Proposed Practice for Alternative Bidding of Highway Drainage Systems (2015) / Chapter Skim
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Pages 6-35
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6State of the Practice Summary To develop a national recommended practice for alternative bidding of culverts and storm sewers, it was necessary to understand the state of gravity drainage system practice for roadway projects across U.S.
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7 DOTs, a 74 percent return rate, as shown in Figure 1. The DOT survey questions and responses are presented in Figures Q1 through Q14 with brief commentary.
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826 11 0 5 10 15 20 25 30 oNseY N um be r o f R es po ns es Figure Q2. Number of DOTs that have or are evaluating new pipe types.
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9 21 6 10 0 5 10 15 20 25 YES NO NO ANSWER / UNKNOWN N um be ro fR es po ns es Figure Q4a. Number of DOTs whose fill height tables are agency-specific.
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10 26 11 0 5 10 15 20 25 30 Ye s N o N um be ro fR es po ns es Figure Q6. Number of DOTs that use the concept of Design Service Life.
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11 2 29 6 0 5 10 15 20 25 30 35 Ye s N o Sp ec ia l Co nd iti on s O nl y N um be ro fR es po ns es Figure Q7. Number of DOTs that plan for future remediation of the pipe system.
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12 Question 9: In the last 5 years, which of the following pipe types has your agency installed for highway drainage systems: concrete, steel, HDPE, PVC, other. Figure Q9 shows an average across all DOTs for the pipe types used in drainage systems.
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13 11 18 4 5 11 21 3 3 0 5 10 15 20 25 Du rin g Co ns tr uc ti on Po st C on st ru cti on N ot In di ca te d N o In sp ec ti on s Co nd uc te d N um be r o f R es po ns es Timing of Inspection Rigid Pipe Flexible Pipe Figure Q10–11g. When does pipe system inspection occur?
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14 16 17 4 0 2 4 6 8 10 12 14 16 18 Ye s N o N o An sw er / U nk no w n N um be ro fR es po ns es Figure Q13. Documented studies on pipe system performance/durability.
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15 3.3 Existing Alternative Pipe Bidding Systems A review of state agency bidding practices and guidelines indicated that while the majority of states surveyed indicated that they have an alternative pipe bidding system in place, the extent to which such a system is implemented and the scope of pipe alternatives permitted are extremely variable. As reported by White and Hurd (2011)
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16 3.4 Literature Review -- Design and Construction Considerations Design and construction considerations were reviewed to determine current practice and guidelines for implementation into the Recommended Practice. In particular, hydraulic, structural, and durability design considerations were reviewed extensively.
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17 The hydraulic factors in Table 1 can be broken out into the following: • Inlet Characteristics (inlet area, inlet edge configuration, and inlet shape) • Site/Geometric Characteristics (headwater elevation, barrel length, barrel slope, and tailwater elevation)
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22 pipes (metal, reinforced concrete, and thermoplastic)
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24 0 20 40 60 80 100 120 140 160 M O U T W V AK F L ID O R W A W Y GA A R M S M D O K N C AZ KS LA VA IA N E IL TN M ax im um F ill H ei gh t ( fe et ) State or Agency Reported Value Figure 11.
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25 0 20 40 60 80 100 120 140 160 M O N D U T W V CO A K FL ID IN O R W A CA W Y GA A R M S M D O K TX KS LA N E AZ N C IL VA TN IA M ax im um F ill H ei gh t ( fe et ) State or Agency Reported Value Figure 12.
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26 0 5 10 15 20 25 30 35 40 N Y N M (T re nc h)
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27 0 5 10 15 20 25 30 35 40 U T CO F L M T (T re nc h)
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30 Differences in allowable fill heights are thought to be the result of the following main factors: • In agency structural evaluations, there are differences in how material factors such as pipe stiffness, corrugation geometries, and backfill/bedding details are considered. The following are some examples of the differences: – Variations in applied loading from trench versus embankment installations – Variations in installation and bedding/backfill specifications among agencies and among pipe materials – Changes in structural capacity with time due to pipe material degradation (e.g., metal corrosion, etc.)
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31 3.4.3 Long Term Performance and Durability A literature review of long term performance and durability of pipe systems was undertaken to evaluate the approaches used for estimating material service life of drainage systems for incorporation into the Recommended Practice. The intent of this project is not to provide an exhaustive review of durability, but to identify the key factors and methods needed for the implementation of a reliable Recommended Practice.
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32 3.4.3.3 pH The pH value is defined as the log of the reciprocal of the concentration of hydrogen ion in a solution. Values of pH in natural waters generally fall within the range of 4 to 10.
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33 3.4.4 Inspection and Post-Installation Certification Experience has shown that one of the critical issues impacting the performance (short and long term) of pipe systems is the quality of the installation.
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34 initial conditions can have time to present themselves. The AASHTO construction specifications commentary expands on this recommendation by stating that soil consolidation continues with time after installation of the pipe.
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35 The survey response graphs included in Chapter 3 and the following observations were made based on the results of the NCHRP Project 10-86 DOT survey: • For rigid pipe systems: visual inspection is the most common, followed by video inspection and laser profiling. • For flexible pipe systems: mandrel testing is the most common, followed by visual inspection, video inspection, and laser profiling.
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