Permeable Pavement Design Guidelines. Prepared for. September 2004 P001-A1

Transcription

1 D R A F T Permeable Pavement Design Guidelines Prepared for September 2004 P001-A1

2 DRAFT Permeable Pavement Design Guidelines September 2004 Project Director: Sioban Hartwell URS New Zealand Limited Authors: Tilaka Diyagama Maunsell Limited Andre Van Huyssteen Sinclair Knight Merz Limited Hock Lee URS New Zealand Limited Helen Shaw URS New Zealand Limited Disclaimer: The information presented in this document is still under development. The authors accept no responsibility for the use of design information presented while this document is still in a draft form.

3 DEFINITIONS Basecourse Bedding sand Concrete haunching Edge Beam or Kerb External overflow Flexible Membrane Liner (FML) Geotextile separation layer 1 Geotextile separation layer 2 Internal overflow Joint sand Outlet Permeable gaps Hard, durable, aggregate base of the permeable paving. Hard, durable, permeable granular bedding material used for bedding blocks in permeable paving. The kerb around the perimeter of a permeable paving needs to be held firm using concrete haunching cast against a firm bearing surface. An edge beam or kerb around the entire perimeter of the permeable paving to provide lateral restraint for the pavement. Without a lateral restraint the blocks in a pavement would move causing structural and hydraulic failure. The kerb also performs the important function of holding the ends of geotextile layers and FML sandwiched between the kerb and blocks Permeable paving is designed for a certain infiltration rate (e.g. 2yr peak flow). For higher intensity events, surface flow over the permeable surface will occur. A catchpit (or similar device), or overland flow path needs to be located strategically to catch and transfer this excess flow to a stormwater system. Due to stability or structural reasons, some permeable paving is designed to prevent infiltration of stormwater into the ground (subgrade). This is achieved by using an impermeable FML to completely line the permeable paving on all sides in contact with the ground. Strong polyethylene (PE) and polypropylene (PP) liners can be used for FML. When using an FML a heavy duty geotextile is needed to protect the FML Permeable geotextile layer used between the bedding sand and basecourse. A geotextile layer used between the permeable paving and the subgrade. This needs to have the required permeability, in the case of permeable paving designed to infiltrate stormwater into the ground (subgrade). An internal overflow arrangement that is used to minimise any upflow of stormwater back through the permeable surface of the pavement Hard, durable, permeable granular filler used in the joints of permeable gaps An outlet pipe that drains the basecourse A paving system where a larger percentage of the surface is

4 impervious (e.g. solid block pavements with permeable gaps). Permeable paving Pervious paving Porous paving Strip drain Upflow (bleeding) Voids ratio A paving system designed to infiltrate stormwater for the purpose of quality and / or quantity management. Pervious paving is one type of permeable paving where a larger percentage of the surface is permeable (e.g. grass block pavements and aggregate pavements) Porous paving is one type of permeable paving where the entire surface of the pavement is permeable (e.g. porous concrete pavements) Strip drains are proprietary, flat, perforated drain strips that can be used to collect basecourse flow and direct to the outlet or to the internal overflow During higher intensity rainfall events, it is possible for water that flows down grade along the basecourse to resurface at low points of the permeable paving Volume of voids in soil / aggregate divided by the total volume of soil / aggregate. For permeable paving, voids ratio of the basecourse plays an important role Typical Permeable Paving Cross Section pavers Bedding layer / Jointing Sand Geotextile Basecourse / Sub Base Liner Subgrade

5 Contents 1 Introduction Purpose of these Guidelines What is permeable paving? The Design Process Regulations and Guidelines Reference Guidelines and Standards Local Government Rules and Regulations Auckland Regional Council Technical Publications Design Traffic Standards Design Objectives and Use Design Objectives Use of Permeable Paving Design Traffic Ultimate Discharge of Stormwater Site Constraints and Limitations Introduction Site Limitations Discussion Permeable Paving Types General Categories Grasspaver (Lattice)/Open Cell Paver Surfacing or interlocking blocks Porous Pavers Aggregate (unsealed) Surface Structural Design Catalogue of Designs Sub-grade Permeable Basecourse Material Specifications Paving Surface Basecourse Permeable Sub-Base Flow Attenuation Design Objectives Design Specifications Infiltration Rates Basecourse 8-1 i

6 Contents Drainage Hydraulic Design Charts Water Quality Design Objectives Design Approach Key factors Design Specifications Pavement Construction Geotextile Specification Infiltration Rate Construction Erosion and Sediment Control Discharge into Basecourse not Permitted Flexible Membrane Liners Joint Sand and Bedding Sand Basecourse Material Commission Testing Concrete Paving Blocks Maintenance and Monitoring of Permeable Paving Maintenance Monitoring Monitoring Manhole(s) Quantity Water Quality Structural Case Studies Help and Advice Section References ii

7 List of Tables, Figures & Appendices Tables Table 4-1 Design Traffic Table 5-1 Design Limitations Table 7-1: Particle Size Distribution of aggregate Figures Figure 1-1: Solid Block (permeable surface) pavers Figure 1-2: Porous block pavers Figure Principal system configurations for permeable pavements (Interpave, 2003) Figure Permeable Paving drainage options Figure Grasspaver (lattice)/open Cell Paver (STMLF, 2003) Figure Small Elemental Surfacing Blocks (Waitakere City, 2004; Pratt et al., 2002) Figure Example of an Interlocking Block Paver (Interpave, 2003) Figure 7-1: Catalogue of Designs Figure Permissible Basecourse Flow Path Length - Basecourse Depth 160mm Figure Permissible Basecourse Flow Path Length - Basecourse Depth 300mm Figure Typical Cross Section Of Permeable Pavement Figure Schematic Section through Monitoring Manhole Appendices Appendix A Appendix B Checklists Discussion and Background Information iii

8 1 Introduction Introduction SECTION Purpose of these Guidelines Permeable paving is a paving system that captures and infiltrates stormwater, and as such, it has the potential to provide a number of beneficial functions within a stormwater management system. Potential benefits are primarily associated with stormwater treatment and lesser runoff rates and volumes being generated than conventional pavement due to infiltration and storage of stormwater within the paving system. There are a number of different permeable paving systems available, and while a number of local authorities in the Auckland region have identified permeable pavement as being a measure that would be beneficial to apply, at the design and consenting stage the lack of design guidance has proved to be a limitation. These guidelines were developed to provide guidance for designers of permeable paving, and in order to assist Councils with the design and review of proposed permeable paving systems. Rodney District Council (RDC), North Shore City Council (NSCC) and Waitakere City Council (WCC) jointly commissioned these guidelines. 1.2 What is permeable paving? Permeable pavements allow for stormwater infiltration and storage during routine use by pedestrians and vehicles. There are essentially two main types of permeable paving; those which use the pavers themselves to infiltrate the stormwater (porous pavers), and those which use gaps between impermeable pavers to infiltrate stormwater (permeable surface). Figure 1-1: Solid Block (permeable surface) pavers Solid block (impermeable) pavers Jointing Sand (permeable) Basecourse / Sub Base (permeable) Subgrade (impermeable or permeable) 1-1

9 Introduction SECTION 1 Figure 1-2: Porous block pavers Porous block (permeable) pavers Jointing Sand (permeable) Basecourse / Sub Base (permeable) Subgrade (impermeable or permeable) Within these two broad categories of solid and porous blocks, there are a number of options Section 6 discusses a number of different permeable paving systems available. Both kinds of pavements have different service and maintenance requirements as well as surface designs. Failure of a permeable paving system would result in the surface becoming impermeable, and behaving like a normal paved surface. Operation and maintenance of a system needs to be considered carefully during design. 1-2

10 The Design Process SECTION 2 2 The Design Process The following diagram depicts the recommended process for designing permeable paving systems in North Shore, Waitakere and Rodney. Each step refers to the applicable section in these guidelines. Step 1 Check the local rules and regulations Section 3 Regulations and Guidelines Step 2 Determine the design objectives / requirements and use of the permeable paving Section 4 Design Objectives and Use Step 3 Review site characteristics and check constraints Section 5 Site Constraints and Limitations Step 4 Determine ultimate discharge point for stormwater Section 4 Design Objectives and Use Step 5 Decide on type of paving to use Section 6 - Permeable Paving Types Step 6 Establish structural specifications of paving based on use / location Section 7- Structural Design Step 7 Check / alter specifications to fit design perspective Section 8- Flow Attenuation Section 9 - Water Quality Step 8 Consider construction steps Section 10 - Construction Step 9 Develop a maintenance plan Section 11 - Maintenance and Monitoring of Permeable Paving 2-1

11 3 Regulatio ns a nd Guidelines Regulations and Guidelines SECTION Reference Guidelines and Standards Permeable paving may be used for a number of purposes, and it is the responsibility of the designer to develop a system that not only serves its intended purpose, but meets the rules and regulations of the appropriate government authorities. The documents referenced below will influence the design and use of permeable paving in the Auckland region Local Government Rules and Regulations Local government will need to be consulted with respect to the rules of the applicable District Plan and Roading, Engineering and Building Standards. The following documents should be consulted, however it should be noted that a number of these documents are frequently updated, and the local council should be contacted to ensure the most up to date version is consulted: North Shore City Council. (2002). North Shore City District Plan. North Shore City Council North Shore City Council (2004). Infrastructure Design Standards. North Shore City Council (2000). North Shore City Council Bylaw. North Shore City (2004). North Shore City Stormwater Policy Manual Rodney District Council (2000). Proposed District Plan. Rodney District Council (2000). Stormwater Strategy. Rodney District Council Rodney District Council (2000). Standards for Engineering Design and Construction. Rodney District Council (2000). Management of Stormwater in Countryside Living Zones (Rural and Town) A Toolbox of Methods. URS (2001). Countryside and Foothills Stormwater Management Code of Practice. Client Report prepared for Waitakere City Council Waitakere City Council Waitakere City Council (2004). Code of Practice for City Infrastructure and Land Development. Waitakere City Council (2003). Waitakere District Plan. Waitakere City Council (2002). Code of Practice for City Infrastructure and Land Development. 3-1

12 Regulations and Guidelines SECTION Auckland Regional Council Technical Publications The Auckland Regional Council (ARC) has developed a series of technical publications relating to management of stormwater in the Auckland region. Of particular relevance are: Low Impact Design Manual for the Auckland Region (Technical Publication 124); Stormwater Treatment Devices: Design Guideline Manual (Technical Publication No 10); and Guidelines for Stormwater Runoff Modelling in the Auckland Region (Technical Publication No 108). Where permeable paving is being put forward as the primary form of stormwater treatment, the design will need to comply with TP10 requirements. This is discussed further under Sections 8 and 9. Flow calculations also need to use TP108 as a basis Design Traffic Standards The structural requirements need to satisfy the Design Traffic standards. These are summarised in Section

13 4 Design Objectives and Use Design Objectives and Use SECTION Design Objectives These guidelines provide specifications for two different applications of permeable paving: 1. Stormwater treatment A permeable paving system is an infiltration device, whereby stormwater contaminants are removed via physical, chemical, and biological mechanisms. 2. Flow management Permeable paving can provide a reduction in stormwater runoff volumes and rates, via storage and infiltration of stormwater. Over-riding both of these design cases is the need for structural integrity. Designers should first identify the minimum requirements for structural integrity, then compare these to requirements for stormwater treatment or flow attenuation. 4.2 Use of Permeable Paving Due to the relatively recent requirement for permeable paving, these guidelines cover the design of these systems in a limited number of locations: Carparks; Laybys; Low-traffic use roads; Speed-dips; and Residential Driveways. 4-1

14 Design Objectives and Use SECTION Design Traffic The engineering design standards contained in the codes of practice of North Shore City Council, Waitakere District Council and Waitakere City Council were used as a basis to determine the design traffic for the selected categories of permeable pavements. Refer to Appendix C for a comparison between the different design standards. It is recommended that the pavements be designed for a 20-year design life with typical cumulative design traffic listed in Table 4-1 below. Table 4-1 Design Traffic Design Traffic Road Category/ Class Function/Description Minimum Road Reserve Width Daily Traffic Volume Cumulative Design Traffic (Typical) Residential Driveway Residential Road (Local Living) Access place or Culde-Sac with: < 50 Household-Unit Catchment (HUC) & <100m length, excluding the turning head < 150 HUC and not a public bus route 12m < 300 vpd 2,000 ESA* 17m < 1,000 vpd 10,000 ESA* Residential Road (Neighbourhood: Collector) > 150 HUC, providing access to properties 20m < 3,000 vpd ESA* * Equivalent Standard Axle - A Standard Axle with 550 kpa has been assumed for the guideline Ultimate Discharge of Stormwater From a final stormwater disposal perspective, three different configurations of these systems can be designed (Interpave, 2003) as shown in Figure 4-1. The type of system is selected based on sub-grade conditions (soil types and geotechnical considerations). For North Shore City, Waitakere City and Rodney District the underlying soils in many locations are clay and have limited infiltration. The total infiltration system will therefore only be applicable in a small number of locations around Auckland. 4-2

15 Design Objectives and Use SECTION 4 Impermeable Barrier total infiltration partial infiltration no infiltration. Figure Principal system configurations for permeable pavements (Interpave, 2003) Figure 4-2 below shows the different drainage options for permeable paving. As identified earlier for North Shore City, Waitakere City and Rodney District the subgrade is expected to be almost impermeable and the low permeable sub-grade design will apply. Figure Permeable Paving drainage options 4-3

16 5 Site Constraints and Limitations Site Constraints and Limitations SECTION Introduction The effectiveness of permeable paving systems is a function of various factors. This includes the geological make up of a region and the intended purpose, structural and hydraulic requirements, sediment retention capacities and clogging of the sediment retaining layers (Hodson and Robinson, 2000; Shackel, 1997; Shackel and Pearson, NA; Anon, 2002; Smith, 2000a; Smith, 2000b). Furthermore, factors such as economics (useful life, costs of installation and maintenance) and social considerations (aesthetic qualities and public approval) must also be recognised when proposing the implementation of such a system. The design information provided in this document has been developed to assist with both the design and review of permeable paving proposals. Permeable paving does not suit all sites and it is important that site characteristics are reviewed carefully. It is also important to define what the objectives are for using this type of system. Key considerations and design steps are outlined below, and a limitations checklist is provided in Appendix A. Key parameters to consider for permeable paving placement include slope, traffic volumes, subgrade, land use (types of contaminant), and stability. The issues to consider with each of these parameters are discussed below. 5.2 Site Limitations All paving systems designed in accordance with these guidelines should meet the limitations outlined in Table 5-1 below: Table 5-1 Design Limitations Parameter Limitation Slope Paving system slope should not exceed 1 in 20 (5%) Traffic Volume Design traffic should be determined using Table 4-1. Subgrade Site CBR should not be less than 3% Land-Use Permeable Paving should not be located downstream of high-sediment generating activities. Stability Discharge type Infiltration from the base of permeable paving should not be undertaken where soils are susceptible to instability. The no infiltration method of permeable paving is to be adopted, except in circumstances where site soils are identified as suitable for infiltration. 5-4

17 Site Constraints and Limitations SECTION Discussion Slope The use of permeable pavement is restricted to gentle slopes up to about a 1 in 20 grade (or about 3 degrees). On steeper slopes the potential for water to seep out of the pavement surface limits use. Subgrade The subgrade should be able to sustain traffic loading without excessive deformation. A minimum CBR has been selected for designs under this guideline. Land Use Permeable pavement may be considered for light vehicle loading including parking areas, driveways, residential roads, laybys and speed dips. A common cause of permeable paving failure is clogging resulting from excessive sediment discharges on to the permeable surface. For this reason, permeable paving is not suitable for treating pervious catchments where potential for sediment generation is high. This applies equally to hard surface catchments where frequent sediment tracking is expected (e.g. access roads within construction sites). In this regard construction sequence of permeable paving is important. Preferably, all pervious areas and high-sediment hard surface areas must be excluded from the catchments treated by permeable paving. Should industrial sites or redeveloped sites be covered with pervious membrane, the potential effect of spillage of non-biodegradable or slow-biodegradable chemicals should be considered. Stability Slope stability issues are exacerbated by water infiltrating and saturating the soil. In areas where there is sloping land downstream of a development, geotechnical advice is essential for the design of permeable paving. It may be necessary to use an impermeable flexible membrane liner (FML) and a protective heavy geotextile to exclude infiltrated water from the soil, or in some cases, permeable paving may not be a suitable option for sloping land. When the basecourse is tanked using an FML, a suitable sized piped outlet is necessary to drain the basecourse at the required rate. 5-5

18 6 Permeable Paving Types Permeable Paving Types SECTION General Categories Permeable paving can be separated into the following broad categories: Solid Block (impermeable block): Grass paver /open cell paver Small surfacing blocks or interlocking blocks with joints (gaps) Porous blocks Porous blocks with gaps Aggregate (unsealed pavements) can also be considered a permeable surface, however, these guidelines do not extend to the design of a gravel surface for stormwater management purposes Grasspaver (Lattice)/Open Cell Paver Open-celled pavers are made of concrete or plastic containing open cells. The cells may be filled with free-draining soil, which allows for the growth of grass, or with aggregate laid on a recommended subbase. The solid portion is intended to transmit structural loads for generally light vehicular loads. The cost are low and this kind of paver can be utilised for temporary or occasional roadways and parking areas and where the appearance of a grassed surface is seen as environmentally desirable, such as car parks and fire access routes. Examples are shown in Figure 6-1. Grass joint pavers Grasspaver (lattice) Figure Grasspaver (lattice)/open Cell Paver (STMLF, 2003) 6-1

19 Permeable Paving Types SECTION Surfacing or interlocking blocks This system consists of concrete blocks constructed with enlarged joints containing permeable joint sand (Figure 6-2). The enlarged gaps are created by spacers or pavers with side nibs on each block. These spacers or nibs provide gaps, which are filled with sharp sand/gravel. The sub-base should be suitable and should contain single size crushed rock or other open-textured support. This type of pavement needs maintenance due to clogging. The system is generally used in areas with high amount of light traffic, such as shopping centre car parks (Interpave, 2003; Pratt et al., 2002). Figure Small Elemental Surfacing Blocks (Waitakere City, 2004; Pratt et al., 2002) Interlocking pavement can be used to achieve increased stability under vehicular load. Voids can be filled with different material. Figure Example of an Interlocking Block Paver (Interpave, 2003) 6-2

20 Permeable Paving Types SECTION Porous Pavers Porous block pavers provide additional permeability through the surface of the paver itself. These are generally manufactured using no-fines concrete, creating many small, interlinked internal voids (Ghafoori and Dutta, 1995). There are structural limitations to the application of these pavers, and additionally, a large degree of maintenance may be required to maintain the permeability of the blocks. These guidelines consider porous pavers to be of equal permeability to a solid-block system Aggregate (unsealed) Surface A paving surface made up entirely of aggregate (e.g. gravel road) can also be considered a permeable paving surface. To serve as permeable paving the sub-grade will need to be designed as per the specifications detailed within this document. 6-3

21 7 Structural Design Structural Design SECTION Catalogue of Designs Recommended specifications for the main layers of the permeable paving structure are given below. These specifications are a guide only and site specific conditions must be taken into account.figure 7-1 below outlines the different cross sectional details required for permeable paving in different locations and with different traffic loadings. It should be noted that from a structural perspective, concrete segmental paving can be both porous and solid blocks. For structural design it is assumed that the resilient modulus of an 80 mm grass block is equivalent to that of an 80 mm concrete segmental paver Sub-grade It needs to be assumed that prolonged ponding of water in the subbase is likely to occur in permeable pavements resulting in softening of the subgrade for much of their service life. Hence the pavement design should be based on the saturated CBR strength for the subgrade. The subgrade strength should be determined by Scala penetrometer testing to a minimum depth of 800 mm below the final road level. The water content of the soil at time of testing to be taken into account and the penetrometer results adjusted to estimate the subgrade strength under saturated conditions. Often a geotextile separation layer at the subbase/subgrade interface is installed to mitigate the migration of fines from the underlying subgrade into the subbase layer. The Design Procedure for Geosynthetic Reinforcement using the Tension Membrane Approach, described in the NZ Supplement to Austroads Pavement Design Guide is recommended to quantify the higher level of support afforded to the subgrade by the geosynthetic. For these guidelines, the relationship E v (MPa) = 10 CBR was used to convert CBR strength of the subgrade to vertical modulus Permeable Basecourse The Concrete Masonry Association of Australia (CMAA) published the Lockpave computer program for designing segmental pavements. Typically, a resilient modulus of 2,250 MPa is recommended for permeable concrete segmental paver of 80 mm thickness. 7-4

22 Structural Design SECTION 7 Figure 7-1: Catalogue of Designs 7-5

23 Structural Design SECTION Material Specifications Paving Surface Grass Block A grass block or turf paver typically consists of an open cell concrete block with typical dimensions 600 mm x 400 mm x 80 mm thick, filled with free-draining topsoil or porous aggregate. Concrete Segmental Paving The pavers must be a minimum of 80 mm thick and the quality and construction thereof must comply with the requirements of NZS 3116: 2002, Concrete Segmental Paving, unless otherwise specified. The paver type must comply with the requirements for application 2, residential driveways, light traffic (NZS 3116, Clause 302 Paver Selection). The pavers must be laid in a herringbone pattern at 45 to traffic flow, with joint widths and jointing sand complying with the infiltration requirements of Section 6, provided that the joints should not be wider than the D 95 of the jointing sand plus 3 mm. The bedding sand must graded between 2mm to 12mm and complying with the requirements of NZS 3116: 2002, Concrete Segmental Paving, Clause Sand Properties. The jointing sand must be graded between 2mm and 5mm and complying with the requirements of NZS 3116: 2002, Concrete Segmental Paving, Clause and Basecourse a) Permeable basecourse should comply with all the requirements of TNZ M/4 AP40 (TNZ, 2003), except for the particle size distribution and requirements specified in this Project Specification. b) The particle size distribution of the aggregate shall conform with the envelope limits defined below, when the aggregate is tested according to NZS 4407, Test Wet Sieving Test: 7-6

24 Structural Design SECTION 7 Table 7-1: Particle Size Distribution of aggregate Sieve Aperture Maximum and Minimum Allowable Percentage Weight Passing c) It shall have a minimum permeability of 10-3 m/s, determined by testing in accordance with Volume 2 Section 10.6 of The Manual of Soil Laboratory Testing by KH Head on samples compacted to the specified density for the construction of the basecourse. d) Minimum porosity of 30% at the compacted density. e) Good workability without segregation. f) Pavement layer compaction of at least 95% of maximum dry density shall be achieved. Maximum density obtained by rodding and vibrating under saturated condition Permeable Sub-Base a) Consist of crushed aggregate graded between 9.5 and 65 mm. b) Comply with the crushing and weathering quality index requirements of TNZ M/4 Specification for Basecourse Aggregates. c) It shall have a minimum permeability of 10-3 m/s, determined by testing in accordance with Volume 2 Section 10.6 of The Manual of Soil Laboratory Testing by KH Head on samples compacted to the specified density for the construction of the subbase. d) Minimum porosity of 30% at the compacted density. e) Good workability without segregation. f) Pavement layer compaction of at least 93% of maximum dry density shall be achieved. Maximum density obtained by rodding and vibrating under saturated condition. 7-7

25 8 Flow Attenuation Flow Attenuation SECTION Design Objectives For these guidelines the quantity management objectives selected are typical of those required to meet ARC (2003) TP10 requirements. One or both of these criteria may apply to the use of permeable paving as a stormwater management device: Hydrological Neutrality (HN): Peak stormwater flows post development are to be less than or equal to greenfield peak flows for the range of return periods up to 10 years. Extended Detention (ED): Stormwater is retained, and released slowly to be equivalent to or better than the ED requirement of ARC TP Design Specifications Infiltration Rates The following requirements apply to a system designed for either HN or ED: The design infiltration rate of a permeable paving system shall be one tenth of the infiltration rate of a new system. The minimum infiltration design rate through the permeable paving surface should be greater than or equal to the peak flow of the rainfall event to be managed, calculated as per ARC TP Basecourse ED: The basecourse voids volume should be equal to the Water Quality Volume (WQV) calculated as per ARC TP108 and ARC TP10. ED and HN: The minimum flow velocity within the basecourse parallel to the base (horizontal or near horizontal) preferably should not exceed 0.006m/s. Flow path distance from the upstream end to the outlet should fit the corresponding curve for permissible baseflow length from Figure 8-1 and Figure Drainage The outlet should not be the only flow control point. The flow control should be achieved by the basecourse. As an additional control measure, the outlet capacity shall be set to the pre-development peak flow for a hydraulic head of 1/3 of the basecourse depth. The outlet shall be sized using an orifice formula. 8-1

26 Flow Attenuation SECTION 8 An overflow arrangement must be provided directly from the basecourse. This should be at a location and a level to allow the highest point of phreatic surface to remain within the basecourse. It is preferable to locate the outlet and overflow next to an edge of the permeable paving to minimise traffic loading. Adequate pipe cover is required to prevent pipes being crushed by external loads (as per relevant local drainage requirements). Allowance should be made for management of stormwater flow from the surface of the permeable paving where the infiltration capacity of the system is exceeded. 8.3 Hydraulic Design Charts Permissible Length The length of the flow path should be balanced between the minimum length required to achieve the required detention within the pavement, and the maximum length achievable without mounding. L H max 8-2

27 Flow Attenuation SECTION 8 Figure Permissible Basecourse Flow Path Length - Basecourse Depth 160mm Permeable Paving - Permissible Basecourse Flow Path Length - Basecourse Depth = 160mm 45 Permissible Flow Path Length (m) % 2% 3% 4% 5% Slope Flow path distance for max permeability (m) Flow path distance for min permeability (m) Figure Permissible Basecourse Flow Path Length - Basecourse Depth 300mm Permeable Paving - Permissible Basecourse Flow Path Length - Basecourse Depth = 300mm 90 Permissible Flow Path Length (m) % 2% 3% 4% 5% Slope Flow path distance for max permeability (m) Flow path distance for min permeability (m) 8-3

28 9 Water Q uality Water Quality SECTION Design Objectives For these guidelines the design criteria for stormwater treatment has been targeted at achieving: 75% removal of suspended sediment as required by TP10 (ARC, 2003) Compliance with TP10 design requirements Removal of all sediments >100Pm and allowance for the capture of fines of up to 20Pm Allow for some capture of dissolved metals 9.2 Design Approach Key factors Permeable pavements have been previously designed as an infiltration device where the pollutant removal capabilities were based on land application and treatment through soils (Debo & Reese after Schueler). Since infiltration is not applicable to a low permeability sub grade the focus of contaminant removal mechanisms is filtration and sedimentation. For filtration systems TP10 considers filtration, adsorption and absorption, and settlement as key contaminant removal mechanisms. 9.3 Design Specifications Pavement Construction Filtration is designed to capture sediments with particle size >100Pm and this shall be in the form of a sand filter layer with a geotextile placed beneath it. Settlement of fines shall be for particles of up to 20Pm, and a retention area is incorporated in the base course layer. Retention time of at least 1.5 hours shall be provided; and The base course shall have a minimum thickness of 200 mm to provide sufficient adsorption space for dissolved chemicals. For stormwater treatment the following profile is recommended. Pavers, sand bedding and the basecourse should be designed based on specifications given in Section

29 Water Quality SECTION 9 Figure Typical Cross Section Of Permeable Pavement pavers Bedding layer / Jointing Sand 50mm Non woven Geotextile Sub Base 200mm minimum Retention time 1.5 hours Liner Subgrade Geotextile Specification Geotextiles should be designed as follows: 1. AOS 100 um 2. k geotechnical k pavement 3. (k geotechnical/ t)*h*ag >+ q required 4. k geotechnical /t = permittivity 0.5 sec -1 where: AOS h Ag q required = apparent opening size = average head = effective geotextile area = flow rate Infiltration Rate The design infiltration rate of a permeable paving system shall be one tenth of the infiltration rate of a new system. Sufficient storage capacity must be provided in the basecourse voids to allow the flow control and treatment. Minimum retention time for water quality objectives is 1.5 hours where extended detention is not required as per TP10 (ARC, 2003). Refer Section 8 for criteria relating to stormwater detention. 9-2

30 10 Constructio n Construction SECTION Erosion and Sediment Control The construction sequence is paramount to the successful performance of the permeable paving. The following aspects must be considered: No sediment-laden stormwater should be allowed to enter the permeable paving area during construction, as it will clog-up the storage voids and the permeable surface. Runoff from exposed surfaces, if any, (i.e. surfaces not grassed/vegetated/paved) should not be allowed to flow across the permeable paving surface. Preferably, all work surrounding the permeable paving should be completed and all surfaces surrounding the permeable paving should be stabilised (i.e. paved or grassed or vegetated, as appropriate) prior to commencing the permeable cell construction Discharge into Basecourse not Permitted No runoff should be allowed to enter or be piped into the basecourse directly. All water must enter the basecourse through the permeable paving Flexible Membrane Liners If a Flexible Membrane Liner (FML) is required the following quality control procedures must be applied as a minimum: The FML and the protective overlay geotextile should be supplied and installed by a specialist Subcontractor competent in this type of work The base and sides of cells should be free of sharp objects and angular objects that may puncture the FML. Cell surfaces must be inspected and approved by the Specialist Subcontractor prior to installing the FML. Daily Test Welds: A test weld, 3 metres long should be made with each welding machine, and each operator, each day prior to welding commencing, and under the same conditions as exist for the FML welding. The testing should be in accordance with ASTM D4437 (ASTM, 2003). As well as on each day of welding, the testing should be repeated any time the machines are restarted after cooling or when weather conditions change. If necessary, random weld samples from the installed welded sheeting should be tested. 10-1

31 Construction SECTION Joint Sand and Bedding Sand Random samples of joint sand and bedding sand must be tested to verify compliance with the design grading Basecourse Material Random samples of basecourse material must be tested to verify compliance with the design grading, voids ratio and compacted permeability. Due to the coarse nature of the materials, permeable aggregates are prone to segregation during the transportation and construction process. Care should be taken to avoid segregation during handling of the materials. The pavement layers should be compacted in layers of uniform thickness not exceeding 150mm to ensure that the maximum density is achieved for the particular aggregate type and grading, without crushing the individual particles Commission Testing Infiltration Test: Based on: Pollution Retention Capability and Maintenance of Permeable Pavements (Dierkes et al., 2002.) At the commissioning, it is recommended that infiltration tests be carried out to verify the new infiltration rate. A suggested method is as follows: Place an open metal cylinder with a minimum diameter of 750mm on the surface of the paving. The bottom end of the cylinder must have a soft thick rubber gasket. Weigh down the cylinder to prevent movement and to achieve seal between the bottom end of the cylinder and the paved surface. Calculate the new infiltration rate as stated in the design (see example below): Example: Test cylinder diameter New infiltration rate stated in the design Rate per minute 3.14 x (0.75) 2 /4 x 1.2 x 1,000 / mm 1200mm/hr 8.84 L/minute Use a nearby hydrant or other suitable source of supply (permit required). Connect a sprinkler head and a water meter to the supply hose. 10-2

32 Construction SECTION 10 Soak the test area within the cylinder for 10 minutes to saturate the blocks. Clean and mop the surrounding area of the cylinder While discharging the hose to a suitable outlet (e.g. catchpit), adjust the discharge rate to the new infiltration rate Direct the discharge into the test cylinder and time it for 5 minutes To pass the test, there should be no standing water within the test cylinder and no visible leaks through the joints between blocks, at any time within the 5 minutes or after the test. If the test fails, reduce the rate by 20% and repeat the test 10.7 Concrete Paving Blocks The construction of the concrete segmental paving including the placing, preparation of the bedding sand and joint filling should be in accordance with NZS 3116:2002 Concrete Segmental Paving. Where appropriate, additional specific information or advice on the construction of a permeable pavement should be sought from the concrete block manufacturer. 10-3

33 11 Maintenance and Monitoring of Permeable Paving Maintenance and Monitoring of Permeable Paving SECTION Maintenance In the first 24 months after construction, arrange for the specialist contractor to carry out the maintenance work, which will include defects liability requirements in accordance with the contract, routine maintenance and mechanical suction brushing at least twice a year to maintain the infiltration capacity. Thereafter, it is recommended that mechanical suction brushing be carried out twice a year or at longer intervals depending on the permeable surface performance. Based on performance of the surface, the minimising of suction brushing whenever possible is preferable because suction may require re-sanding, thus increasing the maintenance cost. The initial permeability of newly installed paving must be 10 times or more than the permeability before the first re-sanding, in order to get a reasonable period (say 5 years) between re-sanding. Some references indicate that this factor of safety of 10 would be sufficient to cover a period of 25 years (Formpave, 2002, and ICPI, 2000), but this guideline assumes a 5-year period, which still needs to be proven for Auckland region conditions. High pressure water jetting should NOT normally be used. Wherever possible, light suction should be used. High pressure water jetting should be used only in a worst-case scenario, when it has been decided to carry out special maintenance due to poor performance of the surface. It is expected that as more and more permeable paving installations are constructed and maintained, it will help to identify optimum maintenance equipment and procedures suitable for Auckland region conditions. Of primary importance to the long term function of permeable paving is the need to keep all contributing catchment areas stabilised (i.e. paved, grassed, vegetated). Sediment loadings into the permeable area must be kept to a minimum. All maintenance inspections must include inspection for catchment stabilisation. The infiltration practice checklist of ARC TP10 recommends annual inspections for sediment accumulation. It is recommended that 3 monthly maintenance inspections be carried out in the first year, 6 monthly in the second year, and as required thereafter with a minimum of annual inspection. TP10 recommends education for reducing maintenance requirements of permeable paving practices. Users must be aware of the permeable nature of the paving surface. Signs need to be placed around the permeable area to notify all users that the surface is permeable, and that sediment tracking must be minimised. The design includes a separation geotextile to act as a filter fabric under the bedding sand layer. This also facilitates future replacement. When replacement is necessary at the end of the service life of the permeable surface, the blocks can be lifted up in individual sections, the bedding sand and the filter fabric under the sand replaced, and the blocks restored to their original places. Some blocks would also need replacement. 11-1

34 Maintenance and Monitoring of Permeable Paving SECTION Monitoring Monitoring Manhole(s) A monitoring manhole(s) could be included in the design for the purpose of quality and quantity performance monitoring. The following requirements are suggested for the monitoring manhole: It should receive total runoff from the permeable paving (i.e. basecourse and excess surface runoff). It should receive no runoff from any other source Locate the manhole in a place where there is unlikely to be backwater effects from the receiving stormwater system Minimum internal diameter 1050mm and cover 600mm clear opening Straight through pipe (i.e. no branches) with minimum straight lengths of 5 x pipe diameter immediately upstream and downstream of the manhole Using 17.5MPa concrete or pre-cast units, provide a channel in the manhole to the exact shape and slope of the pipe up to the spring line of the pipe (i.e. half circle). Using 17.5MPa concrete provide smooth vertical benching up to 100mm above pipe soffit and slope-up 1 on 10 to manhole walls. Vertical benching should NOT be higher than 100mm above the pipe soffit. Figure Schematic Section through Monitoring Manhole 11-2

35 Maintenance and Monitoring of Permeable Paving SECTION 11 Pipe and channel slope should not be steeper than 1% in the above mentioned straight sections 1m x 1m concrete pad next to the manhole, with screw capped 50mm diameter ducting from the pad to the manhole for future sampling tubes (allow only one long radius bend) Quantity (a.1) Infiltration Rate Until permeable paving practice is well established and a local database has been developed, it would be preferable to measure the infiltration rate, 3 monthly in the first year, 6 monthly in the second year and annually thereafter. One test location per every 100m 2 is suggested. (a.2) Attenuation Attenuation performance may be monitored once the aged infiltration rate stated in the design is reached. This may be carried out using continuous recording flow measurement gauges installed in monitoring manholes. It is preferable if a continuous recording rain gauge is also installed in the site, for the purpose of comparing rainfall and runoff. The period of monitoring should be selected so as to capture a wet period including a several high intensity events. A minimum of four weeks period is suggested while a longer period would be preferable Water Quality Continuous sampling of stormwater inflows and outflows could provide valuable information on performance. Allowance for sample collection sites will need to be incorporated into the design. Sample collection should be event based and will preferably target a range of rainfall events. Rainfall and flow data should be collected simultaneously. Contaminants of particular interest include: Total Suspended Solids (TSS) Zinc and copper (total and soluble) Total Petroleum Hydrocarbons (TPH) It is also recommended that a particle size analysis be undertaken of the sediment, and the chemical analysis be undertaken for a number of particle size classes. 11-3

36 Maintenance and Monitoring of Permeable Paving SECTION Structural The surface of the permeable paving shall be periodically inspected for depressions, rutting, cracked or broken blocks and loss of jointing sand. These defects are considered to be detrimental to the structural performance of the pavement or hazards to road users and should be reinstated. 11-4

37 Case Studies SECTION Case Studies A case study of a design following these guidelines is currently underway (Consultant URS, Client Waitakere City Council). Information relating to the design and cost estimates will be provided when the project is completed (2-3 months). 12-1

38 Help and Advice Section SECTION Help and Advice Section Contacts at each Council 13-1

39 Appendix A Checklists 14 References Anon (2002). Research into "Effective Life" of permeable pavement source control installations. Urban water research centre, Division of IT, Engineering and the Environment, University of South Australia: South Australia. ARC (1999). Guidelines for Stormwater Runoff Modelling in the Auckland Region. Auckland Regional Council Technical Publication No. 108 ARC (2003). Stormwater Management Devices: Design guidelines manual. Auckland Regional Council Technical Publication No 10 ARC (2000). Stormwater Low Impact Design Manual for the Auckland Region. Auckland Regional Council Technical Publication No 124 ASTM (2003). Standard Practice for Determining the Integrity of Field Seams in Joining Flexible Polymeric Sheet Geomembranes. American Standard Testing Method D Concrete Masonry Association of Australia. Lockpave Structural Design of Interlocking Concrete Segmental Pavements. Mechanistic pavement analysis software. V.15.1 March 2003 Dierkes, C., Kuhlmann, L., Kandasamy, J., Angelis, G. (2002) Pollution retention capability and maintenance of permeable pavements Formpave (2002) Stormwater Source Control System Ghafoori, N., Dutta S. (1995). Pavement Thickness Design for No-Fines Concrete Parking Lots Journal of Transportation Engineering, Vol (121), No. 6, November/December 1995, pp Head, K.H. (?). The Manual of Soil Laboratory Testing. Hodson, C. and C. Robinson (2000). The practical implications of infiltratible (Ecological) block paving. in The 6th International Conference on Concrete Block Paving Tokyo, Japan: Japan interlocking block pavement engineering association. ICPI (2000) Permeable Interlocking Concrete Pavements Interpave, The Precast Concrete Paving and Kerb Association (2003). Permeable Pavements: Guide to the Design, Construction and Maintenance of Concrete Block Permeable Pavements. Maunsell Ltd (2002/3) Permeable paving designs and specifications for Long Bay structure plan studies Maunsell Ltd (2003) Performance specifications for the design and construction of Silverfield Tank site permeable paving Meyer, P., Singhal, N. (2004) Pervious pavement: A literature review Mincad Systems Pty Ltd. (2004). CIRCLY 5 Mechanistic pavement analysis software. New Zealand Standards (1991) NZS 4407 Test 3.8.1Preferred method by wet sieving

40 Appendix A Checklists North Shore City Council (2000). Infrastructure Design Standards. Issue 7, August 2000 North Shore City Council (2002). North Shore City District Plan. Operative June Pratt, C., Wilson, S., Cooper, P. (2002). Source control using constructed pervious surfaces hydraulic structural and water quality performance issues. CIRIA Project RP 637. Rodney District Council (2000). Standards for Engineering Design and Construction. November Rodney District Council (2000). Proposed District Plan. Rodney District Council. Rodney District Council (2000). Stormwater Strategy. Rodney District Council. Rodney District Council (2000). Management of Stormwater in Countryside Living Zones (Rural and Town) A Toolbox of Methods. Shackel, B. (1997). Water Penetration and structural Evaluations of Permeable Eco-Paving. Betonwerkund Fertigteil-Technik BFT, Heft 3, Sonderdruck. Shackel, B. and A. Pearson (NA). Permeable concrete eco-paving as best management practice in Australian urban road engineering, University of New South Wales, Concrete Masonry Association of Australia. Shueler,T, The Importance of Imperviousness (1994). Watershed ProtectionTechniques (2). Smith, D. R. (2000a). North American design guidelines for permeable interlocking concrete pavements (Part 1). in The 6th International Conference on Concrete Block Paving. Tokyo, Japan: Japan Interlocking Block Pavement Engineering Association. Smith, D. R. (2000b). North American design guidelines for permeable interlocking concrete pavements (Part 2). in The 6th International Conference on Concrete Block Paving Tokyo, Japan: Japan Interlocking Block Pavement Engineering Association. Standards New Zealand (2002). Concrete Segmental Paving. NZS STMLF (Bavaria Regional Council, Germany) Bayrisches Landesministerium für Landwirtschaft und Forsten (2003): Webpage 19 th of December TNZ (2003). Specifications for Basecourse Aggregate. Transit New Zealand. TNZ M/4. URS (2001). Countryside and Foothills Stormwater Management Code of Practice. Client Report prepared for Waitakere City Council Waitakere City Council (2002). Code of Practice for City Infrastructure and Land Development. Issue 3.6, August 2002 Waitakere City Council (2003). Waitakere District Plan. Waitakere City Council (2004). Code of Practice for City Infrastructure and Land Development.