Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance (2022) / Chapter Skim
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20 Introduction A fill-in PDF survey was developed to document current DOT practices regarding the use of subsurface pavement drainage systems. The survey was distributed by email to all voting members of the AASHTO Committee on Pavement and Materials, representing all 50 state departments of transportation (DOTs)
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State of the Practice 21 Created with Mapchart.net. Figure 7.
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22 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Pavement surface Moderate to highly permeable base layer Filter aggregate separation layer Shoulder Porous aggregate-filled longitudinal trench with slotted pipe drain Transverse outlet pipe Type 1 Daylighted edge Pavement surface Permeable base Filter aggregate separation layer Type 2 Shoulder Pavement surface Moderate to highly permeable base layer Geotextile separation layer Shoulder Porous aggregate-filled longitudinal trench with slotted pipe drain Transverse outlet pipe Type 3 Moderate to highly permeable base layer Pavement surface Geotextile separation layer Shoulder Preformed geocomposite longitudinal drain Transverse outlet pipe Type 4 Outside edge of shoulder Edge of lane Centerline Edge of lane Downhill direction Uphill direction Outside edge of shoulder To outlet Aggregate-filled cross drain Type 5 Type 6 Outside edge of shoulder Edge of lane Centerline Edge of lane Outside edge of shoulder Discrete aggregate-filled side drain (typical) Figure 8.
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State of the Practice 23 Figure 9. State of the practice for subsurface pavement drainage design methods.
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24 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Rainwater and snowmelt infiltration through joints and cracks and interception/drawdown of high groundwater were identified as the predominant sources of water in pavement structures that subsurface pavement drainage systems were designed to address. Frost heave was also mentioned as a concern for one DOT.
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State of the Practice 25 4 5 24 4 34 26 19 13 3 25 0 5 10 15 20 25 30 35 40 Other Precipitation rates Subgrade properties Projected traffic Continuous maintenance needs Historical pavement distress Proposed base materials Pavement type Life-cycle cost analysis In-house decision criteria Number of Responses (Q6: 37 total responses, 35 with multiple selections) Figure 13.
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26 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance 3 13 8 15 20 0 5 10 15 20 25 Other Permeable base layer not currently used Using cement-stabilized aggregates Using asphalt-stabilized aggregates Using unstabilized aggregates Number of Responses (Q8: 37 total responses, 16 with multiple selections) 5 12 14 2 5 9 0 2 4 6 8 10 12 14 16 Other Permeable base layers not used Based on agency design standards for structural layer components Based on infiltration quantities Standardized at 6 inches Standardized at 4 inches Number of Responses (Q7: 37 total responses, 11 with multiple selections)
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State of the Practice 27 (one DOT)
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28 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance of permeability is the most common choice (six DOTs)
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State of the Practice 29 Figure 19. State of the practice for longitudinal collection system use.
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30 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Longitudinal edge drains may be installed during new construction or retrofitted into existing pavement systems, as illustrated in Figure 21. One DOT reported that maintenance and performance issues have led to reduced use of longitudinal edge drains, and another DOT indicated that underdrains can only be installed in HMA pavements when there is a minimum of 9.5 in.
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State of the Practice 31 10 5 2 20 2 8 0 5 10 15 20 25 Filter layer not used Clogging resistance of geotextile based on soil gradation Piping resistance of geotextile based on soil gradation Standard geotextile fabric used Aggregate filter layer with size and gradation based on soil Aggregate filter layer with standard gradation Number of Responses (Q13: 37 total responses, 8 with multiple selections) Figure 23.
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32 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance structural number and subgrade resilient modulus, determined using the 1993 AASHTO Design Guide procedures, the researchers concluded that the drainage layer appeared to have a positive impact on the in situ structural number at both locations and on the in situ subgrade resilient modulus at one location. No long-term performance data were provided; however, the researchers did recommend the continued use of bound permeable drainage layers and longitudinal underdrains for new construction on high-priority routes, provided that a maintenance program that included periodic visual or camera inspection of drainage outlet pipes was developed.
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State of the Practice 33 Expected to have >30% longer service life to first rehab (4) Expected to have 21–30% longer service life to first rehab (1)
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34 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance performance expectations for drained asphalt and concrete pavements, respectively, in comparison to their counterpart undrained pavements. Of the 18 DOTs that expressed views on whether asphalt pavements with subsurface drainage systems performed better than asphalt pavements without them, 10 did not expect drained asphalt pavements to have longer service lives to first rehabilitation, while the other eight expected them to have service lives that ranged from less than 10 percent to more than 30 percent longer.
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State of the Practice 35 Figure 28. State of the practice for probing of outlets.
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36 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance 13 4 1 0 0 0 2 4 6 8 10 12 14 Inspections not conducted At intervals > 5 years At 4- to 5-year intervals At 2- to 3-year intervals On an annual basis Number of Responses (Q17d: 18 total responses, 0 with multiple selections) Figure 30.
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State of the Practice 37 27 28 32 19 27 0 5 10 15 20 25 30 35 Transverse outlets missing rodent screens Transverse outlets/headwalls damaged or missing Transverse outlets/headwalls buried Longitudinal drainpipes collapsed Transverse outlet pipes collapsed Number of Responses (Q19: 34 total responses, 33 with multiple selections) Figure 32.
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38 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Summary This chapter has presented an overview of the responses received from 41 DOTs (an 82% response rate) to a survey consisting of 20 multiple-choice questions covering issues related to subsurface pavement drainage system design criteria, construction activities and costs, inspection and maintenance, and effects on pavement performance.
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