GEEGH24-01(B): Title

Type: Bulletin

Topic or Program: Geotechnical Engineering, Engineering Geology, & HazMat  |  Signal Pole Foundations / ADA Program

Final Number: GEEGH24-01(B)

Effective Date: 11/15/2024

Updated Date: 11/15/2024

Signature on File: Susan Ortiz, State Geotechnical Engineer

Many ADA projects have identified a need to lower the grade around signal pole foundations. This bulletin is being issued to provide guidance for when and how to analyze lowering the grades near foundations in an effort to streamline the design process and avoid the need for site specific design on some projects.

Analyzing existing foundations often requires significant engineering effort to decipher the history and condition of the location; furthermore, existing foundations may need remedial work to bring them back to standard condition once they have been uncovered during construction. Therefore, lowering the grade near an existing foundation should only happen when other design alternatives have been exhausted.

This guidance may only be used on foundations designed using previous standard drawings that utilized the Brom’s or Rutledge method. The foundation must be in good condition and allow construction work around it. This guidance may be used without a site-specific geotechnical evaluation. If a foundation does not pass the requirements below or a further lowering of grade is required, then a site specific structural and/or geotechnical evaluation is required.

The following table shows the allowable elevation reduction from the original grade adjacent to an existing foundation, without site specific analysis, based on the depth of the foundation below the original surface elevation:

* Foundations that are socketed into rock may have the surrounding grade lowered up to 12 inches with or without constraint from a concrete sidewalk.

The following criteria must be met to lower the grade adjacent to foundations:

• The signal pole foundation must be functioning well with no significant deterioration.
• If foundation is found to be deteriorating when the grade is excavated, the foundation must be repaired and restored to standard condition.
  
• Where the grade is to be lowered, the foundation must be constrained horizontally by a minimum of 3’ of concrete sidewalk and curb, measured perpendicular to the foundation.
• Do not lower the grade on sides of the foundation that will not be constrained by concrete.
• The surrounding concrete acting as the constraining mechanism must be at least 4” thick.
• Signal foundations that do not have a ¼” preformed expansion joint filler between the existing foundation and sidewalk require locating the sides of the signal foundation, saw cutting the edges, and removing the surrounding concrete without damaging the existing foundation.

The Exhibits show 4 potential options for sidewalk and curb allowable elevation reduction modifications.

Please see the attached sketches that demonstrate the required geometry and components and present various options with and without curbing.

Typically, signal pole foundations have been designed assuming an unconstrained case using methods such as the Rutledge method. Section 1806.8.2.2 of the 1997 edition of the Uniform Building Code lays out a different analysis that may be used when the foundation is constrained by a rigid pavement (such as concrete, asphalt pavement is not considered rigid) (UBC, 1997). By comparing the constrained method to the traditionally used Rutledge method it was found that in several test cases the lateral resistance was increased using the constrained method.

The additional resistance typically allows for the grade around the foundation to be lowered as described above. Should a larger reduction of embedment depth be required a site-specific analysis should be performed by structural and geotechnical engineers. The site-specific analysis should take into account the current installed loading and sitespecific wind speeds. Additionally, if the foundation is square, this may increase the effective width of the foundation. The diagonal dimension of the foundation may be used with the Rutledge Method during the site-specific analysis (UBC, 1997)

International Conference of Building Officials. 1997. Uniform Building Code. 1997 ed.: International Conference of Building Officials.

ODOT Standard Drawings 35009, 35010, 40396, 40397, 47230, 47231, BR963, BR966, TM632, and TM632.

This guidance is only intended for existing signal poles being impacted by ADA projects and should not be used in any other context.

The project engineer must verify that the pole and its foundations are suitable for the given conditions.

• Attachment A