can be used to separate the subgrade from the
granular sub-base. Design CBR is 2 per cent.
Pavers ≥ 50mm
100mm sub-base
Geosynthetic
Note: Pavers can be chosen to contrast with the paved parking area to signify a change of use.
As the footway is not adjacent to a road or wall, edge restraint should be provided on both sides of the
footway. The cross section of the footway is as follows:
EXAMPLE 2
A new school has been built on the outskirts of a rural village. A footway is required to connect the school to the
neighbouring village so that pupils can cycle or walk to school safely. The road running past the school is a rural
lane, but there is ample parking and delivery space in the school grounds. At present the lane has a 3m wide grass
verge bounded by a hedge. The soil along the verge is a soft clay. The length for which a footway is required is
approximately 1 km.
Footway is not physically separated from the carriageway and may be considered to be lightly used.
However, footway is also to be used as a cycleway, which may require the use of clearing and
maintenance vehicles, so it would be wise to design for light-vehicle category.
Soil is very soft clay. A quick test shows that it “exudes from the fingers when squeezed”. According
to Table 2.2, this indicates a CBR of less than 1%.
Width and gradients should be within the limits of Table 2.3. A minimum of 2m width is required
which could usefully be increased to 2.5m to provide space for cyclists to overtake pedestrians. The
gradient will be as for the road. The crossfall will be towards the road utilising existing drainage. The
length and situation of the footway make a bituminous construction the best option. If there are
services in the verge they may need to be moved or made deeper.
CBR < 1%. Assume lime stabilisation is used to raise the design subgrade CBR to over 5 per cent.
Very occasional heavy vehicle overrun may occur, but the treated subgrade now has a CBR > 5% so
the designs in Table 3.3 can be used. The structural design is 70mm of bituminous material on 150mm
of sub-base.
The kerb provides the lateral restraint on one side of the footway, edging is required on the other side.
The cross section of the footway is as follows:
EXAMPLE 3
A footway is to be built alongside an existing road, which now receives some pedestrian traffic due to construction
of an out-of-town shopping area. There will be no verge between the footway and the carriageway, as the existing
verge, on which the footway is to be constructed, is only 1.8m wide. There is a brick wall along the whole length of
verge. It has been decided that concrete blocks will be used as the footway surfacing. The soil is sandy clay.
Delivery vehicles may overrun the footway occasionally if, for example, the road is partly blocked by a broken
down vehicle.
Footway is not physically separated from the carriageway, and is not very lightly used. Heavy vehicle
overrun is likely to occur. Therefore the footway category is heavy-vehicle.
Soil is a sandy clay. From Table 2.1 the subgrade CBR is likely to be approximately 3 per cent. Testing
is required to confirm this.
Width and gradients should be within the limits of Table 2.3. The gradient will be as for the road. The
crossfall will run towards the road utilising existing drainage.
The required sub-base thickness for heavy-vehicle design is 270mm. Concrete blocks should be at
least 60mm thick and should be placed on 30mm compacted thickness of bedding sand. A roadbase of
90mm DBM or 100mm CBM1 or stronger, is required between the sub-base and the bedding sand.
The brick wall provides lateral restraint on one side of the footway and the kerb provides lateral
restraint.