Lpile Analysis for Drilled Shafts socketed into Limestone Bedrock

[sgyurisin]

I am performing Lpile analysis for the first time. The project involves Drilled shafts subject to lateral loading with the requirement being: lateral deflection must be less than 0.25 inches. Also, the shafts are to have a minimum 1 foot rock socket. And of course with any project in karst the bedrock elevation varies from 5 ft. below FF to 80 ft. below FF. Also, the lateral loading is from wind on the multi-story structure and the drilled shafts are tied into the pile cap (fixed condition). Soil conditions are residual clay - limestone/clay seams - limestone bedrock.

So far this is what I've done for the Analysis in Lpile:
Defined the clay soil properties and the limestone as strong rock, apply axial and lateral load, fixing the pile head. Then running the analysis and changing the lateral load until my deflection criteria of 0.25" is met. I have done this with varying shaft diameters and lengths, and always with a 1 ft. rock socket. For a 36" dia shaft I found the controlling case to be a length of 20 ft. that could hold a load of 51 kips to result in a deflection of 0.25".

Is my approach correct?
Are the results reasonalbe?
Can the results for Max Moment be used for structural design?

I am also a bit confused as to if Lpile works for rock socketed shafts because the technical manual states "that the case where moment at the tip of the pile is not equal to zero is not treated by the procedure presented", and if the pile is socketed into rock this would be a fixed-fixed condition and there would be a moment at the tip of the pile

 

[16adams]

I would be leary about using the Max Moment for structural design without checking it against other methods. I think you area on the right track. One way to check the length of shaft is to look at the deflection vs depth graph. Look for the point at which the line crosses the zero deflection line for the second time from the top. This should be the minimum depth to which you need to drill the shaft to obtain fixity. This is,however, NOT to be confused with the point of fixity.

 

[sgyurisin]

ok, thanks.
Do you know of any other methods that I can use to check against?
I think this would be good to have for not only the Max moment but also to check the lateral capacities/deflections.