Determine Lateral Soil Capacity for an embedded pole

[DerekRChristian]

For some backstory - I need to determine required embedment for a bunch of embedded concrete and steel poles subject to lateral load. Ordinarily, I don't have borings for the sites and so I use the presumptive values for lateral bearing pressure given in Table 1806.2 in the FL Building Code (and fairly common in many other building codes, from what I understand), however I now have soil borings and have been instructed to incorporate them, since the client paid for them. Initially, I thought that the lateral earth capacity I need to calculate required embedment was a simple as K[sub]p[/sub]*γ[sub]eff[/sub] (in psf/ft), but I've since come to think this is missing a step.

My question is: How do I calculate the lateral bearing capacity of a soil using common values from a soil boring (N, γ, K[sub]p[/sub], K[sub]a[/sub], etc)?

 

[BridgeSmith]

For hand calculation, I think Brom's method should give you the ultimate lateral bearing capacity. It doesn't give you deflections, though. If there are deflection limits, a P-y curve analysis is the typical approach, but the calculation-intensive nature of the analysis makes it best accomplished using specialized software such as Lpile or Allpile.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[fattdad]

guess at the friction angle. Solve Rankine passive equation, recall that's for plane strain.

Use the Brinch-Hansen (sp) term Cp, which for practical purposes is phi/10. Use Cp as an enhancement to Kp (i.e., owing to arching). So, if phi is 30, Cp would be 3 and Kp would be 9 (3x3).

Now you get to decide whether you are going to exclude the top 3 to 5 ft (i.e., wetting/drying, freezing/thawing, etc.) You also get to decide whether you want the movement associated with Kp.

Somebody has to guess on the k value and then you can do P-Y.

f-d

ípapß gordo ainÆt no madre flaca!

 

[DerekRChristian]

So I have K[sub]P[/sub] given. I have phi, effective unit weight, etc.
I just don't quite understand how to turn it into a lateral capacity.

 

[jdonville]

Find a copy of FHWA IP-84-011. IIRC, it describes all the major methods for doing so (Broms, Wang-Reese, p-y) -or- farm it out to a geotech.

 

[r13]

DerekRChristian,

My impression is that you've already went through the determination of embedment length using IBC presumptive lateral pressure. Can you explain the method you used in conducting such calculation?

It's seemed odd to me that, in the past, your were using the code prescribed soil pressure because the in-situ subgrade information wasn't available, and been able to carrying out the calculation; now that the actual soil properties and parameters are readily available, but you are unable to utilize these information to perform re-calculation. Am I missing something here!?

 

[DerekRChristian]

No, I think you understand. The IBC values are presumptive based on soil type and may not adequately depict the in-situ soil. Now that I have information on my soil, I want to use that to determine the actual lateral bearing capacity, rather than use the tabulated presumptive values. See links below for the table I'm referring to and the required depth equation I'm using with those values.

https://codes.iccsafe.org/content/FBC2017/chapter-18-soils-and-foundations#FBC2017_Ch18_Sec1806

https://codes.iccsafe.org/content/FBC2017/chapter-18-soils-and-foundations#FBC2017_Ch18_Sec1807.3

 

[r13]

DerekRChristian,

Ok, I understand now. I've attached a report (from Colorado DOT) for your information. Pay attention to CH-3, "Design Methods", and "App. B - Brom's Method". Wish it helps.

Link

 

[aaumed]

Just for checking
You can use this free simple laterally loaded pile software.

http://www.yongtechnology.com/pypile/

if you have any questions, please let me know.