NOISY UNDER-GROUNDING VAULT COVERS -- THE ONGOING SAGA

Updated: Apr 6

Since the South Mission Beach undergrounding started in 2018, or maybe two weeks after it started, we have experienced nightime awakenings not from aircraft, not from parties, but from steel covers that various contractors have been putting down under contract from the City. These include SDG&E, Spectrum, and AT&T. The contractural architecture is not that obvious.


In any case, one of the covers that was particularly explosive in nature when it was run over is at the corner of Avalon Court and Bayside Lane. Neighbors in this area tried for a long period of time to get someone to correct the problem. But nothing! Finally, a local attorney who understands how the City works sued the City on behalf of one of the tenants adjacent to the noisy cover.


The City responded and apparently the problem cover plate was corrected. The City requested that the suit be rescinded, but the attorney was still concerned that the fix was going to work, that it had durability. The City proposed a meeting to bring in the stakeholders. This included a City representative, employees from AT&T and Spectrum, Klaus Mendenhall from the MBTC, Marty also from the town council and myself.


The problem is that the cover plates that are bolted down loosen, resulting in a gap between the plate and the interface material. Each time a car or truck drives over the plate, the plate impacts against the support structure as it closes the gap. The loudness of the impact depends on the size of the gap and the speed of the vehicle. In addition, each time the vehicle drives over the plate, as soon as any gap occurs, it causes damage at the interface that increases the gap.


The plates are attached to the understructure using four bolts at the corners. Supposedly, the bolts are attached with a specified torque to achieve the required tension preload in the bolt. The bolt should stay rigid unless the dynamic load from the vehicle results in an external load on the bolt that exceeds the preload in the bolt. Once the preload is exceeded, then the nut can move around, potentially backing off and releasing some of the preload. Given that this is a very rigid interface, it takes very little backing off of the nut to release the preload.


Also, while the bolt preload from the specified torque may be adequate for the sidewalk application may not be sufficient for the street use. And therefore, again, it is likely that the nuts will loosen up over time allowing a gap to form. The other possible contributing issue comes from the flatness requirement if there is one for the plate and the collar. Any unloaded bowing of any kind may result in a rocking motion as the car/truck is driven over the plates.




I have summarized some of the Issues that I saw at the meeting:


1. No clear lines of authority or responsibility among the different parties involved, i.e., City, SFG&E, etc. (Klaus pointed this out)

2. If the city has the ultimate authority, why were they not able to get SDG&E to the meeting?

3. City representative did not seem anxious to say much of anything, probably because anything he says that sounds like direction to AT&T or other contractors could be interpreted as a change in project scope.

4. It was mentioned that the main use for the problem plates is for sidewalks, where the loads are much smaller than on the streets and alleys. No strong rebuttal regarding primary use for sidewalks, and more importantly no test verification of the bolt down design use for this application in the street.  Therefore, no confidence that this design will work for the street application.  The best the AT&T person could say was that this design must be better than the torsion approach.  That is not enough.

5. Acknowledgment that there are many noisy cover plates in SMB, but no way to tell which company has responsibility for which cover plates, and therefore, no company stepping stepping up to confirm that all problem plates will be corrected.

6. No comprehensive schedule.

7. While perhaps some of the SMB residents might input complaints to Get it done, maybe for the loudest plates, I think it likely this will not happen.  It is kind of like the airport issue.  It has been this way for so long, and nothing has been done to correct the problems, no point in complaining now.  I think rather than put this on the residents to report noisy plates, it is the responsibility of the City to do this and to coordinate the fixes, but only after the fix is verified by test. Also, it makes little sense to complain to SDG&E, AT&T, and Spectrum unless we are given specific points of contact who are up to speed on the issues.


There were more issues, but enough for now.


In conclusion, if your objective was to come away from meeting that the problem is solved for El and or all of SMB, then I don’t believe this happened.  

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