Endwalls or other end treatments give culverts positive foundation support at the entrance and exit, control of water flow, and help prevent the erosion of surrounding embankments. All endwalls, except the straight endwall, decrease water flow.
The most common types of end treatment in North Carolina are the straight endwall, U-endwall, paralell pipe end section, mitered end section, and wing endwall.
The plans indicate the type of end treatment to be installed. Standard numbers
310, 320, and
838 in the Roadway Standard Drawings give details of end treatments and endwalls.
On the plans, rip rap is shown at the ends of the pipe.
Standard Drawing 868.02 gives a guide for rip rap at pipe outlets. Read
Section 876 in the Standard Specifications for requirements on the placement of rip rap.
End treatments should be installed soon after pipe installation. Before end treatment construction begins, the pipe should be checked for scour and erosion. If endwalls are to be constructed, they should be constructed after the pipe is laid, but before fill is placed, since the fill will back up to it.
PIPE END TREATMENT GUIDELINES
(from NCDOT Roadway Design Manual, Chapter 5)
The following guidelines apply to TIP projects on the primary system. The guidelines do not apply to the secondary road system. The criteria provided within this section is intended as a guide only. Engineering judgment should be used to determine if a different, but more appropriate, treatment is necessary.
The following guidelines for Pipe End Treatment shall be used in conjunction with the guidelines on clear zone distances. (See Appendix C of this Manual to determine clear zone distances.)
Recommended Pipe End Treatments are listed below in preferential order. Use the first recommendation listed under each heading if practical.
A. PIPE END TREATMENT FOR CROSS PIPES ON ALL ROADWAYS
(For further information, See “Roadway Standard Drawings”, Std. No’s.
310.03 and 310.05 -- Appendix A of this Manual)
1. PIPES OUTSIDE CLEAR ZONE
Use endwall on inlet end for 36 inches or over, unless specified otherwise by Hydraulics Unit.
2. PIPES INSIDE CLEAR ZONE
a. Extend all pipe beyond clear zone and use endwall on inlet end for 36 inches or over, unless specified otherwise by Hydraulics Unit.
b. Use a Cross Pipe end section (4:1 slope) for 30 inches or under. Use guardrail for 36 inches or over with endwall on inlet end, unless specified otherwise by Hydraulics Unit. On the outlet end, use a Cross Pipe end section (4:1 slope) with safety bars, or protect with guardrail.
B. PIPE END TREATMENT FOR PARALLEL PIPES
(For further information, See “Roadway Standard Drawings”, Std. No’s.
310.02 and
310.04 -- See Appendix A of this Manual)
1. AT MEDIAN CROSSOVER LOCATIONS
a. Use a median drop inlet with 10:1 or flatter slopes.
b. At existing locations without sufficient depth for drainage structures, use Parallel Pipe end sections and 6:1 slope.
2. AT GRADE INTERSECTIONS AND DRIVEWAYS
a. * Multilane Highways with Design Speed greater than 50 mph.
2. On approach ends, use a median drop inlet with 6:1 or flatter slopes where practicable and where existing or proposed drainage systems are available.
3. On approach ends, use parallel pipe end section (6:1 slope) for 24 inches or under and use guardrail for 30 inches or over. Trailing ends require no special treatment other than endwalls on the inlet end for 36 inches or over, unless specified otherwise by Hydraulics Unit.
b. * Multilane Highways with Design Speeds = 50 mph and All Two Lane Highways.
No special end treatment is required on two lane highways and multilane highways with design speeds = 50 mph. However, endwall placement is required on inlet end for 36 inches or over, unless otherwise specified by Hydraulics Unit.
* Note: This treatment for multilane highways applies to new construction and major reconstruction projects. It does not apply to resurfacing, bridge replacement, or spot safety projects. Pipe end treatment on these type of projects (including private installations) will be the same as existing pipes unless accident history warrants special consideration.
Endwalls shall be constructed perpendicular to the centerline of pipe unless specific site conditions warrant construction of an endwall parallel to the roadway (See Hydraulics Unit for approval). It will be necessary to extend the pipe to allow the end of the endwall to tie into the toe of the fill. See
NCDOT Roadway Design Manual, Part I, 5-20, F-1 -- See
Appendix C of this Manual, for an example. Any additional backfill material necessary to extend this pipe shall be covered under
Section 300 of the NCDOT Standard Specifications for Roads and Structures. The quantities for the endwalls constructed perpendicular to the centerline of pipe will be based on a 90° skew rather than the skew of the pipe.
On multiple pipe installations, additional pipe length shall be provided such that a line projected along the face of the endwall is perpendicular to the centerline of pipes. On minimum type driveways, the total graded width should not be less than 16 feet. Sound engineering judgment should be used in determining the proper driveway width and length of pipe based upon factors such as skew of drive, height of cover, type of drive and unusual traffic patterns. When sufficient right of way is available, driveway pipe should be located outside the clear roadside recovery area and the roadway ditch should be transitioned accordingly. See
NCDOT Roadway Design Manual, Part I, 5-20, F-2 -- See
Appendix C of this Manual for an example.
Providing a clear roadside recovery area is desirable in all locations, but the design will be more compatible on projects with minimum access points. (For example, partial control of access projects or projects on new locations.)
