Theory,PDA,O'Cell Based on SPT

[fabianjm]

Meyerhof's etc formula for computing the Ultimate Bearing Capacity (UBC) of Pile based on Standart Penetration Test (SPT)data will be giving various value of UBC also I was tried to compare with PDA and O'Cell result so which is better to use?

 

[mudman54]

take care...i recently found out there are huge differences in the bearing capacity factors depending on if you use meyerhoff or someone else; the o-cell being considered a load test is best, the pda is a dynamic test with a large database of experience, and the spt is only used for preliminary designs.

 

[fabianjm]

Thanks mudman54...still need your comment? Generally Ultimate Bearing Capacity of Pile computed based on SPT data is bigger compare than O'Cell or PDA test, because static or dinamic loading test in the filed should take care about the damage of pile. I was found some factor based on the load settlement curves to reduce the UBC based on the SPT data. The factor was computed based on static loading test curve in the field (Load and Settlement)by using Fitting Method (Manoppo and Koumoto compared also with Tjin,Masurkiwics,P-Y curve etc..). The factors(m) are 0.5-0.95 for stiff soil and 0.2-0.45 for soft soil, so to compute the ultimate bearing capacity of pile based on SPT will be Qu Pile = m * Qu-SPT.

 

[BigH]

Mudman is really asking how do you determine the Qu based on SPT? Are you using Meyerhoff's direct capacity based on N? Or are you using N to determine phi - where you then go to charts of Nq, Ngamma and Nc? If one looks at all the different estimations of Nq based on phi, there is a very wide range - Berentzev, Meyerhoff, Terzaghi, Vesic among others. Your correlation Qupile = m*Qu-SPT is hugely dependent on which Nq value you use - and if you are using the direct N to Qu equations of Meyerhoff, they will be off similarly. It's all a crap-shoot and estimation.

 

[fabianjm]

Thanks BigH for your comment's, I was used directly N value based on SPT value without any correction or convert to Phi then Meyerhof Formula (Poulos and Davis book's)for computing the Qu based on SPT. There are two reason why I was used directly and proposed a correction factor m ; 1.All SPT N60 based on some formulas were given different values(NovoSPT..Example Cn Gibs and Holds 1.64,Peck Basara 0.85,Seed 0.8 etc..) consequently Qu based on SPT also were given different values (NovoSPT..Example Qu Meyerhof large displacement with upper cutoff driven pile 5008 KPa,Yves Robert driven pile in granural 2379..etc; 2.In my small experiences were shown that Qu SPT generally bigger than Qu based on Static Loading Test such as O'Cell test or Dynamic Loading Test PDA Test.