## Monopole tower foundation

## Monopole tower foundation

(OP)

Engineers,

I am involved in a small monopole tower geotechnical work.

I understand it is a very high tower, approximately 180 ft, with moments of around 100,000 in-kips, shear 75,000 lbs and vertical of 65,000 lbs.

After reading few similar geotechnical reports, I noticed it is mentioned that this type of structure can be founded either on drilled piers or mats. I have seen these structures only on drilled piers in my experience.

From the geotechnical point of view, I understand this structure needs to be founded in piles for the following reason:

If P x tan phi > Shear, then it is ok to be used in mats, otherwise drilled shafts:

65000 x tan 30 = 37,000 lbs < 75,000 lbs, therefore drilled shafts is needed.

The N values of the strata is between 20 and 50 bpf and is composed of SP, SP-SM.

Do you understand that this is a valid reason to support my decision of using drilled shafts? or do you think additional checks need to be performed.

thanks.

Please let know.

I am involved in a small monopole tower geotechnical work.

I understand it is a very high tower, approximately 180 ft, with moments of around 100,000 in-kips, shear 75,000 lbs and vertical of 65,000 lbs.

After reading few similar geotechnical reports, I noticed it is mentioned that this type of structure can be founded either on drilled piers or mats. I have seen these structures only on drilled piers in my experience.

From the geotechnical point of view, I understand this structure needs to be founded in piles for the following reason:

If P x tan phi > Shear, then it is ok to be used in mats, otherwise drilled shafts:

65000 x tan 30 = 37,000 lbs < 75,000 lbs, therefore drilled shafts is needed.

The N values of the strata is between 20 and 50 bpf and is composed of SP, SP-SM.

Do you understand that this is a valid reason to support my decision of using drilled shafts? or do you think additional checks need to be performed.

thanks.

Please let know.

## RE: Monopole tower foundation

You'll likely get a pretty good p-y from those dense sands; however!

f-d

ípapß gordo ainÆt no madre flaca!

## RE: Monopole tower foundation

## RE: Monopole tower foundation

WT is at 3 FT.

Fd, I agree, probably something higher than 30 would make sense. I just wanted to be conservative. Still, not even having a high phi will provide something close to the 75,000 lbs of shear.

## RE: Monopole tower foundation

The mat foundation will require considerably more concrete, but does not require the the monster drilling rig necessary to auger the large diameter hole for the drilled pier. The more economical option will probably be determined by how far they would have to transport the drill rig (and of course the number of foundations).

## RE: Monopole tower foundation

...but I can't recall if I have ever solved that problem yet.

## RE: Monopole tower foundation

## RE: Monopole tower foundation

180 feet is high for a monopole. As you add antennas for cell service, the overturning moment will increase. Consider a maximum antenna population for your OT moment for the foundation. Each antenna addition will require re-analysis of the structure, but there's not much you can do with the foundation after the initial construction.

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## RE: Monopole tower foundation