Pile Dynamic Load Test

[1967pradyot]

I have lot of questions. First of all, I would like to know how to interprete the data obtained from pile dynamic load test for drilled shaft (high strain). How easily CAPWAP analysis can be done without software programme? Any references or web sites?
Whether we can rely on dynamic load test alone (without performing static load test)? What is the basis of selecting dynamic load test over integrity test? Do you feel a pile resting on sand (SPT>40) can derive 70% of its capacity from end bearing?

Thanks

 

[VAD]

Hello Praydot:

I will try to answer some of your questions:

The understanding of the results one needs to do some reading up on the PDA. Ther is a welth of literature which can be obtained from the companies who perform this type of work or from the internet. Generally, if one examines the reports one can make some preliminary judgements. However, you will be more comfortable reading up on the process.

CAPWAP if I rember well and I am be subject to correction is the matching of the field data by a programme derived from the WEAP Analysis program etc so that the output can be obtained that gives various values of capacity etc. Some call it CAPWEAP. WAPCAP is another term that has some differnt approach I think. It has been a while since I have reviewed this tyoe of info and others may be able to give you more lucid info.

Dynamic load test is often calibrated against conventional static calculations for pile capacity as the depth of embedment needs to be known and hence one chooses a depth generally from static analysis unless you intend to undertake dynamic load tests on piles instaled at varying depths before you decide on the depth of choice etc.

Generally some people like to undertake both types of testing etc but because of costs and if the project does not watrrant same they would rely on one or the other based on experience.

Integrity testing is in my interpretation low strain testing which relates to whether the pile is not defective over its length. The dynamic test gives information pertaining to the capacity components-skin and toe resistances etc.

The last question requires the understanding of the pile length and loading to be applied. Generally there are two aspects of desigh that people use. One relates to skin frictionalor shaft fresitance aloen without end bearing resistance. The other is end bearing if the pile is belled etc. As well others use shatft and skin. Osterberg has shown that end bearing and shaft rsistance should be employed and hence the piles may bea ble to take more load than what is some time spurported.

Other gurus say that end bearing is invoked after a certain movement of the pile toe. I guess you will have to look at your proposed loads abd transfer functions re shaft resistance capabilities/capacities etc.

If the shaft resistance is inadequate then the load is transferred to the base. If settlement is not an issue then I would use the base resistance as well. Some are concerned about base cleanliness as well.

I cannot answer your last question without other information.

[Cheers]

 

[Focht3]

I'm not familiar with "high strain dynamic testing" of drilled piers, so I'll reserve comment until someone lays out that procedure and I get a better handle on what that procedure entails.

On the question, Do you feel a pile resting on sand (SPT>40) can derive 70% of its capacity from end bearing? - the simple answer is 'Yes.' Of course, the proportions of friction and end bearing in a given pier's capacity depend on the soil profile and the pier geometry.

Where is your site?

How is "high strain dynamic testing" of drilled piers performed?