Correlation between pile driving records and SPT N values 1

[Dekay]

thread256-179060
Refer to previous thread by peterb1441 on 21/7/2007, i wish to know the same, is there any correlation between pile driving records and SPT N values? For example, i have a typical borelog with SPT N value which allow me to design a pile foundation (say 250 diam. concrete spun pile with full friction design to a depth of 30m), during installation of pile, i get the driving records, no. of hammers blows every 0.3m until the depth of 30m, so, do we have any method to correlate and justify that the capacity of the actual driven pile is exactly as per designed by using the SPT N value? It might not be the same for different types of soil (Cohesive and Cohesionless), and assume that no PDA or any load test to be carried out to check for capacity, just a correlations study by any professionals.

Thanks alot.

 

[oldestguy]

I am not sure of your question. Perhaps clarify. For instance, are you, with pile driving record in hand trying to see if you have the required capacity by looking at a nearby test boring with N values? If so, that seems not to be a rational way to detrmine if the pile is driven to required capacity.

On the other hand are you, with N values in hand, and using that to estimate how deep the pile should go to get the required capacity? That only provides an estimate ahead of time. N values are highly dependent on small conditions that may not affect pile driving, such as cobbles.

As I view N values and boring logs, they are useful to approximately estimate pile depth required, but only approximately, no precise correlation. The N values and other information, such as experience tables, together are some of the tools.

You didn't mention pile driving formulas. I'd look at that method as more reliable than any method of estimating ahead of time. Usually one or two borings won't tell precisely the full underground condition that many piles will encounter.