Sign Foundation

[Lutfi]

This is an interesting situation:

I am working on a project where the site engineer wants to excavate an area for retention pond. However, in the same area exists a big billboard sign. The sign MUST remain. It appears that the sign is supported via a drilled pier system. All data about the sing is not available.

My civil engineer wants to excavate 7 feet on one side and slope the banks of the pond on two sides. My company does not want the liability for the sign foundation integrity. However, I am recommending that the contractor drive sheet piles all around the drilled pier square in plan. I also intend to starting the sheet piles about 6 feet from the face of the sign pole.

My question,

1. If any one encountered a situation like this what would you do?
2. Is the six-foot enough to eliminate the pressure influence from the foundation? If not, is there a method to calculate the safe set back dimension?

By the way, I intend on contacting the sing owner and have them approve my approach and sign of on it. In other words, have them come back and address our approach.

Your input and thoughts would be appreciated.


Regards,
Lutfi

 

[civilperson]

Perhaps the sign owner would not object to addition of guys to stabilize the sign. Two pair of cables at right angles leading from deadmen to the pole would replace the soil resistance to lateral loads.

 

[WePushPiles]

Lufti, I agree the most economical would win, and since I don't know anything about the soils, sheet pile cofferdams might end up being more expensive than other methods. Dik makes a point about vibration issues if you are 5 or 6 feet from the sign, and you should consult your geotechnical engineer to see if vibration-induced settlement would be a significant problem.

Sheet piles can support the surcharge loads from the foundation but you can greatly reduce cost by getting a pile with a smaller section modulus if you move farther away from the structure.

Now don't quote me on this, but with 7 feet of excavation sheet pile structures can be cantilevered. Of course if the geotech feels that the moment would be too high and cause deflection of the wall would occur with a cantilevered design, add the walers and you should be fine.
On a side note, adding walers decreases the length of the pile you need to drive and could save you money on the additional weight of steel and installation costs necessary for a cantilevered system.

For aesthetics, you can always paint the exposed portion of the pile or place falsework on the pile head. Or you can cut the exposed portion as mentioned before by SlideRuleEra.

Do the math on alternatives, but if sheet pile is most economical, my company can eliminate the issues of vibration and the risk of litigation from noise if you're in a residential or urban environment. We're located in Orlando.

WePushPiles

http://www.gikenamerica.com

 

[PSlem]

I can't recall the number, but there is a spec in the IBC that says you have to notify the neighbor prior to an excavation up to 10' deep and he is responsible to shore his own foundation. The NY bldg code even says piles have to be designed for adjacent excavation to 10'. I never understood how this came into the code, but this might be a good time to use it.

 

[WePushPiles]

Lufti's project is in Florida because he's going to FDOT to pull permits on the sign. Pslem has a point though, hit the books and maybe the law will save you from doing anything about the sign altogether(except your lawyer's billable hours).

WePushPiles

 

[DonPhillips]

I cannot see how any code can require a neighbor to shore up his own foundation. Those costs must be borne by the person disburbing the foundation.

Don Phillips

http://worthingtonengineering.com

 

[PSlem]

Technically, you are only disturbing your own property. That your neighbor chose to gamble and use your soil for lateral restraint was not a problem. But now that you wish to develop it, he is restricting your usage. It should be up to him to reinforce his footing as necessary, not you. Section 3307 "The person making or causing an excavation to be made shall provide written notice to the owners of adjoining buildings advising them that the excavation is to be made and that the adjoining buildings should be protected. Said notification sahll be delivered not less than 10 days prior to the scheduled starting date of the excavation."

 

[PSlem]

That version is not exactly what I was hunting for. There is one that specifically mentions the 10' and under is his, over is yours. It might have been an earlier version or IRC.

 

[Lutfi]

All,

Let me share with you what I find out and what I wound up doing:

1. There are not published papers or documents that deal with this matter. This brings to mind what my college professor used to say “Use your engineering judgment”.
2. Contacting geotechnical engineer would be of no use or value at this juncture since I do not know the sign foundation type, size and depth.
3. Florida DOT only issue sign permits. They do not review or issue construction permits for signs.
4. Florida DOT has a state wide data base for every sign in the state. The data base is impressive. It ahs lots of data and even pictures of the sign.
5. This is a link to the site in case any one is interested:

http://www2.dot.state.fl.us/RightOfWay/dbhome.asp

6. I finally made contact with the sign owner. It turned out they did not design the sign. They bought it from another owner. The researched their records for me. I also had to work with them to coordinate the access to the sign for maintenance.
7. I performed my own wind load calculations and did quick pole embedment depth calculations. I came up with 19.5 feet. For simplicity I used 20.0 feet.
8. Sign owner said that for that particular sign they use 16 foot depth embedment.
9. Based on my conversations with respected geotechnical engineer friend of mine (he is PhD and PE and author of text book) he recommends using a minimum of 5 times the pole diameter. This seemed reasonable to me.
10. SRE provided me with an excellent paper that I read and found to be very interesting and informative. It came to similar conclusion to that my PhD colleague suggested. I think 8 times the pole is more suitable for the paper’s type of soils.
11. Another approach that was reached amongst me and three other engineers. The approach was to use a radial line that is taken from the bottom of the pole at an angle equal to repose with the vertical. This would provide the end of “no disturb zone”. To be conservative, I opted to use 45 degree angle.
12. Using the five times the pole diameter which is 4 feet I come up with 20 feet of “no disturb zone”.
13. Based on my quick pole embedment calculation of 20 feet and using 45 degree, my “no disturb zone” comes up to be 20 feet.
14. I opted to construct “L-shaped” retaining wall on three sides of the sign with the face of the wall being 20 feet from the center line of the sign. The footing will be constructed towards the sign.
15. The civil engineer had to re-work his retention areas and volume of the pond and re-grade all around the sign.

This has been very interesting and challenging task. I appreciate all of the input from everyone.

Some comments on recent input:

A. Use of guy cables is not an option since the sign will be in the front of a shopping/retail mall.
B. There are no issues with neighbors and set back. All we have to maintain is access/easement for the sign company since the easement was deeded.
C. IBC is not applicable in Florida (at least not yet). We use Florida Building Code 2004 edition with 2006 revisions. The 2006 revisions went into effect this month.
D. Sheet piles would have been costlier and the vibration effects were not appealing.



Regards,
Lutfi

 

[DonPhillips]

Here is the full 2003 IBC code text
3307.1 Protection required. Adjoining public and private
property shall be protected from damage during construction, remodeling and demolition work. Protection must be provided for footings, foundations, party walls, chimneys, skylights and roofs. Provisions shall be made to control water runoff and erosion during construction or demolition activities. The person making or causing an excavation to be made shall provide written notice to the owners of adjoining buildings advising them that the excavation is to be made and that the adjoining buildings
should be protected. Said notification shall be delivered not less than 10 days prior to the scheduled starting date of the excavation.


And the commentary text:
This section emphasizes the need to protect all existing
public and private property bordering the proposed construction or demolition operations. The term “property”
only alludes to existing buildings. As such, any building
element or system must be provided with a safeguard that will limit the damage that could be caused from the processes involved to the equipment and materials
used. Additionally, soil erosion and land disbursement
control resulting from the construction or demolition operations must be provided to prevent spillage and
spread of disturbed soil debris. The site must be graded
in accordance with Sections 3303.4 and 3303.5 for demolition
and must be maintained in a similar manner while there is construction taking place. The owner or owner’s agent has the responsibility to provide a written notice 10 days in advance for any demolition or construction activities that may warrant bordering lots to be protected from damage.


As a building official, the way I interpret this is the construction documents being submitted for a permit must show the proposed protection to existing building. It would be unreasonable to put the adjacent owner on notice that his building will be in jeopardy and has 10 days to protect his building. It would take 10 days to get an engineer on contract.

I think the intent is to place that design responsibility upon the owner doing the work and the notification is intended to ensure that vibrations caused by pile driving, or any other activity that is unusual and may affect the building occupants be addressed. Rattling glass is one thing, filing cabinets falling over and killing people are another.

Don Phillips

http://worthingtonengineering.com

 

[Lutfi]

Don,

Florida is way ahead of the rest of the country when it comes to property protection and storm water management. As a matter of fact we are regulated to the hilt when it comes to storm water and erosion. In general, I am in agreement with the IBC.

The sing is not any where near property of any one. It is set back well within the project site.


Regards,
Lutfi

 

[pba]

Lutfi,
A big thanks for posting you final solution to this problem. It's nice to get close out on these!