DS.601 Structural design of pavement upper layers

Rev. Status Created by Date Approved by Date A Final D.Farnham/J.Howe 23.03.12 D.Waters 27.03.12 B Final D.Farnham 04.04.12 D.Waters 10.04.12 C Final D.Farnham 01.11.12 M.Hill 07.11.12 D Final D.Farnham 07.02.13 D.Waters 08.02.13 E Final D.Farnham 03.05.13 D.Waters 08.05.13 F Final D.Farnham 06.11.13 D.Waters 14.11.13 G Final D.Farnham 08.01.14 M.Hill 31.01.14 H Final G Lake 11.02.21 D Foden 01.07.19

Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 1

Table of Contents 5.1.1 Conventional pavements...... 17 5.1.2 Pervious pavements...... 18 1 Introduction...... 3 5.2 Design requirements...... 19 1.1 Notes...... 3 5.2.1 Conventional pavements...... 19 5.2.2 Pervious pavements...... 21 2 General requirements for pavements of all types...... 3 6 Precast concrete block, clay paver 2.1 Pavement Design Statements...... 3 or natural stone sett surfaced 2.2 Surface landscaping of modular unit pavements (bound surface)...... 23 pavements...... 3 6.1 Use requirements...... 22 2.3 Commuted sums...... 4 6.2 Design requirements ...... 24 2.3.1 Method of design ……...... 4 2.3.2 Responsibility for maintaining pavements 7 Natural stone sett surfaced within serviceability limits………………… 4 pavements (unbound surface)...... 26 2.3.3 Increased maintenance liabilities………..... 4 7.1 Use requirements...... 26 2.3.4 Sustainable urban drainage …………………. 4 7.2 Design requirements ...... 26 2.4 Assumed level of trafficking…...... 4 2.4.1 Footway pavements...... 4 8 Bituminous mixture surfaced 2.4.2 Carriageway pavements...... 5 carriageway pavements...... 26 2.5 Evaluating predicted motor vehicle 8.1 Use requirements...... 26 trafficking…...... 5 8.1.1 Flexible pavements (e.g. with bituminous 2.6 Site investigation reports...... 6 mixture base course)...... 26 2.7 Substituting materials and component 8.1.2 Flexible-Composite pavements (e.g. with HBM base course)...... 26 overlay/inlay design methods...... 6 8.1.3 Rigid-Composite design (e.g. pavement 2.7.1 Substituting materials……...... 6 quality concrete CRCB base course with 2.7.2 Overlay/Inlay design methods...... 6 min 100mm bituminous mixture overlay)… 27 2.8 Trafficking of pavements courses 8.1.4 Rigid design (e.g. pavement quality during construction works...... 7 concrete CRCP with or without 30mm 2.9 Movement joints and pre-cracking bituminous mixture overlay)...... 27 within concrete, CBGM & HBM slabs 8.2 Design requirements...... 27 to modular unit surfaced pavements... 8 8.2.1 Design methodology (including 2.9.1 Use requirements...... 8 determination of layer thicknesses)……….. 27 2.9.2 Design requirements...... 8 8.2.2 Milling, transportation, laying and 2.10 Laying courses and compacting surface compaction...... 28 course units to modular pavements..... 10 8.2.3 Joints and Transition details...... 28 2.10.1 Using laying courses for regulating 8.2.4 General requirements for base course...... 28 purposes...... …… 10 8.2.5 General requirements for binder course.... 29 2.10.2 Compacting the surface course and 8.2.6 General requirements for surface course...30 laying course...... 10 8.2.7 Selecting materials for different types of 2.11 Considering filter and separator pavement...... 32

criteria at material interfaces...... 10 9 Bituminous mixture surfaced footway 2.12 Level Surface and Shared Surface and cycleway pavements...... 32 Streets and spaces...... 10 9.1 Use requirements...... 32 2.13 Surface channels within pavements… 11 9.2 Design requirements...... 32

3 Precast concrete flag and natural 10 Self binding gravel surfacing to stone slab surfaced pavements existing pavements disturbed by (unbound surface)……...... 11 tree roots...... 33 3.1 Use requirements...... 11 10.1 Discussion...... 33 3.2 Design requirements...... 11 10.2 Use requirements...... 33

4 Precast concrete flag and natural 10.3 Design requirements...... 33

stone slab surfaced pavements Appendix A - Background discussion...... 34 (bound surface) ……………..……… 13 4.1 Use requirements...... 13 Appendix B - Bituminous pavement upper 4.2 Design requirements...... 15 layer design options for Flexible pavements...... 43 5 Precast concrete block & clay paver surfaced pavements (unbound)…... 17 5.1 Use requirements...... 17 2 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

1 Introduction bespoke ‘no-dig’ design solutions will be needed. See standard DS.501 for further 1.1 Notes related information. a. This standard explains design requirements 2 General requirements for for the upper layers of pavements. It is pavements of all types applicable to carriageway pavements, footway pavements and other non-carriageway 2.1 Pavement Design Statements (PDS) pavements. Pavement upper layers include the pavement surface course, laying course a. The purpose of a PDS is to explain and justify (or binder course), base course and the nature of proposed pavement associated inter-layers. constructions based on site investigation information, constraints and design b. This standard does not consider the visual aspirations. They need not be lengthy design of pavement surfaces. See documents but must be sufficiently detailed to SSDM/SER/Surfacing Material palettes for allow approving officers to understand the details of acceptable materials and standard logic behind design proposals and reasons for DS.130 for broader surface landscaping design choices. Broadly the information requirements. It does not consider the design required includes: of subbases and capping layers (and • Structural statement: Justification of the associated inter-layers) for which see instead proposed pavement construction and standard DS.602. maintenance implications with details of informing design values (e.g. CBR, traffic c. Designers must submit an accompanying evaluation, element stiffness or Pavement Design Statement, setting out compressive strength values for proposed workings, constraints and assumptions and materials etc.) and calculations (e.g. filter explain the logic behind proposed designs. criteria at layer interfaces, equivalence d. A 20 year serviceability design life should be calculations where material substitutions assumed for pavements. If all underground made). Where geo-cellular unit services can be located elsewhere then longer assemblies or other geo-technical serviceability design lives may be permitted. structures are involved (including Where the standard 20 year serviceability basements) then this must be cross design life value cannot be achieved, referenced to information from geo- developers will need to pay commuted sums technical design reports. for the cost of one full reconstruction of the • Pavement sub-drainage statement: upper pavement layers. Any materials from Justification of steps taken to prevent or the original construction that can be reused minimise surface water and ground water will be deducted from this. Commuted sums infiltration into pavements or to dispose of may also be required for other reasons, water should this be unavoidable else including the presence of sustainable urban deliberately intended. Maintenance drainage or other specialist drainage or implications must also be explained. engineering features within the pavement. All the above information relates specifically to Where existing pavements are being brought the construction of pavements. Separate more up to adoptable standards then commuted detailed Design Statements on surface water sums are not normally required providing the drainage and design for street trees must also materials and methods are as per normal be produced. These are discussed in standard requirements. DS.501.

e. Designers are required to carry out a full traffic 2.2 Surface landscaping of modular unit evaluation. pavements f. For modular unit surfaced pavements, a. See standard DS.130 for requirements about unbound surface construction is preferred. the visual design of pavement surfaces, including requirements for selecting g. If entirely new pavements must be surfacing products. constructed over the roots of existing trees b. For modular unit surfaced pavements, within previously soft landscaped areas then standard DS.130 also provides information Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 3

about introducing intermediary restraints, life values that should be assumed for and selecting laying (bond) patterns for surface courses for the purposes of surface courses. These are not only visual determining whether these can be reused concerns as both can play important in reconstruction. However, crack and seat structural roles. techniques may not be assumed. iv. Works should be costed using the Highway 2.3 Commuted sums Authority’s current term contractor rates.

Surface course Assumed durability before 2.3.1 Method of design material serviceability expiry (years) – though see note Only designs that are likely to allow surface course units to be reused by the Highway Footway Carriageway Authority or Statutory Undertakers to carry out Bituminous mixture 25 20 maintenance or reinstatement works to Hydraulically 25 20 pavements are within the Highway Authority’s pressed concrete adoptable standards. blocks Clay pavers 70 60 2.3.2 Responsibility for maintaining Natural stone setts 70 60 pavements within serviceability limits Hydraulically 20 N/A pressed concrete a. If publicly adopting a new or existing flag Highway is proposed then the proponent Natural stone slab 70 N/A must cover the costs of maintaining NOTES associated pavements within serviceability If it is permitted to lay modular units as part of a limit states for a period of 20 years. If the bound surface (as sections 4 or 6) then, unless serviceability design life of a pavement is agreed otherwise, it should assumed that these will be less than this then this will mean providing damaged beyond reuse as part of any reconstruction works and therefore require replacement. commuted sums to cover the cost of pavement reconstruction/rehabilitation works Table 1. Assumed maximum durability before serviceability to maintain the pavement for the residual expiry for surface course materials period. Such sums should cover both the works and the materials. Precise commuted 2.3.3 Sustainable urban drainage features sums will be advised by approving officers on a case specific basis with reference to the Commuted sums may be required if pavements submitted design proposals for the initial incorporate surface water infiltration or attenuation design life and the following principles: features. This is owing to the likely need to i. It should be assumed that all pavement periodically cleanse related geotextiles, upper layers will require removal and aggregates and other filtration or drainage replacement (rather than overlaying or infrastructure. In some instances this may mean inlaying). excavating these from the pavement, replacing ii. Only minimal re-profiling works to them, and reinstating the pavement. subbase layers should normally be assumed as a result of ‘i’. However, if 2.4 Assumed level of trafficking the subbase materials are known to have a serviceability design life that is 2.4.1 Footway pavements less than that of the pavement as a whole (as may be the case for some Table 2 below states minimum daily levels of geo-cellular unit systems) then replacing commercial vehicle overrun that may be these should also be included. assumed to different parts of footway pavements iii. If existing surface course and other (and other non-carriageway pavements). pavement materials from the expired Pavement designs for different areas should be pavement are capable of being based upon the cumulative trafficking across the incorporated back into the works, then the required serviceability design life that follows value of these should be deducted from the from projecting these daily values (see sections cost. Table 1 states serviceability design 2.5 and 2.6). Using lower values requires level 1

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departure. This is only likely to be considered if 2.4.2 Carriageway pavements physical measures are put in place to prevent commercial vehicles from gaining access to a. The road should be assigned to one of the pavements (for example, bollards). Road Categories given in Table 3 based upon

Service- Pave- SSDM/RP/Specification the findings of this evaluation. The upper limit ability design ment Area value for that Road Category should be life (years) area World assumed for design purposes. as section Centre/Town All others b. If modular unit surfacing is proposed to 2.6 Centre carriageway pavements then the Highway Assumed minimum number Authority reserves the right to either refuse of daily commercial vehicle this or to permit it subject to commuted sums standard axles over being provided for particular agreed types of running pavement( see modular unit being used. note 3) Road Design life trafficking thresholds Heavy Category (see (million standard axles) (see note 2) Overrun note 1) Area (see 2.25 1.5 Lower Upper (maximum value to be Typically 20 note 1) assumed for Light design purposes) Overrun Area (see 1.25 0.5 0 30 N/A (value to be note 2) determined on case specific NOTES basis) 1) Heavy Overrun Areas are the front 1.5m of the 1A > 20 ≤ 30.0 pavement width at the carriageway edge, unless 1B > 10 ≤ 20.0 the pavement is ≤ 2.75m in width in which case it 2A > 5.0 ≤ 10.0 applies to the entire width. This distance includes any kerb or other edge restraint at the carriageway 2B > 2.5 ≤ 5.0 edge. Inset Parking Bays should be treated as part 3A > 1.0 ≤ 2.5 of the carriageway and this specification must 3B > 0.5 ≤ 1.0 therefore continue around the kerb inset they 4 0 ≤ 0.5 create. 2) Light Overrun Areas are the residual width of the pavement after Heavy Overrun Areas. NOTES 3) The stated values in this Table are before 1) The Road Categories in this Table are based on applying multipliers on account of channelised those given in ‘New Roads and Streetworks Act: trafficking, slow moving traffic, dynamic Specification for Reinstatements of Openings in the loading/impact or traffic growth factors. As per Highway, Third Edition’ (DfT, HAUC, 2010) (SROH). section 2.5 these should always be applied. All Road Categories assume a 20 year serviceability 4) The only instances when minimum assumed design life. trafficking levels do not form the basis of pavement 2) Values are inclusive of multipliers for channelised design are for bituminous mixture and self-binding trafficking, slow moving traffic, dynamic loading and gravel surfaced footway and cycleway pavements impact (or other stresses) and traffic growth factors. (other than at commercial Vehicle Crossings). See Table 3. Road Category classifications and associated sections 9 and 10 for further information. design life commercial vehicle overrun assumptions for 5) Notwithstanding these assumed minimums, a full carriageway pavements evaluation of predicted cumulative trafficking as section 2.5 is still required for all pavements. If these minimum values are exceeded by 2.5 Evaluating predicted motor vehicle assessments then the greater alternative values trafficking should be used instead. 6) See section 2.13 about trafficking assumptions Notwithstanding the minimum daily standard axle for Level Surface streets and spaces. trafficking values stated for different parts of Table 2. Minimum design life and assumed daily levels of commercial vehicle over run for footway pavements (and pavements in section 2.4, all design submissions other non-carriageway pavements). for Highway pavements should include an evaluation of the predicted level of cumulative trafficking across the pavement serviceability design life. This should be based on the process

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described in the informing pavement design per standard DS.602 (though see also standard that is prescribed in sections 3-8 for the ‘b’). type of pavement in question (e.g. DMRB HD 26 or relevant parts of BS 7533). In addition: NOTE: Equivalence factors used for substituting i. Any amendments to that process or pavement course materials should be based on particular assumptions that are specified in published sources reporting the results of sections 3-9 should be followed. empirical analysis or laboratory testing results. ii. For carriageway pavements: Some known sources of equivalence factors • The measured or estimated level of include BS 7533-1:2001, ‘Londonwide Asphalt traffic in the busiest running lane Specification, 3rd edition (Road Consultants, should be adopted for all other lanes to 2013)’ and ‘Interpave L534 Heavy Duty that section of carriageway. Pavements’. See also‘8.2.1a’ for substitute • Growth factors should be assumed. minimum stiffness modulus values to be used in • If an individual lane width is < 3.5m, or place of named bituminous mixtures within if the width of the carriageway as a DMRB HD26/01 design graphs. whole is ≤7.3m then channelised trafficking should be assumed. b. For foundation layers to main carriageway iii. For modular unit surfaced footway and running lane pavements that have other non-carriageway pavements as bituminous mixture surfaces, if alternative sections 3-7: materials are permitted or required (see note • Worst case factors for dynamic 1) to be substituted for those recommended loading/impact, channelised trafficking for Standard Designs/Restricted Designs as etc. (as specified in the relevant traffic Highways Agency ‘Design Manual for Roads prediction methodology or elsewhere and Bridges’ HD 25, then Performance in this standard) should be assumed to Design as HD 25/06 and Southwark Heavy Overrun Areas (see Table 2). Highway Specification Clauses 890-896 is required. This will entail both laboratory 2.6 Site investigation reports characterisation of materials and the construction and assessment of See standard DS.602 about undertaking various demonstration areas (see note 2). site investigation reports as the basis for design Application of equivalence factors as ‘a’ is proposals. not permitted and requires level 1 departure (see note 3). 2.7 Substituting materials and component overlay/inlay design NOTE 1: See standard DS.602 for details of methods permitted materials to pavement foundation layers.

2.7.1 Substituting materials 2.7.2 Overlay/Inlay design methods a. If alternative pavement course materials to Existing pavements may be overlaid or inlaid those recommended in the required using the component method described in BS informing design standard document (e.g. 7533-1:2001, section 7.3. Retained parts of the BS 7533 or HD 26) are required or permitted existing pavement must provide an equivalent by this standard or DS.602 then, unless structural capacity to omitted layers that would exact thicknesses for those alternatives are otherwise be required if the pavement was being specified at the same time, designers should reconstructed from the subgrade up (see note to apply equivalence factors (sometimes ‘2.7.1a’). Condition factors should also be applied referred to as material conversion factors, to any retained existing courses as BS 7533- see note) to determine the installed 1:2001, clause 7.3.1.4. thicknesses that will provide equivalent

structural capacity to the omitted material. NOTE: Older parts of BS 7533, as used for the This applies both to: design of modular pavements, are based on the i. Pavement upper layer designs as per use of CBMs where semi-rigid base courses are this standard. required. So too is DMRB HD 26/01 (which may ii. Pavement foundation layer designs as

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be used for the design of bituminous mixture graded or pervious materials, this is subject to surfaced pavements in preference to the newer agreeing appropriate measures to allow for the HD 26/06 where wished - see section 8). CBMs through-drainage and dispersal of any surface are no longer included in current SHW clauses water that may succeed in penetrating the which have been updated to newer CBGM surface course (see note). In the case of mixtures. These have a lower 28 day strength bituminous mixture courses, coring 75mm compared with the old CBM specifications. diameter holes on a 750mm x 750mm grid will Where use of CBMs is prescribed in the generally be acceptable. In the case of CBGM, pavement design standards called up in the this HBM, or concrete courses, appropriate measures design standard then any of the modern HBMs or are less easy to define and will likely require wet lean concretes as Table 4 should be used in innovation by the designer and contractor. their place. Note that the compressive strength Gradual cracking of such materials should not be class of each has been promoted one class to relied upon. correct for the lower 28 day strength (and other issues). NOTE: If any surface water that penetrates the pavement surface is allowed to stand in the Historic Equivalent Equivalen Equivalen Equivalen laying course then it is likely to contribute to early CBM CBGM t SBM t FABM t wet lean failure. grade (see notes (see (see concrete 1-3) notes 1- notes 1- (see note 3) 3) 1 and 4) Cold mix in situ recycling of bituminous mixture surfaced pavements CBM3R [CBGM- [SBM- [FABM1- [C-WL3] B/R-C10] B1/R- R-C12] If using cold mix bituminous mixtures is permitted C12] as an option for an upper layer course to a CBM4R [CBGM- [SBM- [FABM1- [C-WL4] carriageway pavement (see section 8.3.1 and B/R-C15] B1/R- R-C16] Appendix B), full or partial in-situ cold mix C16] recycling of that layer and all those beneath must be considered. If cover is limited and this CBM5R [CBGM- [SBM- [FABM1- [C-WL5] prevents overlaying, then planing the upper B/R-C20] B1/R- R-C20] C20] layers and in-situ recycling should be considered.

Slurry surfacing. micro-surfacing and micro- NOTES asphalt surface treatments 1) See section 2.10 about pre-cracking requirements. 2) All base course CBGMs, SBMs and FABMs Slurry surfacing, micro-surfacing and micro- should use crushed rock aggregate with a asphalt surfacing may be used to existing coefficient of thermal expansion <10x10-6 per °C. bituminous mixture surfaces. Products will be Use of materials with gravel aggregate is not acceptable. agreed on a case specific basis. However, this 3) See also standard DS.602 about strength may be for cosmetic or retexturing purposes requirements for concrete and HBM courses prior only. It may not be for structural purposes and no to trafficking/overlay. extension in pavement life may be assumed as a 4) Wet lean concrete is generally only appropriate for result. pavement foundation layers (e.g. subbase) as standard DS.602. It should not be used to upper NOTE 1: Applying slurry surfacing, micro- layer base courses. surfacing and micro-asphalt surface treatments Table 4. Equivalent modern HBMs and wet lean concretes to pavements with existing structural defects will that may be directly substituted for CBMs for use to pavement courses. only serve to mask them. Information about specifying slurry surfacing, micro-asphalt surfacing and micro-asphalt surface treatments Overlaying modular unit surfaces onto existing can be found in the following documents: bound courses - PD 6689:2009 Surface treatments, Guidance on the use of BS EN 12271 and Where it is permitted to overlay existing BS EN 12273 impervious bituminous mixture, CBGM, HBM or - TRL Road NOTE 39. concrete courses with unbound modular unit - SHW clauses 918 and 922 and NG 922 surfaces then, unless these are already open and NG918.

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- Road Surface Treatment Association sensitively designed and spaced. In addition, Codes of Practice units located close to joints carry an increased - DMRB HD 37/99 risk of failure. Consequently, if introducing movement joints cannot be avoided, they must 2.8 Trafficking of pavements courses be carefully designed and detailed. This during construction works requires close liaison between engineers and those responsible for surface landscaping of the The base course thicknesses and materials pavement. prescribed in this design standard assume that heavy vehicles will not traffic the base course 2.9.1 Use requirements during construction of the pavement. Designers must explicitly confirm within traffic evaluations Movement joints should be provided in semi- as section 2.5 whether or not such trafficking rigid and rigid concrete, CBGM and HBM will occur and (if so) the extent of it. If site courses beneath modular unit surfaced trafficking will take place then they must set out pavements as directed in each of the following in Pavement Design Statements as section 2.1: circumstances. i. How proposed pavement course i. [C-NF-C20] or [C-NF-C15] no-fines thicknesses have been adjusted to concretes: N/A owing to low elastic accommodate the additional standard modulus. axles and loading. ii. [C-PQC-C40] pavement quality concrete ii. Any other steps that are proposed to surface and base slabs: Slabs should be prevent damage to the pavement (see laid with expansion, contraction, warping note 1). and isolation joints as ‘2.9.2’ All proposed measures and adjustments are iii. All other HBMs and wet lean concretes subject to agreement by approving officers. The (including CBGMs). same also applies if trafficking foundation layers Where used to base courses is proposed (see note 2). Slabs should be laid and transverse pre-cracked and sealed in accordance with ‘2.9.2’ NOTE 1: For modular unit surfaced pavements, Where used to the upper subbase (or entire relevant parts of BS 7533 typically provide subbase) of modular unit surfaced pavements alternative adjusted thickness values that that do have a separate base course should be assumed where base courses will be Slabs should be transverse pre-cracked and used by construction traffic. sealed in accordance with ‘2.9.2’ Where used to subbases of modular unit NOTE 2: For adjustment of subbase layers to surfaced pavements that include a separate accommodate construction traffic, reference base course should be made to TRL Report LR1132. See in N/A. particular figure C.3. See also standard DS.602 about the potential use of geo-grids to protect 2.9.2 Design requirements foundations subject to trafficking by construction vehicles. Pavement quality concrete (PQC) base slabs

a. Requirements for reinforcing PQC base 2.9 Movement joints and pre-cracking slabs will be agreed on a case specific basis within concrete, CBGM and HBM with approving officers. This includes slabs to modular unit surfaced whether pavements. i. They are to be URC, JRC or CRCB/CRCR (see notes). Denser cement concretes, CBGMs and other ii. Additional micro or macro fibre HBMs with low void contents are typically reinforcement is needed. subject to significant thermal expansion and b. If slabs are used to carriageway pavements, contraction. Movement joints often need to be their thickness will typically need to be locally extended all the way up through to the surface increased along the footway edge as per HD 26 of the pavement. This can have a considerable requirements. This is owing to the near certain negative visual impact if joints are not absence of tied-shoulder details. 8 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

any surface units over the joint is still c. Transition details and movement, warping and likely to be necessary to retain isolation joints should be designed in required joint widths. accordance with the following drawings: LBS/1100/01 to LBS/1100/48 v. For carriageway pavements: • Longitudinal joints must be kept out of i. for movement, warping and isolation joints. wheel paths. This may be an issue in ii. for transition details other than at ramps. narrower carriageways if a iii. for transition details at ramps. conventional crowned profile is iii. Joint spacing should generally be in adopted (bearing in mind that a accordance with DMRB HD 26/06. longitudinal warping joint will normally be required to the crown line, though Typically: see next bullet). • Expansion joints should be provided every • Adopting a side-hung profile may third contraction joint. provide a solution, though this is likely • Isolation and warping joints should be to create other surface drainage issues provided: due to the need to locate all gullies - At significant horizontal or vertical down a single side of the carriageway changes in direction of the pavement at a closer spacing. (including to ramps and at crowns or • On Road Category 4 and 3B streets troughs). (Table 3) it may be acceptable to omit - Around vulnerable structures (including longitudinal warping joints if the manhole and access chambers). relative switch in grade can be kept to • UJC and JRC slabs should use limestone 1.7° or less (equivalent to a joint aggregate as this permits some increase in between two pavements each with joint spacing due to its lower coefficient of opposing ~1:70 falls). However, this linear thermal expansion. See HD 26/06 for may not always provide adequate further details. drainage. • As per HD 26/06, increasing the thickness • At road junctions between multiple of the base slab will often permit an carriageway pavements that each have increase in joint spacing. Subject to expert a PQC base slab, great care must be advice, modest additional increases in joint taken when determining overall joint spacing above the values permitted in HD arrangements and slab/surface 26/06 may be permitted on the basis of gradients in order to address the either: various concerns of: - Depth of cover (e.g. if very deep setts - Keeping the design (and later are used over the slab). construction works) simple. - Using steel or plastic fibre - Minimising the negative visual reinforcement. impact of the joints on surface landscaping. iv. For footway and other non-carriageway - Ensuring effective surface drainage pavements, given the lesser degree of by providing adequate surface falls overrun, it may not always be necessary to: to achieve positive drainage to • Dowel movement joints. collector inlets. • Tie slabs to carriageway edge kerbs. - Minimising in-service maintenance • Provide other transition kerbs/details by keeping lateral joints clear of when transitioning into other types of wheel paths and ensuring correct pavement (e.g. when transitioning from detailing of restraints for surface a bound flag surfaced pavement with a units. PQC base slab into an unbound flag or block surfaced pavement). iv. Avoiding disrupting the visual • Provide warping joints if the relative appearance of surface courses should switch in grades in the slab can be be an important concern in all instance kept shallower than 4° (equivalent to since similarly aligned joints must also a switch from flat to a slope of ~1:15 be provided within the surface course or shallower). However, taper cutting and laying course. This is likely to

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require adjustments to laying patterns. See standard DS.130 for further a. Laying courses to modular unit information. The colour of all joint surfaced pavements should be strictly sealants used within the surface to the specified installed thickness. course should match that of the finish They should not be used as a of adjoining paving units. Products regulating course (e.g. varied in depth must be confirmed with approving in order to achieve certain gradients). officers in advance of use. Instead, the pavement construction should respond to falls by varying the NOTE 1: For carriageway pavements, using gradient of the underlying base course JRC slabs is likely to be the most or subbase (whilst staying within the appropriate option in the majority of minimum thickness requirement for instances since this strikes a reasonable these layers) whilst retaining the balance between maximising joint spacing consistent thickness of the laying (which will typically be in the order of 20-30m course and surface course above. as per HD 26/06) and ease of construction. Whilst CRCB/CRCR slabs can all but b. The depth of a laying course may be eliminate transverse joints (other than varied by up to 10mm in order to construction joints) they are substantially accommodate differences in the more complicated and costly to construct thickness of modular units when since they require ground beam anchors and different types of paver directly lengthy transition bays. They are therefore interface without any intermediary highly unlikely to be practical in most restraint (see note). However, an edge applications. restraint must always be used between the two constructions if: NOTE 2: For footway and other non- i. The difference in unit thickness carriageway pavements, UJC slabs are likely exceeds this maximum value; or to be most appropriate the majority of the ii. There is a material difference in time, since the steel mesh reinforcement the form of construction used to used to JRC slabs introduces practical each interfacing area. difficulties with locating cables and NOTE: For instance, if a 72mm thick flag is laid underground services. Only where these can unbound to the Heavy Overrun Area at the front be located/relocated elsewhere is use of of the footway it would be acceptable to lay a JRC slabs likely to be permitted. 63mm thick flag unbound besides this to adjoining Light Overrun Areas away from the CBGMs, other HBMs and wet lean concretes footway edge.

Where this paragraph applies then wet lean 2.10.2 Compacting the surface course concrete, CBGM and other HBM base and laying course courses slabs should be transverse pre- cracked and sealed at 3-3.5m spacings in For modular pavements with unbound granular accordance with Southwark Highway mixture laying courses, notwithstanding any Specification Clause 818. The individual alternative apparatus and techniques for width of wet lean concrete or HBM base compacting of surface course units permitted in course should be ≤4.75m in order to reduce the relevant Code of Practice part of BS 7533 the risk of early longitudinal cracking if used (as specified for use elsewhere in this design to carriageway pavements. standard), in all instances: i. If more than one option exists for the 2.10 Laying courses and compacting compaction equipment and methods, only surface course units to modular that for a vibratory plate compactor with a pavements minimum mass of 200kg should be used. ii. Neoprene plate covers should be used to 2.10.1 Using laying courses for prevent damage to paving units. regulating purposes

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2.11 Considering filter and separator criteria at material interfaces

Particles from within layers of different unbound granular mixtures have the potential to migrate into one another if the grading of each mixture is not compatible. The same is true at interfaces between foundations and the subgrade (particular where the latter is cohesive). This can affect stability and permeability. Designers should include within Pavement Design Statements a filter and separator compatibility assessment of all unbound pavement layers. 3 Precast concrete flag and natural stone slab surfaced 2.12 Level Surface and Shared Surface pavements (unbound surface) streets and spaces 3.1 Use requirements If it is agreed to allow the creation of Level Surface or Shared Surface areas that will be a. This method of pavement design should trafficked by motor vehicles (see standard not be used to carriageway pavements. DS.224) then all pavements (including those to notional footways) should be constructed to b. This method of pavement design should carriageway trafficking standards unless level 1 not be used to footways (or other non- departure is agreed. This is because of the carriageway areas) in any of the heightened risk of vehicle overrun and related circumstances given in Table 6 (see damage to pavements. Commuted sums may section 4.1). If using flag or slab surfacing also be required for maintenance of these. is desired or required in these circumstances, then only bound surface design as section 4 is acceptable. 2.13 Surface channels within pavements 3.2 Design requirements If it is necessary to introduce surface channels within sections of pavements for drainage a. Pavements of this type should be: purposes then these features should be i. Designed in accordance with BS designed as per relevant details within 7533-8:2003. SSDM/TDR drawings LBS/1100/01-48. ii. Constructed in accordance with BS 7533-4:2003. NOTE: These details always require surface The remainder of this section states units to surface channels to be mortar bedded supplementary Southwark specific onto concrete or HBM footings, even if the requirements that may vary from the pavements they are laid within use an unbound recommendations of those documents. construction as per sections 3 or 5 of this standard. See standard DS.130 about the b. The assumed minimum levels of daily selection of surfacing materials for surface standard axle overrun for pavement design channels within footway pavements. purposes to different areas should be as section 2.4 and 2.5.

c. For Heavy Overrun Areas, the estimated level of daily standard axle overrun should always be multiplied by a factor of 2 to account for dynamic loading and impact.

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d. If some intentional commercial vehicle Use area (see section Required BS EN trafficking is permitted by design then it 2.4) 1339:2003 breaking load may be necessary to introduce concealed (min) transverse intermediary restraints into the Light Overrun Area Class 140 pavement to prevent lateral movement of Minimum value 15.0 kN units and loss of interlock between these. It Heavy Overrun Area Class 140 is the responsibility of designers to raise Minimum value 21.0 kN this prospect with approving officers when they foresee a risk, though approving NOTES officers have discretion to instruct 1) As general guidance, the closer to square the introduction if they consider it appropriate. upper face of a flag or slab is, then the greater If they are required then the restraints the breaking load will be. Units with aspect should be designed as per relevant details ratios (width: length or vice versa) exceeding from SSDM/TDR drawing LBS/1100/01-48. 2:3 for Light Overrun Areas or 3:4 for Heavy Spacings between intermediaries will Overrun Areas are unlikely to achieve the necessary minimums as per this Table. typically be in the order of 8-14m. 2) Part of the reason for these values is to correct

for the fact that the design method in BS 7533-8 Base course assumes that maximum 450x450mm flags are e. Pavements of this type do not require a used. These are smaller than the 600x600mm units that are typically used in Southwark (as base course and should be laid directly well as other central London Boroughs). Being onto subbase foundation layers. See also larger these units are likely to carry increased section 2.8.2 about overlaying units onto loads and so require a somewhat greater existing bound pavements minimum Breaking Load for the design method to remain valid.

Laying course Table 5. Strength requirements for precast concrete flags for unbound use to footways and other non-carriageway f. The laying course should be [L-SS1] sharp areas. sand. However: i. Alternative materials may be permitted i. Natural stone slab units should: by level 1 departure. Designers must i. Conform to BS EN 1341:2012. demonstrate an overriding need to ii. Have a minimum breaking load of vary. 21kN to BS EN 1341:2012 (see notes ii. Approving officers have discretion to 1 and 2). Approving officers have instruct that alternative materials are discretion to instruct that increased used based upon the advice of breaking loads of up to 25kN are met modular unit manufacturers. in areas where significant and regular vehicle overrun and parking is likely g. The compacted thickness of the laying (for instance, alleys in commercial course should be 25-30mm. areas that have narrow unprotected footways). Surface Course iii. Have an aspect ratio (length: width h. Precast concrete flags should: and vice versa) of ≤ 3:2. The length i. Conform to BS EN 1339:2003. should be ≤ 900mm. ii. Meet the breaking load requirements iv. Be ≥ 63mm but ≤ 90mm thick. The given in Table 5. difference in thickness of units used iii. Have an aspect ratio (length: width) of to neighbouring Heavy Overrun ≤ 3:2. The length should be ≤ 900mm. Areas and Light Overrun Areas (see iv. Be ≥ 63mm but ≤ 90mm thick. The section 2.4) within a given length of difference in thickness of units used to pavement should be ≤ 10mm. neighbouring Heavy Overrun Areas v. Be sawn (fine textured) to all sides and Light Overrun Areas (see section with square/sharp arris. In addition, if 2.4) within a given length of pavement slabs are composed of:

should be ≤ 10mm. iv. Have tolerances/deviations on work • Granite (or other igneous rock) dimensions as BS EN 1339:2003. then, further to sawing, their upper faces should be flamed to 12 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

achieve a coarse texture. Joints j. Precast concrete flag surfaces should be 2-5mm close jointed with [J-SS1] sharp sand. If there is concern that cleansing regimes may cause attrition of this material then [J-X1] stabilised jointing sand should be used instead (see note). Approving officers have discretion to instruct this.

• Yorkstone (or other k. Natural stone slab surfaces should be 5- sedimentary rock) then their 7mm jointed with [J-X1] stabilised jointing upper faces should not be sand. Subject to level 1 departure, using subject to any further treatment [J-X2] stabilised gravel may be permitted to after sawing. allow even wider joints for aesthetic purposes.

NOTE: If natural stone slab surfacing is retrofitted to existing pavements as an inlay or overlay then special attention must be paid to draining the laying course during service. This is to account for the likelihood of greater penetration of surface water (owing to the wider joints than used for precast concrete flags) and vi. Have tolerances as BS EN 1341:2012 the possibility that the existing subbase may not of: include adequate drainage measures to • Class 2 (P2) for plan dimensions. disperse it. This may require additional sub • Class 2 (D2) for diagonals. drainage measures to be included in lower • Class 2 (T2) for thickness. pavement courses. Appropriate measures will be agreed with approving officers on a case specific basis. NOTE 1: Part of the reason for this value is to correct for the fact that the design method in BS 7533-8 assumes that maximum 500x500mm 4 Precast concrete flag and slabs are used. These are smaller than the 600x750-900mm units that are typically used in natural stone slab surfaced Southwark (as well as other central London pavements (bound surface)

Boroughs). Being larger these units are likely to Yorkstone flags Granite flags carry increased loads and so require a greater minimum Breaking Load for the design method to remain valid.

NOTE 2: Achieving the breaking load requirement relies upon units having sufficient flexural strength and dimensions. Broadly, shallow units with a longer plan form will be 4.1 Use requirements able to sustain lesser breaking loads than deeper units with a squarer plan form. Providing a. In existing streets and spaces, other than in the flexural strength (lower expected value) of a the limited circumstances described in ‘c’ material is known then the necessary and ‘d’ below, level 2 departure is required dimensions for a unit can be calculated using to use this method of pavement design. the formula provided in BS EN 1341:2012, This is because of its problematic nature Annex A. The safety factor selected from Table and related maintenance risks (see A.1 should be as per those for where slabs are discussion in section 3 of Appendix A). It laid on sand or aggregate. must be demonstrated to the satisfaction of

Approving officers that: Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 13

i. That those risks are proportionate and minimised to acceptable levels. appropriately covered by commuted sums (see ‘e’ and note below). c. As an exception from both ‘a’ and ‘b’ above, ii. why using an unbound surface flag or this method of pavement design may be slab construction as section 3 is used to footway and carriageway pavements inappropriate on structural or for the features as Table 6 without requiring maintenance grounds. any form of departure. This applies to both new and existing streets and spaces. NOTE: Surveys to locate subsurface statutory Conversely, unbound surface design as undertakers apparatus are always required to section 3 may not be used for these demonstrate the level of risk. features. Therefore, if using flag and slab surfacing is desired for these features then b. In new streets and spaces, except for in the only bound surface design in accordance limited circumstances described in ‘c’, level 1 with this section is acceptable. departure is required to use this method of pavement design. To obtain this, proponents d. As an exception from both ‘a’ and ‘b’, must demonstrate to the satisfaction of approving officers have discretion to instruct approving officers that: that this method of pavement design is used i. They have made robust provisions to within new or existing streets and spaces in have services corridorised elsewhere circumstances other than those given in and concluded suitable agreements with Table 6, but only to very limited areas of Statutory Undertakers to ensure this. footway pavement (or other non-carriageway ii. The overwhelming majority of existing pavement) that are exposed to significant services will be diverted so as to be risk of regular commercial vehicle overrun beyond the construction. (the majority of immediately neighbouring iii. The risk of having to excavate the surfaces using unbound slab or flag construction during its service life for constructions as section 3). other reasons has been designed out or

14 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

Feature Further details/requirements

1 Dropped Kerbs This requirement applies also to associated flares if such details are used (see ‘4.2c.iv.’’) 2 Plateaus to Vehicle This requirement applies only to Occasional Use Crossings (as defined in standard Crossings serving DS.132) commercial premises 3 Footway/Cycle Track This requirement applies to each arm within 2.5-7m back from the junction intersection pavements around (see note 2). However, it may be omitted or varied by level 1 departure. This will corners at road generally only be permitted where use of looser junction geometry is permitted (see junctions note 3) and/or substantial kerb steps are used to the carriageway edge giving confidence that larger vehicles will not overrun footways when turning through the junction

4 Footway/Cycle Track Build Outs that have a Total Length measured along the carriageway of ≤ 6m this Build Outs at the requirement applies to their entire length (see note 4) carriageway edge Build Outs that have a Total Length measured along the carriageway of > 6m this

requirement applies to the entire length of each Taper at each end plus the first 0.8 to 1.2m of the Body (see note 4) 5 Pavement on steep Any area of pavement with a surface gradient equal to or steeper than 1:15 gradient

NOTES 1) The extent of such areas of bound construction should be locally minimised around the feature whilst keeping a logical boundary. See ‘4.2c’ for further information. 2) For each side of each arm, this distance should be measured from the projected point of intersection of the edges of the two intersecting carriageways having excluded corner radii. The actual distance used with the range should be kept to the minimum within which occasional heavy vehicle overrun might be expected (given the geometry and traffic conditions) whilst keeping a logical boundary. Approving officers have discretion to instruct the necessary distance within the range to be increased/ decreased as they consider appropriate to context. 3) Designers should note that ‘slack’ corner geometry is not normally acceptable. Designers are normally required to make junctions as tight as practical whilst accommodating those vehicles that can typically be expected to pass through them (rather than the largest vehicle possible at all times). See standard DS.106 for further information. 4) As per standard DS.118, Build Outs are considered to consist of Tapers (one at each end) and a Body. Tapers are the length of the feature during which the kerb line is shifting out or in. The Body is the length during which the Build Out is at its characteristic width (measured across the street). The Total Length is the sum of the Body and both Tapers. Table 6. Circumstances where (for slab and flag surfaces) bound construction as per Section 4 is mandatory and unbound construction as Section 3 is prohibited.

Commuted sums the discretion of approving officers. Similarly, if it is agreed to permit weak cement: sand laying e. Within existing streets and spaces, except course and jointing mortars to be used on the in the limited circumstances explained in ‘c- assumption of no vehicle trafficking then d’, this method of pavement design is approving officers should not normally request outside Highway Authority adoptable commuted sums as it is much easier to lift and standards. The Highway Authority therefore reuse surface units where these materials are requires commuted sums should it permit used. use via departure. f. Within new streets and spaces, if using this NOTE: Where it can be demonstrated that method of pavement design is approved by suitable measures have been taken to reduce departure as ‘b’ then the need for or remove the risk of disturbance by Statutory commuted sums will be agreed with Undertakers (e.g. by relocating utilities approving officers on a case specific basis. elsewhere within confined corridors) then However, if ‘c’ or ‘d’ apply no commuted commuted sums may be reduced or removed at sums are required.

Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 15

4.2 Design requirements - If pedestrian Dropped Kerbs are introduced at the edges of existing a. Pavements should be: footways that use unbound i. designed in accordance with BS 7533- constructions, only the ramp and 12:2006 flares to features (and any brief ii. constructed in accordance with BS areas beyond associated rakes – 7533-4:2006 see ‘iv) should use a bound construction. The residual footway The remainder of this section states (including most of the plateau supplementary Southwark specific requirements behind the ramp) should normally that may vary from the recommendations of use an unbound construction. those documents. In some instances this may mean cutting slabs

or flags to create a straight interface with a b. The assumed minimum levels of daily neighbouring area of unbound construction. standard axle overrun for pavement design However wherever possible the edge of the purposes to different areas should be as construction should be aligned with joints section 2.4. The estimated level of daily between uncut slabs or flags standard axle overrun should be multiplied

by a factor of 2 to account for dynamic If the limit of the bound construction is in the loading/impact and channelised trafficking vicinity of any rakes in the surface (e.g. such as (even where applied to footways or Cycle those used to flares associated with ramps to Tracks). Dropped Kerbs and Vehicle Crossings) then the limit of the bound construction should normally NOTE: For this method of construction the extend a single flag or slab beyond the top of estimated levels of trafficking will influence the cut line to each rake. This is because the foundation design only since standard joint between the units at the rake will often be thicknesses are prescribed for most structural quite wide and will therefore need to be mortar layers in the paragraphs that follow, including the filled. This will only be possible if the units to base course. either side of the joint both use a common c. If it is necessary to use a bound construction underlying bound construction. to a feature located to the front of a footway or other non-carriageway area (for instance Base course to a Dropped Kerb, Vehicle Crossing ramp or d. The base course should be [CBGM-B/R- Build Out) then: C20]. This should be: i. If the footway width is < 3.5m in width, i. 200mm thick in Heavy Overrun Areas. for ease of construction, the bound ii. 160mm thick in Light Overrun Areas. construction should generally be extended to its entire width for that local Exceptionally, approving officers may instruct length of pavement about the feature that even greater thicknesses are used based (unless an obvious break point exists, upon the results of traffic evaluations (see like a surface channel or necessary section 2.5). See also section 6.3 of standard switch in falls). DS.602 about strength requirements prior to ii. If the footway width is ≥ 3.5m in width, trafficking/overlay. Using a [C-PQC-C40] the extent of the bound construction pavement quality concrete slab as should normally be limited to the width recommended in BS 7533-12:2006 requires of the feature only and not extended to level 1 departure (see note 2). This is only likely the entire footway width locally about the to be considered if extreme vehicle overrun is feature. For example: anticipated or if there are special structural - If Build Outs are introduced, only concerns (like basements extending beneath the width of the Build Out should the footway). use a bound construction. An unbound construction should be NOTE 1: If the base course will be trafficked used for the characteristic width of during construction then these thicknesses the footway beside this. should be increased by a further 25%.

16 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

NOTE 2: Pavement quality concrete typically • Class 2 where used to carriageways. requires regular movement joints and steel iv. Have tolerances/deviations on work reinforcement to be introduced. As well as dimensions as BS EN 1339:2003 of: significantly increasing complexity of construction • Class 3R for tolerances on length, and maintenance, any steel reinforcement will width and thickness. interfere with cable identification tools. • Class 3(L) for maximum difference between measurements on Laying course diagonals. f. Paving units should be laid on a 25mm finished thickness of [L-MH1] or [L-MHX] high i. Natural stone slab units should: performance bedding concrete. This i. Be to BS EN 1341:2012. specification is for a 30 MPA compressive ii. Have a minimum thickness as BS 7533- strength mortar as BS 7533-4:2006, Table 4. 12:2006, Table B.3, class 1. This should Priming mortar slurry should always be be: applied to the pavement quality concrete base • ≥ 50mm in any circumstance when slab prior to application as BS 7533-4:2006 ‘f’ applies. clause 5.4.4.1. [L-MHX] is a rapid setting • ≥ 63mm when ‘g’ applies. mortar and should only be used where such Greater widths may be required to avoid qualities are specifically required. damage during lifting for installation. The maximum thickness should be ≤ g. Exceptionally, if a departure is agreed 100mm. In all instances, the difference permitting it to be assumed that no in the thickness of the units used to commercial vehicle overrun of the pavement neighbouring Heavy Overrun Areas and will occur over its design life (see section 2.4) Light Overrun Areas (see section 2.4) then a weaker [L-MWK12] plastic mortar may within a given length of pavement be used as an alternative to ‘f’ above. This should be ≤ 10mm specification is for a class M12 mortar to BS iii. Meet or exceed the requirements of BS EN 998-2:2003 (e.g. 1:3 cement: sand 7533-12:2006, Table C.1. mortar). Applying priming mortar slurry to the • Class 1 where used to footways pavement quality concrete base slab is not (and other non-carriageway areas). necessary if this is used. • Class 2 where used to carriageways. Surface course iv. Be sawn (fine textured) to all sides with NOTE 1: See section 2.2 about selecting surface square/sharp arris. In addition, if slabs unit products and laying patterns. are composed of: • Granite (or other igneous rock) NOTE 2: When ‘f’ applies then the back faces of then, further to sawing, their upper paving units should be primed with a fine mortar faces should be flamed to achieve a slurry prior to placing them on the laying course in coarse texture. accordance with BS 7533-4:2006, clause 5.4.4.2. • Yorkstone (or other sedimentary h. Precast concrete flag units should: rock) then their upper faces should i. Conform with BS EN 1339:2003. not be subject to any further ii. Have a minimum thickness as BS 7533- treatment after sawing. 12:2006, Table B.3. This should be: v. Have tolerances as BS EN 1341:2012 • ≥ 50mm in any circumstance when ‘f’ of: applies. • Class 2 (P2) for plan dimensions. • ≥ 63mm when ‘g’ applies. • Class 2 (D2) for diagonals. Greater widths may be required to avoid • Class 2 (T2) for thickness.

damaging units when they are being lifted NOTE 1: Achieving the breaking load and installed. The maximum thickness requirement relies upon units having sufficient should be ≤ 100mm. flexural strength and dimensions. Broadly, iii. Meet or exceed the requirements of BS shallow units with longer plan forms will be able 7533-12:2006 Table C.2: to sustain lesser breaking loads than deeper • Class 1 where used to footways units with squarer plan forms. Providing the (and other non-carriageway areas). flexural strength (lower expected value) of a Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 17

material is known then the necessary dimensions 5.1 Use Requirements for a unit can be calculated using the formula provided in BS EN 1341:2012, Annex A. If [L- 5.1.1 Conventional pavements MH1 or [L-MHX] high performance mortar is used for the laying course as ‘f’, then the safety a. Except if ‘b’ applies, conventional unbound factor selected from Table A.1 should be as per surfaces composed of precast concrete those for where slabs are laid on mortar. blocks and clay pavers may be used within However, if [L-MWK12] weak mortar is used for the trafficking limits given in section 5.2 the laying course as ‘g’, then the safety factor without requiring any form of departure should be as per those for where slabs are used approval. on sand or aggregate. b. Conventional unbound surfaces composed NOTE 2: Flaming the surface of units may not be of precast concrete blocks and clay pavers appropriate where this method of pavement should not be used in any of the design is used to carriageway pavements as it circumstances identified in ‘6.1c’. If precast can structurally weaken them. Fine picking may concrete blocks, clay pavers or natural be required instead to provide necessary stone setts is desired or required in these slip/skid resistance. circumstances then only bound

Joints construction as section 5.2.2 is acceptable. j. Where ‘f’ applies, joints should be filled with [J-MH2] or [J-MHX] high performance Commuted sums jointing mortar to achieve a 5-8mm joint c. If ‘b’ applies, this method of pavement width (see note). design is not to Highway Authority adoptable standards. The Highway NOTE: The above specification is for a mortar to Authority therefore reserves the right to BS 7533-4:2006 clause 5.4.4.4. This requires the require commuted sums. mortar to have a minimum compressive strength of 40mpa and high adhesive strength. [J-MHX] is 5.1.2 Pervious pavements a rapid setting mortar and should only be used where such qualities are required. k. Where ‘g’ applies, joints should be filled with [J-MWK6] weak mortar to achieve a 5-8mm joint width. This specification is for a class M6 mortar to BS EN 998-2:2003 (e.g. 1:4 cement: sand mortar). l. Surface course joints should be aligned to any movement joints in the concrete base slab below.

5 Precast concrete block and clay paver surfaced pavements (unbound surface)

a. Subject to level 1 departure, pervious block surface designs may be used where: i. The street: • Is Road Category 4, 3B or 3A (see Table 3). • Has a 20mph speed limit or is part of a 20mph zone. ii. The pavement in question:

18 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

• Is part of an Inset Parking Bay (see b. Pervious block surface designs should note 1) which has an under- not be used in circumstances other than pavement rooting zone for street ‘a’. However, the Highway Authority is trees beneath it (see note 2). keen to explore the wider use of full • Is set to falls so that water sheds attenuation or infiltration designs for positively across it to a conventional sustainable urban drainage management collector drainage inlet that has been purposes. It may therefore permit or sized to accommodate this. instruct Design Pilot dispensations to • Does not receive any run-off shed facilitate this on Road Category 4 streets directly or indirectly from main within limited areas outside of main carriageway running lanes. carriageway running lanes..

NOTE 1: Using pervious block surfaces may NOTE 1: Notwithstanding the current general also be permitted to other types of parking bay prohibition on pervious upper layer too, provided these are protected from general constructions, under-pavement surface water vehicle overrun. Examples include spaces in infiltration/ attenuation reservoirs (which are parking courtyards at the ends of cul-de-sacs. permitted in many circumstances as Exceptionally, limited use may also be standards DS.602) may still be created where permitted to footways immediately surface water can be conveyed to them surrounding tree pits, though this will require a using more conventional collector drainage level 1 departure. Approving Officers will need systems (albeit via solids/hydrocarbon to be satisfied that introducing block surfacing separator gullies or channels to reduce the will not visually undermine the intended risk of clogging and restrict the majority of surfacing character for the location as per the maintenance to easily accessible surface relevant SSDM/SER/Surfacing Materials locations. palette. In particular, where the standard footway surfacing material for the location is slabs or flags then, as per the requirements of Commuted sums DS.130, avoiding creating the impression of a continuous front of footway block-paved verge c. Pervious block surfaced pavements are not should be paramount. fully supported by adoptable standards at this stage. Consequently, they will require commuted sums. Exact sums will be NOTE 2: Constructing under-pavement advised by approving officers on a case rooting zones will require load-bearing specific basis. In general, if they are used subbase systems to be used to support the as described in ‘a’ (with the pavement trafficked pavement above (without being set to falls so that much of the water compacting the soil within the zone). passing over it will ultimately be shed to a Examples of such systems include ‘soil vaults’ conventional collector drainage inlet) then constructed from load bearing geo-cellular unit only nominal sums should be required in assembles, and granular rooting zones order to cover the costs of: constructed using load bearing ‘structural soil’ i. Periodic vacuum cleansing and re- unbound granular mixtures. Resorting to using topping of joints on an approximate 6-8 such systems should be avoided wherever year cycle. possible by providing as much of the required ii. Potential total replacement (or soil volume to support a tree as is feasible cleansing) of jointing and laying course within a large open bed. However, at space materials (and any geo-textiles constrained sites, locating the majority of a immediately beneath the laying rooting zone beneath the pavements course) on at least one occasion surrounding a tree pit may be unavoidable. during the pavements serviceability See standards DS.501 and DS.602 for further design life. information.

Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 19

5.2 Design requirements d. For footways and other non-carriageway areas, the laying course should comprise 5.2.1 Conventional pavements of [L-SS1] sharp sand.

a. Pavements of this type should be: e. For carriageway areas, the laying course i. Designed in accordance with BS should be [L-QZ4] quartz arenite sand. 7533-1:2001 or (for non-carriageway However: pavements only where appropriate i. Using [L-SS1] sharp sand may be for the predicted level of trafficking) permitted in Road Category 4 and 3B BS 7533-2:2001. streets (see note) by level 1 ii. Constructed in accordance with BS departure. It must be demonstrated 7533-3:2005. that no significant regular bus or commercial vehicle turning The remainder of this section explains movements will occur. supplementary Southwark specific ii. Alternative materials may be requirements that may vary from the permitted by level 1 departure. An recommendations of those documents. overriding structural reason to vary must be demonstrated. Base course iii. Approving officers have discretion to instruct that alternative materials are b. For footway pavements (and other non- used based upon the advice of carriageway pavements): modular unit manufacturers. i. Base course may be omitted if this is f. The thickness of the laying course should permitted for the anticipated level of be as recommended in either BS 7533- trafficking. However, a base course 1:2001 or BS 7533-2:2001 (based on a must always be provided to minimum combined ‘surface plus laying commercial Vehicle Crossings. course’ thickness of 110mm. Therefore, if ii. If a base course is required then 60mm thick surface units are used, the materials should be as Table 7. The laying course will normally be 50mm thickness should be as BS 7533- thick. By comparison, if 80mm thick 1:2001 or BS 7533-2:2001 using surface course units are used, the laying equivalent performance thicknesses course will normally be 30mm thick). for the selected material (see section However, if anti-shift are used then the 2.8). thickness of the laying course should be 35-40mm. Laying course

NOTE: The Highway Authority may permit or instruct Design Pilots to trial innovative bound laying course materials that differ from the requirements below. Examples include bituminous mixture based materials to protect base courses from surface water penetration and related damage.

20 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

Material Footways Carriageways (see note 1)

A [C-NF-C15] no fines Yes, except for commercial No concrete, air voids Vehicle Crossings content 12-16% (see note 2) B [C-NF-C20] no fines Yes - though (A) above will Yes for Road Category 3A and quieter concrete, air voids normally suffice content 12-16% (see note For Road Category 2A may be used under Inset 2) Parking Bays that are not prescribed or likely to C [B-Ba3OA] open graded Yes - though (D) below will be used for loading, but not in other carriageway asphalt concrete with a normally suffice locations 40/60 pen grade binder

D [B-Ba3OA] open graded Yes – though if exceptional Subject to level 1 departure for Road Category asphalt concrete with a overrun is predicted then 3B and quieter only 100/150 pen grade binder approving officers have discretion No in all other instances to instruct that (A) or (B) is used instead E [Ba3C] 20 Cold Mix Subject to level 1 departure. It Yes for Road Category 2B (see note 3-4) must be demonstrated why using Subject to level 1 departure for Road Category materials (A)-(D) is impractical 3A and quieter. It must be demonstrated why (see note 5). using materials (B)-(C) is impractical (see note

5). No in all other circumstances F [Ba2A] dense base with a No Yes for Road Category 2A and busier 40/60 pen grade binder (see note 4) Subject to level 1 departure in all other circumstances. It must be demonstrated why using all other materials permitted above for the G CBGM or HBM as Table Subject to level 1 departure. It relevant Road Category is impractical (see note 4 (see note 6). must be demonstrated why using 5). all other materials permitted above is impractical (see note 5).

NOTES 1) See Table 3 for details of Road Category classifications. 2) Though much greater void content is possible this should generally be avoided. Whilst greater air voids content increases permeability substantially, significant permeability is not the objective in this instance. Rather it is to provide just enough permeability for the base course to drain any surface water ingress satisfactorily. Increased air voids content will also reduce mechanical strength and increase the risk of laying course materials migrating. Nevertheless, greater voids values may be permitted by level 1 departure. 3) The grade and indirect tensile stiffness modulus of cold-mix options should be as Table 10.. 4) Being impermeable the bituminous mixture layer may need to be perforated with 75mm diameter holes on a 750 x 750mm grid to allow downwards dispersal of any surface water ingress. Holes should typically be filled with open graded gravel that is compatible with the laying course material. Whilst [L-QZ2/6] quartz arenite sand is likely to suffice in many instances, or a fin drain or geogrid installed. 5) Using this material is only likely to be considered for overlay works to existing streets if existing such materials are encountered and it can be demonstrated to the satisfaction of approving officers that replacing/removing these would incur excessive cost to the Council. 6) As these CBGMs and HBMs are impermeable, it will be necessary to provide other drainage measures to prevent surface water that penetrates the surface from becoming trapped in the laying course.

Table 7. Permitted bound base materials for conventional modular pavements that have an unbound surface of precast concrete blocks or clay pavers.

Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 21

Surface course SSDM/RP designation(s). - If the predicted level of design Type of Location laid Minimum Maximum life trafficking meets exceeds Unit within depth of unit length of unit that for Road Category 2A (see (mm) (mm) Table 1) then the Highway Precast Footway 60mm ≤ 4 times Authority again reserves the concrete both their right to require that anti-shift block width and units are used. their depth Carriageway 80mm ≤ 3 times See standard DS.130 for details of acceptable (or 100mm both their laying patterns for anti-shift width and units) their depth NOTE: Examples of locations that may be subject Clay Footway 50mm ≤ 4 times to vehicle turning movements include junctions, paver both their turning heads and car parks. width and their depth. i. If units are laid in footways (and other non- Carriageway 70mm ≤ 4.15 times both their carriageway areas) then reference should be width and made to standard DS.130 for details of laying their depth. pattern requirements. Table 8. Dimensional requirements for precast concrete blocks and clay pavers when laid unbound. Joints j. Units should be 2-5mm close jointed with [J- g. The surface course should be either: X1] stabilised granular jointing material (see i. Precast concrete block paving units note). conforming to BS EN 1338:2003. ii. Clay pavers conforming to BS EN 1344:2002. 5.2.2 Pervious pavements These should meet the dimensional requirements in Table 8. a. Pavements of this type should be: i. Designed in accordance with BS 7533- h. If units are laid in carriageways then: 13:2009. i. If they are laid in a junction space (or ii. Constructed in accordance with BS 7533- other area subject to vehicle turning 3:2005. movements, see note) then they should be anti-shift units as permitted in the The remainder of this section explains SSDM/SER/Surfacing Materials palette supplementary Southwark specific requirements for the relevant SSDM/RP designation(s). that may vary from the recommendations of They should be laid in stretcher bond those documents. perpendicular to the dominant b. The assumed minimum levels of daily carriageway edge as SSDM/TDR standard axle overrun for pavement design drawings LBS/1100/01-48. Using other purposes to different areas should be as units and laying arrangements requires section 2.4 (though see also section 2.5). level 1 departure. However, Approving Officers have discretion to instruct that other laying patterns as LBS/1100/01-48 Base course are used if there is a legitimate structural c. Assuming that use of this type of pavement reason for this. design is restricted to Inset Parking Bays ii. Away from areas subject to vehicle only (and similar, see section 5.1.2) then turning movements, units may be either: introduction of a base course should • Anti-shift units. generally be avoided. However: • Normal units, though: i. See standard DS.602 about the - Only if these are permitted introduction of protective [C-NF-C20] within the SSDM/SER/Surfacing no-fines concrete upper sub-base Materials palette for the relevant layers to prevent disturbance to open 22 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

graded unbound granular mixture lower Laying course subbase materials. e. The laying course should be a 50mm ii. Subject to level 1 departure, a thickness [L-QZ2/6] of quartz arenite sand. bituminous mixture base course However: comprised one of the material options i. Subject to level 1 departure other as per ‘d’ may be introduced. It must be materials may be permitted. Designers demonstrated to the satisfaction of must demonstrate an overriding need to approving officers that there is a vary. significant risk of lower subbase layers ii. Approving officers have discretion to becoming contaminated during instruct the use of alternatives based construction works that cannot upon either the: otherwise be prevented through • Advice of modular unit reasonable phasing or site manufacturers. management practices. If this departure • Need to satisfy filter criteria (see is granted then: ‘iii). • Immediately prior to installing the iii. Introducing a geo-textile separator laying course and surface course to interlayer may be necessary beneath this pavement: the laying course to prevent the - The bituminous mixture base migration of finer particles within it layers should be perforated through the subbase. However, this with 75mm diameter holes on should be avoided wherever possible a 750 x 750mm grid to allow through consideration of filter criteria for downwards dispersal of any and specification of compatible surface water ingress. materials for the two layers. See - The holes should be filled with section 2.12 for further information. the same material as used for the laying course. Surface course - It may be possible to omit the f. The surface course should be either: {C-NF-C20] no-fines upper i. Precast concrete block paving units to subbase layer discussed in BS EN 1338:2003. ‘5.2.2c.i’. See BS 7533- ii. Clay pavers or BS EN 1344:2002. 13:2009 for details. iii. These should meet the dimensional requirements in Table 8 appropriate to d. Permitted material options and thicknesses the location of use. (see note) for bituminous mixture base iv. These should allow surface water to course are: infiltrate/ percolate via joints between i. 110mm thickness of [B-Ba2A] dense the units and not through holes within base with a 40/60 pen binder. the units themselves. Normally this will ii. 130mm thickness of either: be achieved by using over-sized spacer • [B-Ba3A] dense base with a nibs on the sides of the units. 100/150 pen binder. v. These should achieve a percolation • (If permitted as Table 10 given the rate ≥ 3750mm/hour when newly nature of the street or space and its jointed and installed. The exact as-new Road Category) [B-Ba3C] QVE percolation rate for the proposed units (structural grade) cold-mix. The should be confirmed in a Pavement minimum indirect tensile stiffness Design Statement. The design should modulus class should be as be based on a rate equal to 10% of this directed in Table 10. in order to account for clogging over a iii. (If permitted as Table 10 given the 20 year design life. nature of the street or space and its Road Category) 190mm thickness of g. Assuming that use of this type of pavement [B-Ba3C] SVE (storage grade) cold-mix design is restricted to Inset Parking Bays asphalt – but only in existing streets only (and similar, see section 5.1.2) then and spaces. The minimum indirect units should be laid in a stretcher bond as tensile stiffness modulus class should per SSDM/TDR drawing LBS/C/040. This be as directed in Table 10. should be set perpendicular to the dominant Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 23

edge of the carriageway. See also standard b. In new streets and spaces, requirements DS.005 about means of delineating bays are as follows (appropriate to the type of through the use of surfacing materials surfacing). (rather than road markings). i. Natural stone sett surfacing

Joints i. Units should be close jointed with [J- QZ2/4] quartz arenite sand. The joint width will depend upon the nib design of the modular units used. However: i. Alternative materials may be permitted by level 1 departure. Designers must demonstrate an overriding need to vary. ii. Approving officers have discretion to Except for in the limited circumstances instruct alternative materials are based described in ‘c’ and ‘d’, using this form upon either the: of pavement design requires level 1 • advice of modular unit departure (see note). In general, it manufacturers must be demonstrated to the • need to satisfy filter criteria (see satisfaction of approving officers that section 2.12). robust provisions have been made to have services corridorised elsewhere, with suitable agreements reached with 6 Precast concrete block, clay Statutory Undertakers to ensure this: paver or natural stone sett • Any existing services can and will be relocated beyond the surfaced pavements (bound construction. surface) • The risk of needing to excavate the construction during its service life for other reasons has been designed out or minimised to acceptable levels.

ii. Precast concrete block and clay paver surfacing

6.1 Use requirements a. In existing streets and spaces, other than in the limited circumstances described in Except for in the limited circumstances ‘c’ and ‘d’, a level 1 departure is required to described in ‘c’ and ‘d’, using this form use this form of pavement design. This is of pavement design is not permitted. because of maintenance risks. Designers An unbound constructions as section are advised that departures are most likely 5 should be used instead. to be granted where: i. Use is confined to relatively small c. Subject to ‘e’ this form of pavement design areas that minimise the need for may be used in both new and existing movement joints and otherwise avoid streets and spaces for: design and construction complexity i. Ramps and plateaus to Vehicle (see notes 4). Crossings. ii. The risk of future disturbance to the ii. Other areas of pavement with a pavement by Statutory Undertakers. gradient of 1:15 or steeper.

24 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

iii. Footways in the immediate vicinity of required. cellar access hatches to pubs and bars where kegs and barrels are likely to be unloaded. 6.2 Design requirements Conversely, unbound surface construction as section 5 may not be used to these a. Pavements of this type should be: features. i. Designed in accordance with BS 7533- 10:2004 (using Table 7 of that d. If precast concrete block, clay paver or standard). natural stone sett surfacing is required or ii. Constructed in accordance with BS permitted to: 7533-7:2010 (see note). i. The ramps (but not plateaus) of Raised The remainder of this section states Tables in the carriageway supplementary Southwark specific requirements ii. Rumble Strips in the carriageway that may vary from the recommendations of Then, subject to ‘e’, this method of those documents. pavement design should always be used.

However, in these instances those sections Base course of pavement should be designed as per b. In footways (and other non-carriageway SSDM/TDR drawings. areas), the base course should be one of the rigid or semi- rigid bound materials in Table e. For carriageway pavements, if a natural 9. The thickness of the selected material stone sett surface course is proposed then, should be as BS 7533-10:2010, Table 7 for with the exception of ramps to Raised the assumed level of vehicle trafficking. Tables and Rumble Strips, this method of pavement design: c. In carriageways: i. May only be used to 20mph streets i. The base course should be [C-PQC- where either: C40] pavement quality concrete. • The mean average speed is ≤ ii. The thickness of the materials should be 20mph. as BS 7533-10:2010, Table 7 for the • (If it is currently greater than the assumed level of vehicle trafficking. above) it can be demonstrated to iii. Transitions into flexible bituminous the satisfaction of approving officers mixture or unbound precast concrete that the proposed works will block/natural stone sett/clay paver succeed in reducing the mean surfaced pavements should be detailed average speed to ≤ 20mph. as per drawing LBS/1100/01-48. ii. May not be used within the controlled iv. Where movement and warping joints are area (defined by zig zag markings) of required as per section 2.10 then they any controlled Formal Crossing unless a should be detailed as per drawing level 1 departure is agreed. In order for LBS/1100/01-48. They must extend this to be granted, it must be through to the surface of the pavement. demonstrated that the setts will achieve Laying course an appropriate polished skid resistance d. The laying course material and thickness value. Values and testing standards will should be as BS 7533-10:2004, Table 3. If be agreed on a case specific basis and that BS requires: should be confirmed with approving i. Type A bedding concrete then [L-MH3] officers prior to commissioning of tests. fine bedding concrete should be used. ii. Type B bedding concrete then [L-MH2] Commuted sums fine bedding concrete should be used. f. In existing streets and spaces, this method of pavement design is outside Highway Optionally in either instance, if a rapid setting Authority adoptable standards. The bedding concrete is required then [L-MHX] fine Highway Authority therefore reserves the bedding concrete may be used. right to require commuted sums. The exception to this is when ‘c’ or ‘d ‘apply in e. In footways and other non-vehicle which case commuted sums are not trafficked areas it may exceptionally be Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 25

permitted by level 1 departure to use a [L- instead. Joint widths should not exceed the MWK12] weak mortar laying course if the mid-value of the permitted joint range as Table footway will be physically protected from 2 of BS 7533-10:2004. E.g. 10mm for a Size potential vehicle overrun of any kind using Category 3 sett with a design joint width range bollards or other appropriate measures. of 8-12mm.

Surface course h. For precast concrete block and clay paver f. Surface course units should be either surfaces (but not natural stone sett i. Precast concrete blocks to BS EN surfaces), if the pavement is both: 1338:2003. i. Within a footway (or other non- ii. Natural stone setts to BS EN carriageway area) 1342:2012. ii. To one of the features as ‘6.1c.i’ or iii. Clay pavers to BS EN 1344:2002. ‘6.1c.ii’, then units should be jointed using materials and widths required The specification of the units should be in for unbound surfaces in section 5. keeping with any recommendations for the site category given in BS 7533-10:2004. i. Exceptionally, if it is permitted by level 1 departure to use a [LK12] weak mortar Joints laying course, then it may also be g. Except where ‘i’ applies, jointing material permitted by the same level 1 departure should be as BS 7533-10:2004, Table 3. to use [J-MWK6] weak mortar for joints. If that BS requires a: Joint widths should again be as permitted 2 in ‘g’. i. 25 N/mm mortar then [J-MH2] high performance mortar should be used. j. At changes in the surface gradient ii. 40 N/mm2 mortar then [J-MH3] high (including where these coincide with performance mortar should be used. movement joints or edge or transition restraints) the sides of surface units Optionally in either instance, if a rapid setting jointing mortar is required then [J-MHX] high should be taper cut if necessary to maintain the required joint widths. performance jointing mortar may be used

26 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

Material Is use of material permitted? A [C-NF-C15] no fines concrete, air Yes, except to commercial Vehicle Crossings. voids content 12-16% (see note 1) B [C-NF-C20] no fines concrete, air Yes. voids content 12-16% (see note 1) C [B-Ba3OA] open graded asphalt Yes (though since this will require machine laying it may not always be concrete with a 40/60 pen binder practical given likely footway widths and other constraints).

D [Ba3C] 20 Cold Mix (see notes 2 Subject to level 1 departure. It must be demonstrated to the satisfaction of and 3) approving officers why use of any of the materials as (firstly) A-B and (secondly) C is not feasible or suitable (see note 4). E [Ba3A] dense base with either a Subject to level 1 departure. It must be demonstrated why use of any of 40/60 or 100/150 pen binder (see the materials as (firstly) A-B and (secondly) C-D is not feasible or suitable. note 3) Use of the 40/60 pen binder option is only likely to be permitted where excessive vehicle overrun (including by construction traffic) is possible and machine-laying is practical. F CBGM or HBM as Table 4 (see Subject to level 1 departure. It must be demonstrated why the use of any notes 4 and 5) of the materials as (firstly) A-B and (secondly) C-E is not feasible or practical. Use is only likely to be considered for overlay works to existing streets where existing such materials are encountered and replacement/ removal of these would incur excessive cost to the Council.

NOTES 1) Though much greater void content is possible this should be avoided. The objective is to provide just enough permeability for the base course to satisfactorily drain any surface water that succeeds in penetrating the layers above. Increased air voids content will also reduce mechanical strength and increase the risk of laying course materials migrating. Nevertheless, greater voids values may be permitted by level 1 departure 2) The grade and indirect tensile stiffness modulus of cold-mix options should be as Table 10. 3) This bituminous mixture layer should be perforated with 75mm diameter holes on a 750 x 750mm grid to allow downwards dispersal of any surface water ingress. Holes should typically be filled with open graded gravel that is compatible with the laying course material. Whilst [L-QZ2/4] quartz arenite sand is likely to suffice in many instances, exact materials should be agreed with approving officers in advance on a case specific basis having considered filter criteria (see section 2.12). 4) As these concrete, CBGM and HBM materials are impermeable to water, other drainage measures to prevent surface water ingress from becoming trapped in the laying course will need to be introduced. Designers are responsible for proposing suitable measures when making departure requests. For CBGMs and HBMs, gradual development of cracks should not be relied upon. 5) See section 2.10for general requirements and discussion about pre-cracking and provision of movement joints and reinforcement within concrete, HBM and CBGM base courses. Table 9. Permitted bound base course materials for conventional modular pavements to footways (and other non-carriageway areas) that have a bound surface of precast concrete blocks, natural stone setts or clay pavers.

Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 27

expert masons broadly to the method 7 Natural stone sett surfaced provided in BS 7533-10 and 12 (only pavements (unbound surface). using stabilised granular jointing materials like [J-X1] or [J-X2]). Correctly sorting and selecting units to maintain consistent joint widths and adhering to proper compaction procedures (including re-topping of joints and further compaction after initial trafficking) are likely to be crucial. Using intermediary restraints is also likely to be necessary. • Using smaller cube units laid as per section 3, only in arc patterns that 7.1 Use requirements. provide greater interlock. a. Using unbound surfaces composed of natural 8 Bituminous mixture surfaced stone setts may be permitted or instructed as carriageway pavements a Design Pilot. If no such dispensation is agreed then using this design method requires level 2 departure.

Commuted sums b. If it is permitted to use this design method then the Highway Authority reserves the rights to require commuted sums should the agreed specification suggest the need for a considerable degree of maintenance.

7.2 Design requirements. a. If it is permitted to use this design method then design and construction specifications 8.1 Use requirements will be agreed on a case specific basis with 8.1.1 Flexible pavements (e.g. with approving officers. Advice from specialists is bituminous mixture base course) likely to be required. a. This is the preferred method of pavement b Design and construction approaches that design for carriageways and commercial might be explored include: Vehicle Crossings and should be used in all • Using sawn side units (to the circumstances. dimensional tolerances for precast concrete blocks) with base and side 8.1.2 Flexible-Composite pavements (e.g. faces texturised to increase friction with with HBM base course) jointing aggregate and permit laying broadly as section 5. a. In existing streets and spaces, using Flexible- • As per section 5 but with plastic or Composite design is restricted to minor neoprene nib spacers applied to the side maintenance and repair works to existing of units (rather than these being such pavements. However, if the extent of texturised). that repair or reinstatement is significant then • As per section 5 but with ‘X’ or ‘T’ shaped replacing the pavement with a Flexible design plastic spacers used at joints between as section 8.1.1 should be evaluated. units to prevent rotation and loss of interlock. The units themselves might be b. In new streets and spaces, Flexible- sawn to all sides or texturised as section Composite pavement design should not be 5. used. Flexible pavement design as section • Using larger cropped side/base units (to 8.1.1 should be used instead. tight dimensional tolerances) laid by 28 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

8.1.3 Rigid-Composite design (e.g. Authority adoptable standards. If using this pavement quality concrete CRCB base method is exceptionally permitted then course with minimum 100mm commuted sums are required. bituminous mixture overlay) a. In existing streets and spaces using Rigid- 8.2 Design requirements Composite design may be permitted by level 1 departure for minor maintenance and 8.2.1 Design methodology (including repair/reinstate works to existing such determination of layer thicknesses) pavements. However, if the extent of that repair or reinstatement is significant then a. Except where otherwise stated in this design replacing the pavement with a Flexible design standard, pavement design and layer as section 8.1.1 should be evaluated. thickness selection should be carried out in accordance with Highways Agency ‘Design b. In new streets and spaces Rigid-Composite Manual for Roads and Bridges’ HD 26. Either design should not be used to carriageway HD 26/01 or the newer HD 26/06 may be pavements. Flexible pavement design as used (see note 1). However: section 8.1.1 should be used instead. i. It must be expressly stated in Pavement Design Statements which version of HD Commuted sums 26 is being used for a given section of c. Where using this method of design is carriageway pavement. exceptionally permitted for purposes other ii. If HD 26/01 is used then standard than minor maintenance and reinstatement of asphalt materials included in nomograph existing such pavements, then the Highway design lines will need correcting owing to Authority shall require commuted sums. changes in the stiffness of surface course materials in recent specifications. 8.1.4 Rigid design (e.g. pavement quality See note 2 for further information. concrete CRCP with or without 30mm iii. If HD 26/06 is used then designs should bituminous mixture overlay) assume a Class 2 Foundation. iv. For the purposes of establishing the

minimum overall thickness of asphalt a. In existing streets and spaces, using Rigid pavement design may be permitted by level 1 (e.g. base, binder and surface course), if HD 26/01 is being used this may be departure for minor maintenance and repair/reinstate works to existing such reduced beneath the standard 200mm thickness indicated in nomographs (see pavements (see note). However, if the extent of that repair or reinstatement is significant note 3) by downwards extrapolation then replacing the pavement with a Flexible using the underpinning information upon which these are based (see note 4). design as section 8.1.1 should be evaluated. However, the absolute minimum NOTE: One relatively frequent instance where thickness may not be less than 110mm existing rigid pavements are likely to be or that dictated for laying purposes for encountered is at Inset Bays for buses (bus lay- any proposed material. Extrapolation bys). Rigid concrete will frequently have been calculations should be included in used as the restricted working space makes Pavement Design Statements (see laying and compacting stiff bituminous mixtures section 2.1). impractical. NOTE 1: Though HD 26/01 is no longer

available from the Highways Agency website. b. In new streets and spaces using Rigid The continued use of the superseded HD 26/01 pavement design is not permitted. This reflects guidance from ADEPT. applies whether or not an asphalt surface

overlay is provided. NOTE 2: The thicknesses for the materials included in figure 2.2 of HD 26/01 (one of the Commuted sums two key nomographs) assume certain minimum design stiffness values for the overlaying c. Rigid pavement design is not to Highway

Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 29

surface course materials. However, recent the following requirements of that document. editions of the SHW have revised these surface i. Tack coats and/or bond coats should be course material stiffness values downwards. provided between all courses and to These same changes are reflected in Southwark interfaces with edge restraints. Highway Specification clauses. Consequently, in ii. Thickness limitations for laying order to use the nomographs in figure 2.2 with purposes are specified for different confidence it is necessary to use corrected materials. These may constrain choices underpinning minimum stiffness values for of materials, require a greater thickness binder and base course. These should be as of material to be provided than is follows (derived from HD 26/06, para 4.13): needed for structural purposes, or DBM/HRA – Smin1100, DBM50 – Smin1800, require materials to be installed in more HDM – Smin2500, HMB35 – Smin5200. than one layer. Note also that only nominal thicknesses should be used. NOTE 3: DMRB HD 26 is aimed primarily at motorways and other trunk roads. Appropriate to b. When milling existing bituminous mixture these conditions they assume a minimum courses either: overall thickness of asphalt (e.g. base, binder i. A complete layer should be removed and surface course) of 200mm. In HD26/01, plus a further 5mm of the next layer. nomograph lines artificially flat-line for all levels ii. Milling should not take place within of trafficking beneath this thickness. Depending 15mm of a layer interface. upon the material stiffness this typically occurs between 1.7 and 4.4msa. Many roads in Southwark carry significantly less traffic than 8.2.3 Joints and Transition details these associated minimum values for trunk roads. Consequently the standardised use of a a. At transitions between different types of 200mm minimum thickness represents a bituminous mixture carriageway pavement potential wasteful use of resources. Application (e.g. Flexible, Flexible Composite, Rigid or of the underpinning information to extrapolate Rigid-Composite) transition details should further downwards allows lesser thicknesses to be used as per Highways Agency’ MCHW be used at lower levels of traffic, thus making Volume 3 details. more economic and sustainable use of resources. b. Where lengths of new and existing bituminous mixture pavement meet, the new NOTE 4: This information can be found in ‘TRL section should be benched into the existing report LR1132 (Powell W.D et al., 1984)’ for as Figure 2.2 in Highways Agency ‘Design HD26/01, ‘TRL Report TRL 615 (Nunn M)’ for Manual for Roads and Bridges’ DMRB HD HD 26/06 and associated later research 27/04. references in both version of the HD.

b. When using HD 26 as ‘a’ to design a 8.2.4 General requirements for base course pavement then: i. The assumed serviceability design life a. All Polymer Modified Binders (PMB) used in for the pavement should be 20 years as bituminous mixture should be Highway section 2.6. Authorities’ Product Approval Scheme ii. The assumed level of cumulative (HAPAS) approved and certified. serviceability design life standard axle trafficking as section 2.4 and Table 3. b. Where cold-mix bituminous mixture options are permitted for use then the grade and indirect tensile stiffness modulus should be 8.2.2 Milling, transportation, laying and as permitted in Table 10. compaction c. In new streets and spaces all bituminous a. All bituminous mixture pavement materials base course mixtures should be subject to should be transported, laid and compacted in Saturated Ageing Tensile (SATs) testing to accordance with BS 594987. Note in particular determine the moisture sensitivity of the

30 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

mixture and binder adhesion to the substituted for an HRA binder by level aggregate. Refer to the Southwark Highway 1 departure (see note 1). Specification for further details of testing iii. If the surface course in not a TCSC procedures. then the binder course may be either an SMA or an HRA. Cold Circumstance iv. As HD 37/06, the nominal thickness mix Existing street or New Street or Space of binder course should be ≥ 50mm grade space for all mixtures other than SMA which (see may be ≥ 30mm (see note 2). Road Category (see Table 3) note 1) 3 or 4 1 or 2 3 or 4 1 or 2 NOTE 1: Use of SMA binder course is Is use permitted? important because of the pervious nature of SVE Yes No Yes No TSCS. The SMA and bond coat seal the base storage course, preventing the damaging ingress of air grade and moisture. Use of HRA as an alternative QVE Subject (which is typically more expensive) may be struct- to level 1 No No No appropriate where the risk of surface water ural departure ingress is significant (e.g. in areas prone to grade (see note Yes Yes flooding). 2) QH/SH No NOTE 2: The attention of designers is drawn NOTES to the fact that HD 26/01 nomographs assume 1) The indirect tensile stiffness modulus (ITSM) as that the stiffness of the binder course is at Southwark Highway Specification Clause 948, least equal to that of the base course. If the Table 9/14 of either grade of cold mix shall be either Class B3 or B4. For the purposes of binder course is less stiff then its thickness will design nomographs in HD 26/01 and HD 26/06, need to be increased slightly using the Class B4 QVE material may be used to an underlying formulas (see note 2 to ‘8.2.1a’) to equivalent thickness to DBM 50 (see also note provide equivalent performance. However, for 2 to ‘8.2.1a’). Class B3 QVE material will need the purposes of this design standard, where to be used at an appreciably greater thickness. the stiffness is greater than that of the base Class B4 SVE material can be used assuming a course then no reduction in thickness may be 0.75 equivalence factor compared with made. DBM/HRA (e.g. laid approximately a third thicker). Class B3 SVE material will again need to be used at a significantly increased b. When rehabilitating existing Flexible or thickness. Flexible-Composite carriageway 2) Use will normally only be permitted owing to the pavements, a separate binder course need for a faster setting mixture to avoid delays should be provided wherever possible. to traffic during works in critical situations. Omitting the binder course requires level Table 10. Requirements for cold mix base course materials. 1 departure. It must be demonstrated both that:

i. Omitting it will provide greater long 8.2.5 General requirements for binder course term value for money without compromising structural integrity. a. When constructing new Flexible and ii. The level tolerances necessary for Flexible-Composite pavements: laying the surface course can be i. A separate binder course should be achieved using the base course provided unless a Hot Rolled Asphalt mixture that is proposed. (HRA) surface course is used wherein it However, if TSCS surfacing is used the, may optionally be omitted if permitted because of the risk of air and surface as HD 26/01. water penetration, omitting binder courses ii. If a Thin Surface Course System is only acceptable if: (TSCS) surface course is used then a iii. The base course is an HRA , and Stone Mastic Asphalt (SMA) binder iv. It can be demonstrated through site course should be used. This may be investigations and surveys that the

Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 31

existing surface is sound and 921 and Table 9/3 ‘Road Type: Lower reasonable strong – that is exhibiting speed roads’. Actual values should be as a deflection under wheel load of not close to the minimums as possible and more than 0.65mm and having a should not exceed these by more than reasonable surface profile so that the 0.2. Use of elevated macro-texture depths TSCS thickness is always within the is generally unnecessary for lower speed permitted (see note). roads. Where used in areas with heavy turning movements this may result in loss NOTE: If the carriageway has a pronounced of surface aggregate. See also additional camber then planning works should be requirements for TSCS after two years of undertaken to correct this and so facilitate trafficking. laying of the TSCS by pavers to accurate thicknesses. e. Minimum Polished Stone Values (PSV) to BS EN 1097-8:2000 for bituminous c. If an SMA binder course is used on a mixture surfaced carriageways in new street with a Road Category of 3B or streets and spaces with a 20mph speed busier (see Table 3) either: limit or which form part of a 20mph zone i. At or in the vicinity of a bus cage. (other than those forming part of the ii. In any other circumstances where it principal road network) should be as will be trafficked by heavy, slow Table 11. If existing 20mph signed moving traffic (e.g. a narrow slow carriageways are resurfaced then PSV moving high street or Classified values should be brought into accordance Road). with these requirements. Notwithstanding Then it must achieve deformation these minimums, necessary skid resistance equivalent to half the value resistance values should always be permitted for Wheel Track 2 as PD 6691, reviewed by designers and considered in Table D.2 when tested at 60° C (e.g. max Pavement Design Statements. Where the rut rate of 2.5mm/hour and max rut depth need for increased values can be of 3.5mm). demonstrated or is apparent then this may be permitted by level 1 departure else instructed by approving officers (see 8.2.6 General requirements for surface note 1). For minimum carriageway surface PSV values for 30mph streets a. Surface course materials should achieve and streets forming part of the Principal an overall neutral to dark grey Road Network, see standard DS.107. appearance that endures for the majority Also see standard DS.107 about using of the design life of the pavement. high friction surfaces with PSVs of 70+ Surfaces should not contain exposed (and alternatives) in locations with a coloured binder, aggregate or surface history of incidents. chippings.

NOTE 1: Where there is a considerable risk of b. If they are not generic materials to BS EN skidding then, in general, introducing speed 13108 then all materials should be reduction measures is preferable to increasing Highway Authorities’ Product Approval aggregate PSV values. Scheme (HAPAS) approved and certified.

f. Maximum Aggregate Abrasion Values c. See section 2.8 about the potential use of (AAV) to BS EN 1097-8:2000 should be as slurry surfacing, micro surfacing and Highways Agency DMRB HD 36/06. The micro asphalt. See standard DS.107 same levels of AAV and PSV should be about the use of High Friction Surfacing. used on different traffic lanes across the Other surface dressings (e.g. resin carriageway except that - where aggregates bonded aggregate) should not be used. are used for demarcation - a maximum difference of 5 PSV points may be permitted d. The minimum average surface macro- by level 1 departure. texture depth should be to SHW clause 32 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

- 33m if it is a 30mph street. 7am-7pm 12 hour average ii. The TCSC should be a Highway weekday flow (see note 1) Authorities’ Product Approval Scheme Two-way or One-way (HAPAS) certified product. Generic Site Category one-way street without Stone Mastic Asphalts should not be street with contra-flow used. contra-flow iii. The PSV of course and fine aggregate ≤2250 >2250 ≤1000 >1000 should always be the same. iv. Macrotexture should be to HAPAS Minimum PSV value Level 1 unless agreed otherwise. The guarantee period for this must be 5 Within 23m of any Controlled Crossing years. or Signalised 65 v. The TCSC should have a toughness of 2 Junction ≥ 30 N/mm as measured by the tensile Within 40m of any bending test at 0°C (see note 2). pedestrian entrance vi. If it is used on a street with a Road used by pupils of a 60 65 60 65 Category of 3B or busier (see Table 3) school, nursery or either: similar facility • At or in the vicinity of a bus cage. Any carriageway • In any other circumstances where with a longitudinal 60 65 60 65 it will be trafficked by heavy, slow gradient >10% moving traffic (e.g. a narrow slow Carriageways with a moving high street or Classified bend <25m radius 60 65 60 60 Road) then the deformation resistance (as reported on the All other instances 60 HAPAS certificate) should be equivalent to half the value NOTES permitted for Wheel Track 2 as PD 1) This value is the sum of all PCUs using the 6691 Table D.2 when tested at 60° street in all lanes over the period. In existing C (e.g. max rut rate of 2.5mm/hour streets this should be based on the average and max rut depth of 3.5mm). value across surveys on a number of different Approving officers have discretion days. to require even greater 2) Where a Raised Table spans the entire deformation resistance in extreme junction space or any approach and the ramp circumstances. face for this is both within 15m of the junction vi. With respect to aggregate size, space or giveway line and has a gradient equal to or steeper than 1:12 then the PSV notwithstanding the aggregate sizes value may be reduced by 5 down to a permitted as Appendix B, Pavement minimum of 55. Design Statements (see section 2.1) Table 11. PSV values for bituminous mixture surfaced should always expressly evaluate the carriageways on streets with a 20mph speed limit appropriate aggregate size for the site given expected trafficking conditions (see note 3). This should Thin Surface Course Systems (TSCS) make reference to the table in section

4.7.1 of the ‘Londonwide Asphalt g. If use of a TSCS surface is permitted then: Specification, 3rd Edition (Road i. Surface applied grit (SAG) must be Consultants, 2013)’. Greater or lesser applied to the surface and rolled in aggregate sizes than allowed as before final compaction if the Table 13, Table 14 and Table 15 of pavement: Appendix B may be permitted by • Has a gradient steeper than 5% level 1 departure or instructed by • Is located within the following approving officers on the basis of that distance of the limits of a evaluation. controlled Formal Crossing or viii. It is of utmost importance that a Signalised Junction: consistent thickness surface course - 25m if it is a 20mph street. Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 33

is achieved. To aid this, where existing barrelled roads are to be 9 Bituminous mixture surfaced overlaid with a TCSC then the existing receiving pavement should footway and cycleway be planed and regulating materials pavements used to create a new planar cross-fall profile (usually with a central crown).

Hot Rolled Asphalt surfacing (HRA) h. If it is permitted to an HRA surface then: i. Pre-coated chippings (PCC) should be

provided to cover the surface. The rate of spread should be as BS 594987, clause 7.2. The size of chippings should be selected from one of the following to obtain the required PSV, AAV and macro texture (see note). • 6.3/10, Gc85/20 (generally preferable for visual reasons). • 8/14, Gc85/15. • 14/20, Gc85/20. 9.1 Use requirements ii. The binder for the PCC should be as BS EN 13108-4:2006 (see in particular a. Bituminous mixture surfaces may only be clause C.3). used if either: i. It is identified as an acceptable material in the SSDM/SER/surfacing palette(s) for the relevant SSDM/RP 8.2.7 Selecting materials for different types designation(s). of pavement ii. It is instructed by approving officers around mature trees. Flexible pavements (e.g. with bituminous mixture base course) b. This design method may not be used to bituminous mixture surfaced commercial a. Materials for base, binder and surface Vehicle Crossings. These should be design course layers should be selected from using the method in section 8 instead. Appendix B, appropriate to the NRSWA Road Category and environment. See Commuted sums section 8.2.1 about determining layer thicknesses for the various courses. c. Except where permitted or instructed as ‘a’, this method of design is outside Highway b. See standard DS.602 for requirements Authority adoptable standards. Commuted about thickness and materials for subbase sums will be required owing to under- and (where required) capping layer. standard design.

All other types of pavement c. In exceptional circumstances where it is 9.2 Design requirements permitted to use Flexible-Composite, Rigid or Rigid- Composite pavement designs, a. Design is to a bespoke local specification requirements will be agreed on a case based on Highways Agency ‘Design Manual specific basis with approving officers. for Roads and Bridges’ HD 39-01 and ‘Footway and cycle route design, construction and maintenance guide (UK Roads Board, 2003)’.

34 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

Circumstance Pavement Area b. When milling existing bituminous mixture (as Table 2) base courses either: New Existing Heavy Light i. A complete layer should be removed street street or Overrun Over - plus a further 5mm of the next layer. or space Area run ii. Milling should not take place within a space Area 15mm thickness of a layer interface. Is use of material Required permitted? thickness (mm) c. All bituminous mixture pavement materials [B-BiFC] cold should be transported, laid and compacted mix asphalt in accordance with BS 594987:2010. Note QVE (structural No Yes 80 50 in particular the following requirements of grade), ITSM that document. Class B4 (see i. Tack coats and/or bond coats should note 1) be provided between all courses and to [B-BiFC] cold interfaces with edge restraints and iron mix asphalt work. SVE (storage Yes Yes 120 70 ii. Thickness limitations for laying grade), ITSM purposes are specified for different Class B4 (see materials. These may constrain choices note 1) of materials, require a greater thickness [B-BiFA] dense Subject of material than required for structural asphalt No to level 1 100 60 purposes to be provided to meet concrete departure minimum requirements, or require NOTES materials to be installed in more than 1) Refer to Table 10 for further information about one layer. Only nominal thicknesses cold-mix asphalts, including indirect tensile should be used. Minimum thicknesses stiffness modulus (ITSM) classes. Whilst other are to allow for variation on site and lower classes of ITSM may also be used, the should not be used for design thickness values in this Table will then need to purposes. be substantially increased to provide equivalent performance. Combined base and binder course Table 12. Required thickness for base course materials to bituminous mixture surfaced footways. d. Materials and thicknesses should be as Table 12 for the relevant circumstance and Surface course location. e. [B-SFA] should be used to a 30mm thickness.

NOTE: Decorative surface dressings may not be used.

f. Surface course materials should achieve an overall neutral to dark grey appearance that endures for the majority of the design life of the pavement.

g. See section 2.8 about the potential use of slurry surfacing, micro-surfacing and micro- asphalt surfaces. Other surface dressings (e.g. resin bonded aggregate) should not be used.

Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 35

10 Self binding gravel surfacing to 10.3 Design requirements

existing pavements disturbed Base course by tree roots a. Pavements of this type do not require a base course and should be laid directly onto 10.1 Discussion subbase foundation layers.

a. See standard DS.501 for a full discussion Surface course about using self-binding gravel surfaces b. The surface course should be a minimum around existing mature street trees. 50mm compacted thickness of [BG-SB1] b. The permeability of different types of self- self-binding- gravel. Within busier *Town binding gravel products varies significantly Centre – Zone A* and *World Centre* and this will have a major impact on the SSDM/RP Specification Areas, using a suitable design specification – particularly harder wearing [BG-R1] or [BG-R2] resin where the surface is being applied to an bound gravel surface may be permitted as existing pavement construction. an alternative by level 1 departure or instructed by approving officers (see notes). 10.2 Use requirements It must be demonstrated or thought that pedestrian traffic will be heavy and a. Self-binding gravel surfaces should only be therefore risk damaging vulnerable roots. used in existing footways (or other non- carriageway pavements) and only then to NOTE 1: See standard DS.208 for confirmation areas around mature trees that have been disturbed by root heave.

NOTE: Using self-binding gravel in other circumstances may be appropriate where ‘orchard’ style spaces are proposed that would involve a significant grouping of trees in close proximity to one another. However, these must be of the extents of *Town Centre – Zone A*. protected from vehicle overrun and should also not be subject to heavy pedestrian traffic. NOTE 2: Resin bound gravel is a b. See standard DS.501 about using self-binding far from ideal gravel to provide surface infill to new surface. In addition pavement openings for trees. to being very expensive it isn’t c. Any self-binding gravel surfaced areas flexible enough to around trees should be inspected twice move with on- annually for deflection, rutting or de- going root heave and cracks quickly instead. compaction of the surface as this is likely to However, it is a much harder wearing surface result in drainage issues. Inspections should than self-binding-gravel and this quality may be timed to occur during wet months in the outweigh these negatives in heavily trafficked spring and winter when ponding is likely to be areas. most critical. The surface should be re-rolled at least once per year to maintain c. Special care must be taken to lay the compaction of the surface. A greater surface course (and grade the top of the frequency of rolling may be required where underlying subbase) to falls towards a pavements are little trafficked. At this time, drainage outlet as the structural integrity of any weeds or other vegetation evident should the surface will be undermined if it becomes be removed from the pavement and soft saturated. Introducing un-filled weep joints spots or ruts excavated and re-laid to design between kerb units at the edge of levels. If ponding is evident upon inspection carriageway may be appropriate if other at other times of the year (or ruts that may solutions cannot be identified. All other result in this are identified) further rolling and requirements as standards DS.601, DS.602 resurfacing should be undertaken. and DS.603 continue to apply.

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Appendix A - Background with cement, bitumen or other binders. discussion Increasingly special modular plastic crates (geo-cellular units) are also used to 1 General introduction to pavements foundation layers. Either way, the stiffest materials tend to be used closer to the 1.1 The function of pavements surface where loads are more significant. As loads are distributed by the layers and a. In structural terms the main role of a pavement reduced, successively weaker and cheaper is to provide a stable, level surface for people, materials can be used with depth. This helps vehicles and other loads to move across or make efficient use of resources. Surface rest on. This is achieved by using a layers can be made up of bituminous construction that can distribute any loads to the mixtures (e.g. blacktop) or other similar extent that they are within the tolerances that mixtures that can be rolled out, or modular the natural ground (subgrade) below is able to paving units (e.g. flags, slabs, blocks, setts support without distorting. In the case of or pavers). Where modular paving units are modular unit surfaced pavements (e.g. slabs, used these might be bound to one another flags, blocks or setts) the construction must and the layer immediately beneath using also provide enough support to prevent the mortar (rigid construction) else left unbound surface units from breaking when overrun by on a sand or gravel laying course and jointed vehicles or when other loads are applied. with similar material (flexible construction). Occasionally, high strength in-situ cast 1.2 Basic design considerations concrete might also be used for surface courses, though this is uncommon in b. Very broadly, there are two main structural London. approaches used when designing pavements, though combinations d. In all instances effective compaction of the (composite) versions of both are common in materials making up the various layers is practice. important when they are being installed in i. Rigid construction - This aims to make order to minimise future movement that the upper layers as stiff as possible so could undermine support for other layers. that they won’t bow and so that forces Preventing water getting into the pavement are transmitted to the underlying else carefully draining this from within to foundations layers. Typically (though not prevent saturation and gradual washing out necessarily) this is achieved by binding of materials (and potential related frost and all the various pavement upper layers pore pressure damage that might follow) is and the materials in these to one also important to long term performance. It another to create a stiff composite plate might seem that this would be more of a that can distribute loads over a very concern for unbound construction. However, wide area. it is also very important for bound ii. Flexible construction - This allows for a constructions where water may seep in greater degree of movement in the through tiny cracks and often has no means upper layers. The various materials of escape. Since water expands when it making up the pavement layers are left freezes this can result in considerable unbound else only lightly bound so as to damage. Again, it might seem like this might be less stiff than those used in rigid be more of a concern in colder countries constructions. Because of this, imposed and climates (such as Scandinavia or the loads are not distributed as widely and Alps). However in reality the climate in the can pass down through the entire depth UK can be far more challenging since of the pavement through grain to grain temperatures often fluctuate around contact between the aggregates or units freezing during winter months and so water making up the layers. can freeze and thaw often within a single night. c. The materials used for the layers beneath the surface are typically carefully graded 1.3 New demands on pavements aggregate mixtures. These aggregates may be left unbound or can be bound together e. Increasingly environmental concerns are

Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 37

leading to new approaches to pavement pavement construction). design that allow surface water to permeate ii. There is a wish to include new and constructions. This can help recharge unfamiliar materials about which little is ground water, slow down water surges in currently known. drainage infrastructure after heavy rainfall events and control water quality closer to 1.5 Wider design considerations source. Another new approach allows trees h. Pavements in London are subjected to to grow more successfully under paved regular disturbance by works carried out by trafficked surfaces. However, both Statutory Undertakers (public utility approaches rely on specialist materials and companies). They have a statutory right to designs that are very different to those used construct, lay and maintain pipes, sewers, historically. These are not easily retrofitted cables, ducts and associated chambers to existing pavements and are much more (e.g. manholes) within any Highway. complicated than simply replacing the Highway Authorities’ have only very loose surface paving units with ‘pervious’ blocks. powers to control this. The age of central Broadly, the pavement must be redesigned London streets (many of which are quite to the entire depth of the construction. narrow) and the much greater density of 1.4 Empirical vs. analytical design buildings and properties needing approaches connections mean that there are likely to be many utilities in streets. Rigid pavements f. Sometimes for carriageway pavements on with bound surface courses are more likely very busy roads (e.g. trunk roads and to be damaged or visually scarred by such motorways) an ‘analytical’ approach to works than are flexible pavements with design is taken. This involves assessing the unbound surfaces. There is also the appropriate construction from first concern that utility companies may not theoretical engineering principles using accurately reinstall layers deep in the mathematical models. Significant trial pavement and that unseen imperfections in lengths of the resulting proposed design are these will ‘reflect’ through to the surface then constructed and tested to see if they over time leading to eventual failure. perform structurally as was theoretically predicted. i. Footways are also often subject to greater vehicle overrun than in other parts of the g. However, analytical design is seldom cost country. This influences choices about the effective for less busy roads or footways form and robustness of construction. Cost where the level of trafficking, the loads must also be born in mind. Though the imposed, and the consequences of closures whole life costs for longer lived rigid are far less onerous (not to mention the pavements may be lower, initial construction impracticality of constructing significant trial costs may be higher, an important lengths for testing in urban areas). Instead, consideration in times of stretched budgets. design traditionally takes an ‘empirical’ In addition, the assumptions that rigid approach following national or international constructions provide ‘longer life’ may not standards. Broadly, these recommend always apply due to the gradual wear and summary constructions for different loading damage caused by frequent interventions categories based on many years of live made by Statutory Undertakers. Wherever experience and testing of different materials underground services are present these in different combinations – so saving tend to enforce a finite life of around 20 engineers and designers the time and effort years for almost all construction types. of developing and testing bespoke constructions. An analytical approach is j. Finally - except where entirely new streets only likely to be used where: are being created - pavement design in i. Special engineering constraints exist London (or indeed elsewhere) seldom (for instance, where a basement exists involves constructing or reconstructing the beneath a pavement or where it is whole depth of the pavement. This would be proposed to include geo-cellular units very expensive indeed, not least because of or other similar structures within the the impact upon the economy from the

38 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

lengthy road closures required and the unit is (relative to thickness) then the higher sheer number of utilities that may need to its strength will be. The properties of the be moved or worked around. This explains material used also play a part. Units don’t why introducing special pavement need to be capable of holding all the weight constructions that allow surface water to be of vehicles and other loads alone as they stored or stored or infiltrate or which provide will be supported by the underlying rooting zones for trees is so difficult in foundation layers (providing these are existing streets. More likely the pavement properly installed). However, this form of upper layers will be only partly replaced construction is only appropriate for lightly (sometimes by recycling the materials in trafficked footways. It will only be place) else - for certain forms of appropriate for carriageways and other construction) - new upper layers will be heavily trafficked pavements where the installed on top of the existing as ‘overlays’, thickness/strength of the slabs and flags is so gradually increasing the level of the increased significantly. Whilst using very street. In either instance, the structural thick units in the carriageway is common performance of the retained existing place in some parts of Europe, it is not in pavement (and all the various materials the UK where most available units tend to within this) are factored into the new design, be quite thin. standing in for the lower levels and prescribed materials that would be required c. This from of construction is relatively simple were a full new pavement constructed. and easy to reinstate since the entire Reusing parts of the existing pavement in construction can be unbound. This makes it this way helps reduce the carbon footprint of very sustainable. However, various points construction works. Consequently, whilst should be borne in mind. design standards such as this one give fairly d. Loads will not be distributed between the neat design specifications for pavements surface units – only through the subbase. (with different layers of specified This is because, - unlike say flexible precast thicknesses and materials) the reality of concrete block surfaces as section 4 of this most existing pavements in London is much appendix – there is insufficient joint sheer messier – each being composed of a jumble between the units for distribution to occur. of successive overlays of various historic materials. This will be further complicated e. The long term integrity of the pavement by reinstatement works by Statutory relies heavily on compacting and preparing Undertakers who may use different backfill the laying course and subbase well. materials when they reinstate over their Designers must also be aware of the utilities. The only way for designers to know breaking load of the surface slabs and flags. what they are dealing is to carry out intrusive investigations, and even then the f. As with any form of unbound modular construction may vary considerably within a construction, draining the laying course couple of metres. during service to prevent it becoming saturated by any water that may succeed in penetrating the surface is critical to the 2 Precast concrete and natural stone stability of the surface units and the long- flag and slab surfaced pavements term durability of the whole construction. (unbound surface) Historically in London, concerns about the stability of unbound granular laying course a. Slabs and flags can be laid unbound on a mixtures (due to surface water getting in sand or crushed rock laying course directly through the joints and washing out fines) over foundation layers if they have an has led designers to use weak mortars appropriate breaking load and levels of instead. These are also quick and easy to heavy vehicle overrun are relatively low. No install. Unfortunately they have proven too base course is required. brittle and have often broken up under b. The bending strength of units (and their occasional vehicle overrun, letting in water ultimate breaking load) is influenced by and undermining support for the surface various factors. The smaller and squarer the units nonetheless. This issue is behind many of the rocking and damaged slabs Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 39

seen in London’s streets. Consequently, slabs or flags to be bound as a laminate to national standards no longer provide for the laying course and base course beneath weak mortar to be used with this form of (using very strong mortar) to create a stiff construction. A certain degree of surface composite plate that is capable of flexing as water penetration must be accepted and a whole. This serves to spread loads over a designers must use other methods to drain very wide area – rather than just that of the laying course. This is best achieved by each individual surface slab or flag. The ensuring that both the laying course and the base course is normally a steel reinforced underlying subbase are sufficiently pavement quality concrete (PQC) slab. permeable so that moisture can infiltrate down to be dispersed within foundation b. Because it allows wider mortar filled joints to layers by sub-drains or other measures. be used, this method of design is This should not be confused with attempting sometimes favoured for visual reasons to create ‘pervious’ pavement constructions where designers consider that narrow joints as part of a surface water management (often required in the past for unbound strategy. Whereas that involves attempting construction as described in section 2 of this to maximise the penetration of surface appendix) and are inappropriate to local water into pavements, the strategy here is character. This is often the case where to continue to minimise penetration whilst natural stone slabs are used within providing for easy dispersal from the conservation areas. However, new construction of any that does occur. stabilised unbound jointing materials which permit wider joints have now been g. Despite the importance of sub-drainage and introduced and these invalidate this concern permeability to this method of construction, in many circumstances. Whereas in the past in London concerns that Statutory weak cement-sand mortar was often used, Undertakers (public utility companies) may experience has shown that these mixtures reinstate unbound subbase materials are too brittle to adequately support inadequately has tended to encourage flags/slabs outside of fully pedestrianised designers to use impermeable bound areas. Consequently, where mortar joints materials instead (e.g. wet lean concretes). are required modern standards now require British Standards permit this. However, in much stronger and more adhesive ‘high- addition to frustrating drainage of laying performance’ mortars to be used. The courses (see ‘f’), using conventional bound extent to which these will shrink whilst they subbase materials undermines the various cure (harden) is very important to success. maintenance benefits of this method of construction. Recent improvements in how c. The overall design with tightly mortar works by Statutory Undertakers are bonded laminate surface units and a stiff regulated mean that inadequate base slab results in an extremely robust reinstatement is now less of a concern than construction. Providing this is not in the past. Never the less, many existing overloaded it can have a near indeterminate pavements in the borough include concrete design life. In fact, the composite slab is so foundations. Where removing these is not stiff that the surface slabs/flags can be possible then it is likely to be necessary to made relatively thin - like a true laminate. retro fit sub-drainage measures to disperse They only really need to be thick enough to and water that has succeeded in sustain their own weight during laying. penetrating the surface course. Designers keen to conserve expensive surface course materials may therefore prefer this method. 3 Precast concrete and natural stone slab and flag surfaced pavements d. Whilst it is still possible to create surface (bound surface) water infiltration or attenuation reservoirs within the foundation layers of pavements of this type, it is not possible for surface water a. Pavements with large or very thin slab or to percolate directly through the upper layer flag surface courses rely on rigid plate construction in order to reach these. Any construction methods. This requires the conveyance to the reservoir must be via

40 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

other means (typically a conventional carrier damage beyond reuse in the event of future drainage system else via swales or other maintenance/reinstatement. green features adjacent to the pavement). Notwithstanding this, some limited g. Notwithstanding the above, in rare unintended surface water penetration will instances when underground services can always occur and, consistent with most be relocated away from the area of other forms of construction, it remains construction, or where new streets and important for the pavement courses beneath spaces can be designed to constrain to be at least lightly draining so as to allow services to other areas of the street, this this to escape. method of design (including potentially using a PQC base slab) should be strongly e. In general, despite it being extremely robust favoured owing to its robustness. If not and highly recommendable elsewhere, this disturbed then it is unlikely to require any form of construction is problematic within maintenance for its design life. the Highway. This is largely because of the PQC base slab and the almost certain 4 Precast concrete block and clay paver presence of pipes, cables etc. owned by Statutory Undertakers (public utility surfaced pavements (unbound companies) beneath the pavement. surface) i. Steel fabric included in the PQC base slab can interfere with cable detection a. Unbound surfaces with small modular tools, making it difficult to locate units involve placing closely spaced Statutory Undertakers apparatus. This precast concrete blocks or clay pavers on can pose a safety hazard for those a compacted sand or crushed rock laying carrying out construction works course. The joints between the units must ii. Manholes and other larger access be kept to controlled widths and are tightly chambers associated with services are packed with special sand or crushed rock. likely to need to be ‘isolated’ from the This allows loads to be distributed PQC base slab to prevent damage between units when traffic passes over when thermal expansion and them. contraction occurs iii. Because of the robustness of the PQC b. This form of construction has a number of base slab and high adhesive strength of advantages compared to alternatives. The the jointing and laying course mortar, most obvious is that the surface units can any maintenance and reinstatement be easily lifted and relayed if it becomes works by Statutory Undertakers will be necessary to excavate the pavement to inevitably destructive and likely involve access buried utilities (or to correct the damage beyond reuse of many of general defects). This reduces asset the expensive, tightly bonded surface management, sustainability and visual units. In addition, reinstatement is likely quality concerns associated with having to to be expensive, time consuming and source and purchase matching complex. replacement units. In addition, the individual units themselves are at less risk f. Given the above, unbound flag or slab of breaking when loaded than are larger pavements as section 2 of this appendix are flags or slabs as they have a generally significantly preferable within the comparatively high depth to plan size ratio. Highway. If bound construction is This means that they can be safely laid in unavoidable then – as a calculated risk - carriageways within certain limits. Lastly, weaker cement bound materials tend to be any maintenance to the surface that is substituted for the PQC base slab. This necessary is relatively simple and easy to simplifies design by avoiding the need for carry out and typically requires nothing joints and steel reinforcement. Providing this more than occasional resetting of any approach is not taken in a carriageway then units that have come lose or re-screed it is unlikely to result in significant failures. small areas of the underlying sand or However, surface slabs/flags must still be crushed rock laying course. This is all very tightly bonded to the base and so still risk different to modern bound/rigid methods of

Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 41

modular surface construction. where vehicle flows are considerable. This needs to be planned for. Consequently, c. On the continent, precast concrete blocks such surfaces are not something that can and clay pavers are typically quite deep, be built and left unattended until the end of being at least as thick as they are wide the planned design life - except where when used to more heavily trafficked traffic flows are modest. However, areas. Because of the depth of joints provided simple light touch intervention is between units and the overall unit size, carried out when required the intended turning moments are less in both the design life can often be considerably horizontal and vertical plane and joint exceeded. support greater. In the UK however, only relatively shallow units are generally f. Off of the Highway, unbound block and available which makes units more prone to paver surfaces are increasingly specified tipping and twisting. This can compromise to allow for the creation of pervious joints and raises several issues. Firstly, it pavement constructions (where surface means that a slightly thicker base course water percolates into the construction via is required in most instances to support the joints between surface units, to be the surface than would otherwise be the stored in reservoirs within the foundation case. Secondly, it makes correctly layers). This can be used to address flood specifying and installing jointing and laying risk and water quality issues and has the course material very important in order to considerable benefit of all- but eliminating achieve effective load transfer between the need for pavements to be set on units. Lastly, it makes the selecting the cambers or slopes (since there is no need laying pattern for the units important to to shed surface water towards gullies). ensure that these do not work loose with However, this all requires a very different trafficking and compromise the joints. form of design to be used. This carries Laying patterns that provide greater certain maintenance risks that are interlock tend not to be to visual currently not well understood or easy to preferences. overcome. In addition, whilst fine for lesser trafficked private areas (e.g. large car d. Another difference between UK and parks and quiet estate roads) there is continental practice relates to the uncertainty about the durability of the materials used for base courses. On the construction within more highly trafficked continent it is far more common for highways. Given these risks (and the unbound granular mixtures to be used in availability of various alternative ways of carriageways, whereas this is almost directing water beneath pavements for unthinkable in the UK. Using unbound storage that allow for a more conventional granular mixtures in this way requires construction – or otherwise sustainability much greater attention to both how managing it) there is much debate at mixtures are installed and to the resulting present amongst highway designers about stiffness values that are achieved (as whether pervious surface design is the those values need to be significantly best means of addressing flood risk in greater than those often achieved in the existing urban environments. UK). Attention must also be paid to the Consequently a conservative approach is permeability of the material. However, in advisable for the time being. general the continental approach is significantly cheaper and can all but g. Even with conventional design, drainage eliminate issues relating to surface water of surface water within the pavement ingress. remains very important to long term performance. The principal concern is e. As discussed above, whilst any necessary preventing saturation by surface water of maintenance of precast concrete blocks the sand or crushed rock laying course and clay pavers is quite simple and that immediately supports the surface straight forward (and therefore much lower units and washing out of the ‘fines’ within cost than for other forms of construction) it this - much the same as for unbound flag is likely to be required more regularly or slab pavements (though more so given 42 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

the greater joint area in the surface and hydraulic pressures created by regular 5 Precast concrete block, clay paver overrunning vehicles). Where saturation or natural stone sett surfaced and suspension/loss of fines from the pavements (bound surface) laying course material occurs this may undermine support for the surface units a. Like bound and rigid constructions with through various processes and ultimately slabs or flags this method of design lead to rutting of the pavement or other results in a very robust construction. It is types of failure. Irrespective of the width of often used in preference to unbound joints between units, some degree of block, paver or sett construction as it can surface water ingress is always inevitable allow cheaper surface units to be used and crusting of joints due to gradual build- (particularly where these are composed up of detritus should not be relied upon to of natural stone – e.g. cropped side seal them. Various precautions are units), wider joints or particular laying important to avoid these risks to the laying patterns. Any of these may be desirable course. Firstly, the fines content in the for visual reasons. mixture used must be reduced to a very b. Whilst it is still possible to create surface low level (typically a maximum of 1-2% water infiltration or attenuation reservoirs passing depending upon the type of within the foundation layers of this type of trafficking). This will make the mixture pavement, it is not possible for surface permeable and prevent liquefaction of the water to percolate directly through the remaining larger articles by escaping upper layer construction in order to reach fines. Next, for more challenging service this. Any conveyance to the reservoir conditions the selected aggregate for the must be via other means (typically a laying course needs to be very hard to conventional carrier drainage system prevent it fragmenting. Almost pure quartz else via swales or other green features sand (e.g. from crushed quartzite or adjacent to the pavement). natural occurring quartz arenite sand) similar to the industrial sand used in the c. Many of the same maintenance concerns glass making industry is the ideal, though that apply to bound and rigid sands from other rocks/minerals may also constructions with slabs or flags also suffice. Finally, measures must be apply to this type of pavement introduced to allow the inevitable surface construction as it requires the use of water ingress to escape rapidly from the similar high adhesive strength jointing laying course. Ideally this should be and laying course mortar (e.g. achieved by using permeable materials for destruction of surface units should it lower courses so that water can pass become necessary to excavated the through to be dispersed by pavement sub- pavement and complexity of later drains. Alternatively, insufficiently reinstatement). Given this, wherever permeable base or subbase materials can possible laying units as part of an be used whilst employing one of a number unbound surface (as sections 4 or 6 of of strategies. These include setting the this appendix) is generally preferable. impermeable base course on a slight Only where underground services can be gradient to shed water laterally through to located away from the area of sub-drains or weep holes at the edge of construction should this method of the pavement (e.g. wider joints between design be favoured. However, use may kerb units, though geotextiles will likely be still be appropriate to small features like required to retain the laying course); ramp faces and rumble strips (for which perforating the base course with closely unbound construction is not always spaced holes or; using special joint appropriate). sealants to minimise the infiltration of surface water through joints in the first place. However, these alternatives each carry various risks and are far from guaranteed success.

Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 43

6 Natural stone sett surfaced sawn it tends to produce a smooth pavements (unbound surface) ‘slippy’ face that does not interlock well with jointing aggregate. By turns, if it is a. Natural stone setts are typically more cropped by hand then it fractures too expensive than most precast concrete irregularly to achieve the consistent joint blocks or clay pavers. However, they are widths needed. Unbound granite natural often preferred by designers, both for stone sett surfaced pavements therefore visual reasons and because of their require a subtly different design and perceived greater durability. Setts can construction method. range from very small cubed units of around 70mm to all sides (often referred d. The correct method is one of the most to on the continent as ‘mosaic’) to much intensely debated issues in urban larger units of sizes exceeding 300mm in design. Whilst unbound construction with length and 150mm in width. Where they granite and other igneous stone setts is are to be laid in vehicle trafficked areas common place on the continent (and then the thickness of units generally many landscape architects query why it needs to be equal to or greater than their cannot be achieved in the UK given its width. Because of the implied depth of apparent advantages) there is excavation required and the presence of considerable nervousness about its existing below ground constraints (such appropriateness to the particular as shallow underground utilities) this conditions and constraints found here. latter requirement may sometimes make This is in part due to a lack of clarity using very large units in existing streets about certain aspects of continental impractical. design, installation and maintenance practice, reflected in the uncertainty of b. Laying natural stone setts unbound British Standard recommendations. means that they can be easily lifted and Whilst there have been numerous small replaced when maintenance is scale trials, many of these have failed necessary. This is preferable to laying badly. Given this, a cautious approach them bound in mortar since the must be taken for the time being until expensive units are then likely to be greater experience is gained. damaged beyond reuse.

c. It is often assumed that natural stone 7 Bituminous mixture surfaces setts and blocks can be laid unbound (bound surface) using the same method as used for precast concrete block and clay pavers. a. Bituminous mixtures (e.g. asphalt, black This is not entirely true. Precast concrete top, bitmac or tarmac) include a range of blocks and clay pavers can be materials that consist of a mixture of manufactured from moulds or extrusions coarse aggregate, fine aggregate, filler to have very straight sides that allow tight material and a bituminous binder. The uniform joints to be created between relative proportions between these units. These tight joints are very components will vary (as will the strength important to the success of the of the binder) – so imparting different construction. The concrete and clay used properties to the material. Some common for the units also provides good friction types are Hot Rolled Asphalt, Asphalt with jointing materials. However, whilst Concrete, Stone Mastic Asphalts and Thin rougher sedimentary stones like Surface Course Systems. The appropriate yorkstone can be cut and used in the material to use in different circumstances same way, this is much less easy to varies greatly. achieve with igneous natural stones like b. Bituminous mixtures can provide a simple, granite. Granite tends to be the stone of smooth, trafficable surface that is choice for carriageway areas (yorkstone reasonably cost effective. Assuming being too easily stained by tyres and oil suitable space and depth exists this can spills due to its absorbency). The reason be relatively easily and sustainably for this difficulty is that when granite is 44 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

rehabilitated by using ‘milling’ machines complicated and may require several that ‘plane off’, remix and relay the pavement courses to be removed. material else (in certain circumstances) by simply adding a further layer on top of the d. Given the above, the use of bituminous existing. mixture surfaced pavements in Southwark is generally confined to carriageways. c. However, bituminous mixtures have draw Only within particular SSDM/RP backs too. These include the facts that: designations where the surfacing is in i. Being darker they absorb and radiate keeping with established local character more heat than other lighter surfaces (and sufficient canopy cover exists from and so contribute significantly to trees to mitigate its heat urban heat island effects and absorbing/radiating qualities during associated impacts on health and summer months) may it be used to comfort for street users. footways. See SSDM/SER/Surfacing ii. Most mixtures (though not all) require Material palettes for further details. heating during mixing and laying and the energy used for this has a e. It is possible to make bituminous mixture sustainability impact. surface courses (and other deeper iii. As bound granular surfaces they are courses) permeable so that surface water subject to inevitable visual scaring can drain through them. However, at after reinstatement when it is present per the use of permeable necessary to dig them up for bituminous mixture surfaces is not maintenance reasons. Even where supported. Consequently whilst it is still great care is taken the variable wear possible to create surface water infiltration and composition of the mix means or attenuation reservoirs beneath such that exact visual matching of surfaces pavements, it is not possible for surface will never be possible. water to percolate directly through the iv. Lack of space on footways and the upper layer construction in order to reach presence of shallow obstructions these. Any conveyance to reservoirs must from tree roots and utilities mean that be therefore be via other means (typically ‘cold milling’ rehabilitation techniques a conventional carrier drainage system may not always be possible – even in else via swales or other green features carriageways. Where this is the case adjacent to the pavement). rehabilitation becomes much more

Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 45

Appendix B - Bituminous pavement upper layer design options for Flexible pavements

Pavement Option 1 Option 2 Option 3 course/use requirements

Surface [B-ST14] (see note 1) [B-ST14] (see note 1) [B-ST10] with deformation [B-ST10] (see note 1) [B-ST10] (see note 1) resistance as ‘8.2.6g.vi’ in the main [B-ST6] (see note 1) [B-ST6] (see note 1) design standard [B-S1H] (see note 1)

Binder [B-Bi1S] [B-Bi1S] [B-Bi1E] (see note 2)

Base [B-Ba1A] [B-Ba1H] [B-Ba1E] (see note 2)

Use Preferred option that May be used by level 1 departure Should be used to and in the Requirements should be used in if overlaying/inlaying cracked vicinity of bus cages and other most circumstances material or where a risk of surface lengths of carriageway with water ingress exists. Approving severe channelised or slow officers also have discretion to moving traffic (e.g. congested instruct use in such high streets or signalised junction circumstances. TSCS surface approaches). Approving Officers options should generally be used have discretion to instruct use unless the risk of ingress is where they consider it severe appropriate

NOTES 1) The appropriate maximum nominal aggregate size for TSCS surface course options will vary with circumstances. See ‘8.2.6g.vii’ in the main design standard for further details. 2) If an EME 2 base or binder course is used then a rigid HBM subbase is needed in all instances. See standard DS.602 for further discussion. 3) The options in this Table are not applicable for hand-laid Raised Tables, Road Humps and Speed Cushions for which see standard DS.111. 4) Unless otherwise stated, materials may be used at any of the pen grades stated within their item specifications.

Table 13. Permitted bituminous mixture upper layer material combination options for flexible pavements in NRSWA Road Category 1 C/ways.

46 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601

Pavement Option 1 Option 2 Option 3 course/use requirements

Surface [B-ST14] (see note [B-ST14] (see note 1) [B-ST10] with deformation 1) [B-ST10] (see note 1) resistance as ‘8.2.6g.vi’ in the [B-ST10] (see note 1) [B-ST6] (see note 1) main design standard [B-ST6] (see note 1) [B-S2H] (see note 1)

Binder [B-Bi2S] [B-Bi2H] [B-Bi2S] with deformation resistance as ‘8.2.5c’ in the main design standard

Base [B-Ba2A] [B-Ba2H] [B-Ba2A] with 30/45 pen binder

Use Preferred option that May be used by level 1 Should be used to and in the Requirement should be used in most departure if overlaying/inlaying vicinity of bus cages and other circumstances cracked material or where a risk lengths of carriageway with severe of surface water ingress exists. channelised or slow moving traffic Approving officers also have (e.g. congested high streets or discretion to instruct use in such signalized junction approaches). circumstances. Approving Officers have discretion TSCS surface options should to instruct use where they consider generally be used unless the it appropriate risk of ingress is severe

NOTES 1) The appropriate maximum nominal aggregate size for TSCS surface course options will vary with circumstances. See ‘8.2.6g.vii’ in the main design standard for further details. 2) The options in this Table are not applicable for hand-laid Raised Tables, Road Humps and Speed Cushions for which see standard DS.111. 3) Unless otherwise stated, materials may be used at any of the pen grades stated within their item specifications

Table 14. Permitted bituminous mixture upper layer material combination options for flexible pavements in NRSWA Road Category 2 C/ways.

Southwark Streetscape Design Manual SSDM/DSR Standard DS.601 47

Pavement Option 1 Option 2 Option 3 Options 4 course/use requirements

Surface [B-ST14] (see note 1) [B-ST14 (see note 1) [B-S3A] [B-ST10] [B-ST10] (see note 1) [B-ST10 (see note 1) [B-ST6] (see note 1) [B-ST6] (see note 1) [B-S3H]

Binder [B-Bi3S] [B-Bi3H]] [B-Bi3A] [B-Bi2S]

Base [B-Ba3C] [B-Ba3H] [B-Ba3C] [B-Ba2A]

Road Category Preferred option that May be used in Not to be used Should be used to and 3 use should be used in existing streets and in the vicinity of bus requirement most circumstances spaces by level 1 cages And other departure if lengths of carriageway overlaying/ inlaying with severe cracked material or channelized or slow where risk of surface Moving traffic (e.g. water ingress exists. congested high streets Approving officers or signalized junction also have discretion approaches. Approving to instruct use in officers have discretion such circumstances. to instruct use where TSCS surface they consider it options should appropriate generally be used unless the risk of Road Category To be used with a ingress is severe Preferred option In Not to be used 4 use [B-ST10] surface at most requirements and in the vicinity of circumstances for bus cages. Road Category 4 Approving officers also have discretion to instruct use in other circumstances here increased stress is likely

NOTES 1) The appropriate maximum nominal aggregate size for TSCS surface course options will vary with circumstances. 2) The options in this Table are not applicable for hand-laid Raised Tables, Road Humps and Speed Cushions for which see standard DS.111. 3) Unless otherwise stated, materials may be used at any of the pen grades stated within their item specifications.

Table 15. Permitted bituminous mixture upper layer material combination options for flexible pavements in NRSWA Road Category 3 and 4 C/ways

48 Southwark Streetscape Design Manual SSDM/DSR Standard DS.601