Pile Design Help 1

[dr. rifat]

Hello Engineers,
I am new i engineering profession.I have received a soil test report from a geotechnical investigation company.Here are the SPT values:

depth(ft)---------------------SPT N
0---------------------0
5---------------------7
10---------------------9
15---------------------11
20---------------------8
25---------------------11
30---------------------10
35---------------------17
40---------------------22
45---------------------36
50---------------------50
60---------------------50

Now how to calculate the Bearing Capacity of pile(Cast in place 18" diameter),Bearing Capacity of soil at 60 ft depth,And structural design of pile.Please any one can share with me in excel/word/pdf format.Please according to AASSHTO and ACI code.

Thanks all

RIFAT

 

[oldestguy]

Go back to the geotech and ask that question for this job. It should be part of a standard report. If you can, give him the loads you have to carry and ask for his(her) estimated length information you need.

 

[EireChch]

Firstly i would say pick up a copy of Bowels Foundation analysis and design 7th edition and read pg 893.

I presume that you are in cohesive soils since your using a bored pile. You can convert your N values to shear strength using 4.5*N= Cu(kPa). Then you could use 9*Cu for end bearing capacity and then work out shaft capacity (which is shaft area x shaft resistance). Some people may discuss the suitability of utilising bearing capacity and shaft capacity as they are mobilised at different levels of displacement.

Below are some preliminary calculations to Eurocode 7 which includes partial factors which AASSHTO etc doesnt use (i think). Although its not to AASHTO the theoretical basis should be the same.

But as OG says get a geotech involved, my above information is only the first stab.

Also, you should always prove that you have a suitable bearing stratum beneath your pile toe. If you found at 60ft depth, how do you know there is not a peat layer directly below the tip? i would consider founding at 50ft depth since you know you have 10ft of good ground beneath your pile toe.

 

[Okiryu]

dr. rifat, EireChch gave a very good sample. But if the you have fine-grained soils, those N-values are not so bad (you may have medium stiff/stiff soils). If your loads are not too high, why not put the structure on shallow foundations? If you use shallow foundations, verify where the groundwater table is and check the allowable bearing pressures based on settlement considerations.