1. SESSION 4 Drainage Design Considerations

2. Objectives  Identify types of subsurface drainage  Determine need for subsurface drainage  Recognize importance of maintenance  Identify surface drainage design factors

3. Introduction  Moisture is a major cause of distress  Drainage long recognized as key design consideration  Focus on drainage of surface infiltration water

4. Effect of Drainage

5. Moisture-Related Distresses

9. Approaches to Drainage Problems  Seal the pavement  Use moisture-insensitive materials  Install subsurface drainage

10. Types of Subsurface Drainage  Daylighted bases  Longitudinal edge drain system  Drainable pavement system

11. Daylighted Subgrade PCC Slab Agg. Base Shoulder Aggregate Base Carried Out to Ditchline Shoulder Aggregate Base Carried Out to Ditchline Traffic Lane

12. Longitudinal Edge Drain System Slope Inner ShoulderTraveled WayOuter Shoulder TPM Filter Fabric Base (LCB, ACB) Filter Fabric, High Side of Tangents and Superelevations PCC PCCP PCC California Design

13. Example Drainable Pavement System

14. Components of a Drainable Pavement System  Permeable base  Separator layer  Longitudinal collector pipe

15. Permeable Base  Permeability of 300 to 3,000 m/day (1,000 to 10,000 ft/day)  100 to150 mm (4 to 6 in) thick  Treated or untreated

16. Separator Layer  Prevent intrusion of fines into permeable base  Dense-graded aggregate  Geotextile

17. Longitudinal Collector Pipe  Collects water and outlets to ditches  Typically 100 to 150 mm (4 to 6 in) corrugated plastic pipe  Outlet spacing 76 to 150 m (250 to 500 ft)

18. Design and Analysis of Drainage Systems  Define  Material properties  Roadway/pavement geometrics  Climatic data  Determine inflow/outflow characteristics  Determine drainage requirements

20. Consideration of Drainage in Slab Thickness Design  AASHTO Drainage Coefficient  Drainage, Thickness  Reduction in properties of paving materials

21. Determining Need for Subsurface Drainage  Available free moisture  Material properties  Cross sectional design  Subgrade drainability  Traffic levels

22. < 3.0 None 3.0 - 6.0 None/EDS None None None > 6.0 EDS/DPS NCHRP 1-32 Drainage Guidelines EDS = Longitudinal Edge Drain System DPS = Drainable Pavement System WET CLIMATE DRY CLIMATE ESALs, Weak Strong Weak Strong millions Subgrade Subgrade Subgrade Subgrade

23. Inclusion of Subsurface Drainage  Local experience  Past performance  Cost effectiveness  Construction and maintenance practices

24. Maintenance of Drainage Installations  Ensures functionality of drainage system  Often a “forgotten” maintenance item  Activities include:  Reference markers  Cleaning outlets  Flushing/rodding edge drains  Cleaning/reestablishing ditches  Periodic video inspection

25. Video Inspection of Edge Drains

26. Crushed Pipe and Silt Buildup

27. Unwanted Inhabitants

28. Surface Drainage Considerations  Pavement cross slope (tangent section)  2% recommended  Shoulder cross slope  3% recommended  Ditches  Width: 0.9 to 1.2 m (3 to 4 ft)  Depth: 1.2 m (4 ft) beneath pavement Grade: 1%

29. Summary  Moisture-related distresses  Subsurface drainage types  Determining need for subsurface drainage  Maintenance considerations  Surface drainage considerations