1. Material Selection Central Office Hydraulics
Culvert Design
Material Selection
Central Office Hydraulics

2. Steps for Material Selection
Field Review
Culvert Hydraulics
Structural Strength
Service Life
Material Analysis
Plan Alternates

3. Field Review Determine pH of the water
Use an instrument that is capable of accuracy of 0.1
Use Figures through only if no flow is present when performing the field check

4. Do not use unless there is no flow when performing the site visit.

5. Field Review Determine if there is a presence of abrasive material.
Abrasive Material – Presence of gravel, stones, or a course sand in the barrel of an existing conduit (or in the existing stream bed) that has a stream gradient or flow sufficient to cause movement of the abrasive material.
Assume abrasive conditions if there is any question about the bed material.

6. Abrasive Condition

7. Non-Abrasive Condition

8. Field Review Investigate the condition of existing structures.
If a replacement structure, look at the existing structure.
If a new structure look at any adjacent existing structures.

9. Culvert Hydraulics
Use approved methods outlined in the Location and Design, Volume 2 Manual

10. Structural Strength
Structural strength for Metal Conduits (steel and aluminum)
Select the gauge thickness and corrugation profile that is adequate (based upon fill height).
Figures through (steel)
Figures through (aluminum) (NOT Aluminized)

12. Structural Strength Structural Strength for Concrete Conduits
Select the D-load that is adequate for structural strength (based upon fill height).
Figures through

14. Service Life Service life is either 50 or 75 years
Use 50 years as a minimum .
Use 75 years for high fills (>16’), under freeways, or where future costs may be high to replace the structure.

15. Service Life Durability for Metal Conduits
Use the obtained pH and abrasiveness observation to determine the gauge thickness.
Use figures (50) through (75) & the general notes for the figures.

17. Service Life Durability for Concrete Conduits
Check for adequate service life based upon the pH, pipe slope, and pipe rise.
Use figure

19. Material Analysis
For metal conduit, choose the higher gauge thickness from the structural design, or the durability analysis.
When durability thickness is higher than structural thickness, provide the 1-inch corrugation profile for pipe diameters over 48 inches.

20. Plan Alternates
Place all available material options in the plan (all metal alternatives and concrete).
In some cases, only one material may be specified in the plan:
If the outlet velocity in a concrete pipe requires a ring chamber and the velocity of the metal alternative is below 20fps, then metal may be used exclusively.
When encountering excessive cover for a concrete pipe.

21. Plan Alternates
Where a larger corrugated metal pipe would require a higher pavement grade to satisfy minimum cover requirements, concrete may be used exclusively.
Where a metal pipe arch is required hydraulically and a round concrete pipe would work, concrete may be used exclusively.
Do not need to specify minimum D-loads or minimum gauge thicknesses in the item call-out.

22. Plan Alternates Show the following in the plan:
D-load or gauge thickness if it is above the minimum shown in the specifications.
The conduit shown in the plans should be the longest length pipe (the smallest diameter).
Hydraulic Design Information
Other information (see L&D, Vol. 3, Section )

23. Example Problem Given:
Hydraulic design requires 96 inch corrugated or 90 inch smooth lined
Outlet velocities:
Corrugated: V=17.0 fps & Smooth lined: V=21.0 fps
Height of cover = 18 feet
Under a new alignment (minor state route)
pH was measured and found to be 7.5

24. Design Example
Photo from creek:
Is this Abrasive?

25. Example Problem Select the appropriate design alternatives.
As per L&D, we will exclude concrete conduit in the design due to the velocity of 21 fps.
Durability Design
Site was determined to be abrasive in nature
A design service life of 75 years will be used due to the high fill height.
Use Figure (75) for the durability design

27. Example Problem Options from figure & notes are:
10 gauge Aluminum Coated
12 gauge Aluminized & Asphalt Coated & Paved
14 gauge Polymer Coated with 1” corrugations
16 gauge Polymer Coated & Asphalt Coated & Paved
16 gauge with Concrete Field Paving
1 gauge
12 gauge with Concrete Field Paving
(aluminum pipe) with Concrete Field Paving
(aluminum structural plate) with Concrete Field Paving

28. Example Problem Structural Design of Metal Conduit
Use Figure & to check for maximum height of cover:

31. Example Problem
A gauge thickness of (16 gauge) will be satisfactory up to a fill height of 31 feet for all steel options except for (structural plate).
A gauge thickness of (12 gauge) will be satisfactory up to a fill height of 29 feet for steel structural plate.
A thickness of (the minimum for this size) will be satisfactory up to a fill height of 20 feet for aluminum pipe.
A thickness of (the minimum for this size) will be satisfactory up to a fill height of 20 feet for aluminum structural plate.

32. Example Problem Specifying in the Plan
Specify the alternative as per L&D, Volume 3, Section
For this example it would be as follows:
603 – 180 L.F. 96” Conduit, Type A (0.138) Aluminized, with CFP, (0.280), with CFP, (1”) (0.079) Polymer Coated, (1”) Polymer Coated Asphalt Coated and Paved, (0.109) Aluminized Asphalt Coated and Paved, with CFP, with CFP

33. Questions ?