1. Small Structure Design 101
Purdue University Road School 2011

2. Small Structure Design 101
Presenters: Mark Williams, PE INDOT Design, Vincennes District Richard Thomas, PE

3. Site Criteria A culvert should be used
Where a bridge is not hydraulically required.
Where debris and ice are tolerable.
Where it is more economical than a bridge.

4. Site Criteria (Cont.) Length and Slope
Approximate existing topography.
Invert should be aligned with channel bottom and skew angle of stream.
Clear-zone and embankment geometry may dictate length.

5. Site Criteria (Cont.) Location in Plan Location in Profile
Place normal to roadway if no defined channel.
Minimize channel relocation and erosion.
Locate utilities before final location is chosen.
Location in Profile
Approximate natural stream profile.

6. Hydraulic Design Criteria
Allowable Headwater (AHW)
Roadway Serviceability
Maximum Velocity
Minimum Velocity

7. Allowable Headwater (AHW)
New Alignment
1.5 in. Maximum Backwater.
Exceptions
Backwater Dissipates to 1.5 in. or less at R/W.
Backwater is Contained in the Channel.

8. Allowable Headwater (Cont.)
Existing Conditions
Proposed Surcharge ≤ Existing Surcharge.
If Existing Surcharge > 1 ft., Proposed must not be > 1 ft. above the Natural Channel Flood Profile.

9. Allowable Headwater (Cont.)
Right of Way
The Ponding Limit Cannot Exceed the R/W for New Alignment.
Upstream Channel
The Ponding Limit Cannot Exceed the Banks of Upstream Channel for New Alignment.

10. Allowable Headwater (Cont.)
Other Constraints
Grades of Adjacent Drives.
Finished Floor Elevations of Buildings.
Elevation of Existing Cropland or Other Property.

11. Design Storm Frequency

12. Roadway Serviceability
For Q100 Design Storm
Headwater must be at least 2 ft below edge of pavement
For Design Storm less than Q100
Headwater cannot exceed edge of pavement

13. Maximum Velocity Vo ≤ 6.5 ft/s Revetment Riprap
6.5 ft/s ≤ Vo < 10 ft/s
Class 1 Riprap
10 ft/s ≤ Vo < 13 ft/s
Class 2 Riprap
Vo ≥ 13 ft/s
Energy Dissipator
Vo = Outlet Velocity

14. Minimum Velocity
Typical Minimum Outlet Velocity is ft/s.

15. Culvert Sizing Process
Priority System
Interior Designation
Minimum Culvert Size
Cover

16. Priority System Trial 1. Single Circular Pipe.
Trial 2. Single Deformed Pipe.
Trial 3. Single Specialty Structure.
Trial 4. Multiple Circular Pipes.
Trial 5. Multiple Deformed Pipes.
Trial 6. Multiple Specialty Structures.

17. Interior Designation
Run Hydraulic Design for both Smooth Interior and Corrugated Interior.
Four Possible Situations.

18. Interior Designation (Cont.)
Situation 1. Required Smooth and Corrugated Sizes are Identical.
Situation 2. Required Smooth and Corrugated Sizes are Different.
Situation 3. Acceptable Size for one but not the other.
Situation 4. No Acceptable Size.

19. Minimum Culvert Size

20. Pipe Cover Minimum Cover Maximum Cover Circular Pipe 1 Ft 100 Ft
Deformed Corrugated
Pipe
1.5 Ft
13 Ft

21. Pipe Material Selection
Computer Program (INDOT Website)
Information Required
Pipe Classification
Pipe Interior Designation (Smooth/Corrugated)
Pipe Criteria (Size, Cover, Slope)
Pipe Service Life
Abrasive or Non-Abrasive Site
Structure pH

22. Pipe Classification Type 1. Under Mainline or Public Road.
Type 2. Storm Drain.
Type 3. Under Drive or Field Entrance.
Type 4. Underdrain or Drain Tile.
Type 5. Broken Back or other which requires coupled pipe.

23. Pipe Service Life
Based on Functional Classification of Mainline Roadway
75 Years- Freeway, Expressway, Arterial
50 Years- Collector or Local Road

24. Abrasive or Non-Abrasive
Mainline Culvert
Public Road or Drive Culvert Installed in a Natural Channel.
Non-Abrasive
Storm-Drain, Public Road, or Drive Culvert on a Constructed Side Ditch Line.

25. Structure pH Maximum pH. Cannot Exceed the Map pH (Fig. 28-6A IDM).
Lack of Sample. Use pH From Nearest Structure. If Not Available Within Project Limits Use pH Map Value.
Side Ditch Culvert. Use pH for the Most Downstream Culvert for Each Culvert in Ditch Line.

26. Plans
Plan & Profile Sheet. Appropriate Location for Drainage Structure Identification.
Detail Sheet. Detail Drainage Structures and Features that are not included in the Standard Drawings.

27. Plans (Cont.) Structure Data Sheet.
Backfill Method, Structure Backfill (CYS), Type.
Flowable Backfill (CYS), Type.
Scour Protection Information
Sump Depth (IN), Geotextile (SYS),
Riprap (Type & Tons)
Video Inspection Length.
Pipe Material Sheet. List Acceptable Pipe Materials for each Pipe Structure.

28. Structure Backfill Type 1
Longitudinal or Transverse Structure Within 5 ft. of the back of paved Shoulder or back of Sidewalk of a New Facility.
Structure for an Existing Facility Where all Existing Pavement is to be Replaced.

29. Structure Backfill (Cont.)
Type 2
Longitudinal or Transverse Structure Within 5 ft. of the back of paved Shoulder or back of Sidewalk Where Undisturbed Existing Pavement is to Remain.
Precast Concrete 3 Sided or 4 Sided Structure with Cover of 2 ft or Greater.

30. Structure Backfill (Cont.)
Type 3
Behind Mechanically Stabilized Earth Retaining Walls.
Type 4
Trench Where Utility Line is Present.
Behind Reinforced Concrete Slab Bridge End Bent.

31. Structure Backfill (Cont.)
Type 5
Precast Concrete 3 Sided or 4 Sided Structure with Cover Less than 2 ft.
Filling Voids in an Underground Facility.
Filling an Abandoned Pipe or Structure.
Other Application that does not Require Excavation.

32. Backfill Methods Method 1
Under New or Replacement Mainline or Public Road.
Under Median Embankment.
New Structure Under Existing Mainline or Public Road.

33. Backfill Methods (Cont.)
Placed Under a Drive in New or Replacement Work.
Method 3
Under New or Replacement Median Trench.

34. Backfill Quantities Measured by CYD Computed from Neat Line Limits.
Hand Calculation
IDM Chapter 17
Standard Drawings Section 715-BKFL
Computer Program

35. Pavement Replacement
Longitudinal Pay Limits

36. Pipe Under Existing Roadway

37. Culvert Modifications
Culvert Slip Lining
Culvert Extension
Culvert End Treatment
Headwalls and Anchors

38. Culvert Slip Lining Two Common Types
High Density Polyethylene Pipe (HDPE)
Cured in Place (CIPP)

39. Culvert Slip Lining (Cont.)
Review Pipe Inspection Report
Structures with an overall rating of 2 to 5 should be considered for lining.
Overall ratings of 0 or 1 are normally structures that need to be replaced.
Field Review
Pictures
Measurements

40. Culvert Slip Lining (Cont.)
Factors to Consider
Structure barrel should be relatively straight and not significantly deformed.
Existing backfill free from large voids.
Should be sufficient room to work from at least one end of the existing structure.
In a location where road closure is undesirable or impractical.
Hydraulic capacity of liner.
Liner cost vs. replacement cost

41. Lining Design Criteria
Time of Concentration < 1 Hour
May increase backwater over existing if:
Headwater maintains road serviceability.
Headwater does not reach fixed private property structures.
Time of Concentration > 1 Hour
May not increase backwater, unless contained within channel banks or R/W.
Check Outlet Velocity

42. Lining Design Procedure
HDPE Liners
Manning’s n=0.012.
Use maximum pipe liner size from tables in Standard Specification Section 725.
Use largest possible liner, even if smaller liner is hydraulically adequate.

43. Lining Design Procedure (Cont.)
CIPP Liners
Only considered if HDPE will not work (cost).
Manning’s n=0.012.
Structures < 96” diameter or equivalent.
Will reduce existing structure size as follows:
Dia. ≤ 24”, reduce by 1”
Dia. from 27” to 48”, reduce by 2”
Dia. from 54” to 72”, reduce by 3”
Dia. from 78” to 96”, reduce by 4”

44. Culvert Extensions Match Existing Pipe Size and Interior Designation.
Perform Appropriate Hydraulic Analysis.

45. Culvert End Treatment Projecting
Extends beyond the roadway embankment.
Can be damaged during maintenance.
Low construction cost.
Poor hydraulic efficiency.
Anchor should be used for 42” or larger diameter.
Clear zone requirements.

46. Culvert End Treatment (Cont.)
Mitered
Hydraulically more efficient than projecting.
Mitered to match fill slope.
Pipe End Section
For corrugated metal or concrete pipe.
Retards embankment erosion.
May improve hydraulic efficiency.

47. Culvert End Treatment (Cont.)
Wingwall
Retain roadway embankment
Used where side slopes of channel are unstable.
Best hydraulic efficiency if flare angle is between 30° and 60°.
Should be used on precast concrete drainage structures.

48. Culvert End Treatment (Cont.)
Apron
Reduce scour
Should extend at least one pipe diameter.
Should not protrude above normal streambed elevation.
May be constructed of riprap and geotextile or concrete.

49. Culvert End Treatment (Cont.)
Cutoff Wall
Prevent piping along culvert barrel.
Should be used for culverts with headwalls.
Should be minimum of 20” depth.

50. Specialty Structures Precast Concrete Box Culvert
Maximum span is 12 ft.
The recommended layout is to extend the box to the point where the roadway sideslope intercepts stream flowline.
End of box culvert should be protected with guardrail or located beyond the clear zone.

51. Specialty Structures Precast Concrete Oversize Box Structure
12’ < Clear Span ≤ 20’
Three-sided structure with base slab may be an acceptable alternate. Consult with Hydraulics Team for guidance. Run cost comparison.
If distance from top of structure to top of pavement is less than 2’, then all top slab reinforcement should be epoxy coated.
Wingwalls and headwalls required.

52. Wingwalls and Headwalls
Information on Plans
Plan view showing total length of structure, skew angle, distance from roadway centerline to each end, and flare angle of wingwalls.
Elevation view of structure including wingwalls and headwalls. Dimension span, rise, and height of headwalls.

53. Wingwalls and Headwalls (Cont.)
Information on Plans
Label wingwalls A to D and include a table with dimensions, elevations, areas for each wingwall.
Show approximate footing configuration with typical section through each wingwall. Footing dimensions should not be shown. Contractor is responsible for footing design.

54. Wingwalls and Headwalls (Cont.)
Information on Plans
Include a table with soil parameters
Allowable soil bearing pressure.
Angle of friction between wingwall footings and foundation soil.
Angle of internal friction of the foundation soil.
Ultimate cohesion of foundation soil.
Ultimate adhesion between foundation soil and concrete.

55. Wingwalls and Headwalls (Cont.)
Information on Plans
Show conceptual layout for precast concrete structures or precast wingwalls and headwalls.
Fabricator will design and detail structure after work is under contract.
For structures > 12’ span, fabricator will provide design computations and shop drawings for approval.

56. Culvert Sumping
Structure invert elevation and scour protection placed below the stream flowline to satisfy IDEM 401 Permit.
Show scour protection limits on plans.
Identify geotextile and riprap quantities for scour protection in Structure Data Table. These quantities are not pay quantities.

57. Culvert Sumping Three-Sided Structure Pipe or Box Structure
18” sump for sand stream bed.
12” sump for other soil type stream bed.
3” sump for rock stream bed.
Pipe or Box Structure
Refer to Standard Drawings and IDM Figure 31-3B(1).
Structure diameter or rise may need to be increased if sump exceeds 3”.

58. Geotechnical Requirements
Pipe structure replacements require a geotechnical investigation.
Pipe structures < 36 in. diameter or pipe extensions < 5 ft may qualify for geotechnical waiver.
Check with INDOT’s Office of Geotechnical Engineering.

59. References Standard Specifications 211. Structural Backfill
213. Flowable Backfill
714. Concrete Box Structures
715. Pipe Culverts
716. Trenchless Pipe
717. Structural Plate Pipe

60. References (Cont.) Indiana Design Manual (IDM)
Chap. 17. Quantity Estimating
Chap. 28. General Information (Hydraulics)
Chap. 31. Culverts
Chap. 34. Energy Dissipators

61. External Dissipator (Example)
Existing
66” x 260’ CMP
Ample R/W at Outlet.
Proposed
HDPE Liner
Vo = fps
HY8 to design External Dissipator.

62. External Dissipator (Example)

63. External Dissipator (Example)

64. External Dissipator (Example)

65. Internal Dissipator (Example)
Existing
42” x 295’ CMP
Distance from Outlet to R/W = 6 ft.
Proposed
HDPE Pipe Liner
Vo = 18.6 fps
No room for External Dissipator
HY8 to design Internal Dissipator
Vo = 9.0 fps (w/Internal Dissipator)

66. Internal Dissipator (Example)

67. Internal Dissipator (Example)

68. Internal Dissipator (Example)

69. Box Culvert Plans (Example)

70. Box Culvert Plans (Example)

71. Box Culvert Plans (Example)

72. Box Culvert Plans (Example)

73. Box Culvert Plans (Example)

74. Box Culvert Plans (Example)

75. Box Culvert Plans (Example)

76. Box Culvert Plans (Example)