Service Life of Culverts (2015)

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4 CHAPTER TWO SYNTHESIS OF THE STATE OF THE PRACTICE This chapter summarizes the results of the survey of North American transportation agencies regarding the service life of culverts, which was performed from March through July 2014. Summary plots and tables of the results are provided in Appendix A, with select results of interest summarized in this chapter. Through July 9, 2014, 48 agencies submitted complete sur- vey responses—41 from agencies based in the United States and seven from agencies based in Canada. Figures 1a and 1b show the responding states and provinces/territories through shading for the United States and Canada, respectively. Bar chart summaries of each survey question are pro- vided in Appendix A, along with summary tables of manu- ally entered additional information. This section provides general summary commentary on the state of the practice based on the survey responses. PIPE MATERIAL TYPES The past three decades have seen improvements and inno- vations in drainage pipe materials and products, resulting in a wide range of pipe material types available and in use as culverts on highway projects. The range of pipe material types in use across North American practice is demonstrated in the survey results shown in Figure 2. FIGURE 2 Pipe material types in use, or being considered for use. Results show that concrete, high-density polyethylene (HDPE), and corrugated galvanized steel pipes are the three most commonly used pipe types, with 88% or more of respon- dents indicating their use. More than half of the respondents are also using galvanized steel (structural plate or steel cas- ing), aluminized steel, polymer-coated steel, aluminum, and FIGURE 1b Canadian transportation agency responses; shading indicates survey participation. FIGURE 1a U.S. transportation agency responses; shading indicates survey participation.

5 polyvinyl chloride (PVC), while about a quarter are using steel-reinforced HDPE, polypropylene, and ductile iron. It is a noteworthy development that the more recently developed pipe materials are being used fairly widely. Less than a quarter of respondents are using vitrified clay or fiber- glass pipes. In general, the responding agencies are using a wide range of pipes, but with a definite concentration around three primary pipe material types. SERVICE LIFE One focus of the survey was the state of practice regarding service life across the range of available pipe material types, including each of the following main areas: • The bases and values used for design service life (DSL) • The factors and methodologies used to estimate or set material service life (MSL) • The criteria and definitions used to define the end of service life. Design Service Life A wide range of criteria are used to set DSL values across North American practice, with the most common approaches considering roadway classification, usage (i.e., average daily traffic), risk of premature failure, and cost to rehabilitate in either combination or as a standalone basis, as seen in Figure 3. FIGURE 3 Agency bases for determining the design service life of culverts. The large number of “other” responses to the survey question on DSL indicate variability across North Ameri- can practice in this area, and that a number of agencies are not using the concepts of design and material service lives to evaluate and select culverts. DSL requirements were reported to generally range from 25 to 100 years, with the highest DSL required at many agencies being 50 or 75 years. Material Service Life Assumed agencywide values are still the predominant method for estimating MSL during design of all pipe types. Quantitative methods are more commonly used for pipes with a longer history of use (concrete and metal), and are more rare for pipe materials with a shorter history of use. For agencies that complete quantitative MSL evaluations, corrosion and abrasion were the most common factors con- sidered, followed by settlement and stress cracking. Forty-six percent of respondents collect site-specific environmental data on all projects. A further 31% allow the engineer to decide whether to collect data, with another 23% collecting site-specific data only in areas of known environmental concerns. The types of environ- mental parameters collected are widely distributed, as seen in Figure 4. FIGURE 4 Types of environmental parameters collected for MSL evaluations. One-third of agencies maintain maps that indicate regions of environmentally aggressive conditions, with the types of maps in use depicted in Figure 5. FIGURE 5 Types of environmental condition maps maintained by transportation agencies.

6 The tools and aids used to complete MSL evaluations typically including some combination of assumed values, agency-specific data, and industry-supplied data. Software programs are still relatively infrequently used to predict MSL values. Based on the literature review, state transportation agen- cies are often the leaders in developing or improving MSL methods. Only 22% of responding agencies have developed or improved durability methods, which indicates that a focused core group of agencies are engaging on this topic. The other agencies cited a lack of resources (time, money, etc.) and other priorities as the key reasons for not engaging on this topic. Figure 6 presents which pipe materials were deemed in most need of new or improved methods for esti- mating MSL. FIGURE 6 Pipe material types deemed most in need of new or improved MSL estimation methods. The near-universal application of assumed values for all pipes other than concrete and metal may result from the limited methodologies available to complete project-specific evaluations of MSL for thermoplastic and other noncon- crete/metal pipe types. The results of the survey highlight the importance of maintaining complete design, installation, and maintenance records to facilitate service life estimates. Defining the End of Service Life Multiple factors are considered by most agencies in defining the end of service life, with the most common being section failure (crushing, buckling, de-bonding), cracking, joint per- formance, and deflection (flexible pipes only). A number of agencies use inspection rating systems to quantify service- ability, and have threshold values that trigger maintenance, rehabilitation, or replacement. AGENCY POLICIES, SYSTEMS, AND EXPERIENCES Several queries about agency policies, systems, and experi- ences related to culvert service life were included in the state of the practice survey. Installation Quality and External Factors Installation quality has significant influence on realized service life for all pipe material types, with the responses for thermoplastic pipes indicating greater installation influence across agency experience than for the other main material pipe types. Agencies were asked which nontypi- cal external factors have impacted culvert performance. Exposure to chemicals and contaminants, exposure to agricultural runoff, fire damage, vehicle impacts, and “other factors” were all identified in more than 35% of responses. Agencies submitted a wide range of responses in the “other” category, including factors related to local soil or climatological conditions, and installation or main- tenance concerns. Culvert Management Systems More than half (60%) of respondents use no system to man- age culvert pipe installation, maintenance, and service life information. This represents a significant potential oppor- tunity to improve the state of practice in managing culvert assets, reinforced by the fact that 82% of survey respondents indicated that such a culvert system would be helpful. Culvert Rehabilitation Culvert rehabilitation is becoming a more common practice; only two agencies do not use common rehabilitation meth- ods. Sliplining is the most common rehabilitation approach with 89% of respondents successfully using this method. Jacking and boring, joint repair, invert lining, and cured in- place liners are used by more than half of the agencies. Six additional rehabilitation techniques were identified as hav- ing been used successfully; namely, close-fit liner, spiral- wound liner, spray-on liner, concrete liner, micro-tunneling, and pipe bursting. Life-Cycle Costing Life-cycle costing analysis (e.g., considering multiple less durable culvert installations, initial oversizing for future relining) is generally not performed for typical projects, with 58% of agencies not conducting this analysis on any proj- ects. Thirteen percent of respondents use this analysis on all projects, whereas another 16% use it on interstate projects only. Eighteen percent of respondents use life-cycle costing analysis on large projects above a certain value. GENERAL STATE OF THE PRACTICE SURVEY OBSERVATIONS The following general observations can be made based on the 48 survey responses across U.S. and Canadian transpor- tation agencies:

7 • A wide range of practices for evaluating pipe service life are currently in use across North American trans- portation agencies. • Most agencies are comfortable designing for a range of pipe material types and appreciate the differences in performance each provides. • The survey data indicate that agencies are increasingly using asset and inventory management and tracking data- base systems to track their highway drainage networks. • Agencies are at the forefront of developing methods for predicting the service life of culverts and for managing culvert assets, but developments are generally concen- trated within a core group of agencies. • Joint performance is an important issue to agencies, across all materials. • Agencies are using material and installation perfor- mance specifications more often than prescriptive standards and specifications.