Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance (2022) / Chapter Skim
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From page 76... ...
76 A P P E N D I X A Agency Survey Questionnaire NCHRP SYNTHESIS PROJECT 20-05, TOPIC 52-10, "SUBSURFACE DRAINAGE PRACTICES IN PAVEMENT DESIGN, CONSTRUCTION, AND MAINTENANCE" SURVEY OF AGENCY PRACTICE Dear Agency Representative, The Transportation Research Board (TRB) , through the National Cooperative Highway Research Program (NCHRP)
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From page 77... ...
Agency Survey Questionnaire 77 Definitions The following definitions are used in conjunction with this survey of practice: • Subsurface Drainage – an integrated system used to intercept, collect, and discharge water that infiltrates into the pavement section • Pavement Section – any combination of surface, base/subbase above the natural or chemically treated subgrade, located within the right of way and intended to provide safe, efficient, long-term support to vehicular traffic • Drained Asphalt Pavement – any asphalt pavement section that includes a permeable base layer • Drained Concrete Pavement – any concrete pavement section that includes a permeable base layer • Surface Infiltration – water that enters vertically into the pavement section through longitudinal and transverse joints and cracks in and between the travel lanes and the curb/shoulder • Subsurface Infiltration – water that migrates into the pavement section through lateral groundwater seepage, fluctuations in groundwater levels, and/or through capillary action • Drainage Layer – a porous aggregate layer within the pavement section that provides a means to remove infiltrated water (may be unstabilized, asphalt-stabilized, or cement-stabilized, and may be referred to as a permeable layer, an open-graded layer, or a free-draining layer) • Underdrain – a conduit to remove water from a drainage layer • Edgedrain – an underdrain along the longitudinal edge of the pavement • Crossdrain – an underdrain running transversely under the traffic lanes • Filter Layer – a layer below the drainage layer designed to allow water to drain through freely but prevent soil/aggregate particles in the underlying layer (subbase or subgrade/embankment)
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From page 78... ...
78 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Instructions for Completing Survey The survey must be completed in Adobe Acrobat, Adobe Reader, or other compatible pdf reader software and may be saved on local computers and completed in multiple sessions. The survey may also be forwarded to others within your agency for review and/or partial/full completion.
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Agency Survey Questionnaire 79 Part A – Questions Related to Subsurface Drainage Design 1. This survey of practice has been developed to obtain information related to the use of subsurface drainage systems.
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80 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance 2. As illustrated in these figures, subsurface drainage systems of various types may be installed during pavement (re)
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Agency Survey Questionnaire 81 3. The need for subsurface drainage in pavement repair/(re)
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82 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance 4. Subsurface drainage system components may be designed based on site-specific conditions or may be standardized to apply to more generalized regional/soil conditions.
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Agency Survey Questionnaire 83 5. Water from a variety of sources may be intercepted by subsurface drainage systems.
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84 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance 6. The choice to incorporate subsurface drainage in pavement repair/(re)
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Agency Survey Questionnaire 85 7. As indicated in the figure, the minimum thickness of the permeable base must be sufficient to provide for the maximum depth of flow (Hm)
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86 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance 8. Where permeable base layers are utilized, the aggregate gradation (e.g., AASHTO #8, #57, #67)
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Agency Survey Questionnaire 87 9. The maximum aggregate size and gradation of the permeable layer is directly related to its permeability (i.e., hydraulic conductivity)
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88 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance 10. As shown in these figures, various methods may be utilized to transmit water collected by the permeable base layer to side ditches and away from the pavement section.
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Agency Survey Questionnaire 89 Part B – Questions Related to Subsurface Drainage System Construction 11. Permeable base layers with high hydraulic conductivity have been reported to have poor stability under construction/vehicular traffic.
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90 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance 12. To provide for effective drainage, permeable base layers should be protected from contamination during construction.
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Agency Survey Questionnaire 91 13. Aggregate and geotextile filters have been utilized to prevent clogging of permeable base layers during service.
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92 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance 14. Longitudinal edge drains may be installed to drain water away from a permeable base layer and/or to lower the level of the water table below the pavement structure.
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Agency Survey Questionnaire 93 Part C – Questions Related to Subsurface Drainage System Performance 15. Performance studies have been conducted to establish parameters useful for determining the expected service life and/or cost-effectiveness of subsurface drainage systems.
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94 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance 16. The expected service lives of drained pavement sections, compared to undrained pavement sections, have been established by various agencies and are used within the context of life-cycle cost analysis.
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Agency Survey Questionnaire 95 Part D – Questions Related to Subsurface Drainage System Testing/Maintenance 17. Various in-place tests/inspections, conducted by staff, contractors and/or external vendors have been utilized to monitor the functionality of subsurface drainage components.
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96 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance 18. Proper location and maintenance of transverse outlets may be considered necessary for the long-term functionality of subsurface drainage systems.
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Agency Survey Questionnaire 97 19. These photos illustrate common problems observed with subsurface drainage components.
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98 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance 20. Various survey methods have been used to evaluate the influence of subsurface drainage on the functional and structural capacity of the pavement system.
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Agency Survey Questionnaire 99 Agency Policy Documents Please provide links to as many documents and sources of information as necessary to accurately convey your agency's subsurface drainage design practices. These may include contract documents, agency reports, agency manuals (guidelines)
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100 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Follow-Up Interviews Upon review of the agency survey responses as well as the literature reviews, the contractor will conduct phone/Zoom interviews with selected agencies that indicated the current/past usage of subsurface drainage systems and a willingness to participate in the case examples. Follow-up questions/topics will be sent by email for review prior to the phone/Zoom interview to the contact person identified in the agency survey.
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