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83 Recommended Practice for Bidding Alternative Drainage Pipe Systems A P P E N D I X A INTRODUCTION The evaluation and selection of suitable and cost effective drainage pipe systems for highway projects involves consideration of a range of engineering suitability criteria, installation requirements, and construction and post-construction maintenance costs. The availability of a streamlined, rational and reliable design approach that identifies a wide range of appropriate pipe system alternatives on a consistent and unbiased basis would allow owners and agencies to take advantage of increased product competition with lower overall costs for procuring highway drainage systems. In addition, if such an alternative drainage pipe design and selection system also took account of serviceable life and durability, it would allow the appropriate pipe systems to be matched to the functional requirements of the highway, resulting in improved drainage system performance and lower long term maintenance costs. This Recommended Practice (RP) aims to achieve these objectives. By delivering a consistent and technically sound design and selection process for drainage pipe systems this RP also provides agencies the ability to systematically track bid selections and drainage pipe system inventories and performance records for use as input to asset management systems. Additionally, as agencies systematically track design evaluations and compare them over time to actual in-service performance, it will provide the opportunity to continually improve the state of knowledge regarding service life prediction and evaluation methods. This RP is intended to guide agencies and industry in implementing a performance-based process for contractor selection and delivery of drainage pipe systems on highway construction projects. The RP provides guidelines and procedures for (1) agency definition of drainage requirements and (2) contractor bidding of drainage pipe systems to meet those requirements. 1. SCOPE 1.1. This RP presents a methodology to guide transportation agencies in implementing a performance-based process for selecting alternative drainage pipe systems on highway construction projects and is intended for use by transportation agencies, design consultants, and contractors. 1.2. The RP is intended to provide a systematic, rational, comprehensive and technically sound process for the evaluation of alterative highway drainage pipe systems, which includes the pipe dimensions, material and joints, bedding, embedment and backfill. 1.3. The RP utilizes recognized methods for pipe system selection, design, and post-construction acceptance based on performance-based criteria including hydraulics, structural capacity, durability, and environmental compatibility.
84 1.4. The RP also provides guidance for post-installation inspection and agency acceptance of drainage pipe systems. 1.5. The RP is not intended to provide specific guidance for every potential design decision that may arise during a drainage project. Instead, the intent is to provide guidance and recommendations for evaluating suitable alternatives for the majority of routine highway drainage applications. 1.6. Full hydraulic design for the base case design will need to be performed by approved methods, such as HDS-5, outside the framework of the RP. 1.7. The RP is intended to be as inclusive and flexible as possible so as to address specific agency needs and requirements. Agency-specific regulatory policies and practices can be considered within the framework of this RP. 1.8. The RP indicates to the user which related design issues are not inherently addressed, so that these issues may be addressed outside of this methodology. The RP is applicable to circular, elliptical and arch-shaped culverts and storm sewers where a number of other pipe systems are readily available for selection as suitable alternatives. Box culverts, large span structures, and pressurized pipes are not specifically addressed or intended to be evaluated through the RP. 1.9. The RP is based on the research results described in the final report for NCHRP Project 10- 86, including the content of its appendices. (This final report has been published as NCHRP Report 801: Proposed Practice for Alternative Bidding of Highway Drainage Systems). The RP should be used in conjunction with the findings, test methods, and specifications described therein. 1.10. This standard may involve hazardous materials, operations, and equipment. This standard does not propose to address all safety problems associated with its usage. It is the duty and responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ LRFD Bridge Design Specifications LRFD Bridge Construction Specifications Model Drainage Manual Highway Drainage Guidelines Asset Management Data Collection Guide, Task Force 45 Report â¢ â¢ Standard Specifications for Transportation Materials and Methods of Sampling and Testing T 289, Determining pH of Soil for Use in Corrosion Testing T 288, Determining Minimum Laboratory Soil Resistivity T 291, Determining Water-Soluble Chloride Ion Content in Soil T 290, Determining Water-Soluble Sulfate Ion Content in Soil R 13, Conducting Geotechnical Subsurface Investigations
85 2.2. ASTM Standards â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ G51, Test Method for Measuring pH of Soil for Use in Corrosion Testing D1293, Test Methods for pH of Water D5464, Test Method for pH Measurement of Water of Low Conductivity D1125, Test Methods for Electrical Conductivity and Resistivity of Water D512, Test Methods for Chloride Ion In Water D516, Test Method for Sulfate Ion in Water D3858, Test Method for Open-Channel Flow Measurement of Water by Velocity-Area Method D5243, Test Method for Open-Channel Flow Measurement of Water Indirectly at Culverts D420, Standard Practice for Conducting Geotechnical Subsurface Investigations 2.3. Federal Highway Administration (FHWA) Hydraulic Design of Highway Culverts, Hydraulic Design Series Number 5 Culvert Inspection Manual, Supplement to the Bridge Inspectorâs Training Manual Federal Lands Highway, Project Development and Design Manual Durability Analysis of Aluminized Type 2 Corrugated Metal Pipe 2.4. Transportation Research Board (TRB) and National Cooperative Highway Research Program (NCHRP) NCHRP Report 801: Proposed Practice for Alternative Bidding of Drainage Systems NCHRP Synthesis of Highway Practice 254: Service Life of Drainage Pipe NCHRP Web-Only Document 190: Structural Design of Culvert Joints Report submitted to AASHTO for NCHRP Project 20-07, Task 264, Guidance for Design and Selection of Pipes 2.5. State and Other Agency Publications Florida DOT, Drainage Handbook, Optional Pipe Materials Colorado DOT, Development of New Corrosion/Abrasion Guidelines for Selection of Culvert Pipe Materials California Department of Transportation (Caltrans) Highway Design Manual Ministry of Transportation of Ontario (MTO), MTO Gravity Pipe Design Guidelines 2.6. United States Army Corps of Engineers (USACE) Technical Report GL-88-2, Life Cycle Cost for Drainage Structures 3. TERMINOLOGY 3.1. Definition of Terms Abrasion Loss of section or coating of a culvert by the mechanical action of water conveying suspended bedload of sand, gravel, and cobble-size particles at high velocities with appreciable turbulence.
86 Backfill The material used to refill a ditch or other excavation, material placed adjacent to or around a drainage structure, or the process of doing so. Bedding The soil or other material on which a pipe is supported. Chloride Concentration Chloride concentration is a measure of the number of chloride ions present. Corrosion Corrosion is the deterioration of pipe material by chemical action. Design Service Life (DSL) Design service life is the time duration during which a drainage pipe system is expected to provide the desired function with a specified level of maintenance established at the design stage. Durability Ability of pipe and fittings to remain in service during its design life without significant deterioration. Embedment Backfill materials of a pipe trench excavation that surround the pipe which includes the bedding, haunching and backfill. Estimated Material Service Life (EMSL) The number of years of service a particular material, system, or structure will provide before rehabilitation or replacement is necessary. Haunch Zone The zone of backfill on the sides of a pipe from the springline to the bottom of the pipe. Inlet Controlled A condition where the relation between headwater elevation and discharge is controlled by the upstream end of any structure through which water may flow. Outlet Controlled A condition where the relation between headwater elevation and discharge is controlled by the conduit, outlet, or downstream conditions of any structure through which water may flow. In culvert flow, outlet control exists for Flow Types II, III, IV, and VI. pH The pH value is the log of the reciprocal of the concentration of hydrogen ion in a solution. Pipe System A pipe system consists of all components of a culvert or drainage structure installation and how they interact including the following: the base pipe material; pipe joints; pipe lining or coating; bedding and backfill materials; bedding and backfill compaction; installation condition (e.g., trench or embankment); and end treatments. Resistivity Resistivity is a measure of electrical resistance, and is the inverse of conductivity. Silt/Fines Tight Joint A joint that is resistant to infiltration of particles that are smaller than particles passing the No.
87 200 sieve. Silt tight joints provide protection against infiltration of backfill material containing a high percentage of fines. Soil Tight Joint A joint that is resistant to infiltration of particles larger than those retained on the No. 200 sieve. Soil tight joints provide protection against infiltration of backfill material containing a high percentage of coarse grain soils. Sulfate Concentration Sulfate concentration is a measure of the number of sulfate ions present. Water Tight Joint A joint that provides zero leakage of water infiltration and exfiltration for a specified head or pressure application. 3.2. Abbreviations and Acronyms AASHTO: American Association of State Highway and Transportation Officials ACPA: American Concrete Pipe Association ADT: Average Daily Traffic AISI: American Iron and Steel Institute ASCE: American Society of Civil Engineers ASTM: formerly known as the American Society of Testing and Materials Caltrans: California Department of Transportation CIPP: Cured-In-Place Pipe CLSM: Controlled Low-Strength Material CMP: Corrugated Metal Pipe CSP: Corrugated Steel Pipe D: Durability DOT: Department of Transportation DSL: Design Service Life EMSL: Estimated Material Service Life F: Final FDOT: Florida Department of Transportation FHWA: Federal Highway Administration H: Hydraulic HDPE: High Density Polyethylene LRFD: Load Resistance Factor Design MTO: Ministry of Transportation Ontario NCHRP: National Cooperative Highway Research Program NCSPA: National Corrugated Steel Pipe Association NTPEP: National Technical Product Evaluation Protocol PP: Polypropylene
88 PPI: Plastic Pipe Institute PSIC: Pipe System Identification Code PVC: Polyvinyl Chloride RCP: Reinforced Concrete Pipe RCB: Reinforced Concrete Box RSC: Ring Stiffness Constant S: Structural SDR: Standard Dimension Ratio SHRP2: Second Strategic Highway Research Program SIDD: Standard Installation Direct Design SRSP: Spiral Rib Steel Pipe TRB: Transportation Research Board USACE: United States Army Corps of Engineers 4. SIGNIFICANCE AND USE 4.1. The selection and design of drainage pipe systems for use in transportation projects depends upon both economic and technical considerations. Individual agencies currently develop and maintain independent policies to guide the design, bidding, post-construction inspection, and long term asset management of highway drainage pipe systems. This RP is intended to provide a national AASHTO standard for agency implementation of drainage pipe system evaluation and alternative bidding to foster greater harmonization and standardization across AASHTO agencies. With implementation, it should serve to reduce costs through more efficient design, identification of cost effective solutions, and increased local competition between contractors and suppliers. It should also encourage the development of better pipe products and the formation of a more national marketplace for drainage system pricing as policies become more nationally standardized. 4.2. Traditionally, transportation agencies have used a âmeans and methodsâ approach for selection and specification of products such as drainage pipe systems. In this approach, the agencies specify a particular drainage pipe system during the design process and the cost of the specified system is included in the contractorsâ bids for the project. This system often restricts or impedes competition by eliminating many technically suitable alternatives. The inclusion of multiple equivalent options during the bid phase of projects has been shown to reduce costs through increased competition. 4.3. This RP presents a methodology to guide transportation agencies in implementing a performance-based process for evaluating alternative drainage pipe systems with the intent of better matching pipe system performance characteristics to application-specific design requirements, to increase competition and reduce costs while maintaining safety and performance standards. The RP contains elements to guide development of a holistic program that would allow for systematic inventory management and tracking of results that could improve service life predictions and lead to better management of highway drainage assets. 4.4. The RP applies rational performance-based criteria to the selection of pipe systems. It is not intended to be a stand-alone design document, but rather a design guidance and process framework when used in conjunction with other resources including AASHTO LRFD, FWHA Hydraulic Design procedures, and agency policies and design manuals. This methodology
89 promotes the implementation of the latest national standards and other state of the practice design evaluation methodologies with the intent of being as comprehensive as possible while also allowing the flexibility to incorporate agency-specific standards or requirements. The matrix approach developed for technical evaluations within the RP is intended to provide clarity of design decisions and to allow for data tracking and mining for future agency use or for research to improve policies and methods. 4.5. The RP methodology presents a simplified systematic process for identifying drainage pipe systems for a specific defined application based on the application of hydrological, hydraulic, structural and durability principles. However, it is expected that the RP be applied only by engineers experienced in drainage pipe design principles and that the use of the RP will not eliminate the need for the results to be reviewed and checked by a drainage design engineer. The RP incorporates a final design check step to allow for more detailed analyses, where necessary, beyond the basic evaluations and to allow for agency- or project-specific provisions to be applied. 4.6. The RP addresses the design of circular and standard elliptical and closed arch (i.e., pipe arch) drainage elements. Large and special design drainage pipe systems such as box culverts, large span open bottom arches, pressure pipes, etc. are not directly addressed or incorporated. Above all, the RP is intended as a streamlined process for the design of routine highway culvert and storm sewer systems. 4.7. The RP is not intended to provide detailed design solutions or guidance for the full range of highway drainage design issues. External references to address some of these associated issues are highlighted in the RP. 4.8. This RP is not meant to be an inflexible description of process and design evaluation requirements. Other evaluation methods and selection processes may be applied as appropriate. 5. SUMMARY OF PRACTICE 5.1. The RP is intended to be transparent with all inputs, methodologies, and evaluation results clearly defined and presented. The process recommends undertaking evaluations using each agencyâs full inventory of pipe systems, including incorporation of available variations in installation type, backfill material and degree of compaction. Pipe systems are technically evaluated as to their suitability in each of three main design functions: hydraulic, structural and durability. 5.2. The RP recommends evaluating the widest practical range of drainage pipe system options against the system performance requirements for each highway drainage application. This decreases the potential for bias in the selection of pipe system alternatives to be included in the bid documents. An inventory of available pipe systems within a jurisdiction may not currently be available and may have to be developed by the agency. 5.3. The RP should be applied to each drainage application individually, so that site-specific conditions affecting the performance and projected service life can be adequately considered. 5.4. The RP is intended to promote technical evaluation of entire pipe systems as opposed to separately evaluating pipe system components. This allows acceptable combinations of backfill material, joint type, installation criteria, pipe linings, etc. to be considered as separate alternatives. This may require agencies to develop a wider range of specifications to cover the construction aspects of these variations.
90 5.5. The RP is intended to be flexible to account for individual state policies and procedures as well as potential future changes in policy, regulation or availability of new pipe products and evaluation methods. 5.6. The RP follows a systematic five phase approach to evaluating, bidding, inspecting, and tracking alternative drainage pipe systems. The five phases (identified numerically) each consist of multiple steps (identified alphabetically) as illustrated in Figure 1: Phase 1 - Data Gathering and Project Definition Phase 2 - Technical Evaluation Phase 3 - Final Design and Policy Checks Phase 4 - Reporting Results and Incorporating Alternatives into Bid Documents Phase 5 - Construction Quality Control, Inventory Management, and Performance Feedback Figure 1 - Primary Steps in the RP 5.7. The RP promotes the implementation of a thorough and inclusive performance based evaluation process that considers all technically suitable alternatives for a given highway drainage application, leaving economic judgment on the most cost effective suitable alternative to be determined through competitive bid. 5.7.1. Successful evaluation of a large number of pipe system options, as completed during application of the RP requires a systematic process for completing and tracking the results of each evaluation phase. 5.8. To achieve the goals of systematically and clearly presenting the large number of technical and policy evaluations involved in the RP, a matrix approach has been developed to track and report the pipe system selection process. 5.8.1. The matrix approach consists of all pipe system types being compiled into rows, with circular equivalent pipe sizes listed in columns. Three individual matrices for each of the technical
91 evaluation steps: hydraulic (âHâ), structural (âSâ), and durability (âDâ) are constructed and serve as the pallet for completing the individual steps of the RP. A composite matrix with four sub- cells for each pipe system type and size combining the three technical evaluation steps with the final design and policy check (âFâ) stage is then used to create the overall RP results matrix. Schematics of the individual and overall composite results matrix are shown in Figures 2 and 3. 5.8.2. This matrix format illustrates the results from each step in the systematic process with a âgoâ or âno-goâ decision for each pipe option. Matrix cells for which that type and size of pipe are not available are left blank to indicate lack of availability as the reason for elimination of that option. 5.8.3. In addition to the systematic advantages of the matrix approach, the visual presentation of the evaluation results from adjacent sizes in adjacent columns and for similar pipe system types in adjacent rows allows for rapid visual assessment of trends in the presented results. The ability to perform a visual review of trends in the results provides a significant advantage in identifying calculation or transcription errors in the RP process and also to identify gaps or areas of improvement in technical methods and/or agency policies. Figure 2 - Individual Results Matrices for Technical Evaluations
92 Figure 3 - Overall Composite Results Matrix for RP 5.9. Note - While not required as part of implementation, the RP is intended to facilitate database tracking of an in-service drainage pipe system inventory to allow for more systematic and efficient maintenance, renewal, and replacements in line with the goals of the Second Strategic Highway Research Program (SHRP2) and other ongoing AASHTO and agency initiatives. 5.10. Note - The RP could also aid in tracking drainage pipe system failures, failure causation mechanisms, and achieved in-situ service life values across each adopting agencyâs drainage pipe system inventory. For example, if a specific culvert fails within 15 years of installation, it could be back-analyzed using the RP to confirm that that specific pipe would not have been selected for that site and application. The tracking of failures and the loss of service life mechanisms, in combination with tracking the estimated and actual material service lives will allow for research and data-mining to improve and calibrate existing culvert design methods through feedback loops within the RP. Most specifically, the still developing research topics of service life prediction and failure modes can be significantly improved through the tracking and sharing of actual drainage pipe system service life data across and within AASHTO agencies.
93 Pipe Sizeâ¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ Pipe Shape Pipe Profile Pipe Material Type Pipe Coating or Lining Condition Pipe Structural Class (presented as minimum and maximum allowable fill height) Pipe Joint Type Pipe Roughness (in terms of Manningâs n value) Pipe Abrasion Resistance (Refer to Section 8.5) Installation Type, (Embankment or Trench) Installation Class (as per AASHTO, ASTM, or agency-specific classifications defining backfill and bedding geometry, materials, and compaction requirements) 5.11. Note - The RP could also form the basis to simplify and facilitate agency tracking and integration of System Feedback based on the transparent processes included in the RP. The independent parallel assessment for each functional/technical category used in the RP allows the designer to observe why a pipe system was determined to be unsuitable. Agencies are encouraged to incorporate the results and trends in bidding and field performance from their regular agency review of technical evaluation into agency policy reviews and updates. 6. PREPARATORY AGENCY ACTIONS PRIOR TO IMPLEMENTATION OF THE RECOMMENDED PRACTICE 6.1. To optimize the benefits of implementing the RP, initial preparatory work and internal review is recommended. 6.2. Identification of Agency Goals, Requirements, Constraints and Opportunities. Prior to implementing a new or revised alternative pipe system bidding practice it is recommended that agencies identify the requirements, constraints and opportunities associated with any new or revised system, and select a system that will most effectively meet the agencyâs goals. 6.3. Approved Pipe System Inventory. In order to complete technical evaluations it is necessary to define the characteristics of each viable pipe system including the following: 6.3.1. An inventory of available pipe systems within a jurisdiction may not currently be available and may have to be developed by the agency. Comparison of the allowable pipe system inventory to other AASHTO agency inventories and the range of available pipe systems in the marketplace is recommended prior to RP implementation and at regular intervals thereafter. Consideration to piggyback approvals based on research and pilot verification efforts by other AASHTO agencies and leveraging of the NTPEP (National Technical Product Evaluation Protocol) system is recommended to expand the inventory of approved pipe systems to include the widest possible range of pipe materials and installation conditions appropriate. 6.3.2. Note - As noted above, the adopting agency needs to maintain a detailed inventory of available pipe systems approved for use on agency projects. To help promote standardization and efficiency in dealing with the large number of pipe system variations available for use in highway drainage systems, the RP recommends the development and integration of a Pipe System Identification Code (PSIC) for use in uniquely identifying each available pipe system alternative. The unique PSIC code for each available pipe system option can either be agency specific or follow from the example nomenclature presented below. The use of a PSIC to uniquely identify pipe systems is intended to allow for simpler and clearer presentation of pipe
94 systems within the RP matrix (Figures 2 and 3), on construction documents, and on as-built drawings to identify the full range of pipe system characteristics. 6.3.3. The Recommended PSIC Format = PipeSize-PipeClass_Installation is outlined in Tables 1 through 3 and the examples in Table 4. Table 1 - Pipe Identification Codes Size Equivalent Circular Size (Inches) e.g., 30 inch = 030 Shape Class Pipe Arch = a; Circular/Round = c; Horizontal Elliptical = h; Vertical Elliptical = v Profile Smooth = M Type C = C, Type D = D, Type S = S; 1 Â½â x Â¼â = 1; 2 2/3â x Â½â = 2; 3âx1â = 3; 5âx1â = 5; Spiral Rib = R Material Aluminum = AL; Aluminized Type II = AT; Ductile Iron = DI; Fiberglass = FG; Galvanized Metal = GV; Metal Reinforced HDPE = RP; HDPE = PE; Polypropylene = PP; Poly Vinyl Chloride = PV; Reinforced Concrete = RC; Steel Plate = SP; Unreinforced Concrete = UC; Vitrified Clay = VC Structural Class(1) Concrete Classes I through V = 1 through 5, Special Design = S, and Unreinforced = U Metal Wall Gage Thickness (18, 16, 14, 12, 10, 08, etc.) HDPE A through W, depending on wall profile and stiffness or dimension ratio PVC A through D, depending on wall profile and stiffness PP C, D or S, depending on wall profile FG 1 through 4, depending on stiffness Joint Type Soil Tight = S, Silt Tight = M; Water Tight = W; Riveted = R; Lock Seam = L Lining No Lining = nl Asphalt Coated = ac; Asphalt Paved Invert = ap; Asphalt Coated Smooth Lined = as; Concrete Paved = cp; Polymer Coated = pc; Polymer Coated and Paved = pp (1) Refer to Figure 6 for explanation of structural class identification codes. Table 2 - Installation Identification Codes Installation Class As per AASHTO LRFD Bridge Specs, Chapter 12 Concrete â Type I to IV (1 to 4) â¢ â¢ â¢ Metal â No variation specified in AASHTO (Use 2 as default) Thermoplastic â Sn-100 to Cl-85 Installation Type Embankment = E; Trench = T
95 Functional Classification: arterial, collector, local, etc.â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ Roadway Number Drainage System Type: Culvert or Storm Sewer Station of Culvert Inlet or Station Range for Storm Sewers Pipe System ID (as defined in Section 6.3.2 or similar) Installation Date: Month and Year Original Design Service Life in Years Current Estimated Service Life or Achieved Service Life to Failure Failure Causation Mechanism(s) Table 3 â Compiled Pipe System Identification Code (PSIC) Pipe Size D as h Pipe Material Un de r sc o re Installation Size (ID in Inches) Shape Class Profile - Material Structural Class Joint Type Lining _ Class Type ### x # / X - XX # / X / X X xx _ # / Xx-### X Three Number Code Single Letter Code Alpha- numeric Code - Two Letter Code Mixed Code One Letter Code Two Letter Code _ Mixed Code One Letter Code Table 4 - Examples of the PSIC Concept Example PSIC #1: 30 Inch Circular Smooth Walled, Concrete, Unlined, Class III, Water Tight Pipe Installed within a Class II Embankment installation Example PSIC #1: 030cM-RC3Wnl_2E Example PSIC #2: 53â x 41â (Equiv. 48â Inch) 3âx1â Pipe Arch, Aluminized Type II, 12 gauge, Lock Seam, Concrete Paved Invert, Installed within a Class II Trench installation Example PSIC #2: 048a3-AT4Lcp_2T 6.4. Service Performance Criteria. While many agencies have adopted the concept of Design Services Life (DSL) for pipe systems, there is currently no universally accepted method or guidance for establishing it. The general principle for the use of a DSL based system is that the higher the road classification and the higher the consequences from premature failure of a drainage system, then the longer the DSL should be. Typically agencies use DSL values of 25, 50, 75 and 100 years, with design lives of 75 and 100 years being reserved for high volume freeways, and 25 years being used for entrance culverts and similar pipes. 6.5. Note- While not a requirement for implementation of the RP, it may be advantageous for the adopting agency to enhance the benefits of implementation, by maintaining a detailed inventory of in-service drainage pipe systems. To help promote standardization and to allow for potential multi-agency data gathering and research, the RP can be expanded to include an inventory database which would include the following items at a minimum, noting that many agency inventories may have additional items.
96 6.5.1. Note - This inventory could also form the basis for an asset management system for drainage pipe systems, to assist with establishing long term pipe replacement and rehabilitation budgets. The tracking of original design service life, current estimated service life (from regular maintenance inspections), achieved service life to failure, and failure causation mechanisms is intended to allow for evaluation and improvement through calibration of durability prediction methods over time. 6.5.2. Note - In addition to the primary objective of providing a framework for the bidding of alternative drainage pipe systems, the RP incorporates several features that can deliver additional benefits from implementation if integrated into broader agency wide efforts to optimize design, bidding, construction, inspection, and maintenance procedures. 6.6. Note - Incorporation of Automation. The RP is suitable for application as a manual process, but the repetitive nature of completing calculations across multiple pipe system options lends itself to partial or full automation through spreadsheets, stand-alone software, or other efficiency schemes. Several agencies have incorporated partial automation into their current processes for evaluating and designing highway drainage systems, such as the examples listed in Section 2.5. It is understood and recommended that adopting agencies and/or consulting firms using the RP will look to automate the repetitive portions of the process and these upfront efforts will reduce the time required to conduct the RP. 6.6.1. Note - Achievement of automation is simplified at the agency level because many design and policy decisions, such as the approved pipe system inventory, backfill and installation requirements, headwater criteria, durability criteria, design service life, bid formats, amongst other agency-specific policies and requirements, are standardized at the agency level while they are often not standardized across AASHTO agencies. 6.6.2. Note - The widespread implementation of this RP along with other national standard design and evaluation approaches will tend to increase standardization and harmonization, which should increase competition across agency boundaries and allow for greater leveraging of economies of scale through the creation of a more national design and marketplace environment. 7. PHASE 1 â PROJECT DEFINITION 7.1. The purpose of Phase 1 is to define all of the inputs required to implement the RP. This phase is separated into four stages: Stage 1A â Roadway and Geometrical Stage 1B â Hydrology and Waterway Stage 1C â Geotechnical and Environmental Stage 1D â Inventory of Available Pipe Systems 7.2. Stage 1A - Roadway and Geometrical 7.2.1. The initial phase of use for the RP is to define the project details. The fundamental roadway and geometrical parameters are compiled so that they are available for use in the design evaluations completed in Phases 2 and 3.
97 Unique Project, Bid, or Agency-wide identifier â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ Type of installation or pipe function (culvert or storm sewer) Location Road way functional classification Design service life Culvert length Minimum fill height Maximum fill height Maximum pipe size (considering vertical and lateral conflicts) Minimum pipe size (considering maintenance, future rehabilitation, etc.) Upstream invert elevation Downstream invert elevation Design slope Skew Breaks in slope or alignment Installation condition (embankment/trench) 7.3. Stage 1B â Hydrology and Baseline Hydraulic Design 7.3.1. 7.3.2. The basic hydrologic design parameters are: Drainage area Design flow rate Design storm Check storm Allowance for future watershed changes 7.3.3. Perform hydrological analyses to define the drainage system flow requirements using procedures outlined in the most recent version of the following documents: FHWA Hydraulic Design of Highway Culverts â HD5 AASHTO Model Drainage Manual 7.4. Define the hydraulic design parameters: Allowable Headwater Criteria Minimum Allowable Flow Velocity Maximum Allowable Flow Velocity Joint Rating: Soil Tight, Silt/Fines Tight, or Water Tight End Treatments Section Variations (e.g., Bends, Junctions, Wyes, Transitions, etc.) Aquatic Organism Passage Requirements 7.2.2. The following are the recommended roadway and geometrical design parameters: The fundamental hydrologic, waterway, and hydraulic parameters are compiled in this stage for use in the design evaluations completed in Phases 2 and 3 of the RP. At least one baseline hydraulic design for the drainage application being evaluated is also required to be undertaken outside of the RP to provide a starting point for the Phase 2 and 3 design evaluations of available alternatives.
98 7.4.1. 22.214.171.124. The recommended default pipe roughness categories are: Smooth â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ (n = 0.012) Corrugated (n = 0.024) 126.96.36.199. If a more rigorous category classification scheme is desired, the following four categories are recommended: Ultra Smooth (n = 0.009) Smooth (n = 0.012) Corrugated (n = 0.024) Structural Plate (n = 0.036). 7.4.2. Perform baseline hydraulic design for each of the generic baseline pipe roughness categories through use of the FHWA HY-8 Hydraulic Analysis Program or other means. 188.8.131.52. Note - In the absence of minimum flow requirements and other special hydraulic considerations the classification of the drainage application as Inlet or Outlet controlled can be used to streamline the baseline hydraulic evaluations. Starting with analysis of the roughest category first, if the system is found to be inlet controlled, all smoother baseline categories can be set to that same size without requiring independent analysis. If an evaluation results in outlet controlled conditions, the next roughness category evaluation would be completed to determine the potentially smaller baseline pipe size requirements for that roughness condition. 7.5. Stage 1C â Environmental and Geotechnical 7.5.1. Collection of site-specific environmental and geotechnical data from the native soil, backfill, flow and groundwater is necessary to estimate the material service life of drainage pipe systems. 7.5.2. Definition of Site Environmental Parameters. Data on the soil, backfill and water should be collected in accordance with the most recent versions of the following standards: Soil pH: AASHTO T 289 or ASTM G51 Water pH: ASTM D1293 or ASTM D5464 Soil resistivity: AASHTO T 288 Water resistivity: ASTM D1125 Chloride concentration: AASHTO T 291 or ASTM D512 Sulfate concentration: AASHTO T 290 or ASTM D516 Flow rate: ASTM D3858 or ASTM D5243 184.108.40.206. 220.127.116.11. Note - Data collected at a single location at a specific time may not be representative of conditions that exist at a site over the lifetime of the drainage pipe system. To account for potential seasonal and other variations in water characteristics, collection of environmental Define the baseline pipe roughness categories to be used in evaluating hydraulic adequacy of the various pipe system options. Two default options are defined below, noting that agencies may use alternate default category names and representative minimum Manningâs n values as preferred. Relevant standardized test procedures adopted by state transportation agencies may also be used to collect site-specific environmental data. Alternatively, many agencies make use of field kits that are specifically designed for this purpose and are useful in supplementing the data from laboratory testing.
99 18.104.22.168. Note - Test values can be seasonally affected by such factors as rainfall, flooding, drought, decaying vegetation, and man-made influences (e.g., fertilizer or road salt runoff). Whenever possible, environmental tests should be taken during periods considered representative of average environmental conditions. 22.214.171.124. Note â Data collection and analysis should be performed by independent parties that do not have a financial interest in the results of the environmental testing. Specific guidelines for sampling and testing should be adopted to provide consistency between testing parties and between project sites. 7.5.3. In addition to the collection of soil and water environmental data to allow completion of the quantitative durability evaluations in Phase 2, it is strongly recommended that the in-service performance of nearby drainage systems be recorded and used to back calculate estimated environmental parameters for the observed service life conditions through reverse application of the methods discussed in Phase 2. 126.96.36.199. Based on comparison of the field measured and back-calculated environmental parameters the designer would choose the critical value in each category to bring forward through the remainder of the RP. 7.5.4. 188.8.131.52. â¢ â¢ â¢ â¢ â¢ â¢ The focus of the investigation for drainage system design should be on: Determining the ground conditions that will act in support of the drainage pipe system Determining the elevation and fluctuation of groundwater levels Determining the suitability of native materials to be used in construction Considering the compaction characteristics of construction materials Considering the potential for abrasive bedload to be generated from watershed soils Collecting samples for the testing listed in Section 7.5.2 7.5.5. One of the outputs from Stage 1C is to assign an abrasion level using the data collected in Stages 1B and 1C. 7.6. Stage 1D - Additional Considerations 7.6.1. Additional design drivers should also be considered at this time and may cause the drainage application to be designed outside of the RP, and/or for additional design constraints to be placed on the technical evaluations. Examples of such additional considerations include but are not limited to: Earthquake hazards including liquefaction, fault crossings, etc. Ecological factors upstream, downstream, or within the culvert Minimum and Maximum temperatures, and resulting extreme temperature impacts â¢ â¢ â¢ Geotechnical Information. A geotechnical investigation should be performed in accordance with AASHTO Standard Recommended Practice R13-03 âConducting Geotechnical Subsurface Investigationsâ and agency-specific guidance. It is convenient to include the geotechnical data needed for drainage system design in the scope of a pavement rehabilitation investigation. data at multiple locations and at multiple times during the year should be considered depending on the scale of the project. Changes in surrounding land use (e.g., fertilizer impacted runoff from nearby agricultural lands, roadway salting efforts in the winter, etc.) and flow characteristics should also be considered.
100 Ground freezing and other cold weather considerations High maximum temperatures can impact the material service life of thermoplastics and other pipe materials and may require special design considerations â¢ âª âª â¢ â¢ â¢ Erosion and scour potential Fire risk and consequence Roadway chemical spill risk and consequence Other geologic, environmental, or man-made conditions 7.7. Output from Phase 1 - Set the Inventory of Evaluated Pipe Systems 7.7.1. 7.7.2. 184.108.40.206. 220.127.116.11. Note â In line with standard design practice, if the Phase 1 evaluations do not identify a potential need to use non-circular shapes, it is recommended that these shapes not be evaluated to simplify and streamline the implementation of the RP. 18.104.22.168. Note - Multiple barrel drainage systems can be evaluated using the RP through analysis of an individual component with the RP process, noting that the chosen option (size and number of barrels) must meet the geometric constraints defined in Phase 1A. 8. PHASE 2 - TECHNICAL EVALUATIONS 8.1. Following the setting of design performance criteria and the baseline drainage design in Phase 1, the RP moves to Phase 2 where technical evaluations are completed across the portion of the pipe system inventory set in Phase 1D. 8.2. Technical evaluations within the RP are split into three categories, each completed independently and in parallel. Stage 2A â Hydraulic Evaluation â (âHâ) Stage 2B â Structural Evaluation â (âSâ) Stage 2C â Durability Evaluation â (âDâ) In Phase 1 the design engineer should refer to the agency inventory of available and approved pipe systems to set the listing of pipe systems to be included in the matrix and to be evaluated as part of the current application of the RP. This RP stage is included to promote recording of the inventory used in the RP for a given project or drainage application as agency inventories will likely change over time. The range of sizes evaluated in each application of the RP should be sufficient to capture all suitable alternative pipe systems, but be limited to those systems that are practical for a given drainage application. It may be beneficial to evaluate pipe systems within two sizes above the baseline designs during application of the RP so as to increase the bidding options. The evaluation of non-circular shapes (pipe arch, horizontal elliptical, vertical elliptical, etc.) is not required for many standard drainage applications. However, these alternate shapes and/or the use of multiple barrels are common practice and require evaluation when applicable. It is recommended that the potential need for non-circular shapes be identified during Phase 1 through evaluation of the baseline hydraulic design and the roadway and geometrical data, with alternate shapes included in the RP evaluations if it is determined that non-circular shapes are required.
101 8.3. Stage 2A â Hydraulic Evaluation 8.3.1. During Stage 2A the user compares each evaluated pipe systemâs hydraulic capacity to the hydraulic requirements of the drainage application. The RP recommends conducting these evaluations not through detailed hydraulic design of each pipe system, but rather through comparison of pipe size (equivalent circular diameter) and pipe roughness. 8.3.2. Note â While independent rigorous hydraulic capacity evaluation for each pipe system is not considered necessary for most applications, verification of equivalency or the adequacy of the defined pipe roughness categories to adequately achieve all hydraulic requirements can be conducted in Stage 3A for critical drainage applications if desired. 8.3.3. Minimum pipe diameters for standard roughness categories were established in Stage 1B. If the range of pipe roughness in the pipe system inventory can be adequately represented through grouping into one of the Manningâs n categories defined in Phase 1B then no further hydraulic evaluation is required and pipe systems are considered hydraulically acceptable. 8.3.4. If it is desired to hydraulically evaluate each pipe systemâs specific Manningâs n value, or to define the pipe size requirements for additional pipe roughness categories not previously set in Stage 1B, these evaluations are recommended to be performed in Stage 2A using hydraulic equivalency charts. 22.214.171.124. Starting from the baseline hydraulic designs completed in Phase 1B, the Manningâs equation may be used to determine the equivalent hydraulic capacity of different pipe materials under the drainage system flow conditions. 8.3.5. The completion of the hydraulic evaluation step results in each pipe system option being rated as either hydraulically acceptable or unacceptable. This rating is then carried forward to the reporting and presentation of the results stage. 8.3.6. The systematic matrix approach presented in Section 5 is used for tracking the results of each evaluation phase. 8.3.7. While many of these aspects are accounted for in the evaluation of the baseline hydraulic design, the following design aspects are not incorporated directly into the RP. These design considerations should either be set in Phase 1 or accounted for in the final design and policy checks completed in Phase 3: Flow Control and Measurementâ¢ Low Head Installations Siphons Aquatic Organism Passage Scour at Inlets/Outlets Sedimentation and Debris Control Multiple Barrels Perforated Pipes 8.3.8. As with the other technical evaluation steps, the results matrix presents the evaluation results from the hydraulic evaluation stage. The hydraulic matrix is denoted with âHâ identifiers within the box for each pipe system type and highlighted green in cases calculated to be suitable, or highlighted red and crossed out for pipe system options that do not meet the design criteria. â¢ â¢ â¢ â¢ â¢ â¢ â¢
102 8.4. Stage 2B â Structural Evaluation 8.4.1. Evaluate the structural capacity of each pipe system in the inventory using the most recent version of the AASHTO LRFD Bridge Design Specifications. 8.4.2. The use of previously prepared minimum and maximum fill height tables is the most practical and efficient means of performing the structural evaluations. 8.4.3. Structural capacity must be checked for each allowable pipe system combination of pipe material type, material class/thickness, bedding and backfill material, bedding and backfill compaction, and installation condition. 126.96.36.199. Note - In manual applications of the RP (without the benefit of software automation) it is recommended that users evaluate pipe system options starting with the lowest available structural class, as structural classes above the minimum approved class are typically acceptable (except in the rare case when the additional wall thickness of the higher class pipe results in a geometric conflict). 8.4.4. Structural evaluation methods (e.g., fill height tables) not in accordance with the current AASHTO LRFD Bridge Design Specifications should not be used in this stage of the RP. Such fill height tables should be applied in Phase 3 if agency policy is divergent from current AASHTO standards. Note - The use of national standards in the technical evaluation stage is one key component of the RP, in that it is intended to clearly rely on AASHTO-approved procedures. The intent of completing initial technical evaluations using the latest national standards is to maintain the integrity of the RP. Where agencies have not adopted national standards, agency-specific evaluations can be implemented as part of Phase 3. 8.4.5. Presentation of Results. As with the other technical evaluation steps, the results matrix is used to present the evaluation results from the structural evaluation stage. The structural matrix is denoted with âSâ identifiers within the box for each pipe system type and highlighted green in cases calculated to be suitable, or highlighted red and crossed out for pipe system options that do not meet the design criteria. 8.5. Stage 2C â Durability Evaluation 8.5.1. Highway drainage pipe systems deteriorate with time due to in-service loading and environmental exposure. Processes such as abrasion and corrosion can lead to impairment of structural and hydraulic performance and reduce the service life of drainage pipe systems. A key requirement of a rational process to allow bidding of alternative drainage pipe systems is an ability to predict the service life of a drainage pipe system, referred to as the Estimated Material Service Life (EMSL). Note â Different methods for estimating EMSL are available in the technical literature and there is no widespread consensus on the most accurate method for any given pipe material type. Different methods will provide different levels of accuracy depending on how similar the conditions are between the pipe systems being evaluated and the pipe systems and conditions included in the development of the method. Additional details regarding application of the recommended EMSL evaluation methods are provided in the final report for NCHRP Project 10-86 (published as NCHRP Report 801) and within the originating reference documents. 8.5.2. Highway drainage structures are designed with the goal of providing a minimum design service life (DSL). Different drainage pipe system materials respond to environmental conditions in different ways, and thus have different definitions for when the end of the service life is reached.
103 8.5.3. For a design to be technically acceptable the EMSL must be greater than or equal to the DSL. 8.5.4. Durability performance of existing drainage structures in the same watershed or under similar environmental conditions may also be used as a guide to anticipated durability performance. An inspection program and data management system would facilitate the use of in-service durability performance results in the durability evaluation of new systems. Such comparative evaluations are to be considered a complementary approach, and should be used in conjunction with the quantitative methods described in this section. 8.5.5. Durability evaluation in the RP is performed in the sequence shown in Figure 4: Figure 4 - Durability Evaluation Procedure 8.5.6. Step 1a: Use Table 5 to determine what limitations, if any, on pipe material selection are a result of the abrasion level determination made in Phase 1. 188.8.131.52. Abrasion potential is a function of several factors, including pipe material, frequency and velocity of flow in the pipe and composition of the bedload. 184.108.40.206. The most comprehensive abrasion evaluation methodology is the method developed by Caltrans (White and Hurd 2011). Caltrans defines six levels of abrasion for preliminary estimation of abrasion potential based on flow velocities and bedload characteristics. Note - Only some of the more relevant factors are considered in Table 5 and additional factors may need to be considered when assessing abrasion potential. Note â It is noted that the Caltrans abrasion evaluation methodology was based on data from a specific site and Caltrans specifications, and the use of this methodology by other agencies in other conditions may require agency- or site-specific correlation. 220.127.116.11. Table 5 provides guidance on how the six Caltrans abrasion levels are related to pipe material selection: Table 5 - Recommended Abrasion Guidance Level Pipe Material Guidance 1 No restrictions on material types due to abrasion. 2 Generally, no abrasive resistant protective coatings needed for steel pipe. Polymeric, polymerized asphalt or bituminous coating or an additional gauge thickness of metal pipe may be specified if existing pipes in the same vicinity have demonstrated susceptibility to abrasion and thickness for structural requirements is inadequate for abrasion potential. 3 Steel pipe may need an abrasive resistant protective coating or additional gauge thickness if existing pipes in the same vicinity have demonstrated susceptibility to abrasion and thickness for structural requirements is inadequate for abrasion potential. Aluminum pipe may require additional gauge thickness for abrasion if thickness for structural requirements is inadequate for abrasion potential.
104 Level Pipe Material Guidance Aluminized steel (Type 2) not recommended without invert protection or increased gauge thickness (equivalent to galv. steel) where pH < 6.5 and resistivity < 20,000. 4 Steel pipe will typically need an abrasive resistant protective coating or may need additional gauge thickness if thickness for structural requirements is inadequate for abrasion potential. Aluminum pipe not recommended. Aluminized steel (Type 2) not recommended without invert protection or increased gauge thickness (wear rate equivalent to galv. steel) where pH < 6.5 and resistivity < 20,000 if thickness for structural requirements is inadequate for abrasion potential. Increase concrete cover over reinforcing steel for RCB (invert only). RCP generally not recommended. Corrugated HDPE (Type S) limited to > 48" min. diameter. Corrugated HDPE Type C not recommended. Corrugated PVC limited to > 18" min. diameter. 5 Aluminum pipe not recommended. Aluminized steel (Type 2) not recommended without invert protection or increased gauge thickness (wear rate equivalent to galv. steel) where pH < 6.5 and resistivity < 20,000 if thickness for structural requirements is inadequate for abrasion potential. Closed profile and SDR 35 PVC liners are allowed but not recommended for upper range of stone sizes in bedload if freezing conditions are often encountered, otherwise allowed for stone sizes up to 3 in. Most abrasive resistant coatings are not recommended for steel pipe. A concrete invert lining or additional gauge thickness is recommended if thickness for structural requirements is inadequate for abrasion potential. See lining alternatives below. Increase concrete cover over reinforcing steel for RCB (invert only). RCP generally not recommended. 6 Aluminum pipe not recommended. Aluminized steel (Type 2) not recommended without invert protection or increased gauge thickness (wear rate equivalent to galv. steel) where pH < 5.5 and resistivity < 20,000. None of the abrasive resistant protective coatings are recommended for protecting steel pipe. A concrete invert lining and additional gauge thickness is recommended. See lining alternatives below. Corrugated HDPE not recommended. Corrugated and closed profile PVC pipe not recommended. RCP not recommended. Increase concrete cover over reinforcing steel recommended for RCB (invert only) for velocities up to 15 ft/s. RCB not recommended for bedload stone sizes > 3 in. and velocities greater than 15 ft/s unless concrete lining with larger, harder aggregate is placed (see lining alternatives below). SDR 35 PVC liners (> 27 in.) allowed but not recommended for upper range of stone sizes in bedload if freezing conditions are often encountered, otherwise allowed for stone sizes up to 3 in. Source: Caltrans Highway Design Manual, Table 855.2A 8.5.7. Step 1b: Apply the appropriate service life prediction model for the specific pipe material type. While this topic is the subject of on-going research and refinement, the RP relies on a range of prediction models that are currently in use, with the recognition that these will be improved over time as more agencies adopt alternative drainage pipe bidding systems and additional applied research is undertaken. Due to the complexity of different pipe materialsâ performance and associated deterioration mechanisms, not all current prediction models have the same degree of reliability and so caution must be exercised in their application.
105 8.5.8. Concrete Pipe. Table 6 lists methods that can be used to determine EMSL values for reinforced concrete pipes. The EMSL values obtained using these different methods can vary widely so the RP selects the lowest EMSL value from the methods used. The limitations and range of parameters for which each method is applicable are described in detail in the NCHRP Project 10-86 final report (published as NCHRP Report 801) and are summarized in the Table 6 below: Table 6 â Methods for Determining EMSLs for Reinforced Concrete Pipe Durability Method Reference Notes Ohio DOT Model Potter, 1988 Based on large data set over wide range of pH and size values. Includes an abrasive component. Hurd Model Potter, 1988 Method developed for large diameter pipes in acidic environments. Hadipriono Model Potter, 1988 Method includes wide pH range. Florida DOT Model Florida DOT, Optional Pipe Materials Handbook, 2012 Considers corrosion to be the only mechanism of degradation. Comparison with Actual Service Life of Nearby Installations Completed qualitatively or quantitatively through back calculation of environmental conditions as described in Section 7.5.3. 18.104.22.168. Plain Galvanized Steel Pipe. A number of methods are available for estimating the EMSL of galvanized steel pipe. The California Method is the most widely accepted and is recommended for use if no state- or location-specific research is available that indicates another method is more suitable. The other methods are modifications of the original California Method. Table 7 lists the methods that can be used to determine EMSL values for plain galvanized steel pipes: Table 7 - Methods for Determining EMSLs for Plain Galvanized Steel Pipe Durability Method Reference Notes California Method California Test 643, Method for Estimating the Service Life of Steel Culverts, 1999 Includes combined effects of corrosion and abrasion. Based on soil/water pH and resistivity. Service life of pipe considered to be until time of first perforation. American Iron and Steel Institute (AISI) Method Handbook of Steel Drainage and Highway Construction Products, AISI, 1994 Modification of California Method. Service life of pipe considered to be until 25% thickness loss in the invert. Federal Lands Highway Method Federal Lands Highway, Project Development and Design Manual, 2008 Modification of California Method. Increase the EMSL by 25% after first perforation. Colorado DOT Method CDOT-2009-11, Development of New Corrosion/Abrasion Guidelines for Selection of Culvert Pipe Materials, 2009 Calibration of California Method to state- specific conditions with a limited data set. Florida DOT Method Florida DOT Optional Pipe Materials Handbook, 2012 Modification of California Method to include a minimum steel thickness of 16 gage. Comparison with Actual Service Life of Nearby Installations Completed qualitatively or quantitatively through back calculation of environmental conditions as described in Section 7.5.3.
106 22.214.171.124. Aluminized Type 2 Steel Pipe. Table 8 lists the methods that can be used to determine EMSL values for aluminized Type 2 steel pipes: Table 8 - Methods for Determining EMSLs for Aluminized Type 2 Steel Pipe Durability Method Reference Notes Florida DOT Method Florida DOT Optional Pipe Materials Handbook, 2012 Based on anticipated soil/water pH and resistivity. Comparison with Actual Service Life of Nearby Installations Completed qualitatively or quantitatively through back calculation of environmental conditions as described in Section 7.5.3. 126.96.36.199. Aluminum Pipe. Table 9 lists the methods that can be used to determine EMSL values for aluminum pipes: Table 9 - Methods for Determining EMSLs for Aluminum Pipe Durability Method Reference Notes Florida DOT Method Florida DOT Optional Pipe Materials Handbook, 2012 Based on estimated corrosion rates due to pH and resistivity. Comparison with Actual Service Life of Nearby Installations Completed qualitatively or quantitatively through back calculation of environmental conditions as described in Section 7.5.3. 8.5.9. Thermoplastic Pipe 188.8.131.52. The most commonly used thermoplastics in drainage pipe manufacture are polyvinyl chloride (PVC) and high density polyethylene (HDPE). These materials are largely resistant to the chemical and corrosive elements typically found in soils and flow and ground water. 184.108.40.206. Empirical data regarding the durability of thermoplastic pipes is limited when compared to the data available for pipe material types that have longer histories of service. 220.127.116.11. 18.104.22.168. The long term performance of thermoplastic pipes is highly dependent on the quality of the installation. Estimated service lives assume that pipes are installed in compliance with specifications and that such compliance is confirmed by post-installation inspection. 22.214.171.124. Agencies typically assign an estimated service life of between 50 and 100 years for thermoplastic pipes manufactured in accordance with the relevant AASHTO standards and installed in accordance with relevant specifications. 8.5.10. Ductile Iron Pipeâ¢ â¢ â¢ â¢ â¢ Fiberglass Pipe Metal reinforced HDPE pipe Polypropylene Pipe Vitrified Clay Pipe Slow crack growth and oxidative/chemical failure have been identified as the primary long term failure mechanisms for corrugated HDPE pipes, but no methods based on service histories have yet been developed for serviceable life predictions for these materials. Other pipe material types in current use by agencies or recently incorporated into the AASHTO LRFD Bridge Design Specifications in the 2013 revisions are the following:
107 126.96.36.199. The EMSL values for the materials listed in 8.5.10 can be established by past performance history or by application of the above listed methods for pipes with equivalent component materials. In the absence of reliable prediction models, it would be prudent to assign conservative EMSL values, in consultation with the pipe suppliers, until further research and documented case studies are available or until predictive methods become available and widely accepted. 8.5.11. Step 2 â Incorporation of Add-On Service Life Values 188.8.131.52. Coatings and/or invert protection are often applied to culvert pipes (predominantly to metal pipes) to increase their service life. Many different coatings exist, the main types of which are listed as follows: â¢ â¢ â¢ â¢ â¢ â¢ Asphaltic/Bituminous Fiber-bonded bituminous Asphaltic mastic Polymerized asphalt Polymeric sheet Concrete 184.108.40.206. Guidance on the additional service life due to the application of coatings on corrugated steel pipes can be found in the most recent version of the NCSPA Pipe Selection Guide. 8.5.12. Step 3: Selection of EMSL Values for Use in design Evaluations. Where more than one method of estimated EMSL is used, to allow for automation in the process, the RP is to select the lowest of the EMSL values for use in design. Further information and commentary on the available methods is provided in the final report for NCHRP Project 10-86 (published as NCHRP Report 801). 8.5.13. Step 4: The EMSL design value obtained from the previous step is then compared with the DSL. If the EMSL is greater than the DSL, then the pipe option is determined to be acceptable from a durability standpoint. If the EMSL is less than the DSL, the pipe option does not meet the durability evaluation criteria and is eliminated. 220.127.116.11. Failure of individual pipe systems to meet durability requirements will not disqualify entire pipe classifications, as other similar pipe system options that provide higher EMSL values based on increased wall thickness, additional/different coating, improved concrete mix design, or other factors will be independently assessed against the DSL. 8.5.14. Presentation of Results. As with the other technical evaluation steps, the use of a results matrix is used to present the evaluation results from the durability technical evaluation step. The durability matrix is denoted with âDâ identifiers within the box for each pipe system type and highlighted green in cases calculated to be suitable, or highlighted red and crossed out for pipe system options that do not meet the design criteria. 9. PHASE 3 â FINAL CHECK AND POLICY APPLICATION 9.1. Final Design Checks 9.1.1. Phase 3 of the RP is to perform final design checks on the output from Phase 2, and to compare the results of the RP against existing agency policies. It is anticipated that only pipe system options meeting the requirements of all three technical evaluation stages will be carried forward into Phase 3 for completion of final design and policy checks.
108 9.1.2. â¢ â¢ â¢ Output from Phase 2 should be reviewed by the engineer to Identify possible errors and inconsistencies. Develop alternative designs that are outside the scope of the standard RP (e.g., multiple barrels, aquatic organism passage, etc.). If desired, hydraulic design checks can be considered during this final check phase if generalized Manningâs n equivalency charts or other generalizations were applied for efficiency in the initial technical evaluations. 9.1.3. The engineer should record why any options considered technically valid through the technical evaluations are not being forwarded into Phase 4. 9.1.4. The engineer should record why any options not proposed by the RP are being added for inclusion in Phase 4. 9.2. Agency Policy Checks 9.2.1. The engineer should compare the output from Phase 2 and any adjustments made during final design checks to the drainage pipe system options allowed by the agency for the given application. Policy may dictate or restrict pipe size, pipe class, pipe material, backfill type, minimum or maximum fill height, etc. Those systems evaluated to meet the technical design criteria but not meet policy guidelines will be eliminated from further consideration in this phase. If AASHTO or FHWA standards have not been implemented as agency policy for hydraulic, structural, and/or durability evaluations, the previous evaluations should be checked against current agency policy in this stage. The intent of separating agency-specific policy evaluations from the initial technical evaluations is to promote greater standardization and adoption of national standards, and/or to identify areas for refinement of national standards to meet the range of needs expressed by all AASHTO agencies. Note - If agency policy is more restrictive without technical basis, the RP provides the rationale to extend pipe material alternatives beyond the agency policy to explore the possibility of expanding competition, even on a trial basis. 9.2.2. The reason for elimination of a pipe drainage system in the final policy check phase should be recorded to provide full transparency in the design process. It is recommended that adopting agencies regularly review the list of final check eliminations to allow for evaluation and optimization of agency policies. 9.2.3. Presentation of Results. As with the technical evaluation steps, a results matrix is used to present the evaluation results from the final design and policy check stage. The final check matrix is denoted with âFâ identifiers within the box for each pipe system type and highlighted green in cases calculated to be suitable for inclusion in bid documents, or highlighted red and crossed out for pipe system options that do not meet all of the design and policy criteria. 10. PHASE 4A - SUMMARY AND REPORTING OF EVALUATION RESULTS 10.1. One of the defining principles of the RP is to promote transparency in the design and selection of drainage pipe systems. Transparency in the process is achieved by presentation of technical and policy evaluations in a systematic and clear manner across the full range of available pipe systems. 10.2. The output from the evaluations performed as part of the RP consists of a large amount of data and the summary and reporting of this information is best managed through a systematic
109 11. PHASES 4B and 4C - INCORPORATION OF ALTERNATIVES INTO BID DOCUMENTS 11.1. Each agency typically has a detailed and multi-faceted system for bidding highway projects that involves cooperation and coordination amongst multiple agency departments and often coordination with multiple national review and funding agencies. As such, the RP is intended to maintain flexibility for each adopting agency to develop the optimum manner for integration of results from the RP into bid and tender documents. 11.2. The result of the RP is a complete list of technically acceptable pipe system alternatives for a specific drainage application. This information is summarized into a concise alphanumeric code format suitable for use by designers, consultants, estimators, contractors, pipe suppliers, and project managers. This code is termed the tender code. 11.3. The tender code is divided into three main parts; a minimum pipe diameter for smooth pipe (generic Manningâs n of 0.012), a minimum pipe diameter for corrugated pipe (generic Manningâs n of 0.024), and a material code. The use of these generic Manningâs n numbers is recommended; however, other Manningâs n values could also be used. An example tender code is shown in Figure 5: Figure 5 - Format of Tender Code process. The pipe system evaluation results are proposed to be presented via a graphically coded matrix to allow the design engineer, technical reviewers, and other users of the RP (bidders, contract managers, estimators, agency engineers, construction inspectors, etc.) to conduct a visual review of the results. 10.2.1. Transparency and data organization are achieved in the RP through the use of the results matrix presentation which provides a clear and systematic process for recording the adequacy of each pipe system considered versus the various technical and policy criteria. The matrix approach provides a means to conduct a rapid evaluation and check of results through visual recognition and review of patterns within the matrix results. Adjacent rows contain similar pipe systems, and adjacent columns contain similar sizes such that continuous zones of pass and fail for the various technical and final criteria should be apparent in the final results matrices. 10.2.2. The final results from the application of the RP can be converted into a streamlined tender code for bidding purposes, as detailed in Section 11. 10.3. In addition to the results matrices which depict the end result of the three technical evaluations and overall final and policy evaluation, it is important that calculations and other back-up design and decision information relied on are recorded and stored for future reference in line with other document control standards for engineering designs. The RP does not specifically recommend the level or manner in which back-up information is stored, but rather recommends storage and record keeping in line with existing agency standards and protocols. 10.3.1. The main purpose of providing good documentation is to define the design procedure that was used and to show how the final design and decisions were determined. Documentation should be viewed as the record of reasonable and prudent design analysis based on the best available proven technology.
110 11.3.1. Diameter for Baseline Smooth Pipe The first element of the code is a three digit number specifying the minimum equivalent circular diameter for the baseline smooth circular pipe case using a Manningâs n of 0.012. 11.3.2. Diameter for Baseline Corrugated Pipe The second element of the code is a three digit number specifying the minimum equivalent circular diameter for the baseline corrugated circular pipe case using a Manningâs n of 0.024. 11.3.3. Material Code The material code is a nine digit code that specifies what materials are allowed. Each digit position represents a different pipe material. The value in each position specifies a particular class of pipe, wall thickness, or stiffness rating. Figure 6 shows all the options for the material code portion of the tender code. Figure 6 â Material Code Summary 11.4. The material code is interpreted in the following way: 11.4.1. A zero in any position indicates that a particular pipe material is not technically suitable or allowed across all pipe system combinations evaluated for that pipe material type. 11.4.2. An âXâ in any position indicates that that pipe material type was not evaluated during the performance of the RP. 11.4.3. The minimum class technically suitable across the range of installation conditions is always specified, with higher classes being allowed. For example, if a Class II concrete pipe is specified as the minimum, a Class III pipe would also be deemed acceptable. 11.4.4. In order to streamline the tender code into a manageable length, only the minimum pipe class is listed for each pipe material type. Because of this presentational efficiency, bidders will need to confirm the installation requirements to use the minimum listed pipe class, and may want to bid the system with a higher class pipe that may have less stringent installation requirements.
111 11.4.5. The 1st digit represents concrete pipe. Five classes of reinforced concrete pipe can be specified with the numbers 1 through 5. Unreinforced concrete can be specified using the letter âUâ and the need for a special design is indicated with the letter âS.â 11.4.6. The 2nd digit represents HDPE pipe. Three different wall profiles are allowed: profile, corrugated, and solid wall. Profile wall pipe is specified using one of six ring stiffness constants (RSC). Corrugated wall pipe is specified using one of three profile shapes, defined in AASHTO M294 as Type C, Type D, and Type S. Solid wall pipe is specified using one of twelve dimension ratios (DR). A minimum DR is specified. A letter is used to represent each pipe option as shown in Figure 6. For example, a âDâ would indicate that a profile wall pipe with a minimum RSC of 160 was being specified. A âWâ indicates that steel reinforced polyethylene is being specified. Note that the letter âOâ is not included in the code so as not to be confused with the number zero. Note - Three different systems are used for specifying the dimensions of solid wall HDPE pipe. Any of these systems can be used with this code system. 11.4.7. The 3rd digit represents PVC pipe. Profile wall pipe can be specified using the letter âAâ and solid wall pipe can be specified using the letters âBâ through âDâ corresponding to three different pipe stiffness classes. 11.4.8. The 4th digit represents polypropylene (PP) pipe. This pipe is specified using one of three profile shapes, defined in AASHTO MP-21 as Type C, Type D, and Type S. Note â Polypropylene pipe is currently not listed as an available pipe type in the AASHTO LRFD Bridge Design Specifications. 11.4.9. The 5th digit represents glass fiber reinforced pipe and can be specified in one of four pipe stiffness classes; 9, 18, 36, and 72 psi. 18.104.22.168. The 6th, 7th, 8th, and 9th digits represent galvanized steel, polymer laminated steel, aluminized Type 2 steel, and aluminum pipe, respectively. Each of these material options is specified by the minimum gage thickness of the pipe wall. 11.4.10. It is noted that in order to provide a code of realistic length for incorporation and use in bid documents some details regarding the suitability of particular pipe system options such as installation class, installation type, pipe lining, pipe roughness values other than baseline smooth and corrugated, etc. are not uniquely identified in the code. Bidders will be required to refer to the final results matrix (or conduct independent evaluations) to determine which combinations of those factors are suitable for the given performance criteria. 11.4.11. Note - A review of existing alternative and optional bidding approaches is provided in the final report for NCHRP Project 10-86 (published as NCHRP Report 801), and agencies looking to develop a new system different from that described here are referred to that review for a listing of bid approaches that may be useful in helping to guide the development of new agency protocols. 11.4.12. Note - If bidders wish to use larger pipe systems than the minimum specified in the tender documents, it is recommended that a submittal process be used to evaluate these cases. 11.5. Tracking of Bid Results. The RP strongly recommends that agencies record and database bid results such that regular and systematic evaluations of bid results can be made that allow for evaluation of the impact of RP implementation, and also to provide insight into bid trends to direct and guide policy updates as appropriate.
112 Phase 5 of the RP describes the recommended steps for overall quality control, inspection and tracking. The five main steps in this phase are described in separate sections below. 12.1. Material Quality Control 12.1.1. All material used for construction should be checked for conformance with the relevant AASHTO standards 12.1.2. Qualification of manufacturer and manufacturing facility should be performed, together with review of certificates 12.1.3. Inspection of deliveries, which may include inspection of identification markings, date of manufacture, shipping papers, diameter, net length, evidence of poor workmanship, damage during shipping or handling, and measurement of surface cracks 12.1.4. Taking samples of pipe for additional testing 12.2. Construction Quality Control 12.2.1. All construction should be performed in accordance with AASHTO standards, in particular the AASHTO LRFD Bridge Construction Specifications. Foundation materialâ¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ â¢ Trench geometry and dimensions Groundwater conditions Bedding material Line and grade Assembly techniques Structure backfill and compaction methods Joint assembly and materials Pipe deflection (during construction) Damage to pipe coatings Head walls and end treatments 12.2.2. Inspection of the pipe system materials and workmanship during construction allows corrections to be made in assembly and backfill practices before construction is complete, and is of particular importance for deeply buried and high traffic installations. The timing and frequency of such inspections should depend on the significance of the structure and depth of fill. In general, inspections should be conducted when materials arrive at the job site, during pipe installation, during backfilling, and prior to construction of final finishes. Inspections during construction may include examination of the following: 12. DRAINAGE PIPE SYSTEM INSPECTION One of the main objectives of the RP is to encourage highway agencies to allow contractors to bid on a wider range of alternative pipe products and systems. Without an associated appropriate and adequate post-installation inspection protocol, the risk of premature failure of pipe systems will increase. In this context, post-installation inspection is not an optional extra for the RP and must be seen as an essential component of implementation. All the pipe system evaluation components within the RP are based on the assumption that the pipe system has been installed in compliance with agency specifications.
113 12.3. Post-Installation Inspection and Approval 12.3.1. Different pipe materials should be subjected to different post-installation inspection and approval procedures due to the inherent differences in the modes of material behavior. Pipe materials are recommended to be inspected in accordance with the appropriate chapter of the AASHTO LRFD Bridge Construction Specifications: Metal Pipe â¢ â¢ â¢ â¢ â¢ â¢ â Chapter 26 Concrete Pipe â Chapter 27 Thermoplastic Pipe â Chapter 30 12.4. Long Term Inspection and Maintenance 12.4.1. Inspection of drainage pipe systems should be performed in accordance with the FHWA Culvert Inspection Manual (1986). 12.4.2. Note - Two ongoing projects: NCHRP Project 14-19, Culvert Rehabilitation to Maximize Service Life While Minimizing Direct Costs and Traffic Disruption, and NCHRP Project 14-26, Culvert and Storm Drain System Inspection Manual, will provide updated summaries of culvert inspection techniques. 12.5. Tracking of Actual Performance 12.5.1. Collection of performance data will assist designers, researchers, and policy makers to refine durability evaluation models and pipe selection criteria. Collection of this data should be performed using guidance from the Asset Management Data Collection Guide (2006). 12.5.2. At a minimum, the following information on each culvert should be recorded during each major inspection: Environmental parameters of surface water flow in the system Condition assessment Deflection (for flexible pipe) or joint (for rigid pipe) inspection 13. PRECISION AND BIAS 13.1. The intent of the RP is to eliminate potential biases in the selection of pipe system alternatives approved for bidding through implementation of a systematic, thorough, and transparent evaluation and selection process. 13.2. This standard provides qualitative data only; hence, precision and bias are not specifically applicable. 14. KEYWORDS 14.1. Culvert; highway drainage; Manningâs n; corrugated metal pipe; galvanized steel pipe; aluminized Type 2 steel pipe; aluminum pipe; reinforced concrete pipe; concrete pipe; thermoplastic pipe; HDPE pipe; PVC pipe; polypropylene pipe; backfill; bedding; embedment; durability; culvert joint; storm drain; alternative bidding.
114 15. REFERENCE MATERIALS There is a vast and evolving literature on highway drainage pipe systems, and the following list is a sample of the technical literature on the topic. AASHTO LRFD Bridge Construction Specifications. American Association of State Highway and Transportation Officials, Washington DC, 2011. AASHTO Asset Management Data Collection Guide, Task Force 45 Report. American Association of State Highway and Transportation Officials, Washington, DC, 2006. AASHTO Highway Drainage Guidelines. American Association of State Highway and Transportation Officials, Washington, DC, 2007. AASHTO LRFD Bridge Design Specifications. American Association of State Highway and Transportation Officials, Washington, DC, 2013. AASHTO Model Drainage Manual. American Association of State Highway and Transportation Officials, Washington, DC, 2005. American Iron and Steel Institute (AISI). Handbook of Steel Drainage and Highway Construction Products, Fifth Ed., Washington, DC, 1994. California Department of Transportation (Caltrans). Highway Design Manual. Sacramento, CA, 2012. FHWA. Culvert Inspection Manual, Supplement to the Bridge Inspectorâs Training Manual. FHWA-IP-86-2, U.S. Department of Transportation, Washington, DC, 1986. FHWA. Durability Analysis of Aluminized Type 2 Corrugated Metal Pipe. FHWA-RD-97-140, U.S. Department of Transportation, Washington, DC, 2000. FHWA. Federal Lands Highway, Project Development and Design Manual. U.S. Department of Transportation, Washington, DC, 2008. FHWA. Hydraulic Design of Highway Culverts, Third Ed. Hydraulic Design Series Number 5, FHWA-HIF- 12-026, U.S. Department of Transportation, Washington, DC, 2012. Florida DOT. Drainage Handbook, Optional Pipe Materials Handbook, Tallahassee, 2012. Gabriel, L.H., and Moran, E.T. NCHRP Synthesis of Highway Practice 254: Service Life of Drainage Pipe. TRB, National Research Council, Washington, DC, 1998. Ministry of Transportation of Ontario (MTO). MTO Gravity Pipe Design Guidelines, Canada, 2007. Molinas, A., and A. Mommandi. Development of New Corrosion/Abrasion Guidelines for Selection of Culvert Pipe Materials. CDOT-2009-11, Colorado DOT, Denver, 2009. Moore, I.D., D.B. Garcia, H. Sezen, and T. Sheldon T. NCHRP Web-Only Document 190: Structural Design of Culvert Joints. Transportation Research Board of the National Academies, Washington, DC, 2012. Potter, J.C. Life Cycle Cost for Drainage Structures. Technical Report GL-88-2, Department of the Army, Waterways Experiment Station, Vicksburg, MS, 1988. White, K., and J.O. Hurd. Guidance for Design and Selection of Pipes. Report for NCHRP Project 20-07 (Task 264) submitted to AASHTO, Washington, DC, 2011.